English
Tiếng Việt
(en)A non-naturally occurring eukaryotic or prokaryotic organism includes one or more gene disruptions occurring in genes encoding enzymes imparting increased fumarate, malate or acrylate production in the organism when the gene disruption reduces an activity of the enzyme. The one or more gene disruptions confers increased production of acrylate onto the organism. Organisms that produce acrylate have an acrylate pathway that at least one exogenous nucleic acid encoding an acrylate pathway enzyme expressed in a sufficient amount to produce acrylate, the acrylate pathway comprising a decarboxylase. Methods of producing fumarate, malate or acrylate include culturing these organisms.
1.ApplicationNumber: US-48672409-A
1.PublishNumber: US-2010009419-A1
2.Date Publish: 20100114
3.Inventor: BURK MARK J.
BURGARD ANTHONY P.
PHARKYA PRITI
4.Inventor Harmonized: BURK MARK J(US)
BURGARD ANTHONY P(US)
PHARKYA PRITI(US)
5.Country: US
6.Claims:
(en)A non-naturally occurring eukaryotic or prokaryotic organism includes one or more gene disruptions occurring in genes encoding enzymes imparting increased fumarate, malate or acrylate production in the organism when the gene disruption reduces an activity of the enzyme. The one or more gene disruptions confers increased production of acrylate onto the organism. Organisms that produce acrylate have an acrylate pathway that at least one exogenous nucleic acid encoding an acrylate pathway enzyme expressed in a sufficient amount to produce acrylate, the acrylate pathway comprising a decarboxylase. Methods of producing fumarate, malate or acrylate include culturing these organisms.
7.Description:
(en)This application claims the benefit of priority of U.S. Provisional Ser. No. 61/073,348, filed Jun. 17, 2008; U.S. Provisional Ser. No. 61/077,127, filed Jun. 30, 2008; and U.S. Provisional Ser. No. 61/088,628, filed Aug. 13, 2008, each of which is incorporated by reference in their entirety.
BACKGROUND
The present disclosure relates generally to the design of engineered organisms and, more specifically to organisms having selected genotypes for the production of fumarate, malate, and acrylate.
Fumaric acid is used in industrial processes as a raw material in a wide range of chemical syntheses. The presence of a double bond and two carboxyl groups in this compound facilitates its use in making polyesters and other polymers. Some of its industrial applications include manufacturing of synthetic resins and biodegradable polymers. It also finds widespread use as a food acidulant, a dietary supplement and as a beverage ingredient. Fumaric acid is currently derived from maleic anhydride, which is produced by the catalytic oxidation of benzene or butene feedstocks. Even though fumaric acid is approximately 10% more expensive than maleic anhydride, the non-toxic nature of the former and the special properties, such as greater hardness, that it imparts to the polymer structure makes it a good option for polymer industry as compared to maleic anhydride. Recently, two new applications for fumaric acid have been developed: (i) it can be used medicinally for treating a skin condition called psoriasis, and (ii) it can be used as a supplement for cattle feed.
Malic acid is used as an acidulant and taste enhancer in the beverage and food industry. Racemic malic acid is synthesized petrochemically from maleic anhydride whereas enantiometrically pure L-malic acid (used in pharmaceutical production) is produced from fumarate by hydration with fumarase.
Acrylic acid is a large volume petrochemical product. For example, acrylic acid is a commodity monomer intermediate used for the production of polymeric materials such polyacrylic acid, which is a major component of superabsorbant diapers. Acrylic acid also is used for the production of acrylate esters, which are utilized in water-soluble latex coatings, adhesives and inks. Acrylic acid and acrylate esters are manufactured by petrochemical processes such as oxidation of propylene, followed by esterification with alcohols such as methanol, butanol, and 2-ethylhexanol.
Chemicals manufactured from petroleum feedstocks suffer the burden of high and volatile prices, insecure foreign supply chains, and declining reserves (Frost, J. W., Redefining chemical manufacture. Ind. Biotechnol. 1:23-24 (2005)). Therefore, a method of producing large volume chemicals or their intermediates by alternative means that reduce petroleum-based processes and also use less energy- and capital-intensive processes would be beneficial.
Thus, there is a need to gain access to microorganisms having the commercially valuable characteristics of efficiently bio synthesizing fumarate, malate, and acrylate in high yields. The present invention satisfies this need and provides related advantages as well.
SUMMARY OF THE INVENTION
In some embodiments, the present invention provides a non-naturally occurring microbial organism that includes one or more gene disruptions occurring in genes encoding enzymes selected from the group of fumarate reductase (FRD), alcohol dehydrogenase (ADHEr) and lactate dehydrogenase (LDH_D) such that the one or more gene disruptions confers increased production of fumarate onto said non-naturally occurring microbial organism.
In some embodiments, the present invention provides a method for producing fumaric acid that includes culturing a non-naturally occurring microbial organism having one or more gene disruptions occurring in genes encoding enzymes selected from the group of fumarate reductase (FRD), alcohol dehydrogenase (ADHEr) and lactate dehydrogenase (LDH_D) such that the one or more gene disruptions confers increased production of fumarate onto said non-naturally occurring microbial organism.
In some embodiments, the present invention provides a non-naturally occurring microbial organism that includes one or more gene disruptions occurring in genes encoding enzymes selected from a group of fumarate reducatse (FRD), alcohol dehydrogenase (ADHEr), fumarase (FUM) and lactate dehydrogenase (LDH_D), when the gene disruption reduces an activity of the enzyme it confers increased production of malate onto said non-naturally occurring microbial organism.
In some embodiments, the present invention provides a method for producing malic acid that includes culturing a non-naturally occurring microbial organism having one or more gene disruptions occurring in genes encoding enzymes selected from a group of fumarate reducatse (FRD), alcohol dehydrogenase (ADHEr), fumarase (FUM) and lactate dehydrogenase (LDH_D), when the gene disruption reduces an activity of the enzyme it confers increased production of malate onto said non-naturally occurring microbial organism.
In some embodiments, the present invention provides a non-naturally occurring eukaryotic organism, comprising one or more gene disruptions occurring in genes encoding enzymes imparting increased fumarate production in the organism when the gene disruption reduces an activity of the enzyme, whereby the one or more gene disruptions confers increased production of fumarate onto the organism.
In some embodiments, the present invention provides a method for producing fumaric acid that includes culturing a non-naturally occurring eukaryotic organism having one or more gene disruptions occurring in genes encoding an enzyme providing increased fumarate production in the organism when the gene disruption reduces an activity of the enzyme, whereby the one or more gene disruptions confers increased production of fumarate onto the organism.
In some embodiments, the present invention provides a non-naturally occurring eukaryotic organism that includes one or more gene disruptions occurring in genes encoding enzymes imparting increased malate production in the organism when the gene disruption reduces an activity of the enzyme, whereby the one or more gene disruptions confers enhanced production of malate onto the organism.
In some embodiments, the present invention provides a method for producing malic acid that includes culturing a non-naturally occurring eukaryotic organism having one or more gene disruptions occurring in genes encoding enzymes imparting increased malate production to the organism when the gene disruption reduces an activity of the enzyme, whereby the one or more gene disruptions confers increased production of malate onto the organism.
In some embodiments, the present invention provides a non-naturally occurring eukaryotic organism that includes one or more gene disruptions occurring in genes encoding enzymes imparting increased acrylate production in the organism when the gene disruption reduces an activity of the enzyme, whereby the one or more gene disruptions confers increased production of acrylate onto the organism.
In some embodiments, the present invention provides a method for producing acrylic acid that includes culturing a non-naturally occurring eukaryotic organism having one or more gene disruptions occurring in genes encoding enzymes imparting enhanced acrylate production in the organism when the gene disruption reduces an activity of the enzyme, whereby the one or more gene disruptions confers increased production of acrlyate onto the organism.
In some embodiments, the present invention provides a non-naturally occurring microbial organism that includes a microbial organism having an olefin pathway having at least one exogenous nucleic acid encoding an olefin pathway enzyme expressed in a sufficient amount to produce an olefin, the olefin pathway including a decarboxylase.
In some embodiments, the present invention provides a method for producing an olefin that includes culturing a non-naturally occurring microbial organism having an olefin pathway that includes at least one exogenous nucleic acid encoding an olefin pathway enzyme expressed in a sufficient amount to produce an olefin under conditions and for a sufficient period of time to produce an olefin, the olefin pathway including a decarboxylase.
In some embodiments, the present invention provides a non-naturally occurring microbial organism that includes a microbial organism having an acrylate pathway having at least one exogenous nucleic acid encoding an acrylate pathway enzyme expressed in a sufficient amount to produce acrylate, the acrylate pathway including a decarboxylase.
In some embodiments, the present invention provides a method for producing acrylate that includes culturing a non-naturally occurring microbial organism having an acrylate pathway, the pathway includes at least one exogenous nucleic acid encoding an acrylate pathway enzyme expressed in a sufficient amount to produce acrylate under conditions and for a sufficient period of time to produce acrylate, the acrylate pathway including a decarboxylase.
In some embodiments, the present invention provides a method for producing acrylate that includes a) culturing a first non-naturally occurring microbial organism that includes one or more gene disruptions occurring in one or more genes encoding one or more enzymes that enhance fumarate production toin the organism when the one or more genes disruptions reduces an activity of the one or more enzymes, whereby the one or more gene disruptions confers increased production of fumarate onto the non-naturally occurring organism, and b) adding a decarboxylase to the cultured first non-naturally occurring microbial organism, the decarboxylase catalyzing the decarboxylation of fumarate.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows the hypothetical production envelopes of an OptKnock-designed strain contrasted against a typical non-growth-coupled production strain. Note that the potential evolutionary trajectories of the OptKnock strain are fundamentally different in that they will lead to a high producing phenotype.
FIG. 2 shows increased fumarate production characteristics of one strain (black, dashed) compared with those of the wild-type E. coli network (black). At the maximum rate of growth, the wild-type network is not expected to form any fumarate.
FIG. 3 shows increased fumarate production characteristics of another strain (black, dotted) compared with those of the wild-type E. coli network (black). The grey point shows the minimum amount of product formation expected from this strain.
FIG. 4 shows the production curve for still another strain (grey, dashed) compared with the production curve for the wild-type E. coli network (black). Note that this strain design is equivalent to design B if an additional deletion in THD2 is introduced.
FIG. 5 shows the production curve for yet another strain (grey, dashed) compared with the production curve of the wild type E. coli network (black). The black point indicates the minimum amount of product formation expected from this strain.
FIG. 6 shows the production curves for the strains in FIG. 2 (black, dashed), FIG. 3 (black, dotted), FIG. 4 (grey, dashed) and FIG. 5 (grey) compared with each other and with the production characteristics of the wild-type E. coli network (black). Note the reduction in feasible solution space as additional deletions are imposed on the network.
FIG. 7 shows the malate production curve for one strain (light grey) compared with the production curve for the wild type E. coli network (black).
FIG. 8 shows the production curve for a modified malate-producing strain design based on the strain of FIG. 7 , replacing deletion of FRD with deletion of ASPT,(grey) compared with that of the wild-type E. coli network (black).
FIG. 9 shows increased fumarate production characteristics of one strain (black, dotted) compared with those of the wild-type S. cerevisiae network (black). At the maximum rate of growth, the wild-type network is not expected to form any fumarate.
FIG. 10 shows increased fumarate production characteristics of another strain (light gray) compared with those of the wild-type S. cerevisiae network (black). The gray point shows the minimum amount of product formation expected from this strain.
FIG. 11 shows the production curve for yet another strain (dark gray, dashed) compared with the production curve for the wild-type S. cerevisiae network (black). The dark gray point shows the minimum amount of fumarate production expected from this design.
FIG. 12 shows the production curve for still another strain (light gray, dashed) compared with the production curve of the wild type S. cerevisiae network (black). The light gray point indicates the minimum amount of product formation expected from this strain.
FIG. 13 shows the production curves for various strains in FIG. 9 , black, dotted; FIG. 10 , light gray; FIG. 11 dark gray, dashed; and FIG. 12 light gray, dashed, compared with each other and with the production characteristics of the wild-type S. cerevisiae network (black). Note the reduction in feasible solution space as additional deletions are imposed on the network.
FIG. 14 shows the acrylate production curve for one strain (dark gray, dashed) compared with the production curve for the wild type S. cerevisiae network (black).
FIG. 15 shows the acrylate production curve for another strain (black, dotted) compared with the production curve for the wild type S. cerevisiae network (black).
FIG. 16 shows the acrylate production curve for yet another strain (dark gray) compared with the production curve for the wild type S. cerevisiae network (black).
FIG. 17 shows the acrylate production curve for still another strain (light gray) compared with the production curve for the wild type S. cerevisiae network (black).
FIG. 18 shows the acrylate production curve for yet still another strain (light gray, dashed) compared with the production curve for the wild type S. cerevisiae network (black).
FIG. 19 shows the prophetic transformations of a) 1,1- and 1,2-substituted carboxylic acids to terminal olefins catalyzed by a decarboxylase and b) the transformation of a pentadienoic acid to 1,3-butadiene.
FIG. 20 shows a biosynthetic pathway for the direct production of acrylate through decarboxylation of fumarate.
FIG. 21 a shows the prophetic transformation of fumarate to acrylate catalyzed by a decarboxylase.
FIG. 21 b shows the decarboxylation of aconitate to itaconate catalyzed by aconitate decarboxylase.
FIG. 21 c shows the decarboxylation of 4-oxalocrotonate to 2-oxopentenoate catalyzed by 4-oxalocrotonate decarboxylase.
FIG. 21 d shows the decarboxylation of cinnamate derivatives to styrene derivatives catalyzed by a decarboxylase.
DETAILED DESCRIPTION OF THE INVENTION
This invention is directed, in part, to engineered organisms having biosynthetic pathways to fumarate, malate, and acrylate. In some embodiments, the invention utilizes optimization-based approaches based on in silico stoichiometric models of Escherichia coli and Saccharomyces cerevisiae metabolism that identify metabolic designs for increased production of fumarate, malate, and acrylate in these organisms. A bilevel programming framework, OptKnock, is applied within an iterative algorithm to predict multiple sets of gene disruptions, that collectively result in increased production of fumarate, malate, or acrylate. As disclosed herein, various combinations of gene deletions or functional disruptions of genes significantly improve the fumarate, malate, or acrylate production capabilities of E. coli and S. cerevisiae.
Production of acrylate, in particular, involves not only primary metabolic production of fumarate, but also subsequent mono-decarboxylation. Thus, the invention is also directed, in part, to a developing a route to acrylate from fumarate by reaction with a decarboxylase enzyme. The decarboxylase enzyme can be introduced as an exogenous nucleic acid into the same organism that has been engineered for increased fumarate production via gene disruptions, or alternatively through a secondary transformation involving extracellular addition of a decarboxylase to a culture containing over-produced fumarate. Another alternative is to provide a second organism having decarboxylase activity. In such a case, the fumarate-producing organism can be co-cultured or serially cultured with the second organism possessing the requisite decarboxylase.
The engineering designs are equally applicable if an organism other than E. coli or S. cerevisiae is chosen as the production host, even if the organism naturally lacks the activity or exhibits low activity of a subset of the gene products marked for disruption. In those cases, disruptions must only be introduced to eliminate or lessen the enzymatic activities of the gene products that are naturally present in the chosen production host. Production of fumarate, malate, or acrylate for the in silico designs are confirmed by construction of strains having the designed metabolic genotype. These metabolically engineered cells or organisms can also be subjected to adaptive evolution to further augment product production.
In a further embodiment, the invention is directed to an integrated computational and engineering platform for developing metabolically altered microorganism strains having enhanced fumarate, malate, or acrylate producing characteristics. Strains identified via the computational component of the platform are put into actual production by genetically engineering the predicted metabolic alterations which lead to the enhanced production of fumarate, malate, or acrylate. Production of the desired product is optionally coupled to optimal growth of the microorganism. Strains exhibiting increased production of these products can be further subjected to adaptive evolution to further augment product biosynthesis. The levels of product production following adaptive evolution also can be predicted by the computational component of the system where, in this specific embodiment, the elevated product levels are realized following evolution.
Currently, the only organisms known to produce fumarate at a reasonable level are Rhizopus (Tsao et al., Adv. Biochem. Eng. Biotechnol., 65:243-280 (1999); Lee et al., Macromolecular Bioscience, 4:157-164 (1999); Rhodes et al., Appl. Microbiol. 1962, 10(1):9-15; and Rhodes et al., Appl. Microbiol. 7(2):74-80 (1959)). Fumarate production in these organisms utilizes pyruvate carboxylase to fix carbon dioxide, converting pyruvate into oxaloacetate (Kenealy et al., Appl. Environ. Microbiol. 52(1):128-133 (1986)). This is subsequently converted into malate and finally into fumarate. Some reports on fumarate production in Rhizopus have outlined fermentation and culture conditions for obtaining fumarate (Moresi et al., J. Chem. Technol. Biotechnol. 54(3):283-2890 (1992)). Optimum concentrations of metal ions and phosphate have been determined to maximize the fumarate production during the fermentation process (Zhou et al., Appl. Biochem. Biotechnol. 84-86:779-89 (2000)). Another study examined various cassaya bagasse hydrolysates as a cheap carbon source, reporting a yield of 22 g/L of fumarate (Carta et al., Bioresource Technology 68(1):23-28 (1999)). A study of neutralizing agents for fumarate production was also undertaken. It was determined that utilizing CaCO 3 provides the highest fumaric acid weight yield (53.4%) and volumetric productivity (1.03 g/L.hr) (Zhou et al., Bioprocess Biosyst. Eng. 25(3):179-181 (2002)).
However, growing mycelia often form interlocking hyphae mingled with calcium carbonate, resulting in oxygen transfer limitations, thus slowing down the rate of fermentation. Another difficulty involved in fumarate production is the tendency of Rhizopus sporangiospores to grow into mycelial mats or mycelial lumps (Zhou et al., Appl. Biochem. Biotechnol. 84-86:779-89 (2000)), interfering with the function of bafflers and propellers inside a reactor. A rotary biofilm contactor has been utilized in a simultaneous fermentation-adsorption process to obtain yields of 85 g/L of fumarate from 100 g/L of glucose. Finally, R. arrhizus NRR11526 immoblized on a polyurethane sponge was used to facilitate continuous fermentation for fumarate production. Yields of approximately 12.3 g/L of fumaric acid were obtained in this work (Lee et al., Macromolecular Bioscience 4:157-164 (2004)). However, despite the above efforts, the approaches employed have several drawbacks which hinder applicability in commercial settings. Chemical processes remain predominantly used in fumarate production because of (a) the cost benefits of chemical production and (b) the complications associated with maintaining the right size of mycelial particles for fumarate production.
Malic acid production has been reported in a wide range of organisms, including both yeast and bacteria (Jantama, K., et al., Biotechnol Bioeng, 99(5):1140-53 (2008); Moon, S. Y., et al., Biochemical Engineering Journal (2008).). Most recently, malic acid titers of up to 59 g/L with yields of 0.42 mol/mol glucose were reported in Saccharomyces cerevisiae . (Zelle, R. M., et al., Appl Environ Microbiol, 74(9):2766-77 (2008)). This level of malic acid production was achieved by introducing three genetic modifications: (i) overexpression of the native pyruvate carboxylase, (ii) increasing the expression of malate dehydrogenase and retargeting it to cytosol, and (iii) functional expression of a heterologous malate transporter gene. Other yeasts in which malic acid has been produced successfully include Aspergillus flavus, Rhizopus arrhizus , and Zygosaccharomyces rouxii . (Zelle, R. M., et al., Appl Environ Microbiol, 74(9):2766-77 (2008)). The highest malic acid titer has been reported in A. flavus (113 g/L) with malic acid yield at 63% of the maximum theoretical yield on glucose. However, potential aflatoxin production has rendered this organism unusable for the production of food-grade malic acid. Malic acid yields with other yeasts are not high enough to pursue commercial production. (Zelle, R. M., et al., Appl Environ Microbiol, 74(9):2766-77 (2008)). Relatively higher malate yields have been reported in a mutant strain of Escherichia coli C (1.4 mol/mol glucose) which was engineered to inhibit secretion of byproducts such as acetate, lactate, formate, and ethanol. (Jantama, K., et al., Biotechnol Bioeng, 99(5):1140-53 (2008)).
This invention is also directed, in part, to methods for producing olefins by decarboxylation an alpha, beta-unsaturated carboxylic acids as exemplified in FIG. 19 a . The unsaturated carboxylic acid substrate can be of any structural olefin geometry. For example the unsaturated carboxylic acid may be substituted at either the alpha or beta position. Additionally, beta-substituted unsaturated carboxylic acid substrates can have either E or Z olefin geometry. The product will typically be a terminal olefin. Furthermore, the carboxylic acid substrate can be further conjugated as shown in FIG. 19 b , wherein pentadienoic acid is decarboxylated to the commercially valuable commodity chemical 1,3-butadiene. 1,3-butadiene is an important chemical in the manufacture of synthetic rubbers, for example.
In some embodiments this invention is directed to methods of producing acrylic acid involving primary metabolic production of fumaric acid, followed by decarboxylation. FIG. 20 shows a biosynthetic scheme for producing acrylic acid which involves treatment of fumaric acid with a decarboxylase enzyme in a pathway leading directly to acrylate, or alternatively through a secondary transformation involving extracellular addition of a decarboxylase to a culture containing over-produced fumarate.
As shown in FIG. 20 , two moles of acrylic acid are produced from each mole of glucose consumed and carbon is utilized in a very efficient manner. Carbon from 1 mole of glucose provides two moles of phosphoenol pyruvate (PEP) through glycolysis, which then reacts with carbon dioxide (via PEP carboxylase or PEP caboxykinase) to afford a maximum theoretical yield of 2.0 moles of fumaric acid, which upon decarboxylation leads to two moles of acrylic acid. This efficient use of carbon is important for achieving high yields (0.8 g acrylic acid/g glucose) and favorable process economics in the production of acrylic acid from renewable feedstocks. In addition, although the final decarboxylation step leads to release of carbon dioxide, the conversion of phosphoenolpyruvate to oxaloacetate actually consumes one mole of carbon dioxide, leading to an overall process that is CO 2 neutral. The decarboxylation of fumarate to acrylate also will drive the equilibrium between malate and fumarate, thus leading to all carbon being funneled to the desired acrylic acid product.
Production of acrylic acid by fermentation involving renewable feedstocks has been investigated previously, and several designs have been proposed (Straathof, A. J. et al., Appl. Microbiol. Biotechnol., 67:727-34 (2005)). In particular, processes involving conversion of lactate or lactoyl-CoA to acrylate or acryloyl-CoA have been explored, but suffer from unfavorable thermodynamics and undesirably high levels of lactate secretion. Another bioprocess for acrylic acid production proceeds through the intermediate 3-hydroxypropionic acid (3-HP), which is produced first by fermentation and then isolated and dehydrated in a second step under anhydrous conditions (Cameron, D. C. and P. F. Suthers WO0242418).
Such two-step routes to acrylic acid via 3-HP have presented challenges and are still under development. Direct conversion of biomass-derived sugars to acrylic acid is highly desirable due to substantial economic benefits associated with reduction in capital and energy costs relative to multi-step processes.
The maximum theoretical yield of each of the acid products described herein is 2 moles per mole of glucose consumed (see equations 1-3 below), indicating a significant potential for improving the existing biochemical processes further.
C 6 H 12 O 6 +2CO 2 →2C 4 H 4 O 4 +2H 2 O(fumaric acid) equation 1
C 6 H 12 O 6 +2CO 2 →2C 4 H 6 O 5 (malic acid) equation 2
C 6 H 12 O 6 →2C 3 H 4 O 2 +2H 2 O (acrylic acid) equation 3
Many different substrates derived from renewable feedstocks, such as glucose, xylose, arabinose, sorbitol, sucrose, glycerol, or even synthesis gas (a mixture carbon monoxide, hydrogen and carbon dioxide), can serve as carbon and energy sources for a fermentation process. Each of these substrates can be used for biological production of fumarate, malate, or acrylate.
As used herein, the term “non-naturally occurring” when used in reference to a microbial organism or microorganism of the invention is intended to mean that the microbial organism has at least one genetic alteration not normally found in a naturally occurring strain of the referenced species, including wild-type strains of the referenced species. Genetic alterations include, for example, modifications introducing expressible nucleic acids encoding metabolic polypeptides, other nucleic acid additions, nucleic acid deletions and/or other functional disruption of the microbial genetic material. Such modifications include, for example, coding regions and functional fragments thereof, for heterologous, homologous or both heterologous and homologous polypeptides for the referenced species. Additional modifications include, for example, non-coding regulatory regions in which the modifications alter expression of a gene or operon. Exemplary metabolic polypeptides include enzymes or proteins within a cyclohexanone biosynthetic pathway.
As used herein, the term “gene disruption,” or grammatical equivalents thereof, is intended to mean a genetic alteration that renders the encoded gene product inactive. The genetic alteration can be, for example, deletion of the entire gene, deletion of a regulatory sequence required for transcription or translation, deletion of a portion of the gene with results in a truncated gene product or by any of various mutation methods that inactivate the encoded gene product. One particularly useful method of gene disruption is complete gene deletion because it reduces or eliminates the occurrence of genetic reversions in the non-naturally occurring eukaryotic organisms of the invention. The term “gene disruption” is also intended to mean a genetic alteration that lowers the activity of a given gene product relative to its activity in a wild-type organism. This attenuation of activity can be due to, for example, a deletion in a portion of the gene which results in a truncated gene product or any of various mutation methods that render the encoded gene product less active than its natural form, replacement or mutation of the promoter sequence leading to lower or less efficient expression of the gene, culturing the organism under a condition where the gene is less highly expressed than under normal culture conditions, or introducing antisense RNA molecules that interact with complementary mRNA molecules of the gene and alter its expression.
A metabolic modification refers to a biochemical reaction that is altered from its naturally occurring state. Therefore, non-naturally occurring microorganisms can have genetic modifications to nucleic acids encoding metabolic polypeptides or, functional fragments thereof. Exemplary metabolic modifications are disclosed herein.
As used herein, the term “isolated” when used in reference to a microbial organism is intended to mean an organism that is substantially free of at least one component as the referenced microbial organism is found in nature. The term includes a microbial organism that is removed from some or all components as it is found in its natural environment. The term also includes a microbial organism that is removed from some or all components as the microbial organism is found in non-naturally occurring environments. Therefore, an isolated microbial organism is partly or completely separated from other substances as it is found in nature or as it is grown, stored or subsisted in non-naturally occurring environments. Specific examples of isolated microbial organisms include partially pure microbes, substantially pure microbes and microbes cultured in a medium that is non-naturally occurring.
As used herein, the terms “microbial,” “microbial organism” or “microorganism” is intended to mean any organism that exists as a microscopic cell that is included within the domains of archaea, bacteria or eukarya. Therefore, the term is intended to encompass prokaryotic or eukaryotic cells or organisms having a microscopic size and includes bacteria, archaea and eubacteria of all species as well as eukaryotic microorganisms such as yeast and fungi. The term also includes cell cultures of any species that can be cultured for the production of a biochemical.
As used herein the term “parent decarboxylase” refers to both wild-type and previously engineered decarboxylases that serve as a starting point for further optimization of the decarboxylation activity. Optimizations can include not only changes made to the nucleic acid sequence encoding the decarboxylase, but also post-translational modifications to the enzyme product.
As used herein the terms “acrylate” and “acrylic acid” are used interchangeably. One skilled in the art will appreciate that the ionization state of a typical carboxylic acid will depend on the pH of its environment. For example, with a pK a of approximately 4, acrylic acid can be significantly in its ionized acrylate form when the pH is 6 or more. While the final isolated product of any given process can be acrylic acid, the direct product of fermentation will frequently be the corresponding acrylate salt, although this can vary depending on the pH conditions employed. In a similar manner, “fumarate” and “fumaric acid,” “malate” and “malic acid,” and “carboxylate” and “carboxylic acid” are used interchangeably.
As used herein, the term “substantially anaerobic” when used in reference to a culture or growth condition is intended to mean that the amount of oxygen is less than about 10% of saturation for dissolved oxygen in liquid media. The term also is intended to include sealed chambers of liquid or solid medium maintained with an atmosphere of less than about 1% oxygen.
“Exogenous” as it is used herein is intended to mean that the referenced molecule or the referenced activity is introduced into the host microbial organism. The molecule can be introduced, for example, by introduction of an encoding nucleic acid into the host genetic material such as by integration into a host chromosome or as non-chromosomal genetic material such as a plasmid. Therefore, the term as it is used in reference to expression of an encoding nucleic acid refers to introduction of the encoding nucleic acid in an expressible form into the microbial organism. When used in reference to a biosynthetic activity, the term refers to an activity that is introduced into the host reference organism. The source can be, for example, a homologous or heterologous encoding nucleic acid that expresses the referenced activity following introduction into the host microbial organism. Therefore, the term “endogenous” refers to a referenced molecule or activity that is present in the host. Similarly, the term when used in reference to expression of an encoding nucleic acid refers to expression of an encoding nucleic acid contained within the microbial organism. The term “heterologous” refers to a molecule or activity derived from a source other than the referenced species whereas “homologous” refers to a molecule or activity derived from the host microbial organism. Accordingly, exogenous expression of an encoding nucleic acid of the invention can utilize either or both a heterologous or homologous encoding nucleic acid.
The non-naturally occurring microbal organisms of the invention can contain stable genetic alterations, which refers to microorganisms that can be cultured for greater than five generations without loss of the alteration. Generally, stable genetic alterations include modifications that persist greater than 10 generations, particularly stable modifications will persist more than about 25 generations, and more particularly, stable genetic modifications will be greater than 50 generations, including indefinitely.
Those skilled in the art will understand that the genetic alterations, including metabolic modifications exemplified herein, are described with reference to a suitable host organism such as E. coli and their corresponding metabolic reactions or a suitable source organism for desired genetic material such as genes for a desired metabolic pathway. However, given the complete genome sequencing of a wide variety of organisms and the high level of skill in the area of genomics, those skilled in the art will readily be able to apply the teachings and guidance provided herein to essentially all other organisms. For example, the E. coli metabolic alterations exemplified herein can readily be applied to other species by incorporating the same or analogous encoding nucleic acid from species other than the referenced species. Such genetic alterations include, for example, genetic alterations of species homologs, in general, and in particular, orthologs, paralogs or nonorthologous gene displacements.
An ortholog is a gene or genes that are related by vertical descent and are responsible for substantially the same or identical functions in different organisms. For example, mouse epoxide hydrolase and human epoxide hydrolase can be considered orthologs for the biological function of hydrolysis of epoxides. Genes are related by vertical descent when, for example, they share sequence similarity of sufficient amount to indicate they are homologous, or related by evolution from a common ancestor. Genes can also be considered orthologs if they share three-dimensional structure but not necessarily sequence similarity, of a sufficient amount to indicate that they have evolved from a common ancestor to the extent that the primary sequence similarity is not identifiable. Genes that are orthologous can encode proteins with sequence similarity of about 25% to 100% amino acid sequence identity. Genes encoding proteins sharing an amino acid similarity less that 25% can also be considered to have arisen by vertical descent if their three-dimensional structure also shows similarities. Members of the serine protease family of enzymes, including tissue plasminogen activator and elastase, are considered to have arisen by vertical descent from a common ancestor.
Orthologs include genes or their encoded gene products that through, for example, evolution, have diverged in structure or overall activity. For example, where one species encodes a gene product exhibiting two functions and where such functions have been separated into distinct genes in a second species, the three genes and their corresponding products are considered to be orthologs. For the production of a biochemical product, those skilled in the art will understand that the orthologous gene harboring the metabolic activity to be introduced or disrupted is to be chosen for construction of the non-naturally occurring microorganism. An example of orthologs exhibiting separable activities is where distinct activities have been separated into distinct gene products between two or more species or within a single species. A specific example is the separation of elastase proteolysis and plasminogen proteolysis, two types of serine protease activity, into distinct molecules as plasminogen activator and elastase. A second example is the separation of mycoplasma 5′-3′ exonuclease and Drosophila DNA polymerase III activity. The DNA polymerase from the first species can be considered an ortholog to either or both of the exonuclease or the polymerase from the second species and vice versa.
In contrast, paralogs are homologs related by, for example, duplication followed by evolutionary divergence and have similar or common, but not identical functions. Paralogs can originate or derive from, for example, the same species or from a different species. For example, microsomal epoxide hydrolase (epoxide hydrolase I) and soluble epoxide hydrolase (epoxide hydrolase II) can be considered paralogs because they represent two distinct enzymes, co-evolved from a common ancestor, that catalyze distinct reactions and have distinct functions in the same species. Paralogs are proteins from the same species with significant sequence similarity to each other suggesting that they are homologous, or related through co-evolution from a common ancestor. Groups of paralogous protein families include HipA homologs, luciferase genes, peptidases, and others.
A nonorthologous gene displacement is a nonorthologous gene from one species that can substitute for a referenced gene function in a different species. Substitution includes, for example, being able to perform substantially the same or a similar function in the species of origin compared to the referenced function in the different species. Although generally, a nonorthologous gene displacement will be identifiable as structurally related to a known gene encoding the referenced function, less structurally related but functionally similar genes and their corresponding gene products nevertheless will still fall within the meaning of the term as it is used herein. Functional similarity requires, for example, at least some structural similarity in the active site or binding region of a nonorthologous gene product compared to a gene encoding the function sought to be substituted. Therefore, a nonorthologous gene includes, for example, a paralog or an unrelated gene.
Therefore, in identifying and constructing the non-naturally occurring microbial organisms of the invention having cyclohexanone biosynthetic capability, those skilled in the art will understand with applying the teaching and guidance provided herein to a particular species that the identification of metabolic modifications can include identification and inclusion or inactivation of orthologs. To the extent that paralogs and/or nonorthologous gene displacements are present in the referenced microorganism that encode an enzyme catalyzing a similar or substantially similar metabolic reaction, those skilled in the art also can utilize these evolutionally related genes.
Orthologs, paralogs and nonorthologous gene displacements can be determined by methods well known to those skilled in the art. For example, inspection of nucleic acid or amino acid sequences for two polypeptides will reveal sequence identity and similarities between the compared sequences. Based on such similarities, one skilled in the art can determine if the similarity is sufficiently high to indicate the proteins are related through evolution from a common ancestor. Algorithms well known to those skilled in the art, such as Align, BLAST, Clustal W and others compare and determine a raw sequence similarity or identity, and also determine the presence or significance of gaps in the sequence which can be assigned a weight or score. Such algorithms also are known in the art and are similarly applicable for determining nucleotide sequence similarity or identity. Parameters for sufficient similarity to determine relatedness are computed based on well known methods for calculating statistical similarity, or the chance of finding a similar match in a random polypeptide, and the significance of the match determined. A computer comparison of two or more sequences can, if desired, also be optimized visually by those skilled in the art. Related gene products or proteins can be expected to have a high similarity, for example, 25% to 100% sequence identity. Proteins that are unrelated can have an identity which is essentially the same as would be expected to occur by chance, if a database of sufficient size is scanned (about 5%). Sequences between 5% and 24% can represent sufficient homology to conclude that the compared sequences are related. Additional statistical analysis to determine the significance of such matches given the size of the data set can be carried out to determine the relevance of these sequences.
Exemplary parameters for determining relatedness of two or more sequences using the BLAST algorithm, for example, can be as set forth below. Briefly, amino acid sequence alignments can be performed using BLASTP version 2.0.8 (Jan. 5, 1999) and the following parameters: Matrix: 0 BLOSUM62; gap open: 11; gap extension: 1; x_dropoff: 50; expect: 10.0; wordsize: 3; filter: on. Nucleic acid sequence alignments can be performed using BLASTN version 2.0.6 (Sep. 16-1998) and the following parameters: Match: 1; mismatch: −2; gap open: 5; gap extension: 2; x_dropoff: 50; expect: 10.0; wordsize: 11; filter: off. Those skilled in the art will know what modifications can be made to the above parameters to either increase or decrease the stringency of the comparison, for example, and determine the relatedness of two or more sequences.
In some embodiments, the invention provides a non-naturally occurring microbial organism, that includes one or more gene disruptions. The disruptions occur in genes encoding an enzyme that is obligatory to coupling fumarate production to growth of the microorganism when the gene disruption reduces the activity of the enzyme, such that the gene disruptions confer stable growth-coupled production of fumarate onto the non-naturally occurring microorganism. In other embodiments, engineered organisms that include one or more gene disruptions can enhance non-growth coupled production fumarate by linking the production of fumarate to energy generation and/or redox balance.
In other embodiments, the disruptions occur in genes encoding an enzyme obligatory to coupling malate production to growth of the microorganism when the gene disruption reduces the activity of the enzyme, such that the gene disruptions confer stable growth-coupled production of malate onto the non-naturally occurring microorganism. Engineered organisms that include one or more gene disruptions can also enhance non-growth coupled production malate by linking the production of malate to energy generation and/or redox balance.
In other embodiments, the invention provides a non-naturally occurring microbial organism that includes one or more gene disruptions. The disruptions occur in genes encoding an enzyme obligatory to coupling acrylate production to growth of the microorganism when the gene disruption reduces the activity of the enzyme, such that the gene disruptions confer stable growth-coupled production of acrylate onto the non-naturally occurring microorganism. In other embodiments, engineered organisms that include one or more gene disruptions can also enhance non-growth coupled production acrylate by linking the production of acrylate to energy generation and/or redox balance.
In some embodiments, the invention provides a non-naturally occurring prokaryotic organism, that includes one or more gene disruptions. The disruptions occur in genes encoding an enzyme obligatory to coupling fumarate production to growth of the microorganism when the gene disruption reduces the activity of the enzyme, such that the gene disruptions confer stable growth-coupled production of fumarate onto the non-naturally occurring microorganism. In other embodiments, an engineered prokaryotic organism that includes one or more gene disruptions can also enhance non-growth coupled production fumarate by linking the production of fumarate to energy generation and/or redox balance.
In other embodiments, the invention provides a non-naturally occurring prokaryotic organism that includes one or more gene disruptions. The disruptions occur in genes encoding an enzyme obligatory to coupling malate production to growth of the microorganism when the gene disruption reduces the activity of the enzyme, such that the gene disruptions confer stable growth-coupled production of malate onto the non-naturally occurring microorganism. In other embodiments, an engineered prokaryotic organism that includes one or more gene disruptions can also enhance non-growth coupled production malate by linking the production of malate to energy generation and/or redox balance.
In still further embodiments, the invention provides a non-naturally occurring prokaryotic organism that includes one or more gene disruptions. The disruptions occur in genes encoding an enzyme obligatory to coupling acrylate production to growth of the organism when the gene disruption reduces the activity of the enzyme, such that the gene disruptions confer stable growth-coupled production of acrylate onto the non-naturally occurring organism. In other embodiments, an engineered prokaryotic organism that includes one or more gene disruptions can also enhance non-growth coupled production acrylate by linking the production of acrylate to energy generation and/or redox balance.
In some embodiments, the invention provides a non-naturally occurring eurakoytic organism, that includes one or more gene disruptions. The disruptions occur in genes encoding an enzyme obligatory to coupling fumarate production to growth of the organism when the gene disruption reduces the activity of the enzyme, such that the gene disruptions confer stable growth-coupled production of fumarate onto the non-naturally occurring organism. In other embodiments, an engineered eukaryotic organism that includes one or more gene disruptions can also enhance non-growth coupled production fumarate by linking the production of fumarate to energy generation and/or redox balance.
In other embodiments, the invention provides a non-naturally occurring eukaryotic organism that includes one or more gene disruptions. The disruptions occur in genes encoding an enzyme obligatory to coupling malate production to growth of the organism when the gene disruption reduces the activity of the enzyme, such that the gene disruptions confer stable growth-coupled production of malate onto the non-naturally occurring organism. In other embodiments, an engineered eukaryotic organism that includes one or more gene disruptions can also enhance non-growth coupled production malate by linking the production of malate to energy generation and/or redox balance.
In still further embodiments, the invention provides a non-naturally occurring eukaryotic organism that includes one or more gene disruptions. The disruptions occur in genes encoding an enzyme obligatory to coupling acrylate production to growth of the organism when the gene disruption reduces the activity of the enzyme, such that the gene disruptions confer stable growth-coupled production of acrylate onto the non-naturally occurring organism. In other embodiments, an engineered eukaryotic organism that includes one or more gene disruptions can also enhance non-growth coupled production acrylate by linking the production of acrylate to energy generation and/or redox balance.
Further, the present invention provides methods of producing such non-naturally prokaryotic or eukaryotic organisms having stable growth-coupled production of fumarate, malate, or acrylate. For fumarate production, for example, the method includes: (a) identifying in silico a set of metabolic modifications requiring fumarate production during cell growth, and (b) genetically modifying a microorganism to contain the set of metabolic modifications requiring fumarate production.
The engineered organisms described herein are useful not only for enhancing growth-coupled production, but they are also well-suited for enhancing non-growth coupled production because they link the production of fumarate, malate and/or acrylate to energy generation and/or redox balance. Exemplary non-growth coupled production methods include implementing an aerobic growth phase followed by an anaerobic production phase. For example, Vemuri et al. J. Ind. Microbiol. Biotechnol., 6:325-332, (2002) describe a dual-phase process for the production of succinate in E. Coli . A similar non-growth couple production process in a strain of Corynebacterium glutamicum has been described (Okino et al., Appl. Microbiol. Biotechnol. 81:459-464 (2008)).
Another such method involves withholding an essential nutrient from a propagated cell culture, thereby limiting growth, but not precluding production as described in Durner et al., Appl. Environ. Microbiol. 8:3408-3414 (2000). Yet another strategy aimed at decoupling growth from production involves replacing the growth substrate with another compound that is more slowly metabolizable as described in Altamirano et al., Biotechnol. Bioeng. 76:351-360 (2001). Growth decoupled-product formation can also be brought about by specific genetic modifications as described in Blombach et al. Appl. Microbiol. Biotechnol. 79:471-479 (2008).
One computational method for identifying and designing metabolic alterations favoring growth-coupled production of a product is the OptKnock computational framework, Burgard et al., Biotechnol Bioeng, 84:647-657 (2003). OptKnock is a metabolic modeling and simulation program that suggests gene disruption strategies that result in genetically stable microorganisms which overproduce the target product. Specifically, the framework examines the complete metabolic and/or biochemical network of a microorganism in order to suggest genetic manipulations that force the desired biochemical to become an obligatory byproduct of cell growth. By coupling biochemical production with cell growth through strategically placed gene deletions or other functional gene disruption, the growth selection pressures imposed on the engineered strains after long periods of time in a bioreactor lead to improvements in performance as a result of the compulsory growth-coupled biochemical production.
The concept of growth-coupled biochemical production can be visualized in the context of the biochemical production envelopes of a typical metabolic network calculated using an in silico model. These limits are obtained by fixing the uptake rate(s) of the limiting substrate(s) to their experimentally measured value(s) and calculating the maximum and minimum rates of biochemical production at each attainable level of growth. Although exceptions exist, typically the production of a desired biochemical is in direct competition with biomass formation for intracellular resources. Thus, enhanced rates of biochemical production will necessarily result in sub-maximal growth rates. The knockouts suggested by OptKnock are designed to restrict the allowable solution boundaries forcing a change in metabolic behavior from the wild-type strain as depicted in FIG. 1 . Although the actual solution boundaries for a given strain will expand or contract as the substrate uptake rate(s) increase or decrease, each experimental point should lie within its calculated solution boundary. Plots such as these enable one to visualize how close strains are to their performance limits or, in other words, how much room is available for improvement. The OptKnock framework has already been able to identify promising gene deletion strategies for biochemical overproduction, (Burgard et al., Biotechnol Bioeng, 84:647-657 (2003); Pharkya et al., Biotechnol Bioeng, 84:887-899 (2003)) and establishes a systematic framework that will naturally encompass future improvements in metabolic and regulatory modeling frameworks. Lastly, when complete gene deletions are constructed there is a negligible possibility of the designed strains reverting to their wild-type states because the genes selected by OptKnock are completely removed from the genome.
Briefly, OptKnock is a term used herein to refer to a computational method and system for modeling cellular metabolism. The OptKnock program relates to a framework of models and methods that incorporate particular constraints into flux balance analysis (FBA) models. These constraints include, for example, qualitative kinetic information, qualitative regulatory information, and/or DNA microarray experimental data. OptKnock also computes solutions to various metabolic problems by, for example, tightening the flux boundaries derived through flux balance models and subsequently probing the performance limits of metabolic networks in the presence of gene additions or deletions. OptKnock computational framework allows the construction of model formulations that enable an effective query of the performance limits of metabolic networks and provides methods for solving the resulting mixed-integer linear programming problems. The metabolic modeling and simulation methods referred to herein as OptKnock are described in, for example, U.S. patent application Ser. No. 10/043,440, filed Jan. 10, 2002, and in International Patent No. PCT/US02/00660, filed Jan. 10, 2002.
Another computational method for identifying and designing metabolic alterations favoring growth-coupled production of a product is metabolic modeling and simulation system termed SimPheny®. This computational method and system is described in, for example, U.S. patent application Ser. No. 10/173,547, filed Jun. 14, 2002, and in International Patent Application No. PCT/US03/18838, filed Jun. 13, 2003.
SimPheny® is a computational system that can be used to produce a network model in silico and to simulate the flux of mass, energy or charge through the chemical reactions of a biological system to define a solution space that contains any and all possible functionalities of the chemical reactions in the system, thereby determining a range of allowed activities for the biological system. This approach is referred to as constraints-based modeling because the solution space is defined by constraints such as the known stoichiometry of the included reactions as well as reaction thermodynamic and capacity constraints associated with maximum fluxes through reactions. The space defined by these constraints can be interrogated to determine the phenotypic capabilities and behavior of the biological system or of its biochemical components. Analysis methods such as convex analysis, linear programming and the calculation of extreme pathways as described, for example, in Schilling et al., J. Theor. Biol. 203:229-248 (2000); Schilling et al., Biotech. Bioeng. 71:286-306 (2000) and Schilling et al., Biotech. Prog. 15:288-295 (1999), can be used to determine such phenotypic capabilities.
As described above, one constraints-based method used in the computational programs applicable to the invention is flux balance analysis. Flux balance analysis is based on flux balancing in a steady state condition and can be performed as described in, for example, Varma and Palsson, Biotech. Bioeng. 12:994-998 (1994). Flux balance approaches have been applied to reaction networks to simulate or predict systemic properties of, for example, adipocyte metabolism as described in Fell and Small, J. Biochem. 138:781-786 (1986), acetate secretion from E. coli under ATP maximization conditions as described in Majewski and Domach, Biotech. Bioeng. 35:732-738 (1990) or ethanol secretion by yeast as described in Vanrolleghem et al., Biotech. Prog. 12:434-448 (1996). Additionally, this approach can be used to predict or simulate the growth of S. cerevisiae on a variety of single-carbon sources as well as the metabolism of H. influenzae as described in Edwards and Palsson, Proc. Natl. Acad. Sci. 97:5528-5533 (2000), Edwards and Palsson, J. Bio. Chem. 274:17410-17416 (1999) and Edwards et al., Nature Biotech. 19:125-130 (2001).
Once the solution space has been defined, it can be analyzed to determine possible solutions under various conditions. This computational approach is consistent with biological realities because biological systems are flexible and can reach the same result in many different ways. Biological systems are designed through evolutionary mechanisms that have been restricted by fundamental constraints that all living systems must face. Therefore, constraints-based modeling strategy embraces these general realities. Further, the ability to continuously impose further restrictions on a network model via the tightening of constraints results in a reduction in the size of the solution space, thereby enhancing the precision with which physiological performance or phenotype can be predicted.
Given the teachings and guidance provided herein, those skilled in the art will be able to apply various computational frameworks for metabolic modeling and simulation to design and implement growth-coupled production of a biochemical product. Such metabolic modeling and simulation methods include, for example, the computational systems exemplified above as SimPheny® and OptKnock. For simplicity in illustrating the invention, the methods and strains will be described herein with reference to the OptKnock computation framework for modeling and simulation. Those skilled in the art will know how to apply the identification, design and implementation of the metabolic alterations using OptKnock to any of such other metabolic modeling and simulation computational frameworks and methods well known in the art.
The ability of a cell or organism to obligatory couple growth to the production of a biochemical product can be illustrated in the context of the biochemical production limits of a typical metabolic network calculated using an in silico model. These limits are obtained by fixing the uptake rate(s) of the limiting substrate(s) to their experimentally measured value(s) and calculating the maximum and minimum rates of biochemical production at each attainable level of growth. As shown in FIG. 1 , the production of a desired biochemical generally is in direct competition with biomass formation for intracellular resources. Under these circumstances, enhanced rates of biochemical production will necessarily result in sub-maximal growth rates. The knockouts suggested by the above metabolic modeling and simulation programs such as OptKnock are designed to restrict the allowable solution boundaries forcing a change in metabolic behavior from the wild-type strain as depicted in FIG. 1 . Although the actual solution boundaries for a given strain will expand or contract as the substrate uptake rate(s) increase or decrease, each experimental point will lie within its calculated solution boundary. Plots such as these enable accurate predictions of how close the designed strains are to their performance limits which also indicates how much room is available for improvement.
The OptKnock mathematical framework is exemplified herein for pinpointing gene deletions leading to growth-coupled biochemical production as illustrated in FIG. 1 . The procedure builds upon constraint-based metabolic modeling which narrows the range of possible phenotypes that a cellular system can display through the successive imposition of governing physico-chemical constraints, Price et al., Nat Rev Microbiol, 2: 886-97 (2004). As described above, constraint-based models and simulations are well known in the art and generally invoke the optimization of a particular cellular objective, subject to network stoichiometry, to suggest a likely flux distribution.
Briefly, the maximization of a cellular objective quantified as an aggregate reaction flux for a steady state metabolic network comprising a set N={1 . . . , N} of metabolites and a set M={1, . . . , M}of metabolic reactions is expressed mathematically as follows:
maximize
v
cellular
objective
subject
to
∑
j
=
1
M
S
ij
v
j
=
0
,
∀
∈
N
v
substrate
=
v
subsirate_uptake
m
mol
/
gDW
·
hr
∀
∈
{
limiting
substrate
(
s
)
}
v
atp
≥
v
atp_main
m
mol
/
gDW
·
hr
v
j
≥
0
,
∀
∈
{
irrev
.
reactions
}
where S ij is the stoichiometric coefficient of metabolite i in reaction j, v j is the flux of reaction j, V substrate — uptake represents the assumed or measured uptake rate(s) of the limiting substrate(s), and v atp — main is the non-growth associated ATP maintenance requirement. The vector v includes both internal and external fluxes. In this study, the cellular objective is often assumed to be a drain of biosynthetic precursors in the ratios required for biomass formation, Neidhardt, F. C. et al., 2nd ed. 1996, Washington, D.C.: ASM Press. 2 v. (xx, 2822, lxxvi). The fluxes are generally reported per 1 gDW·hr (gram of dry weight times hour) such that biomass formation is expressed as g biomass produced/gDW·hr or l/hr.
The modeling of gene deletions, and thus reaction elimination, first employs the incorporation of binary variables into the constraint-based approach framework, Burgard et al., Biotechnol Bioeng, 74: 364-375 (2001), Burgard et al., Biotechnol Prog, 17: 791-797 (2001). These binary variables,
y
j
=
{
1
,
if
reaction
flux
v
j
is
active
0
,
if
reaction
flux
v
j
is
not
active
,
∀
∈
M
assume a value of 1 if reaction j is active and a value of 0 if it is inactive. The following constraint,
v
j
min
·y
j
≧b
j
≧v
j
next
·y
i
,∀jεM
ensures that reaction flux v j is set to zero only if variable y j is equal to zero. Alternatively, when y j is equal to one, v j is free to assume any value between a lower v j min and an upper v j max bound. Here, v j min and v j max are identified by minimizing and maximizing, respectively, every reaction flux subject to the network constraints described above, Mahadevan et al., Metab Eng, 5: 264-76 (2003).
Optimal gene/reaction knockouts are identified by solving a bilevel optimization problem that chooses the set of active reactions (y j =1) such that an optimal growth solution for the resulting network overproduces the chemical of interest. Schematically, this bilevel optimization problem is illustrated in FIG. 2 . Mathematically, this bilevel optimization problem is expressed as the following bilevel mixed-integer optimization problem:
maximize
y
j
v
chemical
(
OptKnock
)
(
subject
to
v
j
maximize
v
biomass
subject
to
∑
j
=
1
M
S
ij
v
j
=
0
,
∀
∈
N
v
substrate
=
v
substrate_uptake
∀
∈
{
limiting
substrate
(
s
)
}
v
atp
≥
v
atp_main
v
biomass
≥
v
biomass
target
)
v
j
min
·
y
j
≤
v
j
≤
v
j
max
·
y
j
,
∀
j
∈
M
∑
j
∈
M
forward
(
1
-
y
j
)
=
K
y
j
∈
{
0
,
1
}
,
∀
j
∈
M
where v chemical is the production of the desired target product, for example fumarate or other biochemical product, and K is the number of allowable knockouts. Note that setting K equal to zero returns the maximum biomass solution of the complete network, while setting K equal to one identifies the single gene/reaction knockout (y j =0) such that the resulting network involves the maximum overproduction given its maximum biomass yield. The final constraint ensures that the resulting network meets a minimum biomass yield. Burgard et al., Biotechnol Bioeng, 84: 647-57 (2003), provide a more detailed description of the model formulation and solution procedure. Problems containing hundreds of binary variables can be solved in the order of minutes to hours using CPLEX 8.0, GAMS: The Solver Manuals. 2003: GAMS Development Corporation, accessed via the GAMS, Brooke et al., GAMS Development Corporation (1998), modeling environment on an IBM RS6000-270 workstation. The OptKnock framework has already been able to identify promising gene deletion strategies for biochemical overproduction, Burgard et al., Biotechnol Bioeng, 84: 647-57 (2003), Pharkya et al., Biotechnol Bioeng, 84: 887-899 (2003), and establishes a systematic framework that will naturally encompass future improvements in metabolic and regulatory modeling frameworks.
Any solution of the above described bilevel OptKnock problem will provide one set of metabolic reactions to disrupt. Elimination of each reaction within the set or metabolic modification can result in fumarate as an obligatory product during the growth phase of the organism. Because the reactions are known, a solution to the bilevel OptKnock problem also will provide the associated gene or genes encoding one or more enzymes that catalyze each reaction within the set of reactions. Identification of a set of reactions and their corresponding genes encoding the enzymes participating in each reaction is generally an automated process, accomplished through correlation of the reactions with a reaction database having a relationship between enzymes and encoding genes.
Once identified, the set of reactions that are to be disrupted in order to achieve increased fumarate, malate, or acrylate production are implemented in the target cell or organism by functional disruption of at least one gene encoding each metabolic reaction within the set. As described previously, one particularly useful means to achieve functional disruption of the reaction set is by deletion of each encoding gene. However, in some instances, it can be beneficial to disrupt the reaction by other genetic aberrations including, for example, mutation, deletion of regulatory regions such as promoters or cis binding sites for regulatory factors, or by truncation of the coding sequence at any of a number of locations. These latter aberrations, resulting in less than total deletion of the gene set can be useful, for example, when rapid assessments of the product coupling are desired or when genetic reversion is less likely to occur.
To identify additional productive solutions to the above described bilevel OptKnock problem which lead to further sets of reactions to disrupt or metabolic modifications that can result in the growth-coupled production of fumarate, malate, acrylate, or other biochemical products, an optimization method, termed integer cuts, can be implemented. This method proceeds by iteratively solving the OptKnock problem exemplified above with the incorporation of an additional constraint referred to as an integer cut at each iteration. Integer cut constraints effectively prevent the solution procedure from choosing the exact same set of reactions identified in any previous iteration that obligatory couples product biosynthesis to growth. For example, if a previously identified growth-coupled metabolic modification specifies reactions 1, 2, and 3 for disruption, then the following constraint prevents the same reactions from being simultaneously considered in subsequent solutions: y 1 +y 2 +y 3 ≧1. The integer cut method is well known in the art and can be found described in, for example, reference, Burgard et al., Biotechnol Prog, 17:791-797 (2001). As with all methods described herein with reference to their use in combination with the OptKnock computational framework for metabolic modeling and simulation, the integer cut method of reducing redundancy in iterative computational analysis also can be applied with other computational frameworks well known in the art including, for example, SimPheny.
Constraints of the above form preclude identification of larger reaction sets that include previously identified sets. For example, employing the integer cut optimization method above in a further iteration would preclude identifying a quadruple reaction set that specified reactions 1, 2, and 3 for disruption since these reactions had been previously identified. To ensure identification of all possible reaction sets leading to growth-coupled production of a product, a modification of the integer cut method was employed.
Briefly, the modified integer cut procedure begins with iteration ‘zero’ which calculates the maximum production of the desired biochemical at optimal growth for a wild-type network. This calculation corresponds to an OptKnock solution with K equaling 0. Next, single knockouts are considered and the two parameter sets, objstore iter and ystore iter,j , are introduced to store the objective function (v chemical ) and reaction on-off information (y j ), respectively, at each iteration, (y j ). The following constraints are then successively added to the OptKnock formulation at each iteration.
v chemical ≧objstore iter +ε−M·Σ jεystore iter,j =0 y j
In the above equation, ε and M are a small and a large numbers, respectively. In general, ε can be set at about 0.01 and M can be set at about 1000. However, numbers smaller and/or larger then these numbers also can be used. M ensures that the constraint can be binding only for previously identified knockout strategies, while ε ensures that adding knockouts to a previously identified strategy must lead to an increase of at least ε in biochemical production at optimal growth. The approach moves onto double deletions whenever a single deletion strategy fails to improve upon the wild-type strain. Triple deletions are then considered when no double deletion strategy improves upon the wild-type strain, and so on. The end result is a ranked list, represented as desired biochemical production at optimal growth, of distinct deletion strategies that differ from each other by at least one knockout. This optimization procedure as well as the identification of a wide variety of reaction sets that, when disrupted, lead to increased production of a biochemical product are exemplified in detail further below. Given the teachings and guidance provided herein, those skilled in the art will understand that the methods and metabolic engineering designs exemplified herein are applicable to linking cell or microorganism growth to any biochemical product.
Employing the methods exemplified above, one can construct cells and organisms that obligatorily couple the production of a target biochemical product to growth of the cell or organism engineered to harbor the identified genetic alterations. In this regard, metabolic alterations have been identified that obligatorily couple the production of fumarate, malate, or acrylate to organism growth. Prokaryotic or eukaryotic organism strains constructed with the identified metabolic alterations produce elevated levels of fumarate, malate, or acrylate during the exponential growth phase. These strains can be beneficially used for the commercial production of fumarate, malate, or acrylate in continuous fermentation process without being subjected to the negative selective pressures described previously.
As described above, the metabolic alterations also enable non-growth coupled production of fumarate, malate, or acrylate. The invention is described herein with general reference to the metabolic reaction, reactant or product thereof, or with specific reference to one or more genes associated with the referenced metabolic reaction, reactant or product. Unless otherwise expressly stated herein, those skilled in the art will understand that reference to a reaction also constitutes reference to the reactants and products of the reaction. Similarly, unless otherwise expressly stated herein, reference to a reactant or product also references the reaction and that reference to any of these metabolic constitutes also references the gene or genes encoding the enzymes that catalyze the referenced reaction, reactant or product. Likewise, given the well known fields of metabolic biochemistry, enzymology and genomics, reference herein to a gene also constitutes a reference to the corresponding encoded enzyme and the reaction it catalyzes as well as the reactants and products of the reaction.
The methods of the invention provide a set of metabolic modifications that are identified by an in silico method selected from OptKnock. The set of metabolic modifications can include functional disruption of one or more metabolic reactions including, for example, disruption by gene deletion. Exemplary reactions, reaction nomenclature, reactants, products, cofactors and genes encoding enzymes catalyzing a reaction involved in the growth-coupled production of fumarate and malate in E. Coli are set forth in Tables 1, 2, 3, and 4.
The invention provides non naturally occurring microorganisms having increased production of fumarate or malate. Fumarate or malate production can be obligatorily linked to the exponential growth phase of the microorganism by genetically altering the metabolic pathways of the cell. The genetic alterations make fumarate an obligatory product during the growth phase. In some embodiments, fumarate or malate production is not obligatorily linked to growth. In such a case, the production of fumarate or malate takes place during a non-growth phase, for example. Sets of metabolic alterations or transformations that result in elevated levels of fumarate or malate biosynthesis are exemplified in Tables 1 and 2, respectively. Each alteration within a set corresponds to the requisite metabolic reaction that can be functionally disrupted. Functional disruption of all reactions within each set results increased production of fumarate or malate by the engineered strain. The corresponding reactions to the referenced alterations in Tables 1 and 2, and the gene or genes that potentially encode them in E. coli , are set forth in Table 3.
For example, for each strain exemplified in Table 1, the metabolic alterations that can be generated for increased fumarate production are shown in each row. These alterations include the functional disruption of from one to six or more reactions. In particular, 348 strains are exemplified in Table 1 that have non-naturally occurring metabolic genotypes. Each of these non-naturally occurring alterations result in an enhanced level of fumarate production during the exponential growth phase of the microorganism compared to a wild-type strain, under appropriate culture conditions. Appropriate conditions include, for example, those exemplified further below in the Example I such as particular carbon sources or reactant availabilities and/or adaptive evolution.
One such strain design for fumarate production involves deletions in fumarate reductase (FRD), alcohol dehydrogenase (ADHEr), lactate dehydrogenase (LDH_D), and glutamate dehydrogenase (GLUDy). This strain is predicted to have a growth-coupled yield of 1.83 moles of fumarate per mole of glucose consumed and the maximum growth rate is anticipated to be 0.09/hr as shown in FIG. 2 . The deletion of FRD, ADHEr, and LDH_D prevents the formation and secretion of byproducts, namely succinate, ethanol and lactate. The elimination of glutamate dehydrogenase that transaminates alpha-ketoglutarate into glutamate with the utilization of a molecule of NADPH, disrupts a loop of reactions that form and use NADPH for synthesis of amino acids such as alanine and valine. All the disruptions can be implemented sequentially based on the necessity to do so. FIG. 2 shows the growth-coupled fumarate production characteristics of the strain (black, dashed) incorporating these disruptions compared with those of the wild-type E. coli network (black, at the maximum rate of growth, the wild-type network is not expected to form any fumarate.)
Another strain, shown in FIG. 3 , has three common deletions with the strain shown in FIG. 2 and involves elimination of malic enzyme (ME2) and transhydrogenase (THD2) activity additionally. Malic enzyme catalyzes the decarboxylation of malate to form pyruvate with the concomitant reduction of a molecule of NADP to form NADPH. Transhydrogenase catalyzes the oxidation of NADH causing the reduction of NADP into NADPH. The deletion of the NADPH-forming malic enzyme and the membrane-bound proton-translocating transhydrogenase catalyzed by PntAB prevents or reduces the formation of NADPH, thus preventing or reducing carbon from being funneled into amino acids instead of being converted into fumarate. The efficacy of the two latter knockouts for fumarate production can be assessed and implemented sequentially based on the necessity to do so.
The strain of FIG. 3 is expected to have a maximum growth-coupled yield of 1.87 moles of fumarate per mole of glucose consumed at an expected maximum growth rate of 0.08/hr. Note also that the strain is has a minimum theoretical product yield of 0.48 moles per mole of glucose (the grey point on the black, dotted curve). FIG. 3 shows the growth-coupled fumarate production characteristics of the strain (black, dotted) compared with those of the wild-type E. coli network (black). The grey point shows the minimum amount of product formation expected from this strain.
An additional disruption in PFL (pyruvate formate lyase) can improve the theoretical yield of fumarate marginally to 1.89 moles per mole of glucose consumed and the expected growth rate of this strain is 0.07 per hour.
Another strain, shown in FIG. 4 , disrupts the GLCpts mechanism of glucose transport and instead relies on hexokinase activity. This disruption along with disruption of FRD, ADHEr, LDH_D, and ME2 leads to an expected maximum growth rate for the strain at approximately 0.1 per hour. The product yield is expected to be 1.82 moles per mole of glucose consumed. The strain is expected to start producing fumarate once it reaches approximately 36% of its maximum theoretical biomass formation rate. FIG. 4 shows the production curve for this strain (grey, dashed) compared with the production curve for the wild-type E. coli network (black). Note that this strain is equivalent to the strain of FIG. 2 if an additional deletion in THD2 is introduced.
Another strain, shown in FIG. 5 , has deletions in FRD, ADHEr, LDH_D, ME2, THD2 and HEX1. The deletion in HEX1 forces glucose flux through the PTS system, converting an equivalent molar amount of phosphoenolpyruvate (PEP) into pyruvate. To attain a balance of cofactors, the network is forced to convert most of the pyruvate back into PEP through PEP synthase. This is an energy-intensive step and limits the biomass formation in the network. However, the carbon distribution provides PEP to be used by PPCK and subsequent channeling into the reductive TCA cycle. This leads to the very high fumarate yields in the network of up to 1.97 moles per mole of glucose consumed as shown in FIG. 5 . These disruptions reduce the feasible solution space of the mutant network significantly and the strain is expected to have a minimum product yield of at least 1.25 moles per mole of glucose consumed as shown by the black point in FIG. 5 . Although strain is predicted to grow slowly at a rate of approximately 0.02 per hour, the prospect of achieving near maximum theoretical product yields makes this design particularly useful. The strain is expected to secrete very small quantities of acetate and formate. FIG. 5 shows the production curve for the strain (grey, dashed) compared with the production curve of the wild type E. coli network (black). The black point indicates the minimum amount of product formation expected from this strain.
To provide a comparison of the fumarate production characteristics of the four strains discussed above, the production curves are presented on the same plot and compared with those of the wild-type E. coli network as shown in FIG. 6 . Other strains for fumarate production in E. Coli are listed in Table 1. FIG. 6 shows the production curves for the strains in 1) black, dashed, 2) black, dotted, 3) grey, dashed and 4) grey compared with each other and with the production characteristics of the wild-type E. coli network in black. Note the reduction in feasible solution space as additional deletions are imposed on the network.
The anaerobic designs for the formation of malate are described below and utilize disruptions that have already been described for fumarate production. The strain designs for malate production have additional knockouts that preclude fumarate formation in the network.
One strain, shown in FIG. 7 , allows for increased formation of malate by building upon the disruptions in the strain of FIG. 2 . As described above, deletions in ADHEr, LDH_D, FRD, ME2 and THD2 allow for the enhanced formation of either fumarate or malate. An additional deletion in fumarase (FUM) prevents or reduces the conversion of malate into fumarate, leading to increase malate production of 1.86 moles per mole of glucose consumed as shown in FIG. 7 . Small modifications in this strain lead to another high-yielding strain shown in FIG. 8 . Thus, instead of the FRD deletion, this strain has a disruption in aspartase (ASPT). The deletion of ASPT reinforces the effect of the fumarase deletion by preventing the network from converting oxaloacetate into aspartate which can subsequently be transformed into fumarate via aspartase. Without the deletion in ASPT, the strain can produce approximately 1.55 moles of succinate per mole of glucose consumed. This modified strain design with deletions in ADHEr, THD2, LDH_D, ME2, FUM, and ASPT leads to a growth-coupled theoretical yield of 1.85 moles of malate per mole of glucose consumed, shown in FIG. 8 , with an expected growth rate of 0.08 per hour. Each of these strains is expected to have a non-zero minimum rate of malate production. Note the grey and black points in FIGS. 7 and 8 respectively. Several other strains with increased malate yields in E. Coli have been identified and are listed in Table 2.
Based on these strains, the invention also provides a non-naturally occurring microorganism having a set of metabolic modifications coupling fumarate or malate production to growth of the microorganism, the set of metabolic modifications includes disruption of one or more genes selected from the set of genes encoding proteins that include: (a) a fumarate reductase (FRD), an alcohol dehydrogenase (ADHEr), and a lactate dehydrogenase (LDH_D).
Analysis of the strains for fumarate production allows identification of a minimum set of deletions that increase fumarate production in the network. Note that PPCK was assumed to be reversible in the network. Briefly, deletions in fumarate reductase (FRD), alcohol dehydrogenase (ADHEr), and lactate dehydrogenase (LDH_D) prevent the formation of competing byproducts, namely, succinate, ethanol and lactate. The minimum enzyme disruption set based on the aforementioned strains includes disruption of fumarate reductase, alcohol dehydrogenase and lactate dehydrogenase. This corresponds to the following minimal exemplary gene disruption set:
frd (b4151 or b4152 or b4153 or b4154), adhE (b1421), and ldhA (b1380)
Additional disruptions have been identified by the OptKnock framework for the increased formation of fumarate. Note that these disruptions may have been predicted because no regulatory information is accounted for in the metabolic network. Nevertheless, it is predicted that supplementary disruptions or deletions in one or more of the functionalities, namely glutamate dehydrogenase (GLUDy), malic enzyme (ME2), and transhydrogenase (THD2) are useful for increased formation of the diacids of interest. These deletions can be introduced sequentially into E. coli K12. If these deletions/dirsuptions have to be introduced, the minimal set of activities that need to be deleted can be expanded to include the following:
Fumarate reductase, alcohol dehydrogenase, lactate dehydrogenase, and glutamate dehydrogenase, or
Fumarate reductase, alcohol dehydrogenase, lactate dehydrogenase, and malic enzyme, or
Fumarate reductase, alcohol dehydrogenase, lactate dehydrogenase, malic enzyme, and transhydrogenase
Correspondingly, the minimal gene set can be expanded to yield:
frd (b4151 or b4152 or b4153 or b4154), adhE (b1421), ldhA (b1380), and gdhA (b1761), or
frd (b4151 or b4152 or b4153 or b4154), adhE (b1421), ldhA (b1380), and maeB (b2463), or
frd (b4151 or b4152 or b4153 or b4154), adhE (b1421), ldhA (b1380), pntAB (b1602, b1603), and maeB (b2463)
Further improvement in yields can be attained by disrupting one or more of the following functionalities: phosphotransacetylase (PTAr), the PTS mechanism of glucose transport (GLCpts), hexokinase (HEX 1) or pyruvate formate lyase (PFL). Note that all the isozymes capable of carrying out a given activity should be disrupted or deleted given a possibility of the isozymes becoming active due to adaptive evolution. The enzyme disruption set after introducing these auxiliary deletions are listed below:
Fumarate reductase, alcohol dehydrogenase, lactate dehydrogenase, transhydrogenase, malic enzyme, and hexokinase, or
Fumarate reductase, alcohol dehydrogenase, lactate dehydrogenase, malic enzyme, and the PTS transport mechanism of glucose, or
Fumarate reductase, alcohol dehydrogenase, lactate dehydrogenase, transhydrogenase, malic enzyme, and pyruvate formate lyase
The corresponding gene deletion sets are:
frd (b4151 or b4152 or b4153 or b4154), adhE (b1421), ldhA (b1380), pntAB (b1602, b1603), maeB (b2463) and glk (b2388)
frd (b4151 or b4152 or b4153 or b4154), adhE (b1421), ldhA (b1380), maeB (b2463), and pts (b1101 or b2415 or b2416 or b2417)
frd (b4151 or b4152 or b4153 or b4154), adhE (b1421), ldMA (b1380), pntAB (b1602, b1603), maeB (b2463), and pflAB (b0902, b0903)
For homomalate production, a disruption in fumarase (FUM) is utilized in addition to disruptions in alcohol dehydrogenase (ADHEr), lactate dehydrogenase (LDH_D) and fumarate reductase (FRD). Thus, the minimal enzyme deletion set is:
Fumarate reductase, alcohol dehydrogenase, lactate dehydrogenase, and fumarase
The disruption of these activities corresponds to the deletion of the following genes:
frd (b4151 or b4152 or b4153 or b4154), adhE (b1421), ldha (b1380), and fumABC (b1611, b1612, b4122)
An alternative set of enzyme deletions can also enable homomalate production is as follows:
Alcohol dehydrogenase, lactate dehydrogenase, fumarase and L-aspartase
This corresponds to a minimum gene deletion set of:
adhE (b1421), ldhA (b1380), and fumABC (b1611, b1612, b4122) and aspA (b4139)
Thus, in some embodiments, the present invention provides a non-naturally occurring microbial organism that includes one or more gene disruptions occurring in genes encoding enzymes that increase homomalate production when the gene disruption reduces an activity of the enzyme, whereby the one or more gene disruptions confers increased production of homomalate onto said non-naturally occurring microorganism.
However, as explained earlier for fumarate production, disruptions in one or more out of the following reactions, glutamate dehydrogenase (GLUDy), transhydrogenase (THD2) and malic enzyme (ME2), can be useful, yielding the following minimal enzyme sets for deletion:
Fumarate reductase, alcohol dehydrogenase, lactate dehydrogenase, fumarase, and glutamate dehydrogenase, or
Fumarate reductase, alcohol dehydrogenase, lactate dehydrogenase, fumarase, and malic enzyme, or
Fumarate reductase, alcohol dehydrogenase, lactate dehydrogenase, fumarase, transhydrogenase and malic enzyme
Accordingly, the gene deletion sets expand and are listed below:
frd(b4151 or b4152 or b4153 or b4154), adhE (b1421), ldha (b1380),fumABC (b1611, b1612, b4122), and gdhA (b1761), or
frd(b4151 or b4152 or b4153 or b4154), adhE (b1421), ldha (b1380),fumABC (b1611, b1612, b4122), and maeB (b2463), or
frd(b4151 or b4152 or b4153 or b4154), adhE (b1421), ldhA (b1380),fumABC (b1611, b1612, b4122), pntAB (b1602, b1603), and maeB (b2463).
Each of these strains may be supplemented with additional deletions if it is determined that the strain does not sufficiently increase the formation of the product. Alternatively, some other enzymes not known to possess significant activity may become active due to adaptive evolution or random mutagenesis and they will also have to be disrupted as well. For example, succinate dehydrogenase which oxidizes succinate to fumarate and is known to be active only under aerobic conditions may assume significant activity even under anaerobic conditions and may have to be disrupted. However, the list of gene disruption sets provided here serves as a starting point for construction of high-yielding malate and fumarate producing strains.
For fumarate and malate production metabolic modifications in eukarotic organisms sets of metabolic modifications are listed in Table 5. For acrylate production metabolic modifications in eukaryotic organisms can be selected from the set of metabolic modifications listed in Table 6.
The non-naturally occurring eukaryotic organism can have one or more gene disruptions included in a metabolic modification listed in Tables 5 or 6. The one or more gene disruptions can be a deletion. The non-naturally occurring eukaryotic organism of the invention can be selected from a group of eukaryotic organism having a metabolic modification listed in Tables 5 or 6. Non-naturally occurring eukaryotic organisms of the invention include yeast, fungus, or any of a variety of other microorganisms applicable to fermentation processes. Exemplary eukaryotic species include those selected from Saccharomyces cerevisiae, Schizosaccharomyces pombe, Kluyveromyces lactis, Kluyveromyces marxianus, Aspergillus terreus, Aspergillus niger, Rhizopus arrhizus, Rhizopus oryzae , and Pichia pastoris.
The eukaryotic organisms having increased fumarate, malate, or acrylate production are exemplified herein with reference to an S. cerevisiae genetic background. However, with the complete genome sequence available for now more than 550 species (with more than half of these available on public databases such as the NCBI), including 395 microorganism genomes and a variety of yeast, fungi, plant, and mammalian genomes, the identification of an alternate species homolog for one or more genes, including for example, orthologs, paralogs and nonorthologous gene displacements, and the interchange of genetic alterations between organisms is routine and well known in the art. Accordingly, the metabolic alterations enabling increased production of the products described herein with reference to a particular organism such as S. cerevisiae can be readily applied to other microorganisms, especially other eukaryotic organisms. Given the teachings and guidance provided herein, those skilled in the art will know that a metabolic alteration exemplified in one organism can be applied equally to other organisms.
As described previously, homologues can include othologs and/or nonorthologous gene displacements. In some instances, such as when a substitute metabolic pathway exists in the species of interest, functional disruption can be accomplished by, for example, deletion of a paralog that catalyzes a similar, yet non-identical metabolic reaction which replaces the referenced reaction. Because there are differences among metabolic networks between different organisms, those skilled in the art will understand that the actual genes disrupted between different organisms may differ. However, given the teachings and guidance provided herein, those skilled in the art also will understand that the methods of the invention can be applied to all microorganisms to identify the cognate metabolic alterations between organisms and to construct an organism in a species of interest that will enhance the coupling of fumarate, malate, or acrylate biosynthesis to growth.
As described previously and further below, exemplary reactions, reaction nomenclature, reactants, products, cofactors and genes encoding enzymes catalyzing a reaction involved in the increased production of fumarate, malate, and acrylate in S. Cerevisiae are set forth in Tables 5, 6, 7, and 8.
The invention provides non naturally occurring eukaryotic organisms having growth-coupled production of fumarate, malate, or acrylate. Product production can be optionally obligatorily linked to the exponential growth phase of the microorganism by genetically altering the metabolic pathways of the cell. The genetic alterations can make the formation of the desired product obligatory to growth. Sets of metabolic alterations or transformations that result in elevated levels of fumarate, malate, or acrylate biosynthesis are exemplified in Tables 5 and 6, respectively. Each alteration within a set corresponds to the requisite metabolic reaction that should be functionally disrupted. Functional disruption of all reactions within each set results in the obligatory production of fumarate, malate, or acrylate by the engineered strain during the growth phase. The corresponding reactions to the referenced alterations in Tables 5 and 6, and the gene or genes that potentially encode them in S. cerevisiae , are set forth in Table 7.
For example, for each strain exemplified in Table 5, the metabolic alterations that can be generated for increase fumarate or malate production are shown in each row. These alterations include the functional disruption of from one to six or more reactions. In particular, 278 strains are exemplified in Table 5 that have non-naturally occurring metabolic genotypes. Each of these non-naturally occurring alterations result in an enhanced level of fumarate or malate production in the eukaryotic organism compared to a wild-type strain, under appropriate culture conditions. Appropriate conditions include, for example, those exemplified further below in the Example II such as particular carbon sources or reactant availabilities and/or adaptive evolution. Similarly, 495 strains are exemplified in Table 6 that have non-naturally occurring metabolic genotypes. Each of these non-naturally occurring alterations result in an enhanced level of acrylate production during the exponential growth phase of the eukaryotic organism compared to a wild-type strain, under appropriate culture conditions.
Given the teachings and guidance provided herein, those skilled in the art will understand that to disrupt an enzymatic reaction it is necessary to disrupt the catalytic activity of the one or more enzymes involved in the reaction. Disruption can occur by a variety of means including, for example, deletion of an encoding gene or incorporation of a genetic alteration in one or more of the encoding gene sequences as described previously in reference to the disruptions for E. Coli . The encoding genes targeted for disruption can be one, some, or all of the genes encoding enzymes involved in the catalytic activity. For example, where a single enzyme is involved in a targeted catalytic activity disruption can occur by a genetic alteration that reduces or destroys the catalytic activity of the encoded gene product. Similarly, where the single enzyme is multimeric, including heteromeric, disruption can occur by a genetic alteration that reduces or destroys the function of one or all subunits of the encoded gene products. Destruction of activity can be accomplished by loss of the binding activity of one or more subunits in order to form an active complex, by destruction of the catalytic subunit of the multimeric complex or by both. Other functions of multimeric protein association and activity also can be targeted in order to disrupt a metabolic reaction of the invention. Such other functions are well known to those skilled in the art. Further, some or all of the functions of a single polypeptide or multimeric complex can be disrupted according to the invention in order to reduce or abolish the catalytic activity of one or more enzymes involved in a reaction or metabolic modification of the invention. Similarly, some or all of enzymes involved in a reaction or metabolic modification of the invention can be disrupted so long as the targeted reaction is destroyed.
Given the teachings and guidance provided herein, those skilled in the art also will understand that an enzymatic reaction can be disrupted by reducing or eliminating reactions encoded by a common gene and/or by one or more orthologs of that gene exhibiting similar or substantially the same activity. Reduction of both the common gene and all orthologs can lead to complete abolishment of any catalytic activity of a targeted reaction. However, disruption of either the common gene or one or more orthologs can lead to a reduction in the catalytic activity of the targeted reaction sufficient to promote coupling of growth to product biosynthesis. Exemplified herein are both the common genes encoding catalytic activities for a variety of metabolic modifications as well as their orthologs. Those skilled in the art will understand that disruption of some or all of the genes encoding an enzyme of a targeted metabolic reaction can be practiced in the methods of the invention and incorporated into the non-naturally occurring eukaryotic organisms of the invention in order to achieve the growth-coupled product production.
Herein below are described the designs identified for increasing fumarate, malate, and acrylate production in S. cerevisiae . For prediction of the strains, it was assumed that (i) the glucose uptake rate in the network was 10 mmol/gDCW.hr, (ii) a minimum non-growth associated maintenance requirement of 1 mmol/gDCW.hr was imposed upon the network, and
(iii) phosphoenolpyruvate carboxykinase (PPCK) could operate in the carbon-fixing direction towards oxaloacetate. The reversibility of PPCK allows for the fixing of carbon dioxide such that a yield of 2 moles per mole of glucose for each of these products can be attained under microaerobic/anaerobic conditions. More importantly, it allows for production of ATP in the process. The ATP generation accompanying the reverse operability of PPCK supports the energy requirements for biomass formation as well as for product formation and export under anaerobic conditions. Note that the production of fumaric, malic and acrylic acids is otherwise energetically neutral in the S. cerevisiae metabolic network. The native PPCK in S. cerevisiae , encoded by Pckl, plays a key role in gluconeogenesis and operates to consume ATP to form PEP (Haarasilta and Oura, Eur. J. Biochem., 52:1-7 (1975)). Therefore, a heterologous enzyme, for example from Mannheimia succiniciproducens (Lee et al., Appl Environ Microbiol, 72:1939-1948 (2006)), Anaerobiospirillum succiniciproducens (Laivenieks et al., Appl Environ Microbiol, 63:2273-2280 (1997)), or Actinobacillus succinogenes (Kim, P. et al., Appl Environ Microbiol, 70:1238-1241 (2004)) with more favorable kinetics in the desired direction will be introduced into S. cerevisiae . The functioning of the enzyme in the requisite direction may require high concentrations of dissolved carbon dioxide in the fermentation medium. The protein sequences of the PEP carboxykinase enzymes mentioned in the text can be found via the following GenBank accession numbers and are summarized below:
Gene name
Organism
Accession Number
pckA
Mannheimia
YP_089485
succiniciproducens
(GI: 52426348)
pckA
Anaerobiospirillum
O09460
succiniciproducens
(GI: 3122621)
pck
Actinobacillus
ABX39017
succinogenes
(GI: 160415396)
The designs for fumaric and malic acid production, but not for acrylic acid production, use a small supply of oxygen in the network. This is because diacid production in S. cerevisiae is energetically neutral under anaerobic conditions, even upon assuming the reversibility of PPCK. Assuming that the symport of the fumarate or malate dianion is feasible with a proton at moderately low pH values, one additional proton needs to be pumped out to maintain homeostasis. The ATPase in S. cerevisiae uses one ATP for exporting out each proton which makes fumarate and malate production energetically neutral under anaerobic conditions. A limited supply of oxygen therefore provides for favorable energetics that can enable growth and product export. Note that a more favorable proton translocation stoichiometry of the ATPase can render these designs energetically feasible even in the absence of oxygen. It has been recently shown that introducing point mutations into the ATPase encoded by PMA1 in S. cerevisiae can increase or decrease its proton coupling efficiency and in some cases, bring the number of protons excreted per ATP hydrolyzed closer to two (Guerra, G. et al., Biochim Biophys Acta, 1768:2383-2392 (2007)). Alternatively, a non-native ATPase with an increased coupling efficiency can be introduced, as was demonstrated (Morsomme, P. et al., Embo J, 15:5513-5526 (1996)) where a mutated plant ATPase permitted growth of an ATPase-deficient S. cerevisiae strain at a pH of 4.
In some embodiments, microaerobic (substantially anaerobic) designs can be used based on increased formation of the desired product. To examine this, production cones were constructed for each strain by first maximizing and, subsequently minimizing the product yields at different rates of biomass formation feasible in the network. If the rightmost boundary of all possible phenotypes of the mutant network is a single point, it implies that there is a unique optimum yield of the product at the maximum biomass formation rate possible in the network. In other cases, the rightmost boundary of the feasible phenotypes is a vertical line, indicating that at the point of maximum biomass the network can make any amount of the product in the calculated range, including the lowest amount at the bottommost point of the vertical line. Such designs were given a low priority.
The fumarate-production strategies identified by the OptKnock framework were ranked on the basis of their (i) theoretical yields, and (ii) growth-coupled fumarate formation characteristics. All the strains with high product yields involve four or more knockouts because fewer knockouts were found to provide markedly lower yields. Strains with high yields include, for example, those with about 70% or more yield. The engineered strains can include further metabolic modifications aimed at limiting the production of the fumarate precursor, malate that is at the same redox state as fumarate. For example, the fumarase enzyme(s) can be manipulated by using techniques such as directed evolution so that the overall kinetics favors the conversion of malate into fumarate. Another option is to use a fumarase enzyme from any of the Rhizopus species that are known to produce high concentrations of fumarate without malate formation (e.g. fumR from R. oryzae , GenBank accession number: X78576). In another embodiment, one can use the fumarase from Euglena gracilis with a K m value of 0.031 mM for fumaric acid (Shibata et al., J Bacteriol, 164:762-768 1985)). Further, if an additional enzyme activity is introduced into S. cerevisiae to channel fumarate into a different growth-coupled end product, it will drive the metabolism towards fumarate formation and prevent malate formation. A case in point is the production of acrylic acid. The introduction of an appropriate decarboxylase enzyme can shift the equilibrium between malate and fumarate towards fumarate, thus leading to all carbon being funneled to the desired acrylic acid product. Using all the above options will ensure that the conversion of malate into fumarate is at a higher rate than the export of malate via any of the malate transporters.
For the strains that follow, the enzyme names, their abbreviations, and the corresponding reaction stoichiometries are listed in Table 7. The genes that can be mutated in order to prevent the activities of the enzymes identified for disruption are also shown in Table 7. Finally, metabolites names corresponding to the abbreviations in the reaction equations are listed in Table 8.
One strain for fumarate production, shown in FIG. 9 , involves disruptions in glycerol-3-phosphate dehydrogenase (G3PD), pyruvate decarboxylase (PYRDC), mitochondrial fumarase (FUMm), and soluble fumarate reductase (FRDcm). The disruptions in G3PD and PYRDC prevent glycerol secretion and reduce ethanol formation respectively. The disruption in FUMm prevents the carbon flux from being routed into the reductive mitochondrial TCA cycle. The network instead employs the cytosolic TCA cycle reactions to form fumarate. Finally, the disruption in FRDcm prevents the conversion of cytosolic fumarate into succinate. This strain is predicted to have a growth-coupled yield of 1.47 moles of fumarate per mole of glucose consumed and the maximum growth rate is anticipated to be 0.07/hr as shown in FIG. 9 . If required, the sorbitol reductase activity (encoded by YHR104W) can be removed from the network. All the proposed disruptions can be implemented sequentially based on the necessity to do so.
The strain shown in FIG. 10 has four disruptions including malic enzyme (ME1m), pyruvate kinase (PYK), fumarase (FUMm), and soluble fumarate reductase (FRDcm), two of which are the same as those in FIG. 9 . Under microaerobic conditions, this set of disruptions is expected to yield fumarate up to 1.71 moles/mole of glucose consumed. The disruptions in pyruvate kinase and the malic enzyme are targeted at preventing pyruvate formation in the network such that the maximum amount of PEP can be routed into the reductive TCA cycle using the energy-generating PPCK. As explained earlier, the disruptions in mitochondrial fumarase and in the soluble fumarate reductase prevent the carbon flux from being routed into the reductive mitochondrial TCA cycle and prevent further reduction of fumarate into succinate, respectively. With the imposed disruptions, the strain is expected to produce a minimum of 18% of its maximum theoretical yield see gray point in FIG. 10 . The strain is predicted to have a maximum growth rate of 0.045/hr.
The strain in FIG. 11 has an additional disruption in glucose-6-phosphate dehydrogenase as compared to the strain in FIG. 9 . The disruption of G6PDH alters the cofactor balance in the network favorably for fumarate production at the cost of biomass production by preventing the NADPH formation required for biomass synthesis. These disruptions lead to an expected maximum growth rate of approximately 0.041 per hour for the strain as shown in FIG. 11 . The maximum theoretical fumarate yield is 1.79 moles per mole of glucose consumed. The imposed disruptions reduce the feasible phenotypes significantly such that the strain is anticipated to produce a minimum of 84% of its maximum theoretical yield just to grow as shown by the dark gray point in FIG. 11 .
Another strain, shown in FIG. 12 , has an additional disruption in isocitrate dehydrogenase as compared to the strain in FIG. 11 , leading to a marginal increase in the expected maximum theoretical fumarate yield to 1.83 moles per mole of glucose consumed. The rationale is analogous to that explained for the disruption of G6PDH in design. The maximum biomass formation rate is anticipated to decrease from 0.04 per hour to 0.03 per hour.
To provide a comparison of the fumarate production characteristics of the four strains in FIGS. 9-12 , FIG. 13 shows their production curves on the same plot and compares them with those of the wild-type S. cerevisiae network. All the other designs for fumarate production are listed in Table 5. All the designs proposed for fumarate production described above and in Table 5 can be used for malate production under microaerobic conditions by introducing an additional disruption in the cytosolic fumarase gene that will prevent the conversion of malate into fumarate.
The appropriate reactions for acrylate production from fumarate were added to a genome-scale model of S. cerevisiae very similar to the one described in Duarte et al., Genome Res, 14:1298-1309 (2004). Acrylic acid is a monocarboxylic acid and it has been assumed that it is exported by proton symport. This mechanism of acrylate export makes its production energetically feasible even under anaerobic conditions when a reversible PPCK in introduced. Several design strategies for producing acrylic acid were identified, a few of which are described in detail here with the remaining designs listed in Table 6.
One strain for acrylate production, shown in FIG. 14 , has a disruption in pyruvate decarboxylase (PYRDC). Under anaerobic conditions, a disruption in pyruvate decarboxylase reduces ethanol formation significantly. All the carbon flux is instead redirected towards acrylate production which also allows for the regeneration of the NADH generated in the network, leading to a tight coupling with biomass formation in the network. The maximum product yield is predicted to be 1.55 moles per mole of glucose consumed at the highest growth rate of 0.21 per hour.
Another strain, shown in FIG. 15 , has disruptions in pyruvate kinase (PYK) and mitochondrial ATP synthase (ATPSm). The disruption in PYK prevents PEP conversion into pyruvate. The disruption of ATP synthase prevents ATP formation in the mitochondrion, removing the incentive for the network to route carbon flux into the mitochondrion. The product of YRJ121W is directly involved in the formation of F1-ATP synthase (beta subunit), while YMR064W is a translational regulator required for expression of the mitochondrial ATPase subunit 9 in yeast (Saltzgaber-Muller et al., J Biol. Chem. 258:11465-11470 (1983)). Disruption of either of these two genes does not affect viability of the organism, making them good deletion candidates for lowering or eliminating the ATPSm activity. Other genes can also be targeted for elimination of the ATP synthase activity in S. cerevisiae (Tzagoloff and Dieckmann, Microbiol Rev. 54:211-225 (1990)). Under anaerobic conditions, the maximum theoretical acrylate yield of the strain is expected to be 1.55 moles per mole of glucose consumed at the maximum predicted growth rate of 0.21 per hour. In microaerobic conditions, this strain provides a slightly higher acrylate yield at 1.69 moles per mole of glucose and the maximum growth rate of the strain is predicted to be 0.23 per hour.
Another strain, shown in FIG. 16 , has disruptions in malic enzyme (NAD-dependent) (ME1m) and in pyruvate kinase (PYK). These disruptions are geared towards preventing pyruvate formation in the network. Thus, they have a similar effect to the disruption of PYRDC which limits pyruvate formation by preventing its utilization for acetaldehyde and subsequently, ethanol formation. Overall, these two disruptions cause a high flux through PPCK, ultimately leading to a growth-coupled acrylate yield of 1.61 moles per mole of glucose in the network. The strain is calculated to have a maximum growth rate of 0.19 per hour.
Yet another strain, shown in FIG. 17 , has additional disruptions in fumarase (FUMm) and soluble fumarate reductase (FRDcm). These additional disruptions prevent the formation of succinate in the network. The net acrylate yield calculated for this design is 1.62 moles per mole of glucose consumed and the maximum growth rate is predicted to be 0.19 per hour.
Still another strain, shown in FIG. 18 , has additional disruptions in fumarase (FUMm) and soluble fumarate reductase (FRDcm). This strain can be grown in anaerobic conditions leading to acrylate production. The maximum theoretical acrylate yield of the strain is expected to be 1.65 moles per mole of glucose consumed at the maximum predicted growth rate of 0.18 per hour.
Accordingly, the invention also provides a non-naturally occurring eukaryotic organism having a set of metabolic modifications coupling fumarate, malate, or acrylate production to growth of the organism, the set of metabolic modifications includes disruption of one or more genes selected from the set of genes encoding proteins that include: (a) glycerol-3-phosphate dehydrogenase (G3PD), (b) pyruvate decarboxylase (PYRDC), (c) soluble fumarate reductase (FRDcm) and (d) mitochondrial fumarase (FUMm). In other embodiments, the set of metabolic modifications includes disruption of one or more genes selected from the set of genes encoding proteins that include: (a) malic enzyme (ME1m), (b) pyruvate kinase (PYK), (c) soluble fumarate reductase (FRDcm), and (d) mitochondrial fumarase (FUMm).
Based on an analysis of the strains for fumarate production, two alternative minimum set of disruptions can enable growth-coupled fumarate/malate production in the network. Note that PPCK was assumed to be reversible. Briefly, disruptions in glycerol-3-phosphate dehydrogenase (G3PD), pyruvate decarboxylase (PYRDC), soluble fumarate reductase (FRDcm) and mitochondrial fumarase (FUMm) are required for preventing or reducing the formation of competing byproducts, glycerol, ethanol and succinate. An alternative enzyme disruption set entails the removal of malic enzyme (ME1m), pyruvate kinase (PYK), soluble fumarate reductase (FRDcm) and mitochondrial fumarase (FUMm) for coupling fumarate production to growth. These correspond to the following minimal enzyme disruption sets:
Glycerol-3-phosphate dehydrogenase (G3PD), pyruvate decarboxylase (PYRDC), soluble fumarate reductase (FRDcm) and mitochondrial fumarase (FUMm), or Malic enzyme (ME1m), pyruvate kinase (PYK), soluble fumarate reductase (FRDcm) and mitochondrial fumarase (FUMm).
These enzyme disruption sets correspond to the following gene disruption sets: YDL022W (G3PD), YLR044C, YGR087C, YLR134W (isozymes for PYRDC), YPL262W (FUMm), and YEL047C (FRDcm), or YKL029C (ME1m), YOR347c, YAL038W (isozymes for PYK), YPL262W (FUMm), and YEL047C (FRDcm).
Note that all the isozymes capable of carrying out a given activity can be deleted given a possibility of the isozymes becoming active due to adaptive evolution. Further improvement in yields can be attained by deleting one or more of the following functionalities: glucose-6-phosphate dehydrogenase (G6PDH) and cytosolic NADP-dependent isocitrate dehydrogenase (ICDHy). The enzyme disruption sets after introducing these auxiliary disruptions are: Glycerol-3-phosphate dehydrogenase (G3PD), pyruvate decarboxylase (PYRDC), soluble fumarate reductase (FRDcm) and mitochondrial fumarase (FUMm), and glucose-6-phosphate dehydrogenase (G6PDH), or Malic enzyme (ME1m), pyruvate kinase (PYK), soluble fumarate reductase (FRDcm) and mitochondrial fumarase (FUMm), glucose-6-phosphate dehydrogenase (G6PDH) and cytosolic NADP-dependent isocitrate dehydrogenase (ICDHy).
These enzyme sets corresponds to the following gene disruption sets: YDL022W (G3PD), YLR044C, YGR087C, YLR134W (isozymes for PYRDC), YPL262W (FUMm), and YEL047C (FRDcm), YNL241C (G6PDH), or YKL029C (ME1m), YOR347c, YAL038W (isozymes for PYK), YPL262W (FUMm), and YEL047C (FRDcm), YNL241C (G6PDH), and YLR174W (ICDHy).
For malate production, the enzyme disruption sets can be augmented with the disruption of the cytosolic fumarase which is also encoded by YPL262W. Note that YPL262W encodes for both the cytosolic and the mitochondrial fumarases. However, its localization is determined by the N-terminal mitochondrial targeting sequence and its conformation (Sass et al., J Biol. Chem. 278:45109-45116 (2003)).
Acrylate production in S. cerevisiae is feasible under anaerobic conditions assuming the reversibility of PPCK. Three alternative minimum enzyme disruption sets were identified. These entail (i) disruption in pyruvate decarboxylase, or (ii) disruption in malic enzyme in conjunction with a disruption in pyruvate kinase, or (iii) disruptions in pyruvate kinase and mitochondrial ATP synthase. The corresponding gene disruption sets are: YLR044C, YGR087C, YLR134W (PYRDC), or YKL029C (ME1m), YOR347c, YAL038W (PYK), or YOR347c, YAL038W (encode for PYK isozymes), YJR121W and YMR064W or any other combination of genes that eliminates mitochondrial synthase activity.
Each of these minimal sets can be augmented with supplementary disruptions to further enhance the acrylate yields. The auxiliary disruptions include but are not limited to mitochondrial fumarase, soluble fumarate reductase and glycerol-3-phosphate dehydrogenase. The corresponding gene disruptions are: YPL262W (FUMm), and YEL047C (FRDcm) and YDL022W (G3PD).
The disruption of pyruvate decarboxylase is very similar to the disruption of alcohol dehydrogenase in that both are targeted to prevent ethanol formation in the network. The disruption of alcohol dehydrogenase activity can completely eliminate ethanol formation. However, due to the presence of multiple alcohol dehydrogenases and the substrate promiscuity of these dehydrogenases, it can be difficult to completely remove the alcohol dehydrogenase activity. Therefore, PYRDC is included in the minimum enzyme disruption set.
Each of the strains described above can be supplemented with additional disruptions if it is determined that the predicted strain designs do not sufficiently couple the formation of the product with biomass formation. Alternatively, some other enzymes not known to possess significant activity under the growth conditions can become active due to adaptive evolution or random mutagenesis and can also be knocked out. For example, succinate dehydrogenase that oxidizes succinate to fumarate and is known to be active only under aerobic conditions may assume significant activity even under anaerobic conditions and may have to be knocked out. However, the list of gene disruption sets provided here serves as a starting point for construction of high-yielding growth-coupled malate, fumarate and acrylate production strains.
Therefore, the invention provides a method for producing fumaric acid malic acid, or acrylic acid that includes culturing a non-naturally occurring prokaryotic or eukaryotic microbial organism that includes one or more gene disruptions. The disruptions can occur in genes encoding an enzyme obligatory to coupling fumarate or malate production to growth of the microorganism when the gene disruption reduces an activity of the enzyme, such that the disruptions confer stable growth-coupled production of fumarate or malate onto the non-naturally occurring microorganism.
The non-naturally occurring prokaryotic or eukaryotic organisms of the invention can be employed in the growth-coupled production of fumarate, malate, or acrylate. Essentially any quantity, including commercial quantities, can be synthesized using the growth-coupled fumarate, malate, or acrylate producers of the invention. Because the organisms of the invention obligatorily couple fumarate, malate, or acrylate to continuous growth or near-continuous growth processes are particularly useful for biosynthetic production of fumarate, malate, or acrylate. Such continuous and/or near continuous growth processes are described above and exemplified below in the Example I. Continuous and/or near-continuous microorganism growth processes also are well known in the art. Briefly, continuous and/or near-continuous growth processes involve maintaining the microorganism in an exponential growth or logarithmic phase. Procedures include using apparatuses such as the Evolugator™ evolution machine (Evolugate LLC, Gainesville, Fla.), fermentors and the like. Additionally, shake flask fermentation and grown under microaerobic conditions also can be employed. Given the teachings and guidance provided herein those skilled in the art will understand that the growth-coupled fumarate producing microorganisms can be employed in a variety of different settings under a variety of different conditions using a variety of different processes and/or apparatuses well known in the art.
Generally, the continuous and/or near-continuous production of fumarate, malate, or acrylate will include culturing a non-naturally occurring growth-coupled fumarate, malate, or acrylate producing organism of the invention in sufficient nutrients and medium to sustain and/or nearly sustain growth in an exponential phase. Continuous culture under such conditions can be grown, for example, for a day, 2, 3, 4, 5, 6 or 7 days or more. Additionally, continuous cultures can include time durations of 1 week, 2, 3, 4 or 5 or more weeks and up to several months. It is to be understood that the continuous and/or near-continuous culture conditions also can include all time intervals in between these exemplary periods. In particular embodiments, culturing is conducted in a substantially anaerobic culture medium.
Fumarate, malate, or acrylate can be harvested or isolated at any time point during the continuous and/or near-continuous culture period exemplified above. As exemplified below, the longer the microorganisms are maintained in a continuous and/or near-continuous growth phase, the proportionally greater amount of fumarate and malate can be produced.
One consideration for bioprocessing is whether to use a batch or continuous fermentation scheme. One difference between the two schemes that will influence the amount of product produced is the presence of a preparation, lag, and stationary phase for the batch scheme in addition to the exponential growth phase. In contrast, continuous processes are kept in a state of constant exponential growth and, if properly operated, can run for many months at a time. For growth-associated and mixed-growth-associated product formation, continuous processes provide much higher productivities (i.e., dilution rate times cell mass) due to the elimination of the preparation, lag, and stationary phases. For example, given the following reasonable assumptions:
Monod kinetics (i.e., μ=μ m ·S/(K s +S)) μ m =1.0 hr −1
final cell concentration/initial cell concentration=20
t prep +t lag +t stat =5 hr
feed concentration of limiting nutrient >>Ks
increased productivity from a continuous process has been estimated at 8-fold, Shuler et al, Prentice Hall, Inc .: Upper Saddle River, N.J., 245-247.
Despite advantages in productivity, many more batch processes are in operation than continuous processes for a number of reasons. First, for non-growth associated product formation (e.g., penicillin), the productivity of a batch system may significantly exceed that of a continuous process because the latter would have to operate at very low dilution rates. Next, production strains generally have undergone modifications to their genetic material to improve their biochemical or protein production capabilities. These specialized strains are likely to grow less rapidly than their parental complements whereas continuous processes such as those employing chemostats (fermenters operated in continuous mode) impose large selection pressures for the fastest growing cells. Cells containing recombinant DNA or carrying point mutations leading to the desired overproduction phenotype are susceptible to back-mutation into the original less productive parental strain. It also is possible for strains having single gene disruptions to develop compensatory mutations that will tend to restore the wild-type growth phenotype. The faster growing cells usually out-compete their more productive counterparts for limiting nutrients, drastically reducing productivity. Batch processes, on the other hand, limit the number of generations available by not reusing cells at the end of each cycle, thus decreasing the probability of the production strain reverting back to its wild-type phenotype. Finally, continuous processes are more difficult to operate long-term due to potential engineering obstacles such as equipment failure and foreign organism contamination. The consequences of such failures also are much more considerable for a continuous process than with a batch culture.
For small-volume production of specialty chemicals and/or proteins, the productivity increases of continuous processes rarely outweigh the risks associated with strain stability and reliability. However, for the production of large-volume, growth-associated products such as fumarate, the increases in productivity for a continuous process can result in significant economic gains when compared to a batch process. Although the engineering obstacles associated with continuous bioprocess operation would always be present, the strain stability concerns can be overcome through metabolic engineering strategies that reroute metabolic pathways to reduce or avoid negative selective pressures and favor production of the target product during the exponential growth phase.
The invention provides a method for producing fumaric acid, malic acid, or acrylic acid that includes culturing a non-naturally occurring prokaryotic or eukaryotic organism that includes one or more gene disruptions as described above. The disruptions can occur in genes encoding an enzyme obligatory to coupling fumarate, malate, or acrylate production to growth of the microorganism when the gene disruption reduces an activity of the enzyme, such that the disruptions confer increased production of fumarate, malate, or acrylate onto the non-naturally prokaryotic or eukaryotic organism. The gene disruptions can also be non-growth coupled in other embodiments.
In some embodiments, the gene disruption can include a complete gene deletion. In some embodiments other means to disrupt a gene include, for example, frameshifting by omission or addition of oligonucleotides or by mutations that render the gene inoperable. One skilled in the art will recognize the advantages of gene deletions, however, because of the stability it may confer to the non-naturally occurring organism from reverting to its wild-type. In particular, the gene disruptions are selected from the gene set that includes genes detailed herein above.
In order to confirm the computational predictions, the strains can be constructed, evolved, and tested. Gene deletions are introduced into wild-type, haploid S. cerevisiae , for example, by homologous recombination of the gene interrupted by the KanMX cassette, flanked by loxP sites enabling removal and recycling of the resistance marker (Wach et al., PCR - based gene targeting in Saccharomyces cerevisiae , in Yeast Gene Analysis , M. F. Tuite, Editor. 1998, Academic Press: San Diego.). Starting with a loxP-kanMX-loxP sequence on a plasmid, an artificial construct with this sequence flanked by fragments of the gene of interest can be created by PCR using primers containing both 45-50 bp target sequence followed by a region homologous to the above cassette. This linear DNA is transformed into wild-type S. cerevisiae , and recombinants are selected by geneticin resistance. Colonies can be purified and tested for correct double crossover by PCR. To remove the KanMX marker, a plasmid containing the Cre recombinase and bleomycin resistance will be introduced, promoting recombination between the loxP sites (Gueldener, U., et al., A second set of loxP marker cassettes for Cre - mediated multiple gene knockouts in budding yeast , in Nucleic Acids Res. 2002. p. e23.). Finally, the resulting strain can be cured of the Cre plasmid by successive culturing on media without any antibiotic present. The final strain will have a markerless gene deletion, and thus the same method can be used to introduce multiple deletions in the same strain.
The engineered strains can be characterized by measuring the growth rate, the substrate uptake rate, and the product/byproduct secretion rate. Cultures are grown overnight and used as inoculum for a fresh batch culture for which measurements are taken during exponential growth. The growth rate can be determined by measuring optical density using a spectrophotometer (A600). Concentrations of glucose and other organic acid byproducts in the culture supernatant are determined by HPLC using an HPX-87H column (BioRad), and used to calculate uptake and secretion rates. All experiments are performed with triplicate cultures.
The disruption strains are initially expected to exhibit suboptimal growth rates until their metabolic networks have adjusted to their missing functionalities. To assist in this adjustment, the strains are adaptively evolved. By subjecting the strains to adaptive evolution, cellular growth rate becomes the primary selection pressure and the mutant cells are compelled to reallocate their metabolic fluxes in order to enhance their rates of growth. This reprogramming of metabolism has been recently demonstrated for several E. coli mutants that had been adaptively evolved on various substrates to reach the growth rates predicted a priori by an in silico model (Fong and Palsson, Nat Genet, 36:1056-1058 (2004)). Should the OptKnock predictions prove successful; the growth improvements brought about by adaptive evolution will be accompanied by enhanced rates of fumarate, malate or acrylate production. The OptKnock-generated strains are adaptively evolved in triplicate (running in parallel) due to differences in the evolutionary patterns witnessed previously in E. coli ((Fong and Palsson, Nat Genet, 36:1056-1058 (2004); Fong et al., J Bacteriol, 185:6400-6408 (2003); Ibarra et al., Nature 420: 186-189 (2002)) that could potentially result in one strain having superior production qualities over the others. Evolutions will be run for a period of 2-6 weeks, depending upon the rate of growth improvement attained. In general, evolutions will be stopped once a stable phenotype is obtained.
Following the adaptive evolution process, the new strains are characterized again by measuring the growth rate, the substrate uptake rate, and the product/byproduct secretion rate. These results will be compared to the OptKnock predictions by plotting actual growth and production yields along side the production envelopes in the above figures. The most successful OptKnock design/evolution combinations are chosen to pursue further, and are characterized in lab-scale batch and continuous fermentations. The growth-coupled biochemical production concept behind the OptKnock approach should also result in the generation of genetically stable overproducers. Thus, the cultures are maintained in continuous mode for one month to evaluate long-term stability. Periodic samples are taken to ensure that yield and productivity are maintained throughout the experiment.
As will become evident, the teachings contained herein will enable, in a broader sense, the development of methods for decarboxylating alpha, beta-unsaturated carboxylic acids or their salts through the use of naturally occurring or altered decarboxylases. Such alterations can be introduced through a variety of directed and/or adaptive evolution methods.
In some embodiments, the present invention provides a non-naturally occurring microbial organism, that includes a microbial organism having an olefin pathway having at least one exogenous nucleic acid encoding an olefin pathway enzyme expressed in a sufficient amount to produce an olefin. The olefin pathway includes a decarboxylase. In some embodiments, this exogenous nucleic acid is a heterologous nucleic acid. The microbial organism having this decarboxylase can be optionally cultured under substantially anaerobic conditions.
In other embodiments, the present disclosure provides non-naturally occurring microbial organisms having an acrylate pathway that includes at least one exogenous nucleic acid encoding an acrylate pathway enzyme expressed in a sufficient amount to produce acrylate. This acrylate pathway includes a decarboxylase as described herein below. In particular embodiments, the decarboxylase catalyzes fumarate decarboxylation to provide acrylate.
Decarboxylases (also known as carboxy lyases) catalyze the loss of carbon dioxide from an organic compound or a cellular metabolite possessing a carboxylic acid function. Decarboxylases are prevalent in nature and can require either pyridoxal phosphate or pyruvate as a co-factor, although many require no bound co-factors. Over 50 decarboxylase enzymes have been reported and characterized by biochemical and/or analytical methods.
The process in FIGS. 20 and 21A show the decarboxylation of fumaric acid to acrylic acid. Numerous decarboxylase enzymes have been characterized and shown to decarboxylate structurally similar substrates to fumarate( FIGS. 21B-D ). These enzymes are applicable for use in the present invention to decarboxylate fumarate and other unsaturated carboxylic acids, as shown in FIG. 19 . One enzyme with closely related function is aconitate decarboxylase ( FIG. 21B ). This enzyme catalyzes the final step in itaconate biosynthesis in a strain of Candida and also in the filamentous fungus Aspergillus terreus . (Bonnarme et al. J. Bacteriol. 177:3573-3578 (1995); Willke et al. Appl. Microbiol. Biotechnol 56:289-295 (2001)). Aconitate decarboxylase has been purified and characterized from Aspergillus terreus (Dwiarti et al. J. Biosci. Bioeng., 94(1): 29-33 (2002). The gene and protein sequence for the cis-aconitic acid decarboxylase (CAD) enzyme are described in EP2017344 and WO 2009/014437. The protein sequence is listed below along with several close homologs described in EP2017344 and WO2009/014437.
Gene name
GenBankID
Organism
CAD
XP_001209273
Aspergillus terreus
(GI: 115385453)
XP_001217495
Aspergillus terreus
(GI: 115402837)
XP_001209946
Aspergillus terreus
(GI: 115386810)
BAE66063
Aspergillus oryzae
(GI: 83775944)
XP_001393934
Aspergillus niger
(GI: 83775944)
XP_391316
Gibberella zeae
(GI: 46139251)
XP_001389415
Aspergillus niger
(GI: 145230213)
XP_001383451
Pichia stipitis
(GI: 126133853)
YP_891060
Mycobacterium smegmatis
(GI: 118473159)
NP_961187
Mycobacterium avium subsp.
(GI: 41408351)
pratuberculosis
YP_880968
Mycobacterium avium
(GI: 118466464)
ZP_01648681
Salinispora arenicola
(GI: 119882410)
ZP_01648681
Salonispora tropica
(GI: 119882410)
Another enzyme type with similar function is 4-oxalocrotonate decarboxylase ( FIG. 21C ). This enzyme has been isolated from numerous organisms and characterized. Genes encoding this enzyme include dmpH and dmpE in Pseudomonas sp. (strain 600) (Shingler et al. J. Bacteriol. 174:711-724 (1992)), xyIII and xyIII from Pseudomonas putida (Kato et al. Arch. Microbiol. 168:457-463 (1997); Stanley et al. Biochemistry 39:718-726 (2000); Lian et al. J. Am. Chem. Soc. 116, 10403-10411 (1994)) and Reut_B5691 and Reut_B5692 from Ralstonia eutropha JMP134 (Hughes et al. J. Bacteriol. 158:79-83 (1984). The genes encoding the enzyme from Pseudomonas sp. (strain 600) have been cloned and expressed in E. coli (Shingler et al. J. Bacteriol. 174:711-724 (1992)).
Finally, a class of decarboxylases has been characterized that catalyze the conversion of cinnamate (phenylacrylate) and substituted cinnamate derivatives to the corresponding styrene derivatives ( FIG. 21D ). These enzymes are common in a variety of organisms and specific genes encoding these enzymes that have been cloned and expressed in E. coli are: pad I from Saccharomyces cerevisae (Clausen et al. Gene 142:107-112 (1994), pdc from Lactobacillus plantarum (Barthelmebs et al. Appl. Environ. Microbiol. 67, 1063-1069 (2001); Qi et al. Metabolic Engineering 9: 268-276 (2007); Rodriguez et al. J. Agric. Food Chem. 56, 3068-3072 (2008)), pofK (pad) from Klebsiella oxytoca (Hashidoko et al. Biosci. Biotech. Biochem. 58, 217-218 (1994); Uchiyama et al. Biosci. Biotech. Biochem. 72: 116-123 (2008)), and Pedicoccus pentosaceus (Barthelmebs et al. J. Bacteriol. 182: 6724-6731 (2000); Barthelmebs et al. Appl. Environ. Microbiol. 67: 1063-1069 (2001)), and padC from Bacillus subtilis and Bacillus pumilus (Barthelmebs et al. 2001 supra; Qi, et al supra). A ferulic acid decarboxylase from Pseudomonas fluorescens also has been purified and characterized (Huang et al. J. Bacteriol. 176: 5912-5918 (1994)). Importantly, this class of enzymes have been shown to be stable and do not require either exogenous or internally bound co-factors, thus making these enzymes ideally suitable for biotransformations (Sariaslani Annu. Rev. Microbiol. 61: 51-69 (2007)). A summary of genes encoding these various decarboxylases for carrying out the transformations shown in FIGS. 21B-21D are shown below.
Gene name
GenBankID
Organism
dmpH
CAA43228.1
Pseudomonas sp. CF600
(GI: 45685)
dmpE
CAA43225.1
Pseudomonas sp. CF600
(GI: 45682)
xylII
YP_709328.1
Pseudomonas putida
(GI: 111116444)
xylIII
YP_709353.1
Pseudomonas putida
(GI: 111116469)
Reut_B5691
YP_299880.1
Ralstonia eutropha JMP134
(GI: 73539513)
Reut_B5692
YP_299881.1
Ralstonia eutropha JMP134
(GI: 73539514)
pad1
AB368798
Saccharomyces cerevisae
(GI: 188496948)
pdc
U63827
Lactobacillus plantarum
(GI: 1762615)
pofK (pad)
AB330293
Klebsiella oxytoca
(GI: 149941607)
padC
AF017117
Bacillus subtilis
(GI: 2394281)
pad
AJ276891
Pedicoccus pentosaceus
(GI: 11322456)
pad
AJ278683
Bacillus pumilus
(GI: 11691809)
Each of the decarboxylases listed above represents a suitable enzyme for the transformation shown in FIGS. 20 and 21A . If the desired activity or productivity of the enzyme is not observed in the conversion of fumarate to acrylate, or if acrylic acid production inhibits the decarboxylase enzymes, the decarboxylase enzymes can be evolved using known protein engineering methods to achieve the required performance. Importantly, it was shown through the use of chimeric enzymes that the C-terminal region of decarboxylases appears to be responsible for substrate specificity (Barthelmebs et al. (2001) supra). Accordingly, directed evolution experiments to broaden the specificity of decarboxylases in order to gain activity with fumarate can be focused on the C-terminal region of these enzymes.
Some of the decarboxylases can exhibit higher activity on the cis-isomer of fumarate known as maleate. Fumarate can be converted to maleate by maleate cis-trans isomerase encoded by the maiA gene from Alcaligenes faecalis (Hatakeyama, et al., Biochem. Biophys. Research Comm. 239, 74-79 (1997)) or similar genes that can be identified by sequence homology including those from Geobacillus stearothermophilus and Ralstonia pickettii 12D. Additional maleate cis-trans isomerase enzymes are encoded by the enzymes whose amino acid sequences are described (SEQ ID NO: 1-4) in U.S. Pat. No. 6,133,014, which is incorporated by reference in its entirety. Useful GenBank information for some of these isomerases is shown below.
Gene name
GenBankID
Organism
maiA
BAA23002.1
Alcaligenes faecalis
(GI: 2575787)
maiA
BAA77296
Geobacillus
(GI: 4760466)
stearothermophilus
Rpic12DDRAFT_0600
ZP_02009633
Ralstonia pickettii 12D
(GI: 153888491)
The exogenous nucleic acid encoding the decarboxylase can come from another organism such as those described above, thus providing a heterologous nucleic acid. Alternatively, in the case of a microbial organism that already has a native decarboxylase capable of decarboxylating fumarate, additional copies of the decarboxylase can be introduced to increase its expression. In addition to incorporating a decarboxylase, a non-naturally occurring microbial organism will have certain energy requirements for growth and maintenance as outlined below.
Engineering the capability for fumarate decarboxylation into Escherichia coli , for example, results in a redox-balanced pathway for the production of acrylate from carbohydrates. Provided that symport of the acrylate monoanion is the predominant means of product export, the pathway as depicted in FIG. 20 can be energetically negative because the high energy phosphate bond contained in each PEP molecule gained from glycolysis will be lost upon conversion to oxaloacetate by PEP carboxylase, a native E. coli enzyme that is functional during growth on carbohydrates.
This energetic limitation can be remedied by either supplying a limited amount of an external electron acceptor such as oxygen or nitrate to enable energy generation via respiration, or by at least two strain engineering strategies provided herein below. Either strain engineering method ensures that the pathway for production of acrylate via fumarate decarboxylase generates sufficient energy to support cell growth and maintenance under anaerobic or aerobic conditions. Although the non-naturally occurring microbial organism can be grown under aerobic or anaerobic conditions, a substantially anaerobic culture medium is preferred. The two exemplary designs described below can be implemented in order to generate the requisite energy for growth and maintenance under anaerobic conditions.
In one embodiment, a non-naturally occurring microbial organism can include an exogenous nucleic acid encoding at least one malic enzyme to supply the requisite energy for growth and maintenance. Malic enzymes for this purpose can include, without limitation, malic enzyme (NAD-dependent) and malic enzyme (NADP-dependent). For example, one of the native E. coli malic enzymes (Takeo, K., J. Biochem. 66:379-387 (1969)) or a similar non-native enzyme with higher activity can be expressed to enable the conversion of pyruvate and CO 2 to malate. By fixing carbon to pyruvate as opposed to PEP, malic enzyme enables the high-energy phosphate bond from PEP to be conserved by pyruvate kinase whereby ATP is generated in the formation of pyruvate or by the phosphotransferase system for glucose transport. Although malic enzyme is typically assumed to operate in the direction of pyruvate formation from malate, overexpression of the NAD-dependent enzyme, encoded by maeA, has been demonstrated to increase succinate production in E. coli while restoring the lethal Δpfl-ΔldhA phenotype under anaerobic conditions by operating in the carbon-fixing direction (Stols and Donnelly, Appl Environ Microbiol 63:2695-2701 (1997)). Thus, in some embodiments the non-naturally occurring microbial organism can include an exogenous nucleic acid providing a gene such as maeA. A similar observation was made upon overexpressing the malic enzyme from Ascaris suum in E. coli (Stols et al., Appl Biochem. Biotechnol 63-65:153-158 (1997)). The second E. coli malic enzyme, encoded by maeB, is NADP-dependent and also decarboxylates oxaloacetate and other alpha-keto acids (Iwakura et al., J. Biochem. 85:1355-1365 (1979)) Therefore, in other embodiments the non-naturally occurring microbial organism can include an exogenous nucleic acid providing a gene such as maeB. The relevant malic enzyme gene information is shown below.
Gene name
Organism
Accession Number
maeA
E. coli
NP_415996
(GI: 90111281)
maeB
E. coli
NP_416958
(GI: 16130388)
NAD-ME
Ascaris suum
P27443
(GI: 126732)
Another option for providing an energetically favorable pathway involves introducing a reversible phosphoenolpyruvate kinase (PPCK) enzyme, which unlike PEP carboxylase, can generate one ATP per phosphoenolpyruvate molecule converted to oxaloacetate. In some embodiments, the non-naturally occurring microbial organism can also include an exogenous nucleic acid encoding a phosphoenolpyruvate carboxykinase. PEP carboxykinase is known to produce oxaloacetate from PEP in rumen bacteria such as Mannheimia succiniciproducens (Hong et al., Nat Biotechnol 22:1275-1281 (2004)) However, the role of PEP carboxykinase, encoded by pck, in producing oxaloacetate in E. coli is believed to be minor as compared to PEP carboxylase, possibly due to the higher K m for bicarbonate of PEP carboxykinase (Kim et al., Appl Environ Microbiol 70:1238-1241 (2004)) Nevertheless, activity of the native E. coli PEP carboxykinase from PEP towards oxaloacetate has been recently demonstrated in ppc mutants of E. coli K-12 (Kwon et al., J. Microbiol. Biotechnol. 16:1448-1452 (2006)). These strains exhibited no growth defects and had increased succinate production at high NaHCO 3 concentrations. In addition, examples of non-native PEP carboxykinase genes that have been cloned and shown to function in E. coli include those from M. succiniciproducens (Lee et al., Gene. Biotechnol. Bioprocess Eng. 7:95-99 (2002)), Anaerobiospirillum succiniciproducens (Laivenieks et al. Appl Environ Microbiol 63:2273-2280 (1997)), and Actinobacillus succinogenes (Kim et al., Appl Environ Microbiol 70:1238-1241 (2004)). The relevant PEP carboxykinase gene information is shown below.
Gene
name
Organism
Accession Number
pck
E. coli
NP_417862
(GI: 16131280)
pckA
Mannheimia succiniciproducens
YP_089485
(GI: 52426348)
pckA
Anaerobiospirillum succiniciproducens
O09460
(GI: 3122621)
pck
Actinobacillus succinogenes
ABX39017
(GI: 160415396)
In addition to the supplying the requisite energy as described above, the formation of acrylate can also be optimized by modifying the non-naturally occurring microbial organism's metabolic production of fumarate. Toward this end, the non-naturally occurring microbial organism can include one or more gene disruptions in addition to the inserted nucleic acid sequences outline above. Gene disruptions can result from, for example, single nucleotide insertion or deletions, stable mutations, and complete gene deletions. Exemplary pathway designs are described below.
The non-naturally occurring microbial organisms that synthesize acrylate can be produced by introducing expressible nucleic acids encoding one or more of the enzymes or proteins participating in one or more acrylate biosynthetic pathways. Depending on the host microbial organism chosen for biosynthesis, nucleic acids for some or all of a particular acrylate biosynthetic pathway can be expressed. For example, if a chosen host is deficient in one or more enzymes or proteins for a desired biosynthetic pathway, then expressible nucleic acids for the deficient enzyme(s) or protein(s) are introduced into the host for subsequent exogenous expression. Alternatively, if the chosen host exhibits endogenous expression of some pathway genes, but is deficient in others, then an encoding nucleic acid is needed for the deficient enzyme(s) or protein(s) to achieve acrylate biosynthesis. Thus, a non-naturally occurring microbial organism of the invention can be produced by introducing exogenous enzyme or protein activities to obtain a desired biosynthetic pathway or a desired biosynthetic pathway can be obtained by introducing one or more exogenous enzyme or protein activities that, together with one or more endogenous enzymes or proteins, produces a desired product such as acrylate.
Depending on the acrylate biosynthetic pathway constituents of a selected host microbial organism, the non-naturally occurring microbial organisms of the invention will include at least one exogenously expressed acrylate pathway-encoding nucleic acid and up to all encoding nucleic acids for one or more acrylate biosynthetic pathways. For example, acrylate biosynthesis can be established in a host deficient in a pathway enzyme or protein through exogenous expression of the corresponding encoding nucleic acid. In a host deficient in all enzymes or proteins of an acrylate pathway, exogenous expression of all enzyme or proteins in the pathway can be included, although it is understood that all enzymes or proteins of a pathway can be expressed even if the host contains at least one of the pathway enzymes or proteins. For example, exogenous expression of all enzymes or proteins in a pathway for production of acrylate can be included, such as a decarboxylase.
Given the teachings and guidance provided herein, those skilled in the art will understand that the number of encoding nucleic acids to introduce in an expressible form will, at least, parallel the acrylate pathway deficiencies of the selected host microbial organism. Therefore, a non-naturally occurring microbial organism of the invention can have one, two, three, four, up to all nucleic acids encoding the enzymes or proteins constituting an acrylate biosynthetic pathway disclosed herein. In some embodiments, the non-naturally occurring microbial organisms also can include other genetic modifications that facilitate or optimize acrylate biosynthesis or that confer other useful functions onto the host microbial organism. One such other functionality can include, for example, augmentation of the synthesis of one or more of the acrylate pathway precursors such as fumarate.
Generally, a host microbial organism is selected such that it produces the precursor of an acrylate pathway, either as a naturally produced molecule or as an engineered product that either provides de novo production of a desired precursor or increased production of a precursor naturally produced by the host microbial organism. For example, fumarate is produced naturally in a host organism such as E. coli . A host organism can be engineered to increase production of a precursor, as disclosed herein. In addition, a microbial organism that has been engineered to produce a desired precursor can be used as a host organism and further engineered to express enzymes or proteins of an acrylate pathway.
In some embodiments, a non-naturally occurring microbial organism of the invention is generated from a host that contains the enzymatic capability to synthesize acrylate. In this specific embodiment it can be useful to increase the synthesis or accumulation of an acrylate pathway product to, for example, drive acrylate pathway reactions toward acrylate production. Increased synthesis or accumulation can be accomplished by, for example, overexpression of nucleic acids encoding one or more of the above-described acrylate pathway enzymes or proteins. Over expression the enzyme or enzymes and/or protein or proteins of the acrylate pathway can occur, for example, through exogenous expression of the endogenous gene or genes, or through exogenous expression of the heterologous gene or genes. Therefore, naturally occurring organisms can be readily generated to be non-naturally occurring microbial organisms of the invention, for example, producing acrylate, through overexpression of one, two, three, four, five, that is, up to all nucleic acids encoding acrylate biosynthetic pathway enzymes or proteins. In addition, a non-naturally occurring organism can be generated by mutagenesis of an endogenous gene that results in an increase in activity of an enzyme in the acrylate biosynthetic pathway.
In particularly useful embodiments, exogenous expression of the encoding nucleic acids is employed. Exogenous expression confers the ability to custom tailor the expression and/or regulatory elements to the host and application to achieve a desired expression level that is controlled by the user. However, endogenous expression also can be utilized in other embodiments such as by removing a negative regulatory effector or induction of the gene's promoter when linked to an inducible promoter or other regulatory element. Thus, an endogenous gene having a naturally occurring inducible promoter can be up-regulated by providing the appropriate inducing agent, or the regulatory region of an endogenous gene can be engineered to incorporate an inducible regulatory element, thereby allowing the regulation of increased expression of an endogenous gene at a desired time. Similarly, an inducible promoter can be included as a regulatory element for an exogenous gene introduced into a non-naturally occurring microbial organism.
It is understood that, in methods of the invention, any of the one or more exogenous nucleic acids can be introduced into a microbial organism to produce a non-naturally occurring microbial organism of the invention. The nucleic acids can be introduced so as to confer, for example, an acrylate biosynthetic pathway onto the microbial organism. Alternatively, encoding nucleic acids can be introduced to produce an intermediate microbial organism having the biosynthetic capability to catalyze some of the required reactions to confer acrylate biosynthetic capability. For example, a non-naturally occurring microbial organism having an acrylate biosynthetic pathway can comprise at least one exogenous nucleic acids encoding desired enzymes or proteins, such as a decarboxylase, and the like.
In addition to the biosynthesis of acrylate as described herein, the non-naturally occurring microbial organisms and methods of the invention also can be utilized in various combinations with each other and with other microbial organisms and methods well known in the art to achieve product biosynthesis by other routes. For example, one alternative to produce acrylate other than use of the acrylate producers is through addition of another microbial organism capable of converting an acrylate pathway intermediate to acrylate. One such procedure includes, for example, the fermentation of a microbial organism that produces an acrylate pathway intermediate. The acrylate pathway intermediate can then be used as a substrate for a second microbial organism that converts the acrylate pathway intermediate to acrylate. The acrylate pathway intermediate can be added directly to another culture of the second organism or the original culture of the acrylate pathway intermediate producers can be depleted of these microbial organisms by, for example, cell separation, and then subsequent addition of the second organism to the fermentation broth can be utilized to produce the final product without intermediate purification steps.
In other embodiments, the non-naturally occurring microbial organisms and methods of the invention can be assembled in a wide variety of subpathways to achieve biosynthesis of, for example, acrylate. In these embodiments, biosynthetic pathways for a desired product of the invention can be segregated into different microbial organisms, and the different microbial organisms can be co-cultured to produce the final product. In such a biosynthetic scheme, the product of one microbial organism is the substrate for a second microbial organism until the final product is synthesized. For example, the biosynthesis of acrylate can be accomplished by constructing a microbial organism that contains biosynthetic pathways for conversion of one pathway intermediate to another pathway intermediate or the product. Alternatively, acrylate also can be biosynthetically produced from microbial organisms through co-culture or co-fermentation using two organisms in the same vessel, where the first microbial organism produces a fumarate intermediate and the second microbial organism converts the intermediate to acrylate.
Microorganisms capable of directly producing acrylate are constructed by introducing genes encoding decarboxylase enzymes into the strains engineered as described above for maximal fumarate production. The following example describes the creation of a microbial organism that can produce acrylic acid from renewable feedstocks such as glucose or sucrose.
To generate an E. coli strain engineered to produce acrylate or acrylic acid, nucleic acids encoding the decarboxylase enzymes are cloned and expressed in E. coli capable of overproducing fumarate using well known molecular biology techniques and recombinant and detection methods well known in the art. Such methods are described in, for example, Sambrook et al., Molecular Cloning: A Laboratory Manual , Third Ed., Cold Spring Harbor Laboratory, New York (2001); and Ausubel et al., Current Protocols in Molecular Biology , John Wiley and Sons, Baltimore, Md. (1999).
An acrylate producing strain is constructed, by cloning the individual phenylacrylic acid decarboxylase genes pad1 (AB368798), pdc (U63827), pofK (AB330293), padC (AF017117), pad (AJ276891), and pad (AJ278683) into pZA33 or pZE13 vectors (Expressys, Ruelzheim, Germany) under the IPTG-titratable PA1/lacO promoter. The plasmids are transformed into the fumarate overproducing E. coli strain using standard methods such as electroporation. The resulting genetically engineered organism is cultured in glucose-containing medium following procedures well known in the art (see, for example, Sambrook et al., supra, 2001). Expression of the decarboxylase genes are corroborated using methods well known in the art for determining polypeptide expression or enzymatic activity, including for example, Northern blots, PCR amplification of mRNA, immunoblotting, and the like. Enzymatic activities of the expressed enzymes are confirmed using assays specific for the individual activities. The ability of the engineered E. coli strain to produce acrylic acid is confirmed using HPLC, gas chromatography-mass spectrometry (GCMS) and/or liquid chromatography-mass spectrometry (LCMS).
Microbial strains engineered to have a functional acrylic acid synthesis pathway are further augmented by optimization for efficient utilization of the pathway. Briefly, the engineered strain is assessed to determine whether exogenous genes are expressed at a rate limiting level. Flux analysis using 13 C-labeled glucose is performed to assess bottlenecks in the system. Expression is increased for enzymes produced at low levels and that limit the flux through the pathway by, for example, introduction of additional gene copy numbers or changes to the promoter and ribosome binding sites.
To generate better acrylate producers, metabolic modeling is utilized to optimize growth conditions. Modeling is also used to design gene knockouts that additionally optimize utilization of the pathway, as described above. Modeling analysis allows reliable predictions of the effects on cell growth of shifting the metabolism towards more efficient production of acrylic acid. Adaptive evolution is performed to improve both growth and production characteristics (Fong and Palsson, Nat. Genet. 36:1056-1058 (2004)). Based on the results, subsequent rounds of modeling, genetic engineering and adaptive evolution can be applied to the acrylic acid producer to further increase production.
For large-scale production of acrylic acid, the above organism is cultured in a fermenter using a medium known in the art to support growth of the organism under anaerobic conditions. Fermentations are performed in either a batch, fed-batch or continuous manner. Anaerobic conditions are maintained by first sparging the medium with nitrogen and then sealing the culture vessel, for example, flasks can be sealed with a septum and crimp-cap. Microaerobic conditions also can be utilized by providing a small hole in the septum for limited aeration. The pH of the medium is maintained in the optimum range by addition of acids such as H 2 SO 4 or bases such as NaOH or Na 2 CO 3 . The growth rate is determined by measuring optical density using a spectrophotometer (600 nm) and the glucose uptake rate by monitoring carbon source depletion over time. Byproducts such as undesirable alcohols, organic acids, and residual glucose can be quantified by HPLC (Shimadzu, Columbia Md.), for example, using an Aminex® series of HPLC columns (for example, HPX-87 series) (BioRad, Hercules Calif.), using a refractive index detector for glucose and alcohols, and a UV detector for organic acids (Lin et al., Biotechnol. Bioeng. 775-779 (2005)).
E. coli and other microorganisms are known to possess fatty acid and organic acid degradation pathways that could lead to acrylate degradation. While fermentative production of acrylic acid under anaerobic conditions should not be accompanied by degradation, should product degradation be observed, the pathways responsible for product degradation will be deleted.
Given the teachings and guidance provided herein, those skilled in the art will understand that a wide variety of combinations and permutations exist for the non-naturally occurring microbial organisms and methods of the invention together with other microbial organisms, with the co-culture of other non-naturally occurring microbial organisms having subpathways and with combinations of other chemical and/or biochemical procedures well known in the art to produce acrylate.
Sources of encoding nucleic acids for an acrylate pathway enzyme or protein can include, for example, any species where the encoded gene product is capable of catalyzing the referenced reaction. Such species include both prokaryotic and eukaryotic organisms including, but not limited to, bacteria, including archaea and eubacteria, and eukaryotes, including yeast, plant, insect, animal, and mammal, including human. Exemplary species for such sources include, for example, Escherichia coli, Candida albicans, Candida boidinii, Aspergillus terreus, Pseudomonas sp. CF600, Pseudomonas putida, Ralstonia eutropha JMP 134, Saccharomyces cerevisae, Lactobacillus plantarum, Klebsiella oxytoca, Bacillus subtilis, Bacillus pumilus, Pedicoccus pentosaceus , as well as other exemplary species disclosed herein or available as source organisms for corresponding genes. However, with the complete genome sequence available for now more than 550 species (with more than half of these available on public databases such as the NCBI), including 395 microorganism genomes and a variety of yeast, fungi, plant, and mammalian genomes, the identification of genes encoding the requisite acrylate biosynthetic activity for one or more genes in related or distant species, including for example, homologues, orthologs, paralogs and nonorthologous gene displacements of known genes, and the interchange of genetic alterations between organisms is routine and well known in the art. Accordingly, the metabolic alterations enabling biosynthesis of acrylate described herein with reference to a particular organism such as E. coli can be readily applied to other microorganisms, including prokaryotic and eukaryotic organisms alike. Given the teachings and guidance provided herein, those skilled in the art will know that a metabolic alteration exemplified in one organism can be applied equally to other organisms.
In some instances, such as when an alternative acrylate biosynthetic pathway exists in an unrelated species, acrylate biosynthesis can be conferred onto the host species by, for example, exogenous expression of a paralog or paralogs from the unrelated species that catalyzes a similar, yet non-identical metabolic reaction to replace the referenced reaction. Because certain differences among metabolic networks exist between different organisms, those skilled in the art will understand that the actual gene usage between different organisms can differ. However, given the teachings and guidance provided herein, those skilled in the art also will understand that the teachings and methods of the invention can be applied to all microbial organisms using the cognate metabolic alterations to those exemplified herein to construct a microbial organism in a species of interest that will synthesize acrylate.
Host microbial organisms can be selected from, and the non-naturally occurring microbial organisms generated in, for example, bacteria, yeast, fungus or any of a variety of other microorganisms applicable to fermentation processes. Exemplary bacteria include species selected from Escherichia coli, Klebsiella oxytoca, Anaerobiospirillum succiniciproducens, Actinobacillus succinogenes, Mannheimia succiniciproducens, Rhizobium etli, Bacillus subtilis, Corynebacterium glutamicum, Gluconobacter oxydans, Zymomonas mobilis, Lactococcus lactis, Lactobacillus plantarum, Streptomyces coelicolor, Clostridium acetobutylicum, Pseudomonas fluorescens , and Pseudomonas putida . Exemplary yeasts or fungi include species selected from Saccharomyces cerevisiae, Schizosaccharomyces pombe, Kluyveromyces lactis, Kluyveromyces marxianus, Aspergillus terreus, Aspergillus niger and Pichia pastoris. E. coli is a particularly useful host organism since it is a well characterized microbial organism suitable for genetic engineering. Other particularly useful host organisms include yeast such as Saccharomyces cerevisiae.
Methods for constructing and testing the expression levels of a non-naturally occurring acrylate-producing host can be performed, for example, by recombinant and detection methods well known in the art. Such methods can be found described in, for example, Sambrook et al., Molecular Cloning: A Laboratory Manual , Third Ed., Cold Spring Harbor Laboratory, New York (2001); and Ausubel et al., Current Protocols in Molecular Biology , John Wiley and Sons, Baltimore, Md. (1999).
Exogenous nucleic acid sequences involved in a pathway for production of acrylate can be introduced stably or transiently into a host cell using techniques well known in the art including, but not limited to, conjugation, electroporation, chemical transformation, transduction, transfection, and ultrasound transformation. For exogenous expression in E. coli or other prokaryotic cells, some nucleic acid sequences in the genes or cDNAs of eukaryotic nucleic acids can encode targeting signals such as an N-terminal mitochondrial or other targeting signal, which can be removed before transformation into prokaryotic host cells, if desired. For example, removal of a mitochondrial leader sequence led to increased expression in E. coli (Hoffmeister et al., J. Biol. Chem. 280:4329-4338 (2005)). For exogenous expression in yeast or other eukaryotic cells, genes can be expressed in the cytosol without the addition of leader sequence, or can be targeted to mitochondrion or other organelles, or targeted for secretion, by the addition of a suitable targeting sequence such as a mitochondrial targeting or secretion signal suitable for the host cells. Thus, it is understood that appropriate modifications to a nucleic acid sequence to remove or include a targeting sequence can be incorporated into an exogenous nucleic acid sequence to impart desirable properties. Furthermore, genes can be subjected to codon optimization with techniques well known in the art to achieve optimized expression of the proteins.
An expression vector or vectors can be constructed to include one or more acrylate biosynthetic pathway encoding nucleic acids as exemplified herein operably linked to expression control sequences functional in the host organism. Expression vectors applicable for use in the microbial host organisms of the invention include, for example, plasmids, phage vectors, viral vectors, episomes and artificial chromosomes, including vectors and selection sequences or markers operable for stable integration into a host chromosome. Additionally, the expression vectors can include one or more selectable marker genes and appropriate expression control sequences. Selectable marker genes also can be included that, for example, provide resistance to antibiotics or toxins, complement auxotrophic deficiencies, or supply critical nutrients not in the culture media. Expression control sequences can include constitutive and inducible promoters, transcription enhancers, transcription terminators, and the like which are well known in the art. When two or more exogenous encoding nucleic acids are to be co-expressed, both nucleic acids can be inserted, for example, into a single expression vector or in separate expression vectors. For single vector expression, the encoding nucleic acids can be operationally linked to one common expression control sequence or linked to different expression control sequences, such as one inducible promoter and one constitutive promoter. The transformation of exogenous nucleic acid sequences involved in a metabolic or synthetic pathway can be confirmed using methods well known in the art. Such methods include, for example, nucleic acid analysis such as Northern blots or polymerase chain reaction (PCR) amplification of mRNA, or immunoblotting for expression of gene products, or other suitable analytical methods to test the expression of an introduced nucleic acid sequence or its corresponding gene product. It is understood by those skilled in the art that the exogenous nucleic acid is expressed in a sufficient amount to produce the desired product, and it is further understood that expression levels can be optimized to obtain sufficient expression using methods well known in the art and as disclosed herein.
In some embodiments, a method for producing acrylate, includes culturing a non-naturally occurring microbial organism having an acrylate pathway. The pathway includes at least one exogenous nucleic acid encoding an acrylate pathway enzyme expressed in a sufficient amount to produce acrylate under conditions and for a sufficient period of time to produce acrylate. Ideally, the non-naturally occurring microbial organism is in a substantially anaerobic culture medium as described above.
The acrylate pathway includes a decarboxylase gene introduced into an organism that is engineered to produce high levels of fumaric acid under anaerobic conditions from carbon substrates such as glucose or sucrose. Expression of active decarboxylases for the production of chemicals previously has been demonstrated in E. coli (Sariaslani, F. S., Annu. Rev. Microbiol. 61:51-69 (2007)). In this scenario, decarboxylation of fumaric acid occurs intracellularly and acrylate is produced directly and is secreted from the cell and recovered through standard methods employed for acid separation and purification.
One challenge with direct acrylate production could be the known cellular toxicity of acrylic acid and acrylate salts (Straathof et al., Appl. Microbiol. Biotechnol. 67:727-734 (2005)). Selection of an appropriate production organism involves detailed acrylate toxicity assessment in order to determine inherent levels of tolerance. In addition, adaptive evolution methods are applied to the production host to increase tolerance to acrylate up to the required levels of acrylate (e.g., 5-10% final titers). Previous studies have found evolution to be useful for increasing tolerance of microorganisms to organic acids (Steiner 2003; Patnaik 2002). It has been estimated that production of at least 50 g/L acrylate should be possible through fermentation processes (Straathof et al., Appl. Microbiol. Biotechnol. 67, 727-734 (2005)). Should the toxicity of acrylate prove too high for effective production (the world wide web at toxnet.nlm.nih.gov/cgi-bin/sis/search/r?dbs+hsdb:@term+@rn+@rel+79-10-7 indicates that toxicity to bacteria is low), a second approach involves primary production and secretion of fumarate into a fermentation broth, followed by secondary addition of separately produced decarboxylase enzyme. This approach allows effective conversion of fumarate to acrylate without concern for cell viability. Subsequent processing will be the same as above, involving separation and purification of acrylic acid directly from the broth with no need to separate or isolate fumaric acid prior to treatment with decarboxylase.
An alternative to this production mode is to engineer a decarboxylase enzyme so that it is secreted from the fumarate-producing cell, in which case acrylate production occurs in the same vessel as fumarate production. This approach is particularly effective if decarboxylase enzyme production and secretion are subject to inducible programming (e.g., using a temperature sensitive promoter) such that the enzyme is produced and secreted into the broth following completion of fumarate production.
Thus, in some embodiments, the present invention provides a method for producing acrylate, that includes culturing a first non-naturally occurring microbial organism having one or more gene disruptions. Again, the one or more gene disruptions can occur in one or more genes encoding one or more enzymes obligatory to coupling fumarate production to growth of the microorganism when the disruptions reduce an activity of the enzymes such that the disruptions confer stable growth-coupled production of fumarate. Finally, one adds a decarboxylase to the cultured first non-naturally occurring microbial organism, said decarboxylase catalyzing the decarboxylation of fumarate.
In some embodiments, the decarboxylase is expressed in a second non-naturally occurring microbial organism. In such an instance, the first and second non-naturally occurring microbial organisms can be co-cultured. Additionally, the decarboxylase can also be secreted by a second non-naturally occurring microbial organism which still allows for the first and second microbial organisms to be co-cultured.
Suitable purification and/or assays to test for the production of acrylate can be performed using well known methods. Suitable replicates such as triplicate cultures can be grown for each engineered strain to be tested. For example, product and byproduct formation in the engineered production host can be monitored. The final product and intermediates, and other organic compounds, can be analyzed by methods such as HPLC (High Performance Liquid Chromatography), GC-MS (Gas Chromatography-Mass Spectroscopy) and LC-MS (Liquid Chromatography-Mass Spectroscopy) or other suitable analytical methods using routine procedures well known in the art. The release of product in the fermentation broth can also be tested with the culture supernatant. Byproducts and residual glucose can be quantified by HPLC using, for example, a refractive index detector for glucose and alcohols, and a UV detector for organic acids (Lin et al., Biotechnol. Bioeng. 90:775-779 (2005)), or other suitable assay and detection methods well known in the art. The individual enzyme or protein activities from the exogenous DNA sequences can also be assayed using methods well known in the art.
The acrylate can be separated from other components in the culture using a variety of methods well known in the art. Such separation methods include, for example, extraction procedures as well as methods that include continuous liquid-liquid extraction, pervaporation, membrane filtration, membrane separation, reverse osmosis, electrodialysis, distillation, crystallization, centrifugation, extractive filtration, ion exchange chromatography, size exclusion chromatography, adsorption chromatography, and ultrafiltration. All of the above methods are well known in the art.
Any of the non-naturally occurring microbial organisms described herein can be cultured to produce and/or secrete the biosynthetic products of the invention. For example, the acrylate producers can be cultured for the biosynthetic production of acrylate.
For the production of acrylate, the recombinant strains are cultured in a medium with carbon source and other essential nutrients. It is highly desirable to maintain anaerobic conditions in the fermenter to reduce the cost of the overall process. Such conditions can be obtained, for example, by first sparging the medium with nitrogen and then sealing the flasks with a septum and crimp-cap. For strains where growth is not observed anaerobically, microaerobic conditions can be applied by perforating the septum with a small hole for limited aeration. Exemplary anaerobic conditions have been described previously and are well-known in the art. Exemplary aerobic and anaerobic conditions are described, for example, in U.S. patent application Ser. No. 11/891,602, filed Aug. 10, 2007. Fermentations can be performed in a batch, fed-batch or continuous manner, as disclosed herein.
If desired, the pH of the medium can be maintained at a desired pH, in particular neutral pH, such as a pH of around 7 by addition of a base, such as NaOH or other bases, or acid, as needed to maintain the culture medium at a desirable pH. The growth rate can be determined by measuring optical density using a spectrophotometer (600 nm), and the glucose uptake rate by monitoring carbon source depletion over time.
The growth medium can be, for example, any carbohydrate source which can supply a source of carbon to the non-naturally occurring microorganism. Such sources include, for example, sugars such as glucose, xylose, arabinose, galactose, mannose, fructose and starch. Other sources of carbohydrate include, for example, renewable feedstocks and biomass. Exemplary types of biomasses that can be used as feedstocks in the methods of the invention include cellulosic biomass, hemicellulosic biomass and lignin feedstocks or portions of feedstocks. Such biomass feedstocks contain, for example, carbohydrate substrates useful as carbon sources such as glucose, xylose, arabinose, galactose, mannose, fructose and starch. Given the teachings and guidance provided herein, those skilled in the art will understand that renewable feedstocks and biomass other than those exemplified above also can be used for culturing the microbial organisms of the invention for the production of acrylate.
In addition to renewable feedstocks such as those exemplified above, the acrylate microbial organisms of the invention also can be modified for growth on syngas as its source of carbon. In this specific embodiment, one or more proteins or enzymes are expressed in the acrylate producing organisms to provide a metabolic pathway for utilization of syngas or other gaseous carbon source.
Synthesis gas, also known as syngas or producer gas, is the major product of gasification of coal and of carbonaceous materials such as biomass materials, including agricultural crops and residues. Syngas is a mixture primarily of H 2 and CO and can be obtained from the gasification of any organic feedstock, including but not limited to coal, coal oil, natural gas, biomass, and waste organic matter. Gasification is generally carried out under a high fuel to oxygen ratio. Although largely H 2 and CO, syngas can also include CO 2 and other gases in smaller quantities. Thus, synthesis gas provides a cost effective source of gaseous carbon such as CO and, additionally, CO 2 .
The Wood-Ljungdahl pathway catalyzes the conversion of CO and H 2 to acetyl-CoA and other products such as acetate. Organisms capable of utilizing CO and syngas also generally have the capability of utilizing CO 2 and CO 2 /H 2 mixtures through the same basic set of enzymes and transformations encompassed by the Wood-Ljungdahl pathway. H 2 -dependent conversion of CO 2 to acetate by microorganisms was recognized long before it was revealed that CO also could be used by the same organisms and that the same pathways were involved. Many acetogens have been shown to grow in the presence of CO 2 and produce compounds such as acetate as long as hydrogen is present to supply the necessary reducing equivalents (see for example, Drake, Acetogenesis , pp. 3-60 Chapman and Hall, New York, (1994)). This can be summarized by the following equation:
2CO 2 +4H 2 +nADP+nPi →CH 3 COOH+2H 2 O+ nATP
Hence, non-naturally occurring microorganisms possessing the Wood-Ljungdahl pathway can utilize CO 2 and H 2 mixtures as well for the production of acetyl-CoA and other desired products.
The Wood-Ljungdahl pathway is well known in the art and consists of 12 reactions which can be separated into two branches: (1) methyl branch and (2) carbonyl branch. The methyl branch converts syngas to methyl-tetrahydrofolate (methyl-THF) whereas the carbonyl branch converts methyl-THF to acetyl-CoA. The reactions in the methyl branch are catalyzed in order by the following enzymes or proteins: ferredoxin oxidoreductase, formate dehydrogenase, formyltetrahydrofolate synthetase, methenyltetrahydrofolate cyclodehydratase, methylenetetrahydrofolate dehydrogenase and methylenetetrahydrofolate reductase. The reactions in the carbonyl branch are catalyzed in order by the following enzymes or proteins: cobalamide corrinoid/iron-sulfur protein, methyltransferase, carbon monoxide dehydrogenase, acetyl-CoA synthase, acetyl-CoA synthase disulfide reductase and hydrogenase. Following the teachings and guidance provided herein for introducing a sufficient number of encoding nucleic acids to generate an acrylate pathway, those skilled in the art will understand that the same engineering design also can be performed with respect to introducing at least the nucleic acids encoding the Wood-Ljungdahl enzymes or proteins absent in the host organism. Therefore, introduction of one or more encoding nucleic acids into the microbial organisms of the invention such that the modified organism contains the complete Wood-Ljungdahl pathway will confer syngas utilization ability.
Accordingly, given the teachings and guidance provided herein, those skilled in the art will understand that a non-naturally occurring microbial organism can be produced that secretes the biosynthesized compounds of the invention when grown on a carbon source such as a carbohydrate. Such compounds include, for example, acrylate and any of the intermediate metabolites in the acrylate pathway. All that is required is to engineer in one or more of the required enzyme or protein activities to achieve biosynthesis of the desired compound or intermediate including, for example, inclusion of some or all of the acrylate biosynthetic pathways. Accordingly, the invention provides a non-naturally occurring microbial organism that produces and/or secretes acrylate when grown on a carbohydrate or other carbon source and produces and/or secretes any of the intermediate metabolites shown in the acrylate pathway when grown on a carbohydrate or other carbon source. The acrylate producing microbial organisms of the invention can initiate synthesis from an intermediate, for example, fumarate.
The non-naturally occurring microbial organisms of the invention are constructed using methods well known in the art as exemplified herein to exogenously express at least one nucleic acid encoding an acrylate pathway enzyme or protein in sufficient amounts to produce acrylate. It is understood that the microbial organisms of the invention are cultured under conditions sufficient to produce acrylate. Following the teachings and guidance provided herein, the non-naturally occurring microbial organisms of the invention can achieve biosynthesis of acrylate resulting in intracellular concentrations between about 0.1-200 mM or more. Generally, the intracellular concentration of acrylate is between about 3-150 mM, particularly between about 5-125 mM and more particularly between about 8-100 mM, including about 10 mM, 20 mM, 50 mM, 80 mM, or more. Intracellular concentrations between and above each of these exemplary ranges also can be achieved from the non-naturally occurring microbial organisms of the invention.
The fumarate, malate, or acrylate can be separated from other components in the culture using a variety of methods well known in the art. Such separation methods include, for example, extraction procedures as well as methods that include continuous liquid-liquid extraction, pervaporation, membrane filtration, membrane separation, reverse osmosis, electrodialysis, distillation, crystallization, centrifugation, extractive filtration, ion exchange chromatography, size exclusion chromatography, adsorption chromatography, and ultrafiltration. All of the above methods are well known in the art.
Any of the non-naturally occurring microbial organisms described herein can be cultured to produce and/or secrete the biosynthetic products of the invention. For example, the fumarate, malate, or acrylate producers can be cultured for the biosynthetic production of fumarate, malate, or acrylate.
For the production of fumarate, malate, or acrylate, the recombinant strains are cultured in a medium with carbon source and other essential nutrients. It is highly desirable to maintain anaerobic conditions in the fermenter to reduce the cost of the overall process. Such conditions can be obtained, for example, by first sparging the medium with nitrogen and then sealing the flasks with a septum and crimp-cap. For strains where growth is not observed anaerobically, microaerobic conditions can be applied by perforating the septum with a small hole for limited aeration. Exemplary anaerobic conditions have been described previously and are well-known in the art. Exemplary aerobic and anaerobic conditions are described, for example, in U.S. patent application Ser. No. 11/891,602, filed Aug. 10, 2007. Fermentations can be performed in a batch, fed-batch or continuous manner, as disclosed herein.
If desired, the pH of the medium can be maintained at a desired pH, in particular neutral pH, such as a pH of around 7 by addition of a base, such as NaOH or other bases, or acid, as needed to maintain the culture medium at a desirable pH. The growth rate can be determined by measuring optical density using a spectrophotometer (600 nm), and the glucose uptake rate by monitoring carbon source depletion over time.
The growth medium can include, for example, any carbohydrate source which can supply a source of carbon to the non-naturally occurring microorganism. Such sources include, for example, sugars such as glucose, xylose, arabinose, galactose, mannose, fructose and starch. Other sources of carbohydrate include, for example, renewable feedstocks and biomass. Exemplary types of biomasses that can be used as feedstocks in the methods of the invention include cellulosic biomass, hemicellulosic biomass and lignin feedstocks or portions of feedstocks. Such biomass feedstocks contain, for example, carbohydrate substrates useful as carbon sources such as glucose, xylose, arabinose, galactose, mannose, fructose and starch. Given the teachings and guidance provided herein, those skilled in the art will understand that renewable feedstocks and biomass other than those exemplified above also can be used for culturing the microbial organisms of the invention for the production of fumarate, malate, or acrylate.
In addition to renewable feedstocks such as those exemplified above, the fumarate, malate, or acrylate microbial organisms of the invention also can be modified for growth on syngas as its source of carbon. In this specific embodiment, one or more proteins or enzymes are expressed in the fumarate, malate, or acrylate producing organisms to provide a metabolic pathway for utilization of syngas or other gaseous carbon source.
Synthesis gas, also known as syngas or producer gas, is the major product of gasification of coal and of carbonaceous materials such as biomass materials, including agricultural crops and residues. Syngas is a mixture primarily of H 2 and CO and can be obtained from the gasification of any organic feedstock, including but not limited to coal, coal oil, natural gas, biomass, and waste organic matter. Gasification is generally carried out under a high fuel to oxygen ratio. Although largely H 2 and CO, syngas can also include CO 2 and other gases in smaller quantities. Thus, synthesis gas provides a cost effective source of gaseous carbon such as CO and, additionally, CO 2 .
The Wood-Ljungdahl pathway catalyzes the conversion of CO and H 2 to acetyl-CoA and other products such as acetate. Organisms capable of utilizing CO and syngas also generally have the capability of utilizing CO 2 and CO 2 /H 2 mixtures through the same basic set of enzymes and transformations encompassed by the Wood-Ljungdahl pathway. H 2 -dependent conversion of CO 2 to acetate by microorganisms was recognized long before it was revealed that CO also could be used by the same organisms and that the same pathways were involved. Many acetogens have been shown to grow in the presence of CO 2 and produce compounds such as acetate as long as hydrogen is present to supply the necessary reducing equivalents (see for example, Drake, Acetogenesis , pp. 3-60 Chapman and Hall, New York, (1994)). This can be summarized by the following equation:
2CO 2 +4H 2 +nADP+nPi →CH 3 COOH+2H 2 O+ nATP
Hence, non-naturally occurring microorganisms possessing the Wood-Ljungdahl pathway can utilize CO 2 and H 2 mixtures as well for the production of acetyl-CoA and other desired products.
The Wood-Ljungdahl pathway is well known in the art and consists of 12 reactions which can be separated into two branches: (1) methyl branch and (2) carbonyl branch. The methyl branch converts syngas to methyl-tetrahydrofolate (methyl-THF) whereas the carbonyl branch converts methyl-THF to acetyl-CoA. The reactions in the methyl branch are catalyzed in order by the following enzymes or proteins: ferredoxin oxidoreductase, formate dehydrogenase, formyltetrahydrofolate synthetase, methenyltetrahydrofolate cyclodehydratase, methylenetetrahydrofolate dehydrogenase and methylenetetrahydrofolate reductase. The reactions in the carbonyl branch are catalyzed in order by the following enzymes or proteins: methyltetrahydrofolate:corrinoid protein methyltransferase (for example, AcsE), corrinoid iron-sulfur protein, nickel-protein assembly protein (for example, AcsF), ferredoxin, acetyl-CoA synthase, carbon monoxide dehydrogenase and nickel-protein assembly protein (for example, CooC). Following the teachings and guidance provided herein for introducing a sufficient number of encoding nucleic acids to generate a fumarate, malate, or acrylate pathway, those skilled in the art will understand that the same engineering design also can be performed with respect to introducing at least the nucleic acids encoding the Wood-Ljungdahl enzymes or proteins absent in the host organism. Therefore, introduction of one or more encoding nucleic acids into the microbial organisms of the invention such that the modified organism contains the complete Wood-Ljungdahl pathway will confer syngas utilization ability.
Accordingly, given the teachings and guidance provided herein, those skilled in the art will understand that a non-naturally occurring microbial organism can be produced that secretes the biosynthesized compounds of the invention when grown on a carbon source such as a carbohydrate. Such compounds include, for example, fumarate, malate, or acrylate and any of the intermediate metabolites in the fumarate, malate, or acrylate pathway. All that is required is to engineer in one or more of the required enzyme or protein activities to achieve biosynthesis of the desired compound or intermediate including, for example, inclusion of some or all of the fumarate, malate, or acrylate biosynthetic pathways. Accordingly, the invention provides a non-naturally occurring microbial organism that produces and/or secretes fumarate, malate, or acrylate when grown on a carbohydrate or other carbon source and produces and/or secretes any of the intermediate metabolites shown in the fumarate, malate, or acrylate pathway when grown on a carbohydrate or other carbon source. The fumarate, malate, or acrylate producing microbial organisms of the invention can initiate synthesis from any of the aforementioned intermediates.
The non-naturally occurring microbial organisms of the invention are constructed using methods well known in the art as exemplified herein to exogenously express at least one nucleic acid encoding a fumarate, malate, or acrylate pathway enzyme or protein in sufficient amounts to produce fumarate, malate, or acrylate. It is understood that the microbial organisms of the invention are cultured under conditions sufficient to produce fumarate, malate, or acrylate. Following the teachings and guidance provided herein, the non-naturally occurring microbial organisms of the invention can achieve biosynthesis of fumarate, malate, or acrylate resulting in intracellular concentrations between about 0.1-200 mM or more. Generally, the intracellular concentration of fumarate, malate, or acrylate is between about 3-200 mM, particularly between about 10-175 mM and more particularly between about 50-150 mM, including about 50 mM, 75 mM, 100 mM, 125 mM, or more. Intracellular concentrations between and above each of these exemplary ranges also can be achieved from the non-naturally occurring microbial organisms of the invention.
In some embodiments, culture conditions include anaerobic or substantially anaerobic growth or maintenance conditions. Exemplary anaerobic conditions have been described previously and are well known in the art. Exemplary anaerobic conditions for fermentation processes are described herein and are described, for example, in U.S. patent application Ser. No. 11/891,602, filed Aug. 10, 2007. Any of these conditions can be employed with the non-naturally occurring microbial organisms as well as other anaerobic conditions well known in the art. Under such anaerobic conditions, the fumarate, malate, or acrylate producers can synthesize fumarate, malate, or acrylate at intracellular concentrations of 5-10 mM or more as well as all other concentrations exemplified herein. It is understood that, even though the above description refers to intracellular concentrations, fumarate, malate, or acrylate producing microbial organisms can produce fumarate, malate, or acrylate intracellularly and/or secrete the product into the culture medium.
The culture conditions can include, for example, liquid culture procedures as well as fermentation and other large scale culture procedures. As described herein, particularly useful yields of the biosynthetic products of the invention can be obtained under anaerobic or substantially anaerobic culture conditions.
As described herein, one exemplary growth condition for achieving biosynthesis of fumarate, malate, or acrylate includes anaerobic culture or fermentation conditions. In certain embodiments, the non-naturally occurring microbial organisms of the invention can be sustained, cultured or fermented under anaerobic or substantially anaerobic conditions. Briefly, anaerobic conditions refers to an environment devoid of oxygen. Substantially anaerobic conditions include, for example, a culture, batch fermentation or continuous fermentation such that the dissolved oxygen concentration in the medium remains between 0 and 10% of saturation. Substantially anaerobic conditions also includes growing or resting cells in liquid medium or on solid agar inside a sealed chamber maintained with an atmosphere of less than 1% oxygen. The percent of oxygen can be maintained by, for example, sparging the culture with an N 2 /CO 2 mixture or other suitable non-oxygen gas or gases.
The culture conditions described herein can be scaled up and grown continuously for manufacturing of fumarate, malate, or acrylate. Exemplary growth procedures include, for example, fed-batch fermentation and batch separation; fed-batch fermentation and continuous separation, or continuous fermentation and continuous separation. All of these processes are well known in the art. Fermentation procedures are particularly useful for the biosynthetic production of commercial quantities of fumarate, malate, or acrylate. Generally, and as with non-continuous culture procedures, the continuous and/or near-continuous production of fumarate, malate, or acrylate can include culturing a non-naturally occurring fumarate, malate, or acrylate producing organism of the invention in sufficient nutrients and medium to sustain and/or nearly sustain growth in an exponential phase. Continuous culture under such conditions can include, for example, 1 day, 2, 3, 4, 5, 6 or 7 days or more. Additionally, continuous culture can include 1 week, 2, 3, 4 or 5 or more weeks and up to several months. Alternatively, organisms of the invention can be cultured for hours, if suitable for a particular application. It is to be understood that the continuous and/or near-continuous culture conditions also can include all time intervals in between these exemplary periods. It is further understood that the time of culturing the microbial organism of the invention is for a sufficient period of time to produce a sufficient amount of product for a desired purpose.
Fermentation procedures are well known in the art. Briefly, fermentation for the biosynthetic production of fumarate, malate, or acrylate can be utilized in, for example, fed-batch fermentation and batch separation; fed-batch fermentation and continuous separation, or continuous fermentation and continuous separation. Examples of batch and continuous fermentation procedures are well known in the art.
In addition to the above fermentation procedures using the fumarate, malate, or acrylate producers of the invention for continuous production of substantial quantities of fumarate, malate, or acrylate, the fumarate, malate, or acrylate producers also can be, for example, simultaneously subjected to chemical synthesis procedures to convert the product to other compounds or the product can be separated from the fermentation culture and sequentially subjected to chemical conversion to convert the product to other compounds, if desired.
Directed evolution is a powerful approach that involves the introduction of mutations targeted to a specific gene in order to improve and/or alter the properties of an enzyme. Improved and/or altered enzymes can be identified through the development and implementation of sensitive high-throughput screening assays that allow the automated screening of many enzyme variants (e.g., >10 4 ). Iterative rounds of mutagenesis and screening typically are performed to afford an enzyme with optimized properties. Computational algorithms that can help to identify areas of the gene for mutagenesis also have been developed and can significantly reduce the number of enzyme variants that need to be generated and screened.
Numerous directed evolution technologies have been developed (for reviews, see Hibbert et al., Biomol. Eng 22:11-19 (2005); Huisman et al., Biocatalysis in the pharmaceutical and biotechnology industries, pp. 717-742 (2007) CRC Press, R. N. Patel, Ed.); Otten et al., Biomol. Eng 22:1-9 (2005); and Sen et al., Appl Biochem. Biotechnol 143:212-223 (2007).) to be effective at creating diverse variant libraries and these methods have been successfully applied to the improvement of a wide range of properties across many enzyme classes.
Enzyme characteristics that have been improved and/or altered by directed evolution technologies include, for example, selectivity/specificity—for conversion of non-natural substrates; temperature stability—for robust high temperature processing; pH stability—for bioprocessing under lower or higher pH conditions; substrate or product tolerance—so that high product titers can be achieved; binding (K m )—broadens substrate binding to include non-natural substrates; inhibition (K i )—to remove inhibition by products, substrates, or key intermediates; activity (kcat)—increases enzymatic reaction rates to achieve desired flux; expression levels -increases protein yields and overall pathway flux; oxygen stability—for operation of air sensitive enzymes under aerobic conditions; and anaerobic activity—for operation of an aerobic enzyme in the absence of oxygen.
The following exemplary methods have been developed for the mutagenesis and diversification of genes to target desired properties of specific enzymes. Any of these can be used to alter/optimize activity of a decarboxylase enzyme.
EpPCR (Pritchard et al., J. Theor. Biol. 234:497-509 (2005).) introduces random point mutations by reducing the fidelity of DNA polymerase in PCR reactions by the addition of Mn 2+ ions, by biasing dNTP concentrations, or by other conditional variations. The five step cloning process to confine the mutagenesis to the target gene of interest involves: 1) error-prone PCR amplification of the gene of interest; 2) restriction enzyme digestion; 3) gel purification of the desired DNA fragment; 4) ligation into a vector; 5) transformation of the gene variants into a suitable host and screening of the library for improved performance. This method can generate multiple mutations in a single gene simultaneously, which can be useful. A high number of mutants can be generated by EpPCR, so a high-throughput screening assay or a selection method (especially using robotics) is useful to identify those with desirable characteristics.
Error-prone Rolling Circle Amplification (epRCA) (Fujii et al., Nucl. Acids Res 32:e145 (2004); and Fujii et al., Nat. Protoc. 1:2493-2497 (2006).) has many of the same elements as epPCR except a whole circular plasmid is used as the template and random 6-mers with exonuclease resistant thiophosphate linkages on the last 2 nucleotides are used to amplify the plasmid followed by transformation into cells in which the plasmid is re-circularized at tandem repeats. Adjusting the Mn 2+ concentration can vary the mutation rate somewhat. This technique uses a simple error-prone, single-step method to create a full copy of the plasmid with 3-4 mutations/kbp. No restriction enzyme digestion or specific primers are required. Additionally, this method is typically available as a kit.
DNA or Family Shuffling (Stemmer, W. P., Proc Natl Acad Sci U.S.A. 91:10747-10751 (1994); and Stemmer, W. P., Nature 370:389-391 (1994).) typically involves digestion of 2 or more variant genes with nucleases such as Dnase I or EndoV to generate a pool of random fragments that are reassembled by cycles of annealing and extension in the presence of DNA polymerase to create a library of chimeric genes. Fragments prime each other and recombination occurs when one copy primes another copy (template switch). This method can be used with >1 kbp DNA sequences. In addition to mutational recombinants created by fragment reassembly, this method introduces point mutations in the extension steps at a rate similar to error-prone PCR. The method can be used to remove deleterious random neutral mutations that might confer antigenicity.
Staggered Extension (StEP) (Zhao et al., Nat. Biotechnol 16:258-261 (1998).) entails template priming followed by repeated cycles of 2 step PCR with denaturation and very short duration of annealing/extension (as short as 5 sec). Growing fragments anneal to different templates and extend further, which is repeated until full-length sequences are made. Template switching means most resulting fragments have multiple parents. Combinations of low-fidelity polymerases (Taq and Mutazyme) reduce error-prone biases because of opposite mutational spectra.
In Random Priming Recombination (RPR) random sequence primers are used to generate many short DNA fragments complementary to different segments of the template. (Shao et al., Nucleic Acids Res 26:681-683 (1998).) Base misincorporation and mispriming via epPCR give point mutations. Short DNA fragments prime one another based on homology and are recombined and reassembled into full-length by repeated thermocycling. Removal of templates prior to this step assures low parental recombinants. This method, like most others, can be performed over multiple iterations to evolve distinct properties. This technology avoids sequence bias, is independent of gene length, and requires very little parent DNA for the application.
In Heteroduplex Recombination linearized plasmid DNA is used to form heteroduplexes that are repaired by mismatch repair. (Volkov et al., Nucleic Acids Res 27:e18 (1999); and Volkov et al., Methods Enzymol. 328:456-463 (2000).) The mismatch repair step is at least somewhat mutagenic. Heteroduplexes transform more efficiently than linear homoduplexes. This method is suitable for large genes and whole operons.
Random Chimeragenesis on Transient Templates (RACHITT) (Coco et al., Nat. Biotechnol 19:354-359 (2001).) employs Dnase I fragmentation and size fractionation of ssDNA. Homologous fragments are hybridized in the absence of polymerase to a complementary ssDNA scaffold. Any overlapping unhybridized fragment ends are trimmed down by an exonuclease. Gaps between fragments are filled in, and then ligated to give a pool of full-length diverse strands hybridized to the scaffold (that contains U to preclude amplification). The scaffold then is destroyed and is replaced by a new strand complementary to the diverse strand by PCR amplification. The method involves one strand (scaffold) that is from only one parent while the priming fragments derive from other genes; the parent scaffold is selected against. Thus, no reannealing with parental fragments occurs. Overlapping fragments are trimmed with an exonuclease. Otherwise, this is conceptually similar to DNA shuffling and StEP. Therefore, there should be no siblings, few inactives, and no unshuffled parentals. This technique has advantages in that few or no parental genes are created and many more crossovers can result relative to standard DNA shuffling.
Recombined Extension on Truncated templates (RETT) entails template switching of unidirectionally growing strands from primers in the presence of unidirectional ssDNA fragments used as a pool of templates. (Lee et al., J. Molec. Catalysis 26:119-129 (2003).) No DNA endonucleases are used. Unidirectional ssDNA is made by DNA polymerase with random primers or serial deletion with exonuclease. Unidirectional ssDNA are only templates and not primers. Random priming and exonucleases don't introduce sequence bias as true of enzymatic cleavage of DNA shuffling/RACHITT. RETT can be easier to optimize than StEP because it uses normal PCR conditions instead of very short extensions. Recombination occurs as a component of the PCR steps—no direct shuffling. This method can also be more random than StEP due to the absence of pauses.
In Degenerate Oligonucleotide Gene Shuffling (DOGS) degenerate primers are used to control recombination between molecules; (Bergquist et al., Methods Mol. Biol. 352:191-204 (2007); Bergquist et al., Biomol. Eng 22:63-72 (2005); Gibbs et al., Gene 271:13-20 (2001).) This can be used to control the tendency of other methods such as DNA shuffling to regenerate parental genes. This method can be combined with random mutagenesis (epPCR) of selected gene segments. This can be a good method to block the reformation of parental sequences. No endonucleases are needed. By adjusting input concentrations of segments made, one can bias towards a desired backbone. This method allows DNA shuffling from unrelated parents without restriction enzyme digests and allows a choice of random mutagenesis methods.
Incremental Truncation for the Creation of Hybrid Enzymes (ITCHY) creates a combinatorial library with 1 base pair deletions of a gene or gene fragment of interest. (Ostermeier et al., Proc Natl Acad Sci U. S. A 96:3562-3567 (1999); Ostermeier et la., Nat. Biotechnol 17:1205-1209 (1999).) Truncations are introduced in opposite direction on pieces of 2 different genes. These are ligated together and the fusions are cloned. This technique does not require homology between the 2 parental genes. When ITCHY is combined with DNA shuffling, the system is called SCRATCHY (see below). A major advantage of both is no need for homology between parental genes; for example, functional fusions between an E. coli and a human gene were created via ITCHY. When ITCHY libraries are made, all possible crossovers are captured.
Thio-Incremental Truncation for the Creation of Hybrid Enzymes (THIO-ITCHY) is almost the same as ITCHY except that phosphothioate dNTPs are used to generate truncations. (Lutz et al., Nucleic Acids Res 29:E16 (2001).) Relative to ITCHY, THIO-ITCHY can be easier to optimize, provide more reproducibility, and adjustability.
SCRATCHY-ITCHY combined with DNA shuffling is a combination of DNA shuffling and ITCHY; therefore, allowing multiple crossovers. (Lutz et al. 2001, Proc Natl Acad Sci U.S.A. 98:11248-11253 (2001).) SCRATCHY combines the best features of ITCHY and DNA shuffling. Computational predictions can be used in optimization. SCRATCHY is more effective than DNA shuffling when sequence identity is below 80%.
In Random Drift Mutagenesis (RNDM) mutations made via epPCR followed by screening/selection for those retaining usable activity. (Bergquist et al., Biomol. Eng 22:63-72 (2005).) Then, these are used in DOGS to generate recombinants with fusions between multiple active mutants or between active mutants and some other desirable parent. Designed to promote isolation of neutral mutations; its purpose is to screen for retained catalytic activity whether or not this activity is higher or lower than in the original gene. RNDM is usable in high throughput assays when screening is capable of detecting activity above background. RNDM has been used as a front end to DOGS in generating diversity. The technique imposes a requirement for activity prior to shuffling or other subsequent steps; neutral drift libraries are indicated to result in higher/quicker improvements in activity from smaller libraries. Though published using epPCR, this could be applied to other large-scale mutagenesis methods.
Sequence Saturation Mutagenesis (SeSaM) is a random mutagenesis method that: 1) generates pool of random length fragments using random incorporation of a phosphothioate nucleotide and cleavage; this pool is used as a template to 2) extend in the presence of “universal” bases such as inosine; 3) replication of a inosine-containing complement gives random base incorporation and, consequently, mutagenesis. (Wong et al., Biotechnol J 3:74-82 (2008); Wong et al., Nucleic Acids Res 32:e26 (2004); and Wong et al., Anal. Biochem. 341:187-189 (2005).) Using this technique it can be possible to generate a large library of mutants within 2-3 days using simple methods. This is very non-directed compared to mutational bias of DNA polymerases. Differences in this approach makes this technique complementary (or alternative) to epPCR.
In Synthetic Shuffling, overlapping oligonucleotides are designed to encode “all genetic diversity in targets” and allow a very high diversity for the shuffled progeny. (Ness et al., Nat. Biotechnol 20:1251-1255 (2002).) In this technique, one can design the fragments to be shuffled. This aids in increasing the resulting diversity of the progeny. One can design sequence/codon biases to make more distantly related sequences recombine at rates approaching more closely related sequences and it doesn't require possessing the template genes physically.
Nucleotide Exchange and Excision Technology NexT exploits a combination of dUTP incorporation followed by treatment with uracil DNA glycosylase and then piperidine to perform endpoint DNA fragmentation. (Muller et al., Nucleic Acids Res 33:e117 (2005).) The gene is reassembled using internal PCR primer extension with proofreading polymerase. The sizes for shuffling are directly controllable using varying dUPT::dTTP ratios. This is an end point reaction using simple methods for uracil incorporation and cleavage. One can use other nucleotide analogs such as 8-oxo-guanine with this method. Additionally, the technique works well with very short fragments (86 bp) and has a low error rate. Chemical cleavage of DNA means very few unshuffled clones.
In Sequence Homology-Independent Protein Recombination (SHIPREC) a linker is used to facilitate fusion between 2 distantly/unrelated genes; nuclease treatment is used to generate a range of chimeras between the two. Result is a single crossover library of these fusions. (Sieber et al., Nat. Biotechnol 19:456-460 (2001).) This produces a limited type of shuffling; mutagenesis is a separate process. This technique can create a library of chimeras with varying fractions of each of 2 unrelated parent genes. No homology is needed. SHIPREC was tested with a heme-binding domain of a bacterial CP450 fused to N-terminal regions of a mammalian CP450; this produced mammalian activity in a more soluble enzyme.
In Gene Site Saturation Mutagenesis (GSSM) the starting materials are a supercoiled dsDNA plasmid with insert and 2 primers degenerate at the desired site for mutations. (Kretz et al., Methods Enzymol. 388:3-11 (2004).) Primers carry the mutation of interest and anneal to the same sequence on opposite strands of DNA; mutation in the middle of the primer and ˜20 nucleotides of correct sequence flanking on each side. The sequence in the primer is NNN or NNK (coding) and MNN (noncoding) (N=all 4, K=G, T, M=A, C). After extension, DpnI is used to digest dam-methylated DNA to eliminate the wild-type template. This technique explores all possible amino acid substitutions at a given locus (i.e., one codon). The technique facilitates the generation of all possible replacements at one site with no nonsense codons and equal or near-equal representation of most possible alleles. It does not require prior knowledge of structure, mechanism, or domains of the target enzyme. If followed by shuffling or Gene Reassembly, this technology creates a diverse library of recombinants containing all possible combinations of single-site up-mutations. The utility of this technology combination has been demonstrated for the successful evolution of over 50 different enzymes, and also for more than one property in a given enzyme.
Combinatorial Cassette Mutagenesis (CCM) involves the use of short oligonucleotide cassettes to replace limited regions with a large number of possible amino acid sequence alterations. (Reidhaar-Olson et al., Methods Enzymol. 208:564-586 (1991); and Reidhaar-Olson et al., Science 241:53-57 (1988).) Simultaneous substitutions at 2 or 3 sites are possible using this technique. Additionally, the method tests a large multiplicity of possible sequence changes at a limited range of sites. It has been used to explore the information content of lambda repressor DNA-binding domain.
Combinatorial Multiple Cassette Mutagenesis (CMCM) is essentially similar to CCM except it is employed as part of a larger program: 1) Use of epPCR at high mutation rate to 2) ID hot spots and hot regions and then 3) extension by CMCM to cover a defined region of protein sequence space. (Reetz et al., Angew. Chem. Int. Ed Engl. 40:3589-3591 (2001).) As with CCM, this method can test virtually all possible alterations over a target region. If used along with methods to create random mutations and shuffled genes, it provides an excellent means of generating diverse, shuffled proteins. This approach was successful in increasing, by 51-fold, the enantioselectivity of an enzyme.
In the Mutator Strains technique conditional ts mutator plasmids allow increases of 20- to 4000-X in random and natural mutation frequency during selection and to block accumulation of deleterious mutations when selection is not required. (Selifonova et al., Appl Environ Microbiol 67:3645-3649 (2001).) This technology is based on a plasmid-derived mutD5 gene, which encodes a mutant subunit of DNA polymerase III. This subunit binds to endogenous DNA polymerase III and compromises the proofreading ability of polymerase III in any of the strain that harbors the plasmid. A broad-spectrum of base substitutions and frameshift mutations occur. In order for effective use, the mutator plasmid should be removed once the desired phenotype is achieved; this is accomplished through a temperature sensitive origin of replication, which allows plasmid curing at 41° C. It should be noted that mutator strains have been explored for quite some time (e.g., see Winter and coworkers, J. Mol. Biol. 260:359-3680 (1996). In this technique very high spontaneous mutation rates are observed. The conditional property minimizes non-desired background mutations. This technology could be combined with adaptive evolution to enhance mutagenesis rates and more rapidly achieve desired phenotypes.
“Look-Through Mutagenesis (LTM) is a multidimensional mutagenesis method that assesses and optimizes combinatorial mutations of selected amino acids.” (Rajpal et al., Proc Natl Acad Sci U.S.A 102:8466-8471 (2005.) Rather than saturating each site with all possible amino acid changes, a set of 9 is chosen to cover the range of amino acid R-group chemistry. Fewer changes per site allows multiple sites to be subjected to this type of mutagenesis. A >800-fold increase in binding affinity for an antibody from low nanomolar to picomolar has been achieved through this method. This is a rational approach to minimize the number of random combinations and should increase the ability to find improved traits by greatly decreasing the numbers of clones to be screened. This has been applied to antibody engineering, specifically to increase the binding affinity and/or reduce dissociation. The technique can be combined with either screens or selections.
Gene Reassembly is a DNA shuffling method that can be applied to multiple genes at one time or to creating a large library of chimeras (multiple mutations) of a single gene. (on the world-wide web at verenium.com/Pages/Technology/EnzymeTech/TechEnzyTGR.html) Typically this technology is used in combination with ultra-high-throughput screening to query the represented sequence space for desired improvements. This technique allows multiple gene recombination independent of homology. The exact number and position of cross-over events can be pre-determined using fragments designed via bioinformatic analysis. This technology leads to a very high level of diversity with virtually no parental gene reformation and a low level of inactive genes. Combined with GSSM, a large range of mutations can be tested for improved activity. The method allows “blending” and “fine tuning” of DNA shuffling, e.g. codon usage can be optimized.
In Silico Protein Design Automation PDA is an optimization algorithm that anchors the structurally defined protein backbone possessing a particular fold, and searches sequence space for amino acid substitutions that can stabilize the fold and overall protein energetics. (Hayes et al., Proc Natl Acad Sci U.S.A. 99:15926-15931 (2002).) This technology allows in silico structure-based entropy predictions in order to search for structural tolerance toward protein amino acid variations. Statistical mechanics is applied to calculate coupling interactions at each position—structural tolerance toward amino acid substitution is a measure of coupling. Ultimately, this technology is designed to yield desired modifications of protein properties while maintaining the integrity of structural characteristics. The method computationally assesses and allows filtering of a very large number of possible sequence variants (10 50 ). Choice of sequence variants to test is related to predictions based on most favorable thermodynamics and ostensibly only stability or properties that are linked to stability can be effectively addressed with this technology. The method has been successfully used in some therapeutic proteins, especially in engineering immunoglobulins. In silico predictions avoid testing extraordinarily large numbers of potential variants. Predictions based on existing three-dimensional structures are more likely to succeed than predictions based on hypothetical structures. This technology can readily predict and allow targeted screening of multiple simultaneous mutations, something not possible with purely experimental technologies due to exponential increases in numbers.
Iterative Saturation Mutagenesis (ISM) involves 1) Use knowledge of structure/function to choose a likely site for enzyme improvement. 2) Saturation mutagenesis at chosen site using Stratagene QuikChange (or other suitable means). 3) Screen/select for desired properties. 4) With improved clone(s), start over at another site and continue repeating. (Reetz et al., Nat. Protoc. 2:891-903 (2007); and Reetz et al., Angew. Chem. Int. Ed Engl. 45:7745-7751 (2006).) This is a proven methodology assures all possible replacements at a given position are made for screening/selection.
Any of the aforementioned methods for mutagenesis can be used alone or in any combination. Additionally, any one or combination of the directed evolution methods can be used in conjunction with adaptive evolution techniques.
To generate better producers, metabolic modeling can be utilized to optimize growth conditions. Modeling can also be used to design gene disruptions that additionally optimize utilization of the pathway (see, for example, U.S. patent publications US 2002/0012939, US 2003/0224363, US 2004/0029149, US 2004/0072723, US 2003/0059792, US 2002/0168654 and US 2004/0009466, and U.S. Pat. No. 7,127,379). Modeling analysis allows reliable predictions of the effects on cell growth of shifting the metabolism towards more efficient production of fumarate, malate, or acrylate.
Another computational method for identifying and designing metabolic alterations favoring biosynthetic production of a product is a metabolic modeling and simulation system termed SimPheny®. This computational method and system is described in, for example, U.S. publication 2003/0233218, filed Jun. 14, 2002, and in International Patent Application No. PCT/US03/18838, filed Jun. 13, 2003. SimPheny® is a computational system that can be used to produce a network model in silico and to simulate the flux of mass, energy or charge through the chemical reactions of a biological system to define a solution space that contains any and all possible functionalities of the chemical reactions in the system, thereby determining a range of allowed activities for the biological system. This approach is referred to as constraints-based modeling because the solution space is defined by constraints such as the known stoichiometry of the included reactions as well as reaction thermodynamic and capacity constraints associated with maximum fluxes through reactions. The space defined by these constraints can be interrogated to determine the phenotypic capabilities and behavior of the biological system or of its biochemical components.
These computational approaches are consistent with biological realities because biological systems are flexible and can reach the same result in many different ways. Biological systems are designed through evolutionary mechanisms that have been restricted by fundamental constraints that all living systems must face. Therefore, constraints-based modeling strategy embraces these general realities. Further, the ability to continuously impose further restrictions on a network model via the tightening of constraints results in a reduction in the size of the solution space, thereby enhancing the precision with which physiological performance or phenotype can be predicted.
Given the teachings and guidance provided herein, those skilled in the art will be able to apply various computational frameworks for metabolic modeling and simulation to design and implement biosynthesis of a desired compound in host microbial organisms. Such metabolic modeling and simulation methods include, for example, the computational systems exemplified above as SimPheny® and OptKnock. For illustration of the invention, some methods are described herein with reference to the OptKnock computation framework for modeling and simulation. Those skilled in the art will know how to apply the identification, design and implementation of the metabolic alterations using OptKnock to any of such other metabolic modeling and simulation computational frameworks and methods well known in the art.
The methods described above will provide one set of metabolic reactions to disrupt. Elimination of each reaction within the set or metabolic modification can result in a desired product as an obligatory product during the growth phase of the organism. Because the reactions are known, a solution to the bilevel OptKnock problem also will provide the associated gene or genes encoding one or more enzymes that catalyze each reaction within the set of reactions. Identification of a set of reactions and their corresponding genes encoding the enzymes participating in each reaction is generally an automated process, accomplished through correlation of the reactions with a reaction database having a relationship between enzymes and encoding genes.
Once identified, the set of reactions that are to be disrupted in order to achieve production of a desired product are implemented in the target cell or organism by functional disruption of at least one gene encoding each metabolic reaction within the set. One particularly useful means to achieve functional disruption of the reaction set is by deletion of each encoding gene. However, in some instances, it can be beneficial to disrupt the reaction by other genetic aberrations including, for example, mutation, deletion of regulatory regions such as promoters or cis binding sites for regulatory factors, or by truncation of the coding sequence at any of a number of locations. These latter aberrations, resulting in less than total deletion of the gene set can be useful, for example, when rapid assessments of the coupling of a product are desired or when genetic reversion is less likely to occur.
To identify additional productive solutions to the above described bilevel OptKnock problem which lead to further sets of reactions to disrupt or metabolic modifications that can result in the biosynthesis, including growth-coupled biosynthesis of a desired product, an optimization method, termed integer cuts, can be implemented. This method proceeds by iteratively solving the OptKnock problem exemplified above with the incorporation of an additional constraint referred to as an integer cut at each iteration. Integer cut constraints effectively prevent the solution procedure from choosing the exact same set of reactions identified in any previous iteration that obligatorily couples product biosynthesis to growth. For example, if a previously identified growth-coupled metabolic modification specifies reactions 1, 2, and 3 for disruption, then the following constraint prevents the same reactions from being simultaneously considered in subsequent solutions. The integer cut method is well known in the art and can be found described in, for example, Burgard et al., Biotechnol. Prog. 17:791-797 (2001). As with all methods described herein with reference to their use in combination with the OptKnock computational framework for metabolic modeling and simulation, the integer cut method of reducing redundancy in iterative computational analysis also can be applied with other computational frameworks well known in the art including, for example, SimPheny®.
The methods exemplified herein allow the construction of cells and organisms that biosynthetically produce a desired product, including the obligatory coupling of production of a target biochemical product to growth of the cell or organism engineered to harbor the identified genetic alterations. Therefore, the computational methods described herein allow the identification and implementation of metabolic modifications that are identified by an in silico method selected from OptKnock or SimPheny®. The set of metabolic modifications can include, for example, addition of one or more biosynthetic pathway enzymes and/or functional disruption of one or more metabolic reactions including, for example, disruption by gene deletion.
It is understood that modifications which do not substantially affect the activity of the various embodiments of this invention are also included within the definition of the invention provided herein. Accordingly, the following examples are intended to illustrate but not limit the present invention.
Example I
Microorganisms Having Growth-coupled Production of Fumarate
This Example describes the construction in silico designed strains for the increased production of fumarate in E. Coli.
Escherichia coli K-12 MG1655 serves as the wild-type strain into which the deletions are introduced. The strains are constructed by incorporating in-frame deletions using homologous recombination via the λ Red recombinase system of Datsenko and Wanner. (Datsenko and Wanner, Proc Natl Acad Sci U.S.A., 97(12):6640-5 (2000).) The approach involves replacing a chromosomal sequence (i.e., the gene targeted for removal) with a selectable antibiotic resistance gene, which itself is later removed. Knockouts are integrated one by one into the recipient strain. No antibiotic resistance markers will remain after each deletion allowing accumulation of multiple mutations in each target strain. The deletion technology completely removes the gene targeted for removal so as to substantially reduce the possibility of the constructed mutants reverting back to the wild-type.
As described further below, one exemplary growth condition for achieving biosynthesis of fumarate/malate includes anaerobic culture or fermentation conditions. In certain embodiments, the non-naturally occurring microbial organisms of the invention can be sustained, cultured or fermented under anaerobic or substantially anaerobic conditions. Briefly, anaerobic conditions refers to an environment devoid of oxygen. Substantially anaerobic conditions include, for example, a culture, batch fermentation or continuous fermentation such that the dissolved oxygen concentration in the medium remains between 0 and 10% of saturation. Substantially anaerobic conditions also includes growing or resting cells in liquid medium or on solid agar inside a sealed chamber maintained with an atmosphere of less than 1% oxygen. The percent of oxygen can be maintained by, for example, sparging the culture with an N 2 /CO 2 mixture or other suitable non-oxygen gas or gases.
The engineered strains are characterized by measuring the growth rate, the substrate uptake rate, and the product/byproduct secretion rate. Cultures are grown overnight and used as inoculum for a fresh batch culture for which measurements are taken during exponential growth. The growth rate is determined by measuring optical density using a spectrophotometer (A600). Concentrations of glucose, fumarate, malate, and other organic acid byproducts in the culture supernatant are determined by HPLC using an HPX-87H column (BioRad), and are used to calculate uptake and secretion rates. All experiments are performed with triplicate cultures.
The knockout strains can exhibit suboptimal growth rates until their metabolic networks have adjusted to their missing functionalities. To enable this adjustment, the strains are adaptively evolved. By subjecting the strains to adaptive evolution, cellular growth rate becomes the primary selection pressure and the mutant cells are compelled to reallocate their metabolic fluxes in order to enhance their rates of growth. This reprogramming of metabolism has been recently demonstrated for several E. coli mutants that had been adaptively evolved on various substrates to reach the growth rates predicted a priori by an in silico model. (Fong and Palsson, Nat Genet, 36(10):1056-8 (2004).)
Should the OptKnock predictions prove successful; the growth improvements brought about by adaptive evolution will be accompanied by enhanced rates of fumarate and/or malate production. The OptKnock-generated strains are adaptively evolved in triplicate (running in parallel) due to differences in the evolutionary patterns witnessed previously in E. coli (Fong and Palsson, Nat Genet, 36(10):1056-8 (2004); Fong et al., J Bacteriol, 185(21):6400-6408 (2003); Ibarra et al., Nature 420:186-189 (2002)) that could potentially result in one strain having superior production qualities over the others. Evolutions are run for a period of 2-6 weeks, depending upon the rate of growth improvement attained. In general, evolutions are stopped once a stable phenotype is obtained.
The adaptive evolution procedure involves maintaining the cells in prolonged exponential growth by the serial passage of batch cultures into fresh medium before the stationary phase is attained. Briefly, one procedure allows cells to reach mid-exponential growth (A 600 =0.5) before being diluted and passed to fresh medium (i.e., M9 minimal media with 2 g/L carbon source). This process is repeated, allowing for about 500 generations for each culture. Culture samples are taken, frozen with liquid nitrogen, and the optical culture density recorded for each day throughout the course of the evolutions. The conditions required for each evolution are summarized on table 7. The evolutions are performed in triplicate (i.e., 18 evolutions total) due to differences in the evolutionary patterns witnessed previously Donnelly et al., Appl Biochem Biotechnol 70-72: 187-98 (1998); Vemuri et al., Appl Environ Microbiol 68:1715-27 (2002), that could potentially result in one strain having superior production qualities over the others. The adaptive evolution step can take up to about two months or more. The adaptive evolution step also can be less than two months depending on the strain design, for example.
Another process can evolve cells using automation technology and is commercially available by Evolugate, LLC (Gainesville, Fla.) under a service contract. The procedure employs the Evolugator™ evolution machine which results in significant time and effort savings over non-automated evolution techniques. Cells are maintained in prolonged exponential growth by the serial passage of batch cultures into fresh medium before the stationary phase is attained. By automating optical density measurement and liquid handling, the Evolugator can perform serial transfer at high rates using large culture volumes, thus approaching the efficiency of a chemostat for evolution of cell fitness 25 . In contrast to a chemostat, which maintains cells in a single vessel, the machine operates by moving from one “reactor” to the next in subdivided regions of a spool of tubing, thus eliminating any selection for wall-growth. Culture samples are taken, frozen with liquid nitrogen, and the optical culture density recorded each day throughout the course of the evolutions. The Evolugator is used for each strain until a stable growth rate is achieved. Growth rate improvements of nearly 50% have been observed in two weeks using this device. The above-described strains are adaptively evolved in triplicate (running in parallel). At ten day intervals, culture samples are taken from the Evolugator, purified on agar plates, and cultured in triplicate as discussed above to assess strain physiology.
Following the adaptive evolution process, the new strains are again characterized by measuring the growth rate, the substrate uptake rate, and the product/byproduct secretion rate. These results are compared to the OptKnock predictions by plotting actual growth and production yields along side the production envelopes. The most successful OptKnock design/evolution combinations are chosen to pursue further, and is characterized in lab-scale batch and continuous fermentations. The growth-coupled biochemical production concept behind the OptKnock approach should also result in the generation of genetically stable overproducers. Thus, the cultures can be maintained in continuous mode for one month to evaluate long-term stability. Periodic samples will be taken to ensure that yield and productivity are maintained throughout the experiment.
Example II
Microorganisms having Growth-Coupled Production of Fumarate
This Example describes the construction in silico designed strains for the increased production of fumarate in S. cerevisiae.
Gene deletions are introduced into wild-type, haploid S. cerevisiae by homologous recombination of the gene interrupted by the KanMX cassette, flanked by loxP sites enabling removal and recycling of the resistance marker (Wach, A., et al., PCR - based gene targeting in Saccharomyces cerevisiae , in Yeast Gene Analysis , M. F. Tuite, Editor. 1998, Academic Press: San Diego.). Starting with a loxP-kanMX-loxP sequence on a plasmid, an artificial construct with this sequence flanked by fragments of the gene of interest will be created by PCR using primers containing both 45-50 bp target sequence followed by a region homologous to the above cassette. This linear DNA will be transformed into wild-type S. cerevisiae , and recombinants will be selected by geneticin resistance. Colonies will be purified and tested for correct double crossover by PCR. To remove the KanMX marker, a plasmid containing the Cre recombinase and bleomycin resistance will be introduced, promoting recombination between the loxP sites (Gueldener et al., Nucleic Acids Res. 30:e23 (2002)). Finally, the resulting strain can be cured of the Cre plasmid by successive culturing on media without any antibiotic present. The final strain will have a markerless gene deletion, and thus the same method can be used to introduce multiple deletions in the same strain.
As described further below, one exemplary growth condition for achieving biosynthesis of fumarate includes anaerobic culture or fermentation conditions. In certain embodiments, the non-naturally occurring eukaryotic organism of the invention can be sustained, cultured or fermented under anaerobic or substantially anaerobic conditions. Briefly, anaerobic conditions refer to an environment devoid of oxygen. Substantially anaerobic conditions include, for example, a culture, batch fermentation or continuous fermentation such that the dissolved oxygen concentration in the medium remains between 0 and 10% of saturation. One skilled in the art will recognize substantially anaerobic conditions include microaerobic conditions. Substantially anaerobic conditions also includes growing or resting cells in liquid medium or on solid agar inside a sealed chamber maintained with an atmosphere of less than 1% oxygen. The percent of oxygen can be maintained by, for example, sparging the culture with an N 2 /CO 2 mixture or other suitable non-oxygen gas or gases.
The engineered strains are characterized by measuring the growth rate, the substrate uptake rate, and the product/byproduct secretion rate. Cultures are grown overnight and used as inoculum for a fresh batch culture for which measurements are taken during exponential growth. The growth rate is determined by measuring optical density using a spectrophotometer (A600). Concentrations of glucose, fumarate, malate, and other organic acid byproducts in the culture supernatant are determined by HPLC using an HPX-87H column (BioRad), and are used to calculate uptake and secretion rates. All experiments are performed with triplicate cultures.
The knockout strains can exhibit suboptimal growth rates until their metabolic networks have adjusted to their missing functionalities. To enable this adjustment, the strains are adaptively evolved. By subjecting the strains to adaptive evolution, cellular growth rate becomes the primary selection pressure and the mutant cells are compelled to reallocate their metabolic fluxes in order to enhance their rates of growth. This reprogramming of metabolism has been recently demonstrated for several E. coli mutants that had been adaptively evolved on various substrates to reach the growth rates predicted a priori by an in silico model. (Fong and Palsson, Nat Genet, 36:1056-1058 (2004).) These teachings can be applied to S. cerevisiae.
Should the OptKnock predictions prove successful; the growth improvements brought about by adaptive evolution will be accompanied by enhanced rates of fumarate production, and further strains can be engineered in a similar matter to optimize malate or acrylate production. The OptKnock-generated strains are adaptively evolved in triplicate (running in parallel) due to differences in the evolutionary patterns witnessed previously in E. coli (Fong and Palsson, Nat Genet, 36:1056-1058 (2004); Fong et al., J Bacteriol, 185:6400-6408 (2003); Ibarra et al., Nature 420:186-189 (2002)) that could potentially result in one strain having superior production qualities over the others. Evolutions are run for a period of 2-6 weeks, depending upon the rate of growth improvement attained. In general, evolutions are stopped once a stable phenotype is obtained.
The adaptive evolution procedure involves maintaining the cells in prolonged exponential growth by the serial passage of batch cultures into fresh medium before the stationary phase is attained. Briefly, one procedure allows cells to reach mid-exponential growth (A 600 =0.5) before being diluted and passed to fresh medium (i.e., M9 minimal media with 2 g/L carbon source). This process is repeated, allowing for about 500 generations for each culture. Culture samples are taken, frozen with liquid nitrogen, and the optical culture density recorded for each day throughout the course of the evolutions. The evolutions are performed in triplicate due to differences in the evolutionary patterns witnessed previously Donnelly et al., Appl Biochem Biotechnol 70-72: 187-98 (1998); Vemuri et al., Appl Environ Microbiol 68:1715-27 (2002), that could potentially result in one strain having superior production qualities over the others. The adaptive evolution step can take up to about two months or more. The adaptive evolution step also can be less than two months depending on the strain design, for example.
Another process can evolve cells using automation technology and is commercially available by Evolugate, LLC (Gainesville, Fla.) under a service contract. The procedure employs the Evolugator™ evolution machine which results in significant time and effort savings over non-automated evolution techniques. Cells are maintained in prolonged exponential growth by the serial passage of batch cultures into fresh medium before the stationary phase is attained. By automating optical density measurement and liquid handling, the Evolugator can perform serial transfer at high rates using large culture volumes, thus approaching the efficiency of a chemostat for evolution of cell fitness. In contrast to a chemostat, which maintains cells in a single vessel, the machine operates by moving from one “reactor” to the next in subdivided regions of a spool of tubing, thus eliminating any selection for wall-growth. Culture samples are taken, frozen with liquid nitrogen, and the optical culture density recorded each day throughout the course of the evolutions. The Evolugator is used for each strain until a stable growth rate is achieved. Growth rate improvements of nearly 50% have been observed in two weeks using this device. The above-described strains are adaptively evolved in triplicate (running in parallel). At ten day intervals, culture samples are taken from the Evolugator, purified on agar plates, and cultured in triplicate as discussed above to assess strain physiology.
Following the adaptive evolution process, the new strains are again characterized by measuring the growth rate, the substrate uptake rate, and the product/byproduct secretion rate. These results are compared to the OptKnock predictions by plotting actual growth and production yields along side the production envelopes. The most successful OptKnock design/evolution combinations are chosen to pursue further, and is characterized in lab-scale batch and continuous fermentations. The growth-coupled biochemical production concept behind the OptKnock approach should also result in the generation of genetically stable overproducers. Thus, the cultures can be maintained in continuous mode for one month to evaluate long-term stability. Periodic samples will be taken to ensure that yield and productivity are maintained throughout the experiment.
Example III
Acrylate Biosynthesis
This Example describes the generation of a microbial organism capable of producing acrylate using a decarboxylase metabolic pathway.
Escherichia coli is used as a target organism to engineer a decarboxylase pathway ( FIG. 1 ), and testing growth and acrylate production from glucose. E. coli provides a good model for developing a non-naturally occurring microorganism capable of producing acrylate, from glucose since it is amenable to genetic manipulation and is known to be capable of producing various products, like ethanol, effectively under anaerobic conditions from glucose.
To generate an E. coli strain engineered to produce primary alcohol, nucleic acids encoding proteins and enzymes required for the acrylate production pathway via fumarate decarboxylation as described above, are expressed in E. coli using well known molecular biology techniques (see, for example, Sambrook, supra, 2001; Ausubel supra, 1999; Roberts et al., supra, 1989). The pad1 gene (AB368798), encoding a decarboxylase under anaerobic conditions, are cloned into the pZE13 vector under the PA1/lacO promoter. The of plasmid is transformed into E. coli strain MG1655 to express the enzyme aconitate decarboxylase required for decarboxylation of fumarate to acrylate.
The engineered production organism containing a decarboxylase enzyme is grown in a 10 L bioreactor sparged with an N 2 /CO 2 mixture, using 5 L broth containing 5 g/L potassium phosphate, 2.5 g/L ammonium chloride, 0.5 g/L magnesium sulfate, and 30 g/L corn steep liquor, and an initial glucose concentration of 20 g/L. As the cells grow and utilize the glucose, additional 70% glucose is fed into the bioreactor at a rate approximately balancing glucose consumption. The temperature of the bioreactor is maintained at 30 degrees C. Growth continues for approximately 24 hours, until acrylate reaches a concentration of between 10-200 g/L, with the cell density being between 5 and 50 g/L. Upon completion of the cultivation period, the fermenter contents are passed through a cell separation unit (e.g., centrifuge) to remove cells and cell debris, and the fermentation broth and acrylate is separated from the broth and purified by standard methods for organic acid recovery.
Example IV
Acrylate from Biologically Produced Fumarate
Escherichia coli K-12 MG1655 is used as one reference wild-type strain into which the deletions are introduced. The knockouts are integrated, for example, one-by-one into the recipient strain allowing the accumulation of several deletions. The deletion methodology completely removes the gene targeted for removal so as to avoid the possibility of the constructed mutants reverting back to their wild-type.
The strains are constructed by incorporating in-frame deletions using homologous recombination by well known methods such as the λ Red recombinase system (Datsenko and Wanner, Proc Natl Acad Sci U.S.A., 97:6640-6645 (2000)). The approach involves replacing a chromosomal sequence (i.e., the gene targeted for removal) with a selectable antibiotic resistance gene, which itself is later removed. The knockouts are integrated sequentially into the recipient strain. Antibiotic resistance markers are removed after each deletion, thus allowing accumulation of multiple mutations in each target strain.
An organism engineered for high level fumarate production is grown in a 10 L bioreactor sparged with an N 2 /CO 2 mixture, using 5 L broth containing 5 g/L potassium phosphate, 2.5 g/L ammonium chloride, 0.5 g/L magnesium sulfate, and 30 g/L corn steep liquor, and an initial glucose concentration of 20 g/L. As the cells grow and utilize the glucose, additional 70% glucose is fed into the bioreactor at a rate approximately balancing glucose consumption. The temperature of the bioreactor is maintained at 30 degrees C. Growth continues for approximately 24 hours, until fumarate reaches a concentration of between 10-200 g/L, with the cell density being between 5 and 50 g/L. Upon completion of the cultivation period, a decarboxylase enzyme is added either directly to the fermenter or after initial removal of cells and cell debris. After agitating for the required length of time required for complete conversion of fumarate to acrylate, the acrylate is recovered as described above.
TABLE 1
The list of all strains identified by OptKnock that are most likely to provide increased
fumarate yields in E. Coli.
1.
ACKr
ADHEr
AKGD
ASNS2
ATPS4r
LDH_D
2.
ACKr
ADHEr
AKGD
ATPS4r
CBMK2
LDH_D
3.
ACKr
ADHEr
AKGD
ATPS4r
GLUDy
LDH_D
4.
ACKr
ADHEr
AKGD
ATPS4r
LDH_D
5.
ACKr
ADHEr
AKGD
ATPS4r
LDH_D
RPE
6.
ACKr
ADHEr
AKGD
ATPS4r
LDH_D
TAL
7.
ACKr
ADHEr
AKGD
ATPS4r
LDH_D
TKT1
8.
ACKr
ADHEr
AKGD
ATPS4r
LDH_D
TKT2
9.
ACKr
ADHEr
ASNS2
ATPS4r
LDH_D
SUCOAS
10.
ACKr
ADHEr
ASNS2
LDH_D
ME2
SUCD4
11.
ACKr
ADHEr
ATPS4r
CBMK2
LDH_D
SUCOAS
12.
ACKr
ADHEr
ATPS4r
GLUDy
LDH_D
SUCOAS
13.
ACKr
ADHEr
ATPS4r
LDH_D
PDH
PFLi
14.
ACKr
ADHEr
ATPS4r
LDH_D
RPE
SUCOAS
15.
ACKr
ADHEr
ATPS4r
LDH_D
SUCOAS
16.
ACKr
ADHEr
ATPS4r
LDH_D
SUCOAS
TAL
17.
ACKr
ADHEr
ATPS4r
LDH_D
SUCOAS
TKT1
18.
ACKr
ADHEr
ATPS4r
LDH_D
SUCOAS
TKT2
19.
ACKr
ADHEr
CBMK2
FRD2
LDH_D
ME2
THD2
20.
ACKr
ADHEr
CBMK2
LDH_D
ME2
SUCD4
21.
ACKr
ADHEr
FRD2
G5SD
LDH_D
ME2
THD2
22.
ACKr
ADHEr
FRD2
GLCpts
GLUDy
LDH_D
ME2
23.
ACKr
ADHEr
FRD2
GLU5K
LDH_D
ME2
THD2
24.
ACKr
ADHEr
FRD2
LDH_D
ME2
PFLi
THD2
25.
ACKr
ADHEr
FRD2
LDH_D
ME2
THD2
26.
ACKr
ADHEr
GLCpts
GLUDy
LDH_D
ME2
SUCD4
27.
ACKr
ADHEr
GLCpts
LDH_D
ME2
SUCD4
28.
ACKr
ADHEr
GLUDy
LDH_D
ME2
SUCD4
29.
ACKr
ADHEr
LDH_D
ME2
SUCD4
30.
ACKr
AKGD
ASNS2
ATPS4r
31.
ACKr
AKGD
ASNS2
ATPS4r
CBMK2
32.
ACKr
AKGD
ASNS2
ATPS4r
GLUDy
33.
ACKr
AKGD
ASNS2
ATPS4r
RPE
34.
ACKr
AKGD
ASNS2
ATPS4r
TAL
35.
ACKr
AKGD
ASNS2
ATPS4r
TKT1
36.
ACKr
AKGD
ASNS2
ATPS4r
TKT2
37.
ACKr
AKGD
ATPS4r
38.
ACKr
AKGD
ATPS4r
CBMK2
39.
ACKr
AKGD
ATPS4r
CBMK2
GLUDy
40.
ACKr
AKGD
ATPS4r
CBMK2
RPE
41.
ACKr
AKGD
ATPS4r
CBMK2
TAL
42.
ACKr
AKGD
ATPS4r
CBMK2
TKT1
43.
ACKr
AKGD
ATPS4r
CBMK2
TKT2
44.
ACKr
AKGD
ATPS4r
GLUDy
45.
ACKr
AKGD
ATPS4r
GLUDy
RPE
46.
ACKr
AKGD
ATPS4r
GLUDy
TAL
47.
ACKr
AKGD
ATPS4r
GLUDy
TKT1
48.
ACKr
AKGD
ATPS4r
GLUDy
TKT2
49.
ACKr
AKGD
ATPS4r
PPCK
PYK
50.
ACKr
AKGD
ATPS4r
RPE
51.
ACKr
AKGD
ATPS4r
TAL
52.
ACKr
AKGD
ATPS4r
TKT1
53.
ACKr
AKGD
ATPS4r
TKT2
54.
ACKr
ASNS2
ATPS4r
CBMK2
SUCOAS
55.
ACKr
ASNS2
ATPS4r
GLUDy
SUCOAS
56.
ACKr
ASNS2
ATPS4r
RPE
SUCOAS
57.
ACKr
ASNS2
ATPS4r
SUCOAS
58.
ACKr
ASNS2
ATPS4r
SUCOAS
TAL
59.
ACKr
ASNS2
ATPS4r
SUCOAS
TKT1
60.
ACKr
ASNS2
ATPS4r
SUCOAS
TKT2
61.
ACKr
ATPS4r
CBMK2
GLUDy
SUCOAS
62.
ACKr
ATPS4r
CBMK2
RPE
SUCOAS
63.
ACKr
ATPS4r
CBMK2
SUCOAS
64.
ACKr
ATPS4r
CBMK2
SUCOAS
TAL
65.
ACKr
ATPS4r
CBMK2
SUCOAS
TKT1
66.
ACKr
ATPS4r
CBMK2
SUCOAS
TKT2
67.
ACKr
ATPS4r
FUM
PPCK
68.
ACKr
ATPS4r
GLUDy
RPE
SUCOAS
69.
ACKr
ATPS4r
GLUDy
SUCOAS
70.
ACKr
ATPS4r
GLUDy
SUCOAS
TAL
71.
ACKr
ATPS4r
GLUDy
SUCOAS
TKT1
72.
ACKr
ATPS4r
GLUDy
SUCOAS
TKT2
73.
ACKr
ATPS4r
MDH
PPCK
74.
ACKr
ATPS4r
PDH
PFLi
75.
ACKr
ATPS4r
PPCK
PYK
SUCOAS
76.
ACKr
ATPS4r
RPE
SUCOAS
77.
ACKr
ATPS4r
SUCOAS
78.
ACKr
ATPS4r
SUCOAS
TAL
79.
ACKr
ATPS4r
SUCOAS
TKT1
80.
ACKr
ATPS4r
SUCOAS
TKT2
81.
ACKr
FRD2
ME1x
ME2
PYK
82.
ACKr
ME1x
ME2
PYK
SUCD4
83.
ADHEr
AKGD
ASNS2
ATPS4r
LDH_D
PTAr
84.
ADHEr
AKGD
ATPS4r
CBMK2
LDH_D
PTAr
85.
ADHEr
AKGD
ATPS4r
GLUDy
LDH_D
PTAr
86.
ADHEr
AKGD
ATPS4r
LDH_D
PTAr
87.
ADHEr
AKGD
ATPS4r
LDH_D
PTAr
RPE
88.
ADHEr
AKGD
ATPS4r
LDH_D
PTAr
TAL
89.
ADHEr
AKGD
ATPS4r
LDH_D
PTAr
TKT1
90.
ADHEr
AKGD
ATPS4r
LDH_D
PTAr
TKT2
91.
ADHEr
ALAR
ASNS2
LDH_D
ME2
PRO1z
SUCD4
92.
ADHEr
ALAR
CBMK2
GLUDy
LDH_D
PRO1z
SUCD4
93.
ADHEr
ALAR
CBMK2
LDH_D
ME2
PRO1z
SUCD4
94.
ADHEr
ALAR
FUM
LDH_D
PRO1z
SUCD4
95.
ADHEr
ALAR
G5SD
LDH_D
ME2
PRO1z
SUCD4
96.
ADHEr
ALAR
GLCpts
LDH_D
ME2
PRO1z
SUCD4
97.
ADHEr
ALAR
GLU5K
LDH_D
ME2
PRO1z
SUCD4
98.
ADHEr
ALAR
GLUDy
LDH_D
ME2
PRO1z
SUCD4
99.
ADHEr
ALAR
GLUDy
LDH_D
PRO1z
SUCD4
100.
ADHEr
ALAR
GLUDy
LDH_D
PRO1z
SUCD4
THD2
101.
ADHEr
ALAR
LDH_D
ME2
PRO1z
SUCD4
102.
ADHEr
ALAR
LDH_D
ME2
PRO1z
SUCD4
THD2
103.
ADHEr
ASNS2
ATPS4r
LDH_D
PDH
PFLi
104.
ADHEr
ASNS2
ATPS4r
LDH_D
PTAr
SUCOAS
105.
ADHEr
ASNS2
CBMK2
FRD2
G5SD
GLUDy
LDH_D
106.
ADHEr
ASNS2
CBMK2
FRD2
G5SD
LDH_D
ME2
107.
ADHEr
ASNS2
CBMK2
FRD2
GLU5K
GLUDy
LDH_D
108.
ADHEr
ASNS2
CBMK2
FRD2
GLU5K
LDH_D
ME2
109.
ADHEr
ASNS2
CBMK2
FRD2
LDH_D
ME2
110.
ADHEr
ASNS2
DAAD
LDH_D
ME2
PRO1z
SUCD4
111.
ADHEr
ASNS2
FRD2
G5SD
GLUDy
LDH_D
112.
ADHEr
ASNS2
FRD2
G5SD
GLUDy
LDH_D
ME2
113.
ADHEr
ASNS2
FRD2
G5SD
GLUDy
LDH_D
THD2
114.
ADHEr
ASNS2
FRD2
G5SD
LDH_D
ME2
115.
ADHEr
ASNS2
FRD2
G5SD
LDH_D
ME2
THD2
116.
ADHEr
ASNS2
FRD2
GLU5K
GLUDy
LDH_D
117.
ADHEr
ASNS2
FRD2
GLU5K
GLUDy
LDH_D
ME2
118.
ADHEr
ASNS2
FRD2
GLU5K
GLUDy
LDH_D
THD2
119.
ADHEr
ASNS2
FRD2
GLU5K
LDH_D
ME2
120.
ADHEr
ASNS2
FRD2
GLU5K
LDH_D
ME2
THD2
121.
ADHEr
ASNS2
FRD2
LDH_D
ME2
122.
ADHEr
ASNS2
FRD2
LDH_D
ME2
123.
ADHEr
ASNS2
G5SD
GLUDy
LDH_D
PRO1z
SUCD4
124.
ADHEr
ASNS2
G5SD
LDH_D
ME2
SUCD4
THD2
125.
ADHEr
ASNS2
GLU5K
GLUDy
LDH_D
PRO1z
SUCD4
126.
ADHEr
ASNS2
GLU5K
LDH_D
ME2
SUCD4
THD2
127.
ADHEr
ASNS2
LDH_D
ME2
PTAr
SUCD4
128.
ADHEr
ATPS4r
CBMK2
LDH_D
PDH
PFLi
129.
ADHEr
ATPS4r
CBMK2
LDH_D
PTAr
SUCOAS
130.
ADHEr
ATPS4r
G5SD
LDH_D
PDH
PFLi
131.
ADHEr
ATPS4r
GLU5K
LDH_D
PDH
PFLi
132.
ADHEr
ATPS4r
GLUDy
LDH_D
PDH
PFLi
133.
ADHEr
ATPS4r
GLUDy
LDH_D
PTAr
SUCOAS
134.
ADHEr
ATPS4r
LDH_D
NADH12
PFLi
THD2
135.
ADHEr
ATPS4r
LDH_D
PDH
PFLi
136.
ADHEr
ATPS4r
LDH_D
PDH
PFLi
PTAr
137.
ADHEr
ATPS4r
LDH_D
PDH
PFLi
RPE
138.
ADHEr
ATPS4r
LDH_D
PDH
PFLi
TAL
139.
ADHEr
ATPS4r
LDH_D
PDH
PFLi
TKT1
140.
ADHEr
ATPS4r
LDH_D
PDH
PFLi
TKT2
141.
ADHEr
ATPS4r
LDH_D
PTAr
RPE
SUCOAS
142.
ADHEr
ATPS4r
LDH_D
PTAr
SUCOAS
143.
ADHEr
ATPS4r
LDH_D
PTAr
SUCOAS
TAL
144.
ADHEr
ATPS4r
LDH_D
PTAr
SUCOAS
TKT1
145.
ADHEr
ATPS4r
LDH_D
PTAr
SUCOAS
TKT2
146.
ADHEr
CBMK2
DAAD
GLUDy
LDH_D
PRO1z
SUCD4
147.
ADHEr
CBMK2
DAAD
LDH_D
ME2
PRO1z
SUCD4
148.
ADHEr
CBMK2
FRD2
G5SD
LDH_D
ME2
149.
ADHEr
CBMK2
FRD2
GLCpts
GLUDy
LDH_D
ME2
150.
ADHEr
CBMK2
FRD2
GLCpts
LDH_D
ME2
151.
ADHEr
CBMK2
FRD2
GLU5K
LDH_D
ME2
152.
ADHEr
CBMK2
FRD2
GLUDy
LDH_D
153.
ADHEr
CBMK2
FRD2
GLUDy
LDH_D
ME2
154.
ADHEr
CBMK2
FRD2
GLUDy
LDH_D
ME2
THD2
155.
ADHEr
CBMK2
FRD2
GLUDy
LDH_D
THD2
156.
ADHEr
CBMK2
FRD2
LDH_D
ME2
157.
ADHEr
CBMK2
FRD2
LDH_D
ME2
PFLi
THD2
158.
ADHEr
CBMK2
FRD2
LDH_D
ME2
PTAr
THD2
159.
ADHEr
CBMK2
FRD2
LDH_D
ME2
THD2
160.
ADHEr
CBMK2
GLUDy
LDH_D
ME2
PRO1z
SUCD4
161.
ADHEr
CBMK2
GLUDy
LDH_D
ME2
SUCD4
THD2
162.
ADHEr
CBMK2
GLUDy
LDH_D
PRO1z
SUCD4
163.
ADHEr
CBMK2
GLUDy
LDH_D
PRO1z
SUCD4
THD2
164.
ADHEr
CBMK2
LDH_D
ME2
PTAr
SUCD4
165.
ADHEr
CBMK2
LDH_D
ME2
SUCD4
THD2
166.
ADHEr
DAAD
FUM
LDH_D
PRO1z
SUCD4
167.
ADHEr
DAAD
G5SD
LDH_D
ME2
PRO1z
SUCD4
168.
ADHEr
DAAD
GLCpts
LDH_D
ME2
PRO1z
SUCD4
169.
ADHEr
DAAD
GLU5K
LDH_D
ME2
PRO1z
SUCD4
170.
ADHEr
DAAD
GLUDy
LDH_D
ME2
PRO1z
SUCD4
171.
ADHEr
DAAD
GLUDy
LDH_D
PRO1z
SUCD4
172.
ADHEr
DAAD
GLUDy
LDH_D
PRO1z
SUCD4
THD2
173.
ADHEr
DAAD
LDH_D
ME2
PRO1z
SUCD4
174.
ADHEr
DAAD
LDH_D
ME2
PRO1z
SUCD4
THD2
175.
ADHEr
FDH2
GLUDy
LDH_D
NADH12
NADH6
PRO1z
176.
ADHEr
FDH2
LDH_D
ME2
NADH12
NADH6
THD2
177.
ADHEr
FRD2
FUM
LDH_D
178.
ADHEr
FRD2
FUM
LDH_D
MDH
PYK
179.
ADHEr
FRD2
G5SD
GLCpts
LDH_D
ME2
180.
ADHEr
FRD2
G5SD
LDH_D
ME2
181.
ADHEr
FRD2
G5SD
LDH_D
ME2
PTAr
THD2
182.
ADHEr
FRD2
GLCpts
GLU5K
LDH_D
ME2
183.
ADHEr
FRD2
GLCpts
GLUDy
LDH_D
ME2
184.
ADHEr
FRD2
GLCpts
GLUDy
LDH_D
ME2
PTAr
185.
ADHEr
FRD2
GLCpts
LDH_D
ME1x
ME2
PYK
186.
ADHEr
FRD2
GLCpts
LDH_D
ME2
187.
ADHEr
FRD2
GLU5K
LDH_D
ME2
188.
ADHEr
FRD2
GLU5K
LDH_D
ME2
PTAr
THD2
189.
ADHEr
FRD2
GLUDy
HEX1
LDH_D
ME2
THD2
190.
ADHEr
FRD2
GLUDy
HEX1
LDH_D
THD2
191.
ADHEr
FRD2
GLUDy
LDH_D
192.
ADHEr
FRD2
GLUDy
LDH_D
ME2
193.
ADHEr
FRD2
GLUDy
LDH_D
ME2
PFLi
THD2
194.
ADHEr
FRD2
GLUDy
LDH_D
ME2
THD2
195.
ADHEr
FRD2
GLUDy
LDH_D
THD2
196.
ADHEr
FRD2
HEX1
LDH_D
ME2
THD2
197.
ADHEr
FRD2
LDH_D
ME2
198.
ADHEr
FRD2
LDH_D
ME2
PFLi
PTAr
THD2
199.
ADHEr
FRD2
LDH_D
ME2
PFLi
THD2
200.
ADHEr
FRD2
LDH_D
ME2
PTAr
THD2
201.
ADHEr
FRD2
LDH_D
ME2
THD2
202.
ADHEr
FRD2
ME1x
ME2
PYK
203.
ADHEr
GLCpts
GLUDy
LDH_D
ME2
PRO1z
SUCD4
204.
ADHEr
GLCpts
GLUDy
LDH_D
ME2
PTAr
SUCD4
205.
ADHEr
GLCpts
LDH_D
ME1x
ME2
PYK
SUCD4
206.
ADHEr
GLCpts
LDH_D
ME2
PTAr
SUCD4
207.
ADHEr
GLU5K
LDH_D
208.
ADHEr
GLUDy
HEX1
LDH_D
ME2
SUCD4
THD2
209.
ADHEr
GLUDy
HEX1
LDH_D
PRO1z
SUCD4
THD2
210.
ADHEr
GLUDy
LDH_D
ME2
PRO1z
SUCD4
211.
ADHEr
GLUDy
LDH_D
ME2
PRO1z
SUCD4
THD2
212.
ADHEr
GLUDy
LDH_D
ME2
PTAr
SUCD4
213.
ADHEr
GLUDy
LDH_D
ME2
SUCD4
THD2
214.
ADHEr
GLUDy
LDH_D
PRO1z
SUCD4
215.
ADHEr
GLUDy
LDH_D
PRO1z
SUCD4
THD2
216.
ADHEr
GLUDy
LDH_D
SUCOAS
TKT2
217.
ADHEr
HEX1
LDH_D
ME2
SUCD4
THD2
218.
ADHEr
LDH_D
ME2
PTAr
SUCD4
219.
ADHEr
LDH_D
ME2
SUCD4
THD2
220.
ADHEr
THD2
221.
AKGD
ASNS2
ATPS4r
CBMK2
PTAr
222.
AKGD
ASNS2
ATPS4r
GLUDy
PTAr
223.
AKGD
ASNS2
ATPS4r
PTAr
224.
AKGD
ASNS2
ATPS4r
PTAr
RPE
225.
AKGD
ASNS2
ATPS4r
PTAr
TAL
226.
AKGD
ASNS2
ATPS4r
PTAr
TKT1
227.
AKGD
ASNS2
ATPS4r
PTAr
TKT2
228.
AKGD
ATPS4r
CBMK2
GLUDy
PTAr
229.
AKGD
ATPS4r
CBMK2
PTAr
230.
AKGD
ATPS4r
CBMK2
PTAr
RPE
231.
AKGD
ATPS4r
CBMK2
PTAr
TAL
232.
AKGD
ATPS4r
CBMK2
PTAr
TKT1
233.
AKGD
ATPS4r
CBMK2
PTAr
TKT2
234.
AKGD
ATPS4r
GLUDy
PTAr
235.
AKGD
ATPS4r
GLUDy
PTAr
RPE
236.
AKGD
ATPS4r
GLUDy
PTAr
TAL
237.
AKGD
ATPS4r
GLUDy
PTAr
TKT1
238.
AKGD
ATPS4r
GLUDy
PTAr
TKT2
239.
AKGD
ATPS4r
PPCK
PTAr
PYK
240.
AKGD
ATPS4r
PTAr
241.
AKGD
ATPS4r
PTAr
RPE
242.
AKGD
ATPS4r
PTAr
TAL
243.
AKGD
ATPS4r
PTAr
TKT1
244.
AKGD
ATPS4r
PTAr
TKT2
245.
ALAR
FUM
PRO1z
SUCD4
246.
ASNS2
ATPS4r
CBMK2
PTAr
SUCOAS
247.
ASNS2
ATPS4r
FRD2
PFLi
248.
ASNS2
ATPS4r
GLUDy
PTAr
SUCOAS
249.
ASNS2
ATPS4r
PDH
PFLi
250.
ASNS2
ATPS4r
PTAr
RPE
SUCOAS
251.
ASNS2
ATPS4r
PTAr
SUCOAS
252.
ASNS2
ATPS4r
PTAr
SUCOAS
TAL
253.
ASNS2
ATPS4r
PTAr
SUCOAS
TKT1
254.
ASNS2
ATPS4r
PTAr
SUCOAS
TKT2
255.
ATPS4r
CBMK2
FRD2
PFLi
256.
ATPS4r
CBMK2
GLUDy
PTAr
SUCOAS
257.
ATPS4r
CBMK2
PDH
PFLi
258.
ATPS4r
CBMK2
PTAr
RPE
SUCOAS
259.
ATPS4r
CBMK2
PTAr
SUCOAS
260.
ATPS4r
CBMK2
PTAr
SUCOAS
TAL
261.
ATPS4r
CBMK2
PTAr
SUCOAS
TKT1
262.
ATPS4r
CBMK2
PTAr
SUCOAS
TKT2
263.
ATPS4r
FBA
FRD2
GLUDy
PFLi
264.
ATPS4r
FBA
FRD2
PFLi
265.
ATPS4r
FDH2
PTAr
THD5
266.
ATPS4r
FRD2
G5SD
PFLi
267.
ATPS4r
FRD2
GLU5K
PFLi
268.
ATPS4r
FRD2
GLUDy
PFK
PFLi
269.
ATPS4r
FRD2
GLUDy
PFLi
270.
ATPS4r
FRD2
GLUDy
PFLi
PGI
271.
ATPS4r
FRD2
GLUDy
PFLi
TPI
272.
ATPS4r
FRD2
ME1x
ME2
PYK
273.
ATPS4r
FRD2
ME2
PFLi
THD2
274.
ATPS4r
FRD2
PFK
PFLi
275.
ATPS4r
FRD2
PFLi
276.
ATPS4r
FRD2
PFLi
PGI
277.
ATPS4r
FRD2
PFLi
PPCK
PYK
278.
ATPS4r
FRD2
PFLi
TPI
279.
ATPS4r
FUM
PPCK
PTAr
280.
ATPS4r
G5SD
PDH
PFLi
281.
ATPS4r
GLCpts
ME1x
ME2
PYK
282.
ATPS4r
GLU5K
PDH
PFLi
283.
ATPS4r
GLUDy
PDH
PFLi
284.
ATPS4r
GLUDy
PTAr
RPE
SUCOAS
285.
ATPS4r
GLUDy
PTAr
SUCOAS
286.
ATPS4r
GLUDy
PTAr
SUCOAS
TAL
287.
ATPS4r
GLUDy
PTAr
SUCOAS
TKT1
288.
ATPS4r
GLUDy
PTAr
SUCOAS
TKT2
289.
ATPS4r
MDH
PPCK
PTAr
290.
ATPS4r
ME1x
ME2
PYK
SUCD4
291.
ATPS4r
ME2
NADH12
PFLi
THD2
292.
ATPS4r
PDH
PFLi
293.
ATPS4r
PDH
PFLi
PPCK
PYK
294.
ATPS4r
PDH
PFLi
PTAr
295.
ATPS4r
PDH
PFLi
RPE
296.
ATPS4r
PDH
PFLi
TAL
297.
ATPS4r
PDH
PFLi
TKT1
298.
ATPS4r
PDH
PFLi
TKT2
299.
ATPS4r
PPCK
PTAr
PYK
SUCOAS
300.
ATPS4r
PTAr
RPE
SUCOAS
301.
ATPS4r
PTAr
SUCOAS
302.
ATPS4r
PTAr
SUCOAS
TAL
303.
ATPS4r
PTAr
SUCOAS
TKT1
304.
ATPS4r
PTAr
SUCOAS
TKT2
305.
CBMK2
PGDH
TKT1
306.
DAAD
FUM
PRO1z
SUCD4
307.
EDA
FRD2
FUM
MDH
PYK
308.
EDA
FRD2
ME1x
ME2
PYK
309.
EDA
FUM
MDH
PYK
SUCD4
310.
EDA
ME1x
ME2
PYK
SUCD4
311.
ENO
FUM
SUCD4
312.
FRD2
FUM
313.
FRD2
FUM
G6PDHy
MDH
PYK
314.
FRD2
FUM
GLCpts
MDH
PYK
315.
FRD2
FUM
MDH
PGDHY
PYK
316.
FRD2
FUM
MDH
PGL
PYK
317.
FRD2
FUM
MDH
PYK
318.
FRD2
G6PDHy
ME1x
ME2
PYK
319.
FRD2
GLCpts
ME1x
ME2
PYK
320.
FRD2
GLUDy
ME1x
ME2
PYK
321.
FRD2
MDH
ME1x
ME2
322.
FRD2
ME1x
ME2
PFLi
PYK
323.
FRD2
ME1x
ME2
PGDHY
PYK
324.
FRD2
ME1x
ME2
PGL
PYK
325.
FRD2
ME1x
ME2
PTAr
PYK
326.
FRD2
ME1x
ME2
PYK
327.
FRD2
ME1x
ME2
PYK
RPE
328.
FRD2
ME1x
ME2
PYK
TKT2
329.
FUM
G6PDHy
MDH
PYK
SUCD4
330.
FUM
GLCpts
MDH
PYK
SUCD4
331.
FUM
GLUDy
PRO1z
SUCD4
332.
FUM
MDH
PGDHY
PYK
SUCD4
333.
FUM
MDH
PGL
PYK
SUCD4
334.
FUM
MDH
SUCD4
335.
FUM
ME2
SUCD4
336.
FUM
PGM
SUCD4
337.
FUM
PPCK
SUCD4
338.
G6PDHy
ME1x
ME2
PYK
SUCD4
339.
GLCpts
ME1x
ME2
PYK
SUCD4
340.
GLUDy
ME1x
ME2
PYK
SUCD4
341.
MDH
ME1x
ME2
SUCD4
342.
ME1x
ME2
PFLi
PYK
SUCD4
343.
ME1x
ME2
PGDHY
PYK
SUCD4
344.
ME1x
ME2
PGL
PYK
SUCD4
345.
ME1x
ME2
PTAr
PYK
SUCD4
346.
ME1x
ME2
PYK
RPE
SUCD4
347.
ME1x
ME2
PYK
SUCD4
348.
ME1x
ME2
PYK
SUCD4
TKT2
TABLE 2
The list of all strains identified by OptKnock that are most likely to
provide increased malate yields in E. Coli . Note that some of the
malate production strategies overlap with the fumarate production
strains.
1.
AKGD
ATPS4r
PTAr
2.
ACKr
AKGD
ATPS4r
3.
ACKr
ATPS4r
SUCOAS
4.
ATPS4r
PTAr
SUCOAS
5.
ATPS4r
PDH
PFLi
6.
ATPS4r
FRD2
PFLi
7.
LDH_D
PFK
SUCOAS
8.
ADHEr
FRD2
GLUDy
LDH_D
9.
ADHEr
FRD2
LDH_D
ME2
10.
ACKr
AKGD
ATPS4r
GLUDy
11.
AKGD
ATPS4r
GLUDy
PTAr
12.
ATPS4r
GLUDy
PTAr
SUCOAS
13.
ACKr
ATPS4r
GLUDy
SUCOAS
14.
AKGD
ATPS4r
PTAr
TKT2
15.
ACKr
AKGD
ATPS4r
TKT2
16.
ATPS4r
PTAr
SUCOAS
TKT2
17.
ACKr
ATPS4r
SUCOAS
TKT2
18.
ATPS4r
FUM
GLUDy
PFLi
19.
ACKr
AKGD
ATPS4r
RPE
20.
AKGD
ATPS4r
PTAr
RPE
21.
ACKr
ATPS4r
RPE
SUCOAS
22.
ATPS4r
PTAr
RPE
SUCOAS
23.
ACKr
AKGD
ATPS4r
TKT1
24.
AKGD
ATPS4r
PTAr
TAL
25.
AKGD
ATPS4r
PTAr
TKT1
26.
ACKr
AKGD
ATPS4r
TAL
27.
AKGD
ATPS4r
CBMK2
PTAr
28.
ACKr
AKGD
ATPS4r
CBMK2
29.
ACKr
ATPS4r
SUCOAS
TAL
30.
ATPS4r
PTAr
SUCOAS
TAL
31.
ACKr
ATPS4r
SUCOAS
TKT1
32.
ATPS4r
PTAr
SUCOAS
TKT1
33.
ACKr
AKGD
ASNS2
ATPS4r
34.
AKGD
ASNS2
ATPS4r
PTAr
35.
ATPS4r
CBMK2
PTAr
SUCOAS
36.
ACKr
ATPS4r
CBMK2
SUCOAS
37.
ACKr
ASNS2
ATPS4r
SUCOAS
38.
ASNS2
ATPS4r
PTAr
SUCOAS
39.
ATPS4r
FRD2
PFLi
PGI
40.
ATPS4r
FRD2
PFK
PFLi
41.
ATPS4r
FRD2
PFLi
TPI
42.
ATPS4r
FBA
FRD2
PFLi
43.
FRD2
ME1x
ME2
PYK
44.
ME1x
ME2
PYK
SUCD4
45.
ATPS4r
FRD2
GLUDy
PFLi
46.
ATPS4r
GLUDy
PDH
PFLi
47.
ACKr
ATPS4r
PDH
PFLi
48.
ATPS4r
PDH
PFLi
PTAr
49.
ATPS4r
PDH
PFLi
TKT2
50.
ATPS4r
PDH
PFLi
RPE
51.
ATPS4r
PDH
PFLi
TAL
52.
ATPS4r
PDH
PFLi
TKT1
53.
ATPS4r
CBMK2
PDH
PFLi
54.
ATPS4r
GLU5K
PDH
PFLi
55.
ATPS4r
G5SD
PDH
PFLi
56.
ASNS2
ATPS4r
PDH
PFLi
57.
ASPT
ATPS4r
FUM
PFLi
58.
ATPS4r
CBMK2
FRD2
PFLi
59.
ATPS4r
FRD2
GLU5K
PFLi
60.
ATPS4r
FRD2
G5SD
PFLi
61.
ASNS2
ATPS4r
FRD2
PFLi
62.
ADHEr
ATPS4r
FUM
GLUDy
63.
MDH
ME1x
ME2
SUCD4
64.
FRD2
MDH
ME1x
ME2
65.
ATPS4r
MDH
PPCK
PTAr
66.
ACKr
ATPS4r
MDH
PPCK
67.
ADHEr
FRD2
LDH_D
ME2
THD2
68.
ADHEr
FRD2
GLUDy
LDH_D
THD2
69.
ADHEr
FRD2
GLUDy
LDH_D
ME2
70.
ADHEr
CBMK2
FRD2
GLUDy
LDH_D
71.
ADHEr
LDH_D
ME2
SUCD4
THD2
72.
ADHEr
FUM
GLUDy
LDH_D
SUCD4
73.
ADHEr
ASPT
FUM
GLUDy
LDH_D
74.
ADHEr
FRD2
GLCpts
LDH_D
ME2
75.
ADHEr
GLUDy
LDH_D
PRO1z
SUCD4
76.
ADHEr
CBMK2
FRD2
LDH_D
ME2
77.
ADHEr
FRD2
GLU5K
LDH_D
ME2
78.
ADHEr
FRD2
G5SD
LDH_D
ME2
79.
ADHEr
ASNS2
FRD2
LDH_D
ME2
80.
ADHEr
FUM
GLUDy
LDH_D
NADH6
81.
ADHEr
ASPT
FUM
LDH_D
ME2
82.
FRD2
GLCpts
ME1x
ME2
PYK
83.
GLCpts
ME1x
ME2
PYK
SUCD4
84.
ACKr
ADHEr
LDH_D
ME2
SUCD4
85.
ADHEr
LDH_D
ME2
PTAr
SUCD4
86.
ADHEr
FRD2
ME1x
ME2
PYK
87.
FRD2
ME1x
ME2
PGL
PYK
88.
FRD2
G6PDHy
ME1x
ME2
PYK
89.
FRD2
ME1x
ME2
PGDHY
PYK
90.
EDA
ME1x
ME2
PYK
SUCD4
91.
EDA
FRD2
ME1x
ME2
PYK
92.
ME1x
ME2
PGDHY
PYK
SUCD4
93.
ME1x
ME2
PGL
PYK
SUCD4
94.
G6PDHy
ME1x
ME2
PYK
SUCD4
95.
ACKr
AKGD
ATPS4r
PPCK
PYK
96.
AKGD
ATPS4r
PPCK
PTAr
PYK
97.
FRD2
ME1x
ME2
PFLi
PYK
98.
ACKr
ATPS4r
PPCK
PYK
SUCOAS
99.
ATPS4r
PPCK
PTAr
PYK
SUCOAS
100.
FRD2
ME1x
ME2
PTAr
PYK
101.
ACKr
ME1x
ME2
PYK
SUCD4
102.
ME1x
ME2
PTAr
PYK
SUCD4
103.
ACKr
FRD2
ME1x
ME2
PYK
104.
ACKr
AKGD
ATPS4r
GLUDy
TKT2
105.
AKGD
ATPS4r
GLUDy
PTAr
TKT2
106.
ATPS4r
GLUDy
PTAr
SUCOAS
TKT2
107.
ACKr
ATPS4r
GLUDy
SUCOAS
TKT2
108.
AKGD
ATPS4r
GLUDy
PTAr
RPE
109.
ACKr
AKGD
ATPS4r
GLUDy
RPE
110.
ATPS4r
GLUDy
PTAr
RPE
SUCOAS
111.
ACKr
ATPS4r
GLUDy
RPE
SUCOAS
112.
AKGD
ATPS4r
GLUDy
PTAr
TAL
113.
ACKr
AKGD
ATPS4r
GLUDy
TAL
114.
AKGD
ATPS4r
GLUDy
PTAr
TKT1
115.
ACKr
AKGD
ATPS4r
GLUDy
TKT1
116.
ATPS4r
FRD2
PFLi
PPCK
PYK
117.
ATPS4r
GLUDy
PTAr
SUCOAS
TKT1
118.
ACKr
ATPS4r
GLUDy
SUCOAS
TKT1
119.
ACKr
ATPS4r
GLUDy
SUCOAS
TAL
120.
ATPS4r
GLUDy
PTAr
SUCOAS
TAL
121.
ACKr
AKGD
ATPS4r
CBMK2
GLUDy
122.
AKGD
ATPS4r
CBMK2
GLUDy
PTAr
123.
ACKr
AKGD
ASNS2
ATPS4r
GLUDy
124.
AKGD
ASNS2
ATPS4r
GLUDy
PTAr
125.
ATPS4r
CBMK2
GLUDy
PTAr
SUCOAS
126.
ACKr
ATPS4r
CBMK2
GLUDy
SUCOAS
127.
ASNS2
ATPS4r
GLUDy
PTAr
SUCOAS
128.
ACKr
ASNS2
ATPS4r
GLUDy
SUCOAS
129.
ATPS4r
FUM
GLUDy
PFLi
TKT2
130.
ATPS4r
FUM
ME2
PFLi
THD2
131.
ACKr
AKGD
ATPS4r
CBMK2
TKT2
132.
AKGD
ATPS4r
CBMK2
PTAr
TKT2
133.
ATPS4r
ME2
NADH12
PFLi
THD2
134.
ATPS4r
FUM
GLUDy
PFLi
RPE
135.
AKGD
ASNS2
ATPS4r
PTAr
TKT2
136.
ACKr
AKGD
ASNS2
ATPS4r
TKT2
137.
ACKr
ATPS4r
CBMK2
SUCOAS
TKT2
138.
ATPS4r
CBMK2
PTAr
SUCOAS
TKT2
139.
ATPS4r
FUM
GLUDy
PFLi
TKT1
140.
ATPS4r
FUM
GLUDy
PFLi
TAL
141.
ACKr
ASNS2
ATPS4r
SUCOAS
TKT2
142.
ASNS2
ATPS4r
PTAr
SUCOAS
TKT2
143.
ATPS4r
CBMK2
FUM
GLUDy
PFLi
144.
ACKr
ATPS4r
FUM
GLUDy
PFLi
145.
ATPS4r
FUM
GLUDy
PFLi
PTAr
146.
ACKr
AKGD
ATPS4r
CBMK2
RPE
147.
AKGD
ATPS4r
CBMK2
PTAr
RPE
148.
ATPS4r
FUM
GLU5K
GLUDy
PFLi
149.
ATPS4r
FUM
G5SD
GLUDy
PFLi
150.
ASNS2
ATPS4r
FUM
GLUDy
PFLi
151.
AKGD
ASNS2
ATPS4r
PTAr
RPE
152.
ACKr
AKGD
ASNS2
ATPS4r
RPE
153.
ACKr
ATPS4r
CBMK2
RPE
SUCOAS
154.
ATPS4r
CBMK2
PTAr
RPE
SUCOAS
155.
ASNS2
ATPS4r
PTAr
RPE
SUCOAS
156.
ACKr
ASNS2
ATPS4r
RPE
SUCOAS
157.
AKGD
ATPS4r
CBMK2
PTAr
TAL
158.
AKGD
ATPS4r
CBMK2
PTAr
TKT1
159.
ACKr
AKGD
ATPS4r
CBMK2
TAL
160.
ACKr
AKGD
ATPS4r
CBMK2
TKT1
161.
ACKr
AKGD
ASNS2
ATPS4r
TAL
162.
AKGD
ASNS2
ATPS4r
PTAr
TKT1
163.
AKGD
ASNS2
ATPS4r
PTAr
TAL
164.
ACKr
AKGD
ASNS2
ATPS4r
TKT1
165.
ACKr
ATPS4r
CBMK2
SUCOAS
TKT1
166.
ACKr
ATPS4r
CBMK2
SUCOAS
TAL
167.
ATPS4r
CBMK2
PTAr
SUCOAS
TKT1
168.
ATPS4r
CBMK2
PTAr
SUCOAS
TAL
169.
AKGD
ASNS2
ATPS4r
CBMK2
PTAr
170.
ACKr
AKGD
ASNS2
ATPS4r
CBMK2
171.
ACKr
ASNS2
ATPS4r
SUCOAS
TAL
172.
ASNS2
ATPS4r
PTAr
SUCOAS
TKT1
173.
ASNS2
ATPS4r
PTAr
SUCOAS
TAL
174.
ACKr
ASNS2
ATPS4r
SUCOAS
TKT1
175.
ACKr
ASNS2
ATPS4r
CBMK2
SUCOAS
176.
ASNS2
ATPS4r
CBMK2
PTAr
SUCOAS
177.
ATPS4r
GLCpts
ME1x
ME2
PYK
178.
ATPS4r
FRD2
ME2
PFLi
THD2
179.
ME1x
ME2
PFLi
PYK
SUCD4
180.
FRD2
GLUDy
ME1x
ME2
PYK
181.
GLUDy
ME1x
ME2
PYK
SUCD4
182.
FRD2
ME1x
ME2
PYK
TKT2
183.
ME1x
ME2
PYK
SUCD4
TKT2
184.
ATPS4r
FRD2
GLUDy
PFLi
PGI
185.
ATPS4r
FRD2
GLUDy
PFLi
TPI
186.
ATPS4r
FBA
FRD2
GLUDy
PFLi
187.
ATPS4r
FRD2
GLUDy
PFK
PFLi
188.
ATPS4r
PDH
PFLi
PPCK
PYK
189.
ME1x
ME2
PYK
RPE
SUCD4
190.
FRD2
ME1x
ME2
PYK
RPE
191.
ATPS4r
FRD2
ME1x
ME2
PYK
192.
ATPS4r
ME1x
ME2
PYK
SUCD4
193.
FUM
GLUDy
ME1x
ME2
PYK
194.
ASPT
ATPS4r
FUM
PFLi
PGI
195.
FRD2
ME1x
ME2
PYK
TKT1
196.
ME1x
ME2
PYK
SUCD4
TAL
197.
ME1x
ME2
PYK
SUCD4
TKT1
198.
FRD2
ME1x
ME2
PYK
TAL
199.
ASPT
ATPS4r
FUM
PFLi
TPI
200.
ASPT
ATPS4r
FUM
PFK
PFLi
TABLE 3
A list of all the reaction stoichiometries and the associated genes known to be
associated with the reactions identified for deletion in the strains listed in Tables 1 and 2.
Reaction
Abbreviation
Reaction Name
Reaction Stoichiometry
Associated genes
ACKr
Acetate kinase
[c]: ac + atp <==> actp + adp
(b3115 or b2296 or b1849)
ADHEr
Alcohol dehydrogenase
[c]: accoa + (2) h + (2) nadh <==> coa +
(b0356 or b1478 or b1241)
etoh + (2) nad
AKGD
Alpha-ketoglutarate
[c]: akg + coa + nad --> co2 + nadh + succoa
(b0116 and b0726 and b0727)
dehydrogenase
ALAR
Alanine racemase
[c]: ala-L <==> ala-D
b4053
ASNS2
Asparagine synthetase
[c]: asp-L + atp + nh4 --> amp + asn-L + h + ppi
b3744
ASPT
L-aspartase
[c]: asp-L --> fum + nh4
b4139
ATPS4r
ATP synthase
adp[c] + (4) h[p] + pi[c] <==> atp[c] +
(((b3736 and b3737 and b3738)
(3) h[c] + h2o[c]
and (b3731 and b3732 and b3733
and b3734 and b3735)) or ((b3736
and b3737 and b3738) and (b3731
and b3732 and b3733 and b3734 and
b3735) and b3739))
CBMK2
Carbamate kinase
[c]: atp + co2 + nh4 --> adp + cbp + (2) h
(b0521 or b0323 or b2874)
DAAD
D-amino acid
[c]: ala-D + fad + h2o --> fadh2 + nh4 + pyr
b1189
dehydrogenase
EDA
2-dehydro-3-deoxy-
[c]: 2ddg6p --> g3p + pyr
b1850
phosphogluconate
aldolase
ENO
Enolase
[c]: 2pg <==> h2o + pep
b2779
FBA
Fructose-bis-phosphate
[c]: fdp <==> dhap + g3p
(b2097 or b2925 or b1773)
aldolase
FRD
Fumarate reductase
[c]: fum + mq18 --> mqn8 + succ
(b4151 and b4152 and b4153 and
b4154)
FUM
Fumarase
[c]: fum + h2o <==> mal-L
(b1612 or b4122 or b1611)
G5SD
Glutamate-5-
[c]: glu5p + h + nadph --> glu5sa + nadp + pi
b0243
semialdehyde
dehyrogenase
G6PDHy
Glucose-6-phosphate
[c]: g6p + nadp <==> 6pgl + h + nadph
b1852
dehydrogenase
GLCpts
D-glucose transport via
glc-D[e] + pep[c] --> g6p[c] + pyr[c]
((b2417 and b1101 and b2415 and
PTS mechanism
b2416) or (b1817 and b1818 and
b1819 and b2415 and b2416) or
(b2417 and b1621 and b2415 and
b2416))
GLU5K
Gluatmate-5-kinase
[c]: atp + glu-L --> adp + glu5p
b0242
GLUDy
Glutamate
[c]: glu-L + h2o + nadp <==> akg + h + nadph + nh4
b1761
dehydrogenase
HEX1
Hexokinase
[c]: atp + glc-D --> adp + g6p + h
b2388
LDH_D
Lactate dehydrogenase
[c]: lac-D + nad <==> h + nadh + pyr
b1380 or b2133
MDH
Malate dehydrogenase
[c]: mal-L + nad <==> h + nadh + oaa
b3236
ME1x
Malic enzyme (NAD)
[c]: mal-L + nad --> co2 + nadh + pyr
b1479
ME2
Malic enzyme (NADP)
[c]: mal-L + nadp --> co2 + nadph + pyr
b2463
NADH12
NADH dehydrogenase
[c]: h + nadh + ubq8 -->
b1109
(ubiquinone-8)
nad + ubq8h2
NADH6
NADH dehydrogenase
(4.5) h[c] + nadh[c] + ubq8[c] --> (3.5) h[e] +
(b2276 and b2277 and b2278 and
(ubiquinone-8 and 3.5
nad[c] + ubq8h2[c]
b2279 and b2280 and b2281 and
protons)
b2282 and b2283 and b2284 and
b2285 and b2286 and b2287 and
b2288)
PDH
Pyruvate dehydrogenase
[c]: coa + nad + pyr --> accoa + co2 + nadh
((b0114 and b0115 and b0116) or (b0116
and b0726 and b0727) or (b0116 and
b2903 and b2904 and b2905))
PFK
Phosphofructokinase
[c]: atp + f6p --> adp + fdp + h
(b3916 or b1723)
PFLi
Pyruvate formate lyase
[c]: coa + pyr --> accoa + for
(((b0902 and b0903) and b2579) or
(b0902 and b0903) or (b0902 and
b3114) or (b3951 and b3952))
PGDH
Phosphogluconate
[c]: 6pgc + nadp --> co2 + nadph + ru5p-D
b2029
dehyrogenase
PGDHY
Phosphogluconate
[c]: 6pgc --> 2ddg6p + h2o
b1851
dehydratase
PGI
Glucose-6-phosphate
[c]: g6p <==> f6p
b4025
isomerase
PGL
6-
[c]: 6pgl + h2o --> 6pgc + h
b0767
Phosphogluconolactonase
PGM
Phosphoglycerate mutase
[c]: 3pg <==> 2pg
b3612
PPC
Phosphoenolpyruvate
[c]: co2 + h2o + pep --> h + oaa + pi
b3956
carboxylase
PPCK
Phosphoenolpyruvate
[c]: atp + oaa --> adp + co2 + pep
b3403
carboxykinase
PRO1z
Proline oxidase
[c]: fad + pro-L --> 1pyr5c + fadh2 + h
b1014
PTAr
Phosphotransacetylase
[c]: accoa + pi <==> actp + coa
b2297
PYK
Pyruvate kinase
[c]: adp + h + pep --> atp + pyr
(b1854 or b1676)
RPE
Ribulose-5-phosphate-5-
[c]: ru5p-D <==> xu5p-D
(b4301 or b3386)
epimerase
SUCD4
Succinate dehydrogenase
[c]: fadh2 + ubq8 <==> fad + ubq8h2
(b0721 and b0722 and b0723 and
b0724
SUCOAS
Succinyl-CoA synthetase
[c]: atp + coa + succ <==> adp + pi + succoa
(b0728 and b0729)
TAL
Transaldoalse
[c]: g3p + s7p <==> e4p + f6p
(b2464 or b0008)
THD2
NADP transhydrogenase
(2) h[e] + nadh[c] + nadp[c] --> (2) h[c] +
(b1602 and b1603)
nad[c] + nadph[c]
THD5
NAD transhydrogenase
[c]: nad + nadph --> nadh + nadp
(b3962 or (b1602 and b1603))
TKT1
Transketolase
[c]: r5p + xu5p-D <==> g3p + s7p
(b2935 or b2465)
TKT2
Transketolase
[c]: e4p + xu5p-D <==> f6p + g3p
(b2935 or b2465)
TPI
Triosephosphate
[c]: dhap <==> g3p
b3919
isomerase
VALTA
Valine transaminase
[c]: akg + val-L <==> 3mob + glu-L
b3770
TABLE 4
List of the metabolite abbreviations, the corresponding names and
locations of all the metabolites that participate in the reactions listed
in Table 3.
Metabolite
Abbreviation
Compartment
Metabolite Name
13dpg
Cytosol
3-Phospho-D-glyceroyl phosphate
1pyr5c
Cytosol
1-Pyrroline-5-carboxylate
2ddg6p
Cytosol
2-Dehydro-3-deoxy-D-gluconate
6-phosphate
2pg
Cytosol
D-Glycerate 2-phosphate
3mob
Cytosol
3-Methyl-2-oxobutanoate
3pg
Cytosol
3-Phospho-D-glycerate
6pgc
Cytosol
6-Phospho-D-gluconate
6pgl
Cytosol
6 phospho-D-glucono-1,5-lactone
ac
Cytosol
Acetate
accoa
Cytosol
Acetyl-CoA
actp
Cytosol
Acetyl phosphate
adp
Cytosol
Adenosine diphosphate
akg
Cytosol
2-Oxoglutarate
ala-D
Cytosol
D-alanine
ala-L
Cytosol
L-alanine
amp
Cytosol
Adenosine monophosphate
asn-L
Cytosol
L-asparagine
asp-L
Cytosol
L-aspartate
atp
Cytosol
Adenosine triphosphate
cbp
Cytosol
Carbamoyl phosphate
co2
Cytosol
Carbon dioxide
coa
Cytosol
Coenzyme A
dha
Cytosol
Dihydroxyacetone
dhap
Cytosol
Dihydroxyacetone phosphate
e4p
Cytosol
D-Erythrose 4-phosphate
etoh
Cytosol
Ethanol
f6p
Cytosol
D-Fructose 6-phosphate
fad
Cytosol
Flavin adenine dinucleotide
fadh2
Cytosol
Flavin adenine dinucleotide-reduced
fdp
Cytosol
D-Fructose 1,6-bisphosphate
for
Cytosol
Formate
fum
Cytosol
Fumarate
g3p
Cytosol
Glyceraldehyde 3-phosphate
g6p
Cytosol
D-Glucose 6-phosphate
glc-D[e]
Extra-organism
D-Glucose
glu5p
Cytosol
L-glutamate 5-phosphate
glu5sa
Cytosol
L-glutamate 5-semialdehyde
glu-L
Cytosol
L-Glutamate
h
Cytosol
H +
h[e]
Extra-organism
H +
h2o
Cytosol
Water
lac-D
Cytosol
D-Lactate
mal-L
Cytosol
L-Malate
mql-8
Cytosol
Menaquinol-8
mqn-8
Cytosol
Menaquinone-8
nad
Cytosol
Nicotinamide adenine dinucleotide
nadh
Cytosol
Nicotinamide adenine
dinucleotide-reduced
nadp
Cytosol
Nicotinamide adenine dinucleotide
phosphate
nadph
Cytosol
Nicotinamide adenine dinucleotide
phosphate-reduced
nh4
Cytosol
Ammonium
o2
Cytosol
Oxygen
oaa
Cytosol
Oxaloacetate
pep
Cytosol
Phosphoenolpyruvate
pi
Cytosol
Phosphate
ppi
Cytosol
Diphosphate
pyr
Cytosol
Pyruvate
r5p
Cytosol
alpha-D-Ribose 5-phosphate
ru5p-D
Cytosol
D-Ribulose 5-phosphate
s7p
Cytosol
Sedoheptulose 7-phosphate
succ
Cytosol
Succinate
succoa
Cytosol
Succinyl-CoA
ubq8
Cytosol
Ubiquinone-8
ubq8h2
Cytosol
Ubiquinol-8
val-L
Cytosol
L-valine
xu5p-D
Cytosol
D-Xylulose 5-phosphate
TABLE 5
The list of all strains identified by OptKnock that are most likely to provide increased
fumarate yields in S. Cerevisiae under microaerobic culture conditions. These same designs can
be used for malate production if the cytosolic fumarase (FUM) is deleted additionally.
1
FRDm
FUM
2
ME1m
PYK
FRDm
FUMm
3
ME1m
G3PDm
PYK
SUCD3-u6m
4
G3PDm
GLY3PP
SUCD3-u6m
ALCD2x
5
GLY3PP
FRDm
FUMm
ALCD2x
6
G3PD
FRDm
FUMm
ALCD2x
7
G3PD
G3PD1irm
SUCD3-u6m
ALCD2x
8
G3PD
G3PDm
SUCD3-u6m
ALCD2x
9
G3PDm
PYK
MDHm
SUCD3-
u6m
10
PYK
FRDm
FUMm
MDHm
11
G3PD
G3PDm
SUCD3-u6m
PYRDC
12
G3PDm
GLY3PP
SUCD3-u6m
PYRDC
13
GLY3PP
FRDm
FUMm
PYRDC
14
G3PD
FRDm
FUMm
PYRDC
15
G3PD
G3PD1irm
SUCD3-u6m
PYRDC
16
G3PDm
SUCD3-u6m
PYRDC
ATPtm-
3H
17
FRDm
FUMm
PYRDC
ATPtm-
3H
18
ATPSm
FRDm
FUMm
PYRDC
19
G3PDm
ATPSm
SUCD3-u6m
PYRDC
20
FRDm
FUMm
ALCD2x
ATPtm-
3H
21
G3PDm
SUCD3-u6m
ALCD2x
ATPtm-
3H
22
ATPSm
FRDm
FUMm
ALCD2x
23
G3PDm
ATPSm
SUCD3-u6m
ALCD2x
24
ME1m
FRDm
FUMm
PYRDC
25
ME1m
G3PDm
SUCD3-u6m
PYRDC
26
G3PDm
MDHm
SUCD3-u6m
PYRDC
27
FRDm
FUMm
MDHm
PYRDC
28
ME1m
G3PDm
SUCD3-u6m
ALCD2x
29
ME1m
FRDm
FUMm
ALCD2x
30
G3PDm
MDHm
SUCD3-u6m
ALCD2x
31
FRDm
FUMm
MDHm
ALCD2x
32
ASPTA1
G3PDm
GLY3PP
SUCD3-
u6m
33
ASPTA1
G3PD
FRDm
FUMm
34
ASPTA1
GLY3PP
FRDm
FUMm
35
ASPTA1
G3PD
G3PDm
SUCD3-
u6m
36
ASPTA1
G3PD
G3PD1irm
SUCD3-
u6m
37
G3PDm
GLY3PP
HSK
SUCD3-
u6m
38
G3PDm
GLY3PP
SUCD3-u6m
THRS
39
G3PD
FRDm
FUMm
THRS
40
GLY3PP
HSK
FRDm
FUMm
41
G3PD
G3PDm
HSK
SUCD3-u6m
42
G3PD
G3PD1irm
HSK
SUCD3-u6m
43
G3PD
G3PD1irm
SUCD3-u6m
THRS
44
GLY3PP
FRDm
FUMm
THRS
45
G3PD
HSK
FRDm
FUMm
46
G3PD
G3PDm
SUCD3-u6m
THRS
47
G3PD
FRDm
FUMm
PGL
48
G3PD
FRDm
FUMm
PGDH
49
G3PD
G3PD1irm
SUCD3-u6m
PGDH
50
G3PD
G3PDm
SUCD3-u6m
PGDH
51
G3PDm
GLY3PP
SUCD3-u6m
G6PDH
52
G3PD
G3PDm
SUCD3-u6m
G6PDH
53
G3PDm
GLY3PP
SUCD3-u6m
PGL
54
G3PDm
GLY3PP
SUCD3-u6m
PGDH
55
GLY3PP
FRDm
FUMm
G6PDH
56
G3PD
G3PDm
SUCD3-u6m
PGL
57
G3PD
G3PD1irm
SUCD3-u6m
PGL
58
GLY3PP
FRDm
FUMm
PGL
59
GLY3PP
FRDm
FUMm
PGDH
60
G3PD
G3PD1irm
SUCD3-u6m
G6PDH
61
G3PD
FRDm
FUMm
G6PDH
62
G3PD
G3PDm
SUCD3-u6m
TKT1
63
G3PDm
GLY3PP
SUCD3-u6m
TKT1
64
G3PD
FRDm
FUMm
TKT1
65
G3PD
G3PD1irm
SUCD3-u6m
TKT1
66
GLY3PP
FRDm
FUMm
TKT1
67
G3PDm
GLY3PP
SUCD3-u6m
RPE
68
G3PD
G3PDm
SUCD3-u6m
RPE
69
GLY3PP
FRDm
FUMm
RPE
70
G3PD
G3PD1irm
SUCD3-u6m
RPE
71
G3PD
FRDm
FUMm
RPE
72
G3PDm
SERD_L
PGI
SUCD3-
u6m
73
SERD_L
PGI
FRDm
FUMm
74
GLY3PP
FRDm
FUMm
THRA
75
G3PD
FRDm
FUMm
THRA
76
G3PDm
GLY3PP
SUCD3-u6m
THRA
77
G3PD
G3PDm
SUCD3-u6m
THRA
78
G3PD
G3PD1irm
SUCD3-u6m
THRA
79
ALATA_L
ASPTA1
SUCOASAm
PSP_L
80
ALATA_L
ASPTA1
PSERT
PDHcm
81
ALATA_L
ASPTA1
AKGDbm
PGCD
82
ALATA_L
ASPTA1
SUCOASAm
PSERT
83
ALATA_L
ASPTA1
SUCOASAm
PGCD
84
ALATA_L
ASPTA1
AKGDam
PSERT
85
ALATA_L
ASPTA1
AKGDbm
PSERT
86
ALATA_L
ASPTA1
PSP_L
PDHcm
87
ALATA_L
ASPTA1
AKGDbm
PSP_L
88
ALATA_L
ASPTA1
PGCD
PDHcm
89
ALATA_L
ASPTA1
AKGDam
PSP_L
90
ALATA_L
ASPTA1
AKGDam
PGCD
91
ASPTA1
ICL
SUCOASAm
PSP_L
92
ASPTA1
SUCOASAm
AGT
PSP_L
93
ASPTA1
SUCOASAm
AGT
PSERT
94
ASPTA1
SUCOASAm
AGT
PGCD
95
ASPTA1
ICL
SUCOASAm
PSERT
96
ASPTA1
ICL
SUCOASAm
PGCD
97
ASPTA1
AGT
PSP_L
PDHcm
98
ASPTA1
ICL
AKGDbm
PSP_L
99
ASPTA1
AKGDam
AGT
PSP_L
100
ASPTA1
AGT
PGCD
PDHcm
101
ASPTA1
AKGDbm
AGT
PGCD
102
ASPTA1
AKGDbm
AGT
PSERT
103
ASPTA1
ICL
PGCD
PDHcm
104
ASPTA1
ICL
AKGDbm
PGCD
105
ASPTA1
AGT
PSERT
PDHcm
106
ASPTA1
ICL
PSP_L
PDHcm
107
ASPTA1
ICL
AKGDam
PSERT
108
ASPTA1
ICL
AKGDam
PSP_L
109
ASPTA1
ICL
PSERT
PDHcm
110
ASPTA1
AKGDbm
AGT
PSP_L
111
ASPTA1
ICL
AKGDam
PGCD
112
ASPTA1
AKGDam
AGT
PSERT
113
ASPTA1
AKGDam
AGT
PGCD
114
ASPTA1
ICL
AKGDbm
PSERT
115
GLY3PP
HSDxi
FRDm
FUMm
116
G3PD
HSDxi
FRDm
FUMm
117
G3PD
G3PDm
HSDxi
SUCD3-
u6m
118
G3PD
G3PD1irm
HSDxi
SUCD3-
u6m
119
G3PDm
GLY3PP
HSDxi
SUCD3-
u6m
120
G3PDm
FUm
SUCD1rm
SUCD3-
u6m
121
G3PDm
FUm
FUMm
SUCD3-
u6m
122
G3PDm
MDH
NADH2-u6cm
NADH2-
u6m
123
ASPTA1
ME1m
PSERT
PDHm
PYK
124
ASPTA1
ME1m
PSP_L
PDHm
PYK
125
ASPTA1
ME1m
PGCD
PDHm
PYK
126
ASPTA1
ME1m
ME2m
PSP_L
PYK
127
ASPTA1
ME1m
ME2m
PGCD
PYK
128
ASPTA1
ME1m
ME2m
PSERT
PYK
129
ASPTA1
ORNTA
ME1m
PSP_L
PYK
130
ASPTA1
ORNTA
ME1m
PGCD
PYK
131
ASPTA1
ORNTA
ME1m
PSERT
PYK
132
ASPTA1
ME1m
PRO1xm
PSP_L
PYK
133
ASPTA1
ME1m
P5CDm
PSERT
PYK
134
ASPTA1
ME1m
P5CDm
PSP_L
PYK
135
ASPTA1
ME1m
PRO1xm
PGCD
PYK
136
ASPTA1
ME1m
P5CDm
PGCD
PYK
137
ASPTA1
ME1m
PRO1xm
PSERT
PYK
138
ASPTA1m
ME1m
PSP_L
PDHm
PYK
139
ASPTA1m
ME1m
PSERT
PDHm
PYK
140
ASPTA1m
ME1m
PGCD
PDHm
PYK
141
ASPTA1m
ME1m
PRO1xm
PSP_L
PYK
142
ASPTA1m
ME1m
P5CDm
PGCD
PYK
143
ASPTA1m
ME1m
PRO1xm
PGCD
PYK
144
ASPTA1m
ME1m
PRO1xm
PSERT
PYK
145
ASPTA1m
ME1m
P5CDm
PSERT
PYK
146
ASPTA1m
ME1m
P5CDm
PSP_L
PYK
147
ASPTA1m
ME1m
PSERT
PDHcm
PYK
148
ASPTA1m
ME1m
SUCOASAm
PSERT
PYK
149
ASPTA1m
ME1m
AKGDam
PSP_L
PYK
150
ASPTA1m
ME1m
AKGDbm
PSERT
PYK
151
ASPTA1m
ME1m
SUCOASAm
PGCD
PYK
152
ASPTA1m
ME1m
AKGDam
PGCD
PYK
153
ASPTA1m
ME1m
SUCOASAm
PSP_L
PYK
154
ASPTA1m
ME1m
AKGDam
PSERT
PYK
155
ASPTA1m
ME1m
PSP_L
PDHcm
PYK
156
ASPTA1m
ME1m
PGCD
PDHcm
PYK
157
ASPTA1m
ME1m
AKGDbm
PGCD
PYK
158
ASPTA1m
ME1m
AKGDbm
PSP_L
PYK
159
ASPTA1m
ORNTA
ME1m
PSP_L
PYK
160
ASPTA1m
ORNTA
ME1m
PGCD
PYK
161
ASPTA1m
ORNTA
ME1m
PSERT
PYK
162
ME1m
ME2m
ACONTm
PSP_L
PYK
163
ME1m
ME2m
ACONTm
PGCD
PYK
164
ME1m
ME2m
ACONTm
PSERT
PYK
165
ASPTA1m
ME1m
ME2m
PSP_L
PYK
166
ASPTA1m
ME1m
ME2m
PGCD
PYK
167
ASPTA1m
ME1m
ME2m
PSERT
PYK
168
ME1m
ME2m
ICDHy
PSERT
PYK
169
ME1m
ME2m
ACONT
PSERT
PYK
170
ME1m
ME2m
ACONT
PSP_L
PYK
171
ME1m
ME2m
ICDHy
PSP_L
PYK
172
ME1m
ME2m
ICDHy
PGCD
PYK
173
ME1m
ME2m
ACONT
PGCD
PYK
174
ME1m
ME2m
ICDHxm
PSP_L
PYK
175
ME1m
ME2m
ICDHxm
PGCD
PYK
176
ME1m
ME2m
ICDHxm
PSERT
PYK
177
ME1m
ME2m
G3PDm
PYK
SUCD3-
u6m
178
ME1m
ME2m
PYK
FRDm
FUMm
179
ME1m
PYK
FRDm
FUMm
PGDH
180
ME1m
G3PDm
PYK
SUCD3-u6m
PGDH
181
ME1m
PYK
FRDm
FUMm
PGL
182
ME1m
PYK
FRDm
FUMm
G6PDH
183
ME1m
G3PDm
PYK
SUCD3-u6m
PGL
184
ME1m
G3PDm
PYK
SUCD3-u6m
G6PDH
185
ME1m
G3PDm
PYK
SUCD3-u6m
TKT1
186
ME1m
PYK
FRDm
FUMm
TKT1
187
ME1m
G3PDm
PYK
SUCD3-u6m
RPE
188
ME1m
PYK
FRDm
FUMm
RPE
189
ME1m
PYK
FRDm
FUMm
TKT2
190
ME1m
G3PDm
PYK
SUCD3-u6m
TKT2
191
ME1m
ME2m
PSP_L
PYK
PGDH
192
ME1m
ME2m
PSERT
PYK
PGDH
193
ME1m
ME2m
PGCD
PYK
PGDH
194
ME1m
ME2m
PSERT
PYK
PGL
195
ME1m
ME2m
PSERT
PYK
G6PDH
196
ME1m
ME2m
PGCD
PYK
PGL
197
ME1m
ME2m
PSP_L
PYK
PGL
198
ME1m
ME2m
PSP_L
PYK
G6PDH
199
ME1m
ME2m
PGCD
PYK
G6PDH
200
ME1m
ME2m
PSERT
PYK
TKT1
201
ME1m
ME2m
PGCD
PYK
TKT1
202
ME1m
ME2m
PSP_L
PYK
TKT1
203
ME1m
ME2m
PSERT
PYK
RPE
204
ME1m
ME2m
PSP_L
PYK
RPE
205
ME1m
ME2m
PGCD
PYK
RPE
206
ME1m
ME2m
PSP_L
PYK
TKT2
207
ME1m
ME2m
PSERT
PYK
TKT2
208
ME1m
ME2m
PGCD
PYK
TKT2
209
ATPSm
FRDm
FUMm
PGDH
PYRDC
210
G3PDm
ATPSm
SUCD3-u6m
PGDH
PYRDC
211
ATPSm
FRDm
FUMm
G6PDH
PYRDC
212
G3PDm
ATPSm
SUCD3-u6m
PGL
PYRDC
213
ATPSm
FRDm
FUMm
PGL
PYRDC
214
G3PDm
ATPSm
SUCD3-u6m
G6PDH
PYRDC
215
G3PDm
ATPSm
SUCD3-u6m
TKT1
PYRDC
216
ATPSm
FRDm
FUMm
TKT1
PYRDC
217
G3PDm
SUCD3-u6m
PGL
PYRDC
ATPtm-
3H
218
FRDm
FUMm
PGDH
PYRDC
ATPtm-
3H
219
G3PDm
SUCD3-u6m
PGDH
PYRDC
ATPtm-
3H
220
G3PDm
SUCD3-u6m
G6PDH
PYRDC
ATPtm-
3H
221
FRDm
FUMm
PGL
PYRDC
ATPtm-
3H
222
FRDm
FUMm
G6PDH
PYRDC
ATPtm-
3H
223
G3PDm
SUCD3-u6m
TKT1
PYRDC
ATPtm-
3H
224
FRDm
FUMm
TKT1
PYRDC
ATPtm-
3H
225
G3PDm
ATPSm
SUCD3-u6m
RPE
PYRDC
226
ATPSm
FRDm
FUMm
RPE
PYRDC
227
G3PDm
SUCD3-u6m
RPE
PYRDC
ATPtm-
3H
228
FRDm
FUMm
RPE
PYRDC
ATPtm-
3H
229
G3PDm
ATPSm
SUCD3-u6m
TKT2
PYRDC
230
ATPSm
FRDm
FUMm
TKT2
PYRDC
231
FRDm
FUMm
TKT2
PYRDC
ATPtm-
3H
232
G3PDm
SUCD3-u6m
TKT2
PYRDC
ATPtm-
3H
233
ME2m
FRDm
FUMm
ALCD2x
ATPtm-
3H
234
ME2m
G3PDm
SUCD3-u6m
ALCD2x
ATPtm-
3H
235
ME1m
ME2m
MTHFD
SERD_L
PYK
G6PDH
236
ME1m
ME2m
MTHFD
SERD_L
PYK
PGL
237
ME1m
ME2m
MTHFD
SERD_L
PYK
PGDH
238
ASPTA1
GHMT2
ME1m
SERD_L
PDHm
PYK
239
ORNTA
ME1m
MTHFD
SERD_L
PYK
G6PDH
240
G3PD
FRDm
FUm
PYRDC
241
G3PD
FRDm
FUMmPGDH
PYRDC
242
G3PD
FRDm
FUMmPGL
PYRDC
243
G3PD
G3PD1irm
SUCD3-u6m
G6PDH
PYRDC
244
G3PD
G3PDm
SUCD3-u6m
PGL
PYRDC
245
G3PD
G3PD1irm
SUCD3-u6m
PGDH
PYRDC
246
G3PD
FRDm
FUMm
G6PDH
PYRDC
247
G3PD
G3PDm
SUCD3-u6m
G6PDH
PYRDC
248
G3PD
G3PD1irm
SUCD3-u6m
PGL
PYRDC
249
G3PD
G3PDm
SUCD3-u6m
PGDH
PYRDC
250
G3PD
G3PDm
SUCD3-u6m
TKT1
PYRDC
251
G3PD
G3PD1irm
SUCD3-u6m
TKT1
PYRDC
252
G3PD
FRDm
FUMm
TKT1
PYRDC
253
G3PD
G3PD1irm
SUCD3-u6m
RPE
PYRDC
254
G3PD
G3PDm
SUCD3-u6m
RPE
PYRDC
255
G3PD
FRDm
FUMm
RPE
PYRDC
256
G3PD
G3PD1irm
SUCD3-u6m
TKT2
PYRDC
257
G3PD
G3PDm
SUCD3-u6m
TKT2
PYRDC
258
G3PD
FRDm
FUMm
TKT2
PYRDC
259
ASPTA1
G3PD
G3PD1irm
SUCD3-
PYRDC
u6m
260
ASPTA1
G3PD
G3PDm
SUCD3-
PYRDC
u6m
261
ASPTA1
G3PD
FRDm
FUMm
PYRDC
262
G3PD
G3PD1irm
HSDxi
SUCD3-u6m
PYRDC
263
G3PD
G3PDm
HSDxi
SUCD3-u6m
PYRDC
264
G3PD
HSDxi
FRDm
FUMm
PYRDC
265
G3PD
G3PD1irm
SUCD3-u6m
ALCD2x
PYRDC
266
G3PD
G3PDm
SUCD3-u6m
ALCD2x
PYRDC
267
G3PD
FRDm
FUMmALCD2x
PYRDC
268
ACONT
GLUDC
G3PD
PYRDC
ALDD2y
269
ICDHyG3PD
G3PD1irm
SUCD3-u6m
PGL
PYRDC
270
ICDHyG3PD
FRDm
FUMm
G6PDH
PYRDC
271
ACONT
G3PD
G3PD1irm
SUCD3-
PGL
PYRDC
u6m
272
ACONT
G3PD
FRDm
FUMm
PGDH
PYRDC
273
ACONT
G3PD
G3PD1irm
SUCD3-
G6PDH
PYRDC
u6m
274
ICDHyG3PD
G3PDm
SUCD3-u6m
G6PDH
PYRDC
275
ACONT
G3PD
FRDm
FUMm
G6PDH
PYRDC
276
ACONT
G3PD
G3PDm
SUCD3-
G6PDH
PYRDC
u6m
277
ACONT
G3PD
G3PDm
SUCD3-
PGDH
PYRDC
u6m
278
ICDHyG3PD
G3PDm
SUCD3-u6m
PGL
PYRDC
TABLE 6
The list of all strains identified by OptKnock that are most likely to provide increased
acrylate yields in S. cerevisiae under anaerobic conditions.
1
PYRDC
2
ALCD2x
3
ATPtm-3H
4
ATPSm
5
ME1m
6
PDHm
PYRDC
7
ME1m
PYK
8
ATPSm
ATPS
9
ME1m
ATPS
10
ATPS
ATPtm-3H
11
PDHm
ATPtm-3H
12
PDHm
ALCD2x
13
PDHm
ATPSm
14
PSERT
ALCD2x
15
PSP_L
ALCD2x
16
PGCD
ALCD2x
17
ALCD2x
ATPS
18
PYRDC
IPPSm
19
PGCD
PYRDC
20
PSP_L
PYRDC
21
PSERT
PYRDC
22
PYRDC
ATPS
23
PGCD
ATPSm
24
PSP_L
ATPSm
25
PSERT
ATPSm
26
PSERT
ATPtm-3H
27
PGCD
ATPtm-3H
28
PSP_L
ATPtm-3H
29
ME1m
PDHm
30
ME1m
PGCD
31
ME1m
PSP_L
32
ME1m
PSERT
33
GLU5K
PYRDC
34
GHMT2m
ATPSm
35
ATPtm-3H
IPPSm
36
ALCD2x
IPPSm
37
ATPSm
IPPSm
38
PYK
ATPSm
39
ORNTA
ATPtm-3H
40
MDHm
DHORD4u
41
G3PDm
SUCD3-u6m
ALCD2x
42
G3PDm
ATPSm
SUCD3-u6m
43
GLU5K
PDHm
PYRDC
44
PDHm
PYRDC
IPPS
45
G3PDm
SUCD3-u6m
ATPtm-3H
46
ME1m
G3PDm
SUCD3-u6m
47
PGCD
PDHm
ATPSm
48
PSP_L
PDHm
ATPSm
49
PSERT
PDHm
ATPSm
50
PSERT
PDHm
ALCD2x
51
PGCD
PDHm
ALCD2x
52
PSP_L
PDHm
ALCD2x
53
PDHm
PYK
ATPSm
54
ME1m
PSP_L
PYK
55
ME1m
PSERT
PYK
56
ME1m
PGCD
PYK
57
G3PDm
SUCD3-u6m
PYRDC
58
PSERT
PDHm
ATPtm-3H
59
PSP_L
PDHm
ATPtm-3H
60
PGCD
PDHm
ATPtm-3H
61
PGCD
ATPSm
ALCD2x
62
PSP_L
ATPSm
ALCD2x
63
PSERT
ATPSm
ALCD2x
64
ME2m
ATPSm
ATPS
65
ME1m
PGCD
PDHm
66
ME1m
PSERT
PDHm
67
ME1m
PSP_L
PDHm
68
ME2m
ATPS
ATPtm-3H
69
ME2m
PYRDC
ATPS
70
ORNTA
ATPS
ATPtm-3H
71
GHMT2m
PDHm
ATPSm
72
ACONT
ATPS
ATPtm-3H
73
ICDHyATPS
ATPtm-3H
74
GHMT2
ATPS
ATPtm-3H
75
ME1m
PSP_L
ALCD2x
76
ME1m
PGCD
ALCD2x
77
ME1m
PSERT
ALCD2x
78
ASPTA1m
ATPS
ATPtm-3H
79
FTHFLm
PYK
ATPSm
80
MTHFDm
PYK
ATPSm
81
MTHFCm
PYK
ATPSm
82
MTHFC
ATPS
ATPtm-3H
83
GHMT2
ALCD2x
ATPS
84
PSP_L
PYRDC
IPPSm
85
PSERT
PYRDC
IPPSm
86
PGCD
PYRDC
IPPSm
87
ICDHy
PYRDC
ATPS
88
ACONT
PYRDC
ATPS
89
PGCD
ATPSm
IPPSm
90
PSP_L
ATPSm
IPPSm
91
PSERT
ATPSm
IPPSm
92
ORNTA
PYRDC
ATPS
93
PGCD
ATPtm-3H
IPPSm
94
PSERT
ATPtm-3H
IPPSm
95
PSP_L
ATPtm-3H
IPPSm
96
GLU5K
ALCD2x
ATPS
97
ALCD2x
ATPS
IPPS
98
GLU5K
PYRDC
IPPSm
99
GLU5K
PGCD
PYRDC
100
GLU5K
PSP_L
PYRDC
101
GLU5K
PSERT
PYRDC
102
GLU5K
PYRDC
ATPS
103
ORNTA
PGCD
ATPtm-3H
104
ORNTA
PSERT
ATPtm-3H
105
ORNTA
PSP_L
ATPtm-3H
106
PYK
ATPSm
ATPtm-3H
107
ASPTA1m
PSERT
ATPtm-3H
108
ASPTA1m
PSP_L
ATPtm-3H
109
ASPTA1m
PGCD
ATPtm-3H
110
PYK
ATPSm
IPPSm
111
GHMT2
GHMT2m
ALCD2x
112
MTHFC
PSP_L
ATPtm-3H
113
MTHFC
PGCD
ATPtm-3H
114
MTHFC
PSERT
ATPtm-3H
115
GHMT2m
ATPSm
IPPSm
116
GHMT2
GHMT2m
ATPtm-3H
117
GHMT2
GHMT2m
PYRDC
118
GHMT2m
PYK
ATPSm
119
GLU5K
GHMT2m
ATPSm
120
G5SD
G5SD2
PYRDC
121
GHMT2m
ATPSm
ALCD2x
122
ORNTA
ATPtm-3H
IPPSm
123
MTHFC
GHMT2m
ALCD2x
124
MTHFC
GHMT2m
ATPtm-3H
125
ME2m
ICDHym
ATPtm-3H
126
ME2m
ACONTm
ATPtm-3H
127
GLU5K
ALCD2x
THRA
128
ASPTA1m
THRA
ATPtm-3H
129
GHMT2
ME1m
GHMT2m
130
PSERT
MDHm
DHORD4u
131
PSP_L
MDHm
DHORD4u
132
PGCD
MDHm
DHORD4u
133
ME1m
MTHFC
GHMT2m
134
MDHm
DHORD4u
ATPS
135
PDHm
MDHm
DHORD4u
136
MDHm
DHORD4u
IPPSm
137
ORNTA
MDHm
DHORD4u
138
MDHm
DHORD4u
ALDD2y
139
ASPTA1m
MDHm
DHORD4u
140
MDHm
NADH2-u6m
SUCD3-u6m
141
TPI
MDH
DHORD4u
142
MDH
DHORD4u
ATPS
143
FUM
SUCD1rm
ATPS
144
FUM
FUMmATPS
145
TPI
FUM
SUCD1rm
146
TPI
FUM
FUMm
147
G3PDm
PDHm
SUCD3-u6m
PYRDC
148
GLU5K
G3PDm
SUCD3-u6m
ALCD2x
149
G3PDm
SUCD3-u6m
ALCD2x
IPPS
150
GLU5K
PDHm
PYRDC
IPPS
151
G5SD
G5SD2
PDHm
PYRDC
152
ASPTA1m
ACONTm
PDHm
PYRDC
153
ME1m
G3PDm
PYK
SUCD3-u6m
154
ORNTA
G3PDm
SUCD3-u6m
ATPtm-3H
155
ME2m
G3PDm
SUCD3-u6m
ATPtm-3H
156
ICDHy
G3PDm
SUCD3-u6m
ATPtm-3H
157
ACONT
G3PDm
SUCD3-u6m
ATPtm-3H
158
GHMT2
G3PDm
SUCD3-u6m
ATPtm-3H
159
ASPTA1m
G3PDm
SUCD3-u6m
ATPtm-3H
160
MTHFC
G3PDm
SUCD3-u6m
ATPtm-3H
161
ME2m
G3PDm
SUCD3-u6m
PYRDC
162
ME1m
ME2m
PGCD
PYK
163
ME1m
ME2m
PSP_L
PYK
164
ME1m
ME2m
PSERT
PYK
165
PDHm
PYK
ATPSm
IPPSm
166
ORNTA
ME1m
PSP_L
PYK
167
ORNTA
ME1m
PSERT
PYK
168
ORNTA
ME1m
PGCD
PYK
169
ICDHy
G3PDm
SUCD3-u6m
PYRDC
170
ACONT
G3PDm
SUCD3-u6m
PYRDC
171
ORNTA
G3PDm
SUCD3-u6m
PYRDC
172
ORNTA
PGCD
PDHm
ATPtm-3H
173
ORNTA
PSERT
PDHm
ATPtm-3H
174
ORNTA
PSP_L
PDHm
ATPtm-3H
175
ME1m
PGCD
PYK
ATPSm
176
ME1m
PSERT
PYK
ATPSm
177
ME1m
PSP_L
PYK
ATPSm
178
G3PD
G3PD1irm
ATPSm
SUCD3-u6m
179
MTHFD
PSP_L
PDHm
ALCD2x
180
MTHFD
PGCD
PDHm
ALCD2x
181
MTHFD
PSERT
PDHm
ALCD2x
182
ME1m
G3PD
G3PD1irm
SUCD3-u6m
183
MTHFC
PSP_L
PDHm
ALCD2x
184
MTHFC
PSERT
PDHm
ALCD2x
185
MTHFC
PGCD
PDHm
ALCD2x
186
ASPTA1m
PSP_L
PDHm
ALCD2x
187
ASPTA1m
PGCD
PDHm
ALCD2x
188
ASPTA1m
PSERT
PDHm
ALCD2x
189
ME2m
PGCD
PDHm
ATPtm-3H
190
ME2m
PSERT
PDHm
ATPtm-3H
191
ME2m
PSP_L
PDHm
ATPtm-3H
192
ME1m
MTHFC
PSP_L
PYK
193
ME1m
MTHFC
PSERT
PYK
194
ME1m
MTHFC
PGCD
PYK
195
ASPTA1m
PGCD
ATPSm
ALCD2x
196
ASPTA1m
PSERT
ATPSm
ALCD2x
197
ASPTA1m
PSP_L
ATPSm
ALCD2x
198
GHMT2
PSP_L
PDHm
ATPtm-3H
199
GHMT2
PGCD
PDHm
ATPtm-3H
200
GHMT2
PSERT
PDHm
ATPtm-3H
201
ASPTA1m
PGCD
PDHm
ATPtm-3H
202
ASPTA1m
PSERT
PDHm
ATPtm-3H
203
ASPTA1m
PSP_L
PDHm
ATPtm-3H
204
ACONT
PSP_L
PDHm
ATPtm-3H
205
ACONT
PSERT
PDHm
ATPtm-3H
206
ACONT
PGCD
PDHm
ATPtm-3H
207
ICDHyPSP_L
PDHm
ATPtm-3H
208
ICDHyPGCD
PDHm
ATPtm-3H
209
ICDHyPSERT
PDHm
ATPtm-3H
210
MTHFC
PSP_L
PDHm
ATPtm-3H
211
MTHFC
PGCD
PDHm
ATPtm-3H
212
MTHFC
PSERT
PDHm
ATPtm-3H
213
GLU5K
G3PDm
SUCD3-u6m
PYRDC
214
G3PD
G3PD1irm
SUCD3-u6m
ATPtm-3H
215
GHMT2
GHMT2m
PDHm
ATPtm-3H
216
MTHFDm
PYK
ATPSm
IPPSm
217
MTHFCm
PYK
ATPSm
IPPSm
218
FTHFLm
PYK
ATPSm
IPPSm
219
ME2m
PSP_L
ALCD2x
ATPtm-3H
220
ME2m
PSERT
ALCD2x
ATPtm-3H
221
ME2m
PGCD
ALCD2x
ATPtm-3H
222
GHMT2
GHMT2m
PDHm
ALCD2x
223
ME2m
MTHFC
ATPS
ATPtm-3H
224
ME2m
MTHFC
PYRDC
ATPS
225
GLU5K
GHMT2m
PDHm
ATPSm
226
ORNTA
ACONT
ATPS
ATPtm-3H
227
ORNTA
ICDHyATPS
ATPtm-3H
228
ORNTA
ICDHy
PYRDC
ATPS
229
ORNTA
ACONT
PYRDC
ATPS
230
ASPTA1m
FTHFLm
PYK
ATPSm
231
ASPTA1m
MTHFDm
PYK
ATPSm
232
ASPTA1m
MTHFCm
PYK
ATPSm
233
ORNTA
MTHFC
ATPS
ATPtm-3H
234
GHMT2
GHMT2m
PDHm
ATPSm
235
MTHFC
PSERT
PYK
ATPSm
236
MTHFC
PGCD
PYK
ATPSm
237
MTHFC
PSP_L
PYK
ATPSm
238
GHMT2
ICDHyATPS
ATPtm-3H
239
GHMT2
ACONT
ATPS
ATPtm-3H
240
G3PD
G3PD1irm
SUCD3-u6m
PYRDC
241
FTHFLr
PSERT
PYK
ATPSm
242
FTHFLr
PSP_L
PYK
ATPSm
243
FTHFLr
PGCD
PYK
ATPSm
244
ACONT
PSERT
ALCD2x
ATPtm-3H
245
ICDHyPSP_L
ALCD2x
ATPtm-3H
246
ACONT
PGCD
ALCD2x
ATPtm-3H
247
ICDHyPGCD
ALCD2x
ATPtm-3H
248
ICDHyPSERT
ALCD2x
ATPtm-3H
249
ACONT
PSP_L
ALCD2x
ATPtm-3H
250
ICDHyPYK
ATPSm
ATPtm-3H
251
ACONT
PYK
ATPSm
ATPtm-3H
252
ICDHyMTHFC
ATPS
ATPtm-3H
253
ACONT
MTHFC
ATPS
ATPtm-3H
254
ORNTA
PGCD
ALCD2x
ATPtm-3H
255
ORNTA
PSERT
ALCD2x
ATPtm-3H
256
ORNTA
PSP_L
ALCD2x
ATPtm-3H
257
MTHFDm
PSP_L
PYK
ATPSm
258
FTHFLm
PGCD
PYK
ATPSm
259
MTHFCm
PSP_L
PYK
ATPSm
260
MTHFDm
PSERT
PYK
ATPSm
261
MTHFDm
PGCD
PYK
ATPSm
262
MTHFCm
PGCD
PYK
ATPSm
263
MTHFCm
PSERT
PYK
ATPSm
264
FTHFLm
PSERT
PYK
ATPSm
265
FTHFLm
PSP_L
PYK
ATPSm
266
MTHFD
MTHFD2
ATPS
ATPtm-3H
267
ORNTA
PYK
ATPSm
ATPtm-3H
268
ASPTA1m
MTHFC
ATPS
ATPtm-3H
269
MTHFC
PYK
ATPSm
ATPtm-3H
270
ICDHyGLY3PP
PYRDC
ATPS
271
ACONT
GLY3PP
PYRDC
ATPS
272
ICDHyG3PD
PYRDC
ATPS
273
ACONT
G3PD
PYRDC
ATPS
274
MTHFC
GHMT2m
PDHm
ATPtm-3H
275
MTHFC
GHMT2m
PDHm
ALCD2x
276
GHMT2
PSERT
ALCD2x
ATPS
277
GHMT2
PGCD
ALCD2x
ATPS
278
GHMT2
PSP_L
ALCD2x
ATPS
279
FTHFLr
PYK
ATPSm
ATPtm-3H
280
PYK
ATPSm
ATPtm-3H
IPPSm
281
ACONT
MTHFC
PYRDC
ATPS
282
ICDHyMTHFC
PYRDC
ATPS
283
ORNTA
MTHFC
PYRDC
ATPS
284
GHMT2
FTHFCLm
ALCD2x
ATPS
285
GHMT2
THFATm
ALCD2x
ATPS
286
GHMT2
ALCD2x
ATPS
IPPS
287
ORNTA
PDHm
THRA
ATPtm-3H
288
GLU5K
PSERT
PYRDC
IPPSm
289
GLU5K
PGCD
PYRDC
IPPSm
290
GLU5K
PSP_L
PYRDC
IPPSm
291
ASPTA1m
ORNTA
PYRDC
ATPS
292
ORNTA
PGCD
ATPtm-3H
IPPSm
293
ORNTA
PSERT
ATPtm-3H
IPPSm
294
ORNTA
PSP_L
ATPtm-3H
IPPSm
295
PGCD
PYK
ATPSm
ATPtm-3H
296
PSP_L
PYK
ATPSm
ATPtm-3H
297
PSERT
PYK
ATPSm
ATPtm-3H
298
ASPTA1m
PSERT
ATPtm-3H
IPPSm
299
ASPTA1m
PGCD
ATPtm-3H
IPPSm
300
ASPTA1m
PSP_L
ATPtm-3H
IPPSm
301
ME1m
G3PD
MDHm
SUCD3-u6m
302
MTHFC
PGCD
ATPtm-3H
IPPSm
303
MTHFC
PSP_L
ATPtm-3H
IPPSm
304
MTHFC
PSERT
ATPtm-3H
IPPSm
305
GHMT2
PSERT
ALCD2x
ATPtm-3H
306
GHMT2
PSP_L
ALCD2x
ATPtm-3H
307
GHMT2
PGCD
ALCD2x
ATPtm-3H
308
G3PD
MDHm
SUCD3-u6m
PYRDC
309
GHMT2
GHMT2m
ALCD2x
ATPtm-3H
310
GLU5K
PSP_L
ALCD2x
ATPS
311
GLU5K
PSERT
ALCD2x
ATPS
312
GLU5K
PGCD
ALCD2x
ATPS
313
PSERT
PDHm
MDHm
DHORD4u
314
PSP_L
PDHm
MDHm
DHORD4u
315
PGCD
PDHm
MDHm
DHORD4u
316
GLU5K
PSP_L
ALCD2x
PYRDC
317
GLU5K
PGCD
ALCD2x
PYRDC
318
GLU5K
PSERT
ALCD2x
PYRDC
319
GLU5K
ALCD2x
ATPS
IPPS
320
PSP_L
ALCD2x
ATPS
IPPS
321
PGCD
ALCD2x
ATPS
IPPS
322
PSERT
ALCD2x
ATPS
IPPS
323
ASPTA1m
PYK
ATPSm
ATPtm-3H
324
GHMT2
ME1m
GHMT2m
PDHm
325
MTHFD
G3PD
PYRDC
ATPS
326
MTHFD
GLY3PP
PYRDC
ATPS
327
G5SD
G5SD2
ALCD2x
ATPS
328
ACONT
ICDHxm
PYK
ATPSm
329
ICDHxm
ICDHyPYK
ATPSm
330
ASPTA1m
ACONTm
ALCD2x
ATPS
331
ASPTA1m
G5SD2
ALCD2x
ATPS
332
G5SD
G5SD2
PYRDC
IPPSm
333
G5SD
G5SD2
PSP_L
PYRDC
334
G5SD
G5SD2
PSERT
PYRDC
335
G5SD
G5SD2
PGCD
PYRDC
336
MTHFC
G3PD
PYRDC
ATPS
337
MTHFC
GLY3PP
PYRDC
ATPS
338
G5SD
G5SD2
PYRDC
ATPS
339
GLU5K
GHMT2m
ATPSm
ALCD2x
340
GHMT2
GHMT2m
ATPtm-3H
IPPSm
341
GHMT2m
PYK
ATPSm
ATPtm-3H
342
G3PD
MDHm
SUCD3-u6m
ALCD2x
343
ASPTA1m
MTHFC
PGCD
ATPtm-3H
344
ASPTA1m
MTHFC
PSERT
ATPtm-3H
345
ASPTA1m
MTHFC
PSP_L
ATPtm-3H
346
ASPTA1m
ME2m
PSP_L
ATPtm-3H
347
ASPTA1m
ME2m
PSERT
ATPtm-3H
348
ASPTA1m
ME2m
PGCD
ATPtm-3H
349
GHMT2m
PYK
ATPSm
IPPSm
350
GLU5K
GHMT2m
ATPSm
IPPSm
351
ME2m
ICDHym
PGCD
ATPtm-3H
352
ME2m
ACONTm
PSP_L
ATPtm-3H
353
ME2m
ICDHym
PSP_L
ATPtm-3H
354
ME2m
ACONTm
PSERT
ATPtm-3H
355
ME2m
ACONTm
PGCD
ATPtm-3H
356
ME2m
ICDHym
PSERT
ATPtm-3H
357
MTHFD
MTHFD2
GHMT2m
ALCD2x
358
MTHFD
MTHFD2
PSP_L
ATPtm-3H
359
MTHFD
MTHFD2
PSERT
ATPtm-3H
360
MTHFD
MTHFD2
PGCD
ATPtm-3H
361
GHMT2
GHMT2m
ATPSm
IPPSm
362
GHMT2m
PYK
ATPSm
ALCD2x
363
ME1m
MTHFC
GHMT2m
PDHm
364
THFATm
PYK
ATPtm-3H
IPPSm
365
FTHFCLm
PYK
ATPtm-3H
IPPSm
366
ACONT
GHMT2m
PYK
ATPSm
367
ICDHyGHMT2m
PYK
ATPSm
368
GHMT2
ORNTA
GHMT2m
ATPtm-3H
369
GHMT2
THFATm
GHMT2m
PYRDC
370
GHMT2
FTHFCLm
GHMT2m
PYRDC
371
ME2m
GLU5K
ACONTm
PYRDC
372
ME2m
GLU5K
ICDHym
PYRDC
373
MTHFD
MTHFD2
GHMT2m
ATPtm-3H
374
MTHFD
MTHFD2
GHMT2m
PYRDC
375
G5SD2
GHMT2m
PYK
ATPSm
376
GLU5K
GHMT2m
PYK
ATPSm
377
ASPTA1m
GHMT2m
PYK
ATPSm
378
MTHFD
MTHFD2
GHMT2m
ATPSm
379
G5SD
G5SD2
GHMT2m
ATPSm
380
MTHFC
GHMT2m
ATPtm-3H
IPPSm
381
ASPTA1m
ACONTm
GHMT2m
ATPSm
382
MTHFC
GHMT2m
ALCD2x
IPPSm
383
ME2m
MTHFC
PYK
ATPSm
384
ASPTA1m
G5SD2
GHMT2m
ATPSm
385
G5SD2
MTHFD
GHMT2m
ATPSm
386
ME2m
FTHFLr
PYK
ATPSm
387
THFATm
PYK
TKT2
ATPtm-3H
388
FTHFCLm
PYK
TKT2
ATPtm-3H
389
ORNTA
THFATm
PYK
ATPtm-3H
390
ORNTA
FTHFCLm
PYK
ATPtm-3H
391
ASPTA1m
FTHFCLm
PYK
ATPtm-3H
392
ASPTA1m
THFATm
PYK
ATPtm-3H
393
ORNTA
MTHFC
GHMT2m
ATPtm-3H
394
PDHm
ATPSm
MDHm
PPND
395
MTHFC
THFATm
PYK
ATPtm-3H
396
FTHFCLm
MTHFC
PYK
ATPtm-3H
397
GHMT2
THFATm
PYK
ATPtm-3H
398
GHMT2
FTHFCLm
PYK
ATPtm-3H
399
GHMT2
ORNTA
FTHFCLm
ALCD2x
400
GHMT2
ORNTA
THFATm
ALCD2x
401
G5SD
G5SD2
ALCD2x
THRA
402
PSP_L
MDHm
DHORD4u
IPPSm
403
PSERT
MDHm
DHORD4u
IPPSm
404
PGCD
MDHm
DHORD4u
IPPSm
405
ORNTA
PSERT
MDHm
DHORD4u
406
ORNTA
PSP_L
MDHm
DHORD4u
407
ORNTA
PGCD
MDHm
DHORD4u
408
GHMT2
ORNTA
ME1m
GHMT2m
409
ME1m
MTHFD
MTHFD2
GHMT2m
410
PSERT
MDHm
DHORD4u
ALDD2y
411
PGCD
MDHm
DHORD4u
ALDD2y
412
PSP_L
MDHm
DHORD4u
ALDD2y
413
ASPTA1m
PGCD
MDHm
DHORD4u
414
ASPTA1m
PSP_L
MDHm
DHORD4u
415
ASPTA1m
PSERT
MDHm
DHORD4u
416
PGCD
MDHm
NADH2-u6m
SUCD3-u6m
417
PSERT
MDHm
NADH2-
SUCD3-u6m
u6m
418
PSP_L
MDHm
NADH2-u6m
SUCD3-u6m
419
PYK
MDHm
DHORD4u
ATPS
420
MDHm
NADH2-u6m
SUCD3-u6m
ATPS
421
PDHm
MDHm
DHORD4u
ALDD2y
422
GHMT2
GHMT2m
MDHm
DHORD4u
423
ORNTA
PDHm
MDHm
DHORD4u
424
ASPTA1m
PDHm
MDHm
DHORD4u
425
PDHm
MDHm
NADH2-u6m
SUCD3-u6m
426
ORNTA
MDHm
DHORD4u
IPPSm
427
MDHm
DHORD4u
ALDD2y
IPPSm
428
ASPTA1m
MDHm
DHORD4u
IPPSm
429
MDHm
NADH2-u6m
SUCD3-u6m
IPPSm
430
MTHFC
GHMT2m
MDHm
DHORD4u
431
ORNTA
MDHm
DHORD4u
ALDD2y
432
ME2m
ICDHym
MDHm
DHORD4u
433
ME2m
ACONTm
MDHm
DHORD4u
434
ORNTA
MDHm
NADH2-
SUCD3-u6m
u6m
435
ASPTA1m
MDHm
DHORD4u
ALDD2y
436
MDHm
NADH2-u6m
SUCD3-u6m
ALDD2y
437
ASPTA1m
MDHm
NADH2-
SUCD3-u6m
u6m
438
PSERT
TPI
MDH
DHORD4u
439
PSP_L
TPI
MDH
DHORD4u
440
PGCD
TPI
MDH
DHORD4u
441
TPI
MDH
DHORD4u
THRA
442
PDHm
TPI
MDH
DHORD4u
443
TPI
FDH
MDH
DHORD4u
444
TPI
MDH
NADH2-u6m
SUCD3-u6m
445
G3PDm
TPI
MDH
NADH2-
u6m
446
G3PD1irm
TPI
MDH
NADH2-
u6m
447
GLYCLm
PGI
MDH
DHORD4u
448
GHMT2
PGI
MDH
DHORD4u
449
GHMT2m
PGI
MDH
DHORD4u
450
G3PD1irm
PGI
MDH
NADH2-
u6m
451
G3PDm
PGI
MDH
NADH2-
u6m
452
MDH
DHORD4u
ATPS
ALDD2y
453
ME2m
MDH
DHORD4u
ATPS
454
ICDHy
MDH
DHORD4u
ATPS
455
ACONT
MDH
DHORD4u
ATPS
456
GHMT2
MDH
DHORD4u
ATPS
457
ORNTA
MDH
DHORD4u
ATPS
458
MTHFC
MDH
DHORD4u
ATPS
459
MDH
NADH2-
SUCD3-u6m
ATPS
u6m
460
G3PD1irm
MDH
NADH2-u6m
ATPS
461
G3PDm
MDH
NADH2-u6m
ATPS
462
ASPTA1
FUM
FUMmATPS
463
PSERT
TPI
FUM
FUMm
464
PSP_L
TPI
FUM
FUMm
465
PGCD
TPI
FUM
FUMm
466
G3PDm
FUM
FUMm
SUCD3-u6m
467
G3PDm
FUM
SUCD1rm
SUCD3-u6m
468
G3PDm
MDH
SUCD3-u6m
DHORD4u
469
G3PDm
MDH
NADH2-u6m
SUCD3-u6m
470
ASPTA1
TPI
FUM
FUMm
471
FTHFLr
TPI
FUM
FUMm
472
MTHFC
TPI
FUM
FUMm
473
GHMT2
TPI
FUM
FUMm
474
GLU5K
G3PDm
PDHm
SUCD3-u6m
PYRDC
475
G3PDm
PDHm
SUCD3-u6m
PYRDC
IPPS
476
GLU5K
G3PDm
SUCD3-u6m
ALCD2x
IPPS
477
G5SD
G5SD2
G3PDm
SUCD3-u6m
ALCD2x
478
ASPTA1m
ACONTm
G3PDm
SUCD3-u6m
ALCD2x
479
G3PDm
NADH2-u6cm
NADH2-
DHORD4u
ALCD2x
u6m
480
G3PD
PDHm
MDHm
SUCD3-u6m
PYRDC
481
G5SD
G5SD2
PDHm
PYRDC
IPPS
482
G3PDm
ATPSm
NADH2-
NADH2-
DHORD4u
u6cm
u6m
483
ASPTA1m
ACONTm
PDHm
PYRDC
IPPS
484
ASPTA1m
ICDHxm
ICDHym
PDHm
PYRDC
485
ORNTA
MTHFC
G3PDm
SUCD3-u6m
ATPtm-3H
486
G3PD
PDHm
MDHm
SUCD3-u6m
ALCD2x
487
ME2m
MTHFD
G3PDm
SUCD3-u6m
ATPtm-3H
488
GHMT2
ME2m
G3PDm
SUCD3-u6m
ATPtm-3H
489
ACONT
MTHFC
G3PDm
SUCD3-u6m
ATPtm-3H
490
ICDHyMTHFC
G3PDm
SUCD3-u6m
ATPtm-3H
491
MTHFD
MTHFD2
G3PDm
SUCD3-u6m
ATPtm-3H
492
ASPTA1m
GHMT2
G3PDm
SUCD3-u6m
ATPtm-3H
493
ASPTA1m
MTHFC
G3PDm
SUCD3-u6m
ATPtm-3H
494
MTHFD
G3PDm
GHMT2m
SUCD3-u6m
ATPtm-3H
495
G3PDm
NADH2-u6cm
NADH2-
DHORD4u
ATPtm-3H
u6m
TABLE 7
A list of all the reaction stoichiometries and the associated genes known to be
associated with the reactions identified for disruption in the strains listed in Tables 5 and 6. [c]
refers to cytosol and [m] refers to mitochondrion, indicating the organelle where the reaction
takes place
Reaction
Abbreviation
Reaction Name
Reaction Stoichiometry
Associated genes
ACONT
aconitase
[c]: cit <==> icit
YLR304C
ACONTm
aconitate hydratase
[m]: cit <==> icit
YJL200C, YLR304C
AGT
alanine-glyoxylate
[c]: ala-L + glx <==> gly + pyr
YFL030W
transaminase
AKGDam
oxoglutarate
[m]: akg + h + lpam <==> co2 + sdhlam
YIL125W, YDR148C, YFL018C
dehydrogenase
(lipoamide)
AKGDbm
oxoglutarate
[m]: coa + sdhlam --> dhlam + succoa
YIL125W, YDR148C, YFL018C
dehydrogenase
(dihydrolipoamide S-
succinyltransferase)
ALATA_L
L-alanine transaminase
[c]: akg + ala-L <==> glu-L + pyr
YDR111C
ALCD2x
alcohol dehydrogenase
[c]: etoh + nad <==> acald + h + nadh
YGL256W, YMR303C, YDL168W,
(ethanol: NAD)
YOL086C, YBR145W
ASPTA1
aspartate transaminase
[c]: akg + asp-L <==> glu-L + oaa
YLR027C
ASPTA1m
aspartate transaminase,
[m]: akg + asp-L <==> glu-L + oaa
YKL106W
mitochondrial
ATPSm
ATP synthase,
adp[m] + (3) h[c] + pi[m] --> atp[m] +
YBL099W + YPL078C +
mitochondrial
(2) h[m] + h2o[m]
YDL004W + YDR377W + YOL077W-
A + YJR121W + YDR322C-
A + Q0080 + YBR039W + YDL181W +
Q0130 + YKL016C +
YDR298C + YML081C-
A + YPL271W + Q0085 + YPR020W + YLR295C,
YBL099W + YDL004W + YPL078C +
YDR377W + YJR121W +
Q0080 + YBR039W + YDL181W + YKL016C +
Q0130 + YDR298C + YML081C-
A + YPL271W + Q0085 + YLR295C
ATPtm-3H
ADP/ATP transporter,
adp[c] + atp[m] + (3) h[c] --> adp[m] +
YBL030C, YBR085W, YMR056C
mitochondrial
atp[c] + (3) h[m]
FRDcm
fumarate reductase,
fadh2[m] + fum[c] --> fad[m] + succ[c]
YEL047C
cytosolic/mitochondrial
FRDm
fumarate reductase
[m]: fadh2 + fum --> fad + succ
YJR051W
FUMm
fumarase, mitochondrial
[m]: fum + h2o <==> mal-L
YPL262W
G3PD
Glycerol-3-phosphate
[c]: dhap + h + nadh --> glyc3p + nad
YDL022W
dehydrogenase (NAD)
G3PD1irm
glycerol-3-phosphate
[m]: dhap + h + nadh --> glyc3p + nad
YOL059W
dehydrogenase (NAD),
mitochondrial
G3PDm
glycerol-3-phosphate
[m]: fad + glyc3p --> dhap + fadh2
YIL155C
dehydrogenase
G6PDH
glucose 6-phosphate
[c]: g6p + nadp --> 6pgl + h + nadph
YNL241C
dehydrogenase
GHMT2
glycine
[c]: ser-L + thf --> gly + h2o + mlthf
YLR058C
hydroxymethyltransferase
GLY3PP
glycerol-3-phosphatase
[c]: glyc3p + h2o --> glyc + pi
YER062C, YIL053W
HSDxi
homoserine
[c]: aspsa + h + nadh --> hom-L + nad
YJR139C
dehydrogenase
(NADH), irreversible
HSK
homoserine kinase
[c]: atp + hom-L --> adp + h + phom
YHR025W
ICDHxm
Isocitrate
[m]: icit + nad --> akg + co2 + nadh
YOR136W + YNL037C
dehydrogenase (NAD+)
ICDHy
isocitrate
[c]: icit + nadp <==> akg + co2 + nadph
YLR174W
dehydrogenase (NADP)
ICL
Isocitrate lyase
[c]: icit --> glx + succ
YER065C
MDH
malate dehydrogenase
[c]: mal-L + nad <==> h + nadh + oaa
YOL126C
MDHm
malate dehydrogenase,
[m]: mal-L + nad <==> h + nadh + oaa
YKL085W
mitochondrial
ME1m
malic enzyme (NAD),
[m]: mal-L + nad --> co2 + nadh + pyr
YKL029C
mitochondrial
ME2m
malic enzyme (NADP),
[m]: mal-L + nadp --> co2 + nadph + pyr
YKL029C
mitochondrial
MTHFD
methylenetetrahydrofolate
[c]: mlthf + nadp <==> methf + nadph
YGR204W
dehydrogenase
(NADP)
NADH2-u6cm
NADH dehydrogenase,
h[c] + nadh[c] + q6[m] --> nad[c] + q6h2[m]
YMR145C, YDL085W
cytosolic/mitochondrial
ORNTA
ornithine transaminase
[c]: akg + orn-L --> glu-L + glu5sa
YLR438W
P5CDm
1-pyrroline-5-
[m]: 1pyr5c + (2) h2o + nad --> glu-L + h + nadh
carboxylate
dehydrogenase,
mitochondrial
PDHcm
part of pyruvate
[m]: dhlam + nad --> h + lpam + nadh
YIL125W, YDR148C, YFL018C
dehydrogenase
(dihydrolipoamide
dehydrogenase)
PDHm
pyruvate
[m]: coa + nad + pyr --> accoa + co2 + nadh
YER178W + YBR221C, YNL071W,
dehydrogenase,
YFL018C
mitochondrial
PGCD
phosphoglycerate
[c]: 3pg + nad --> 3php + h + nadh
YIL074C, YER081W
dehydrogenase
PGDH
phosphogluconate
[c]: 6pgc + nadp --> co2 + nadph + ru5p-D
YHR183W, YGR256W
dehydrogenase
PGL
6-
[c]: 6pgl + h2o --> 6pgc + h
YNR034W, YGR248W, YHR163W
phosphogluconolactonase
PRO1xm
proline oxidase (NAD),
[m]: nad + pro-L --> 1pyr5c + (2) h + nadh
YLR142W
mitochondrial
PSERT
phosphoserine
[c]: 3php + glu-L --> akg + pser-L
YOR184W
transaminase
PSP_L
phosphoserine
[c]: h2o + pser-L --> pi + ser-L
YGR208W
phosphatase (L-serine)
PYK
pyruvate kinase
[c]: adp + h + pep --> atp + pyr
YAL038W, YOR347C
PYRDC
pyruvate decarboxylase
[c]: h + pyr --> acald + co2
YGR087C, YLR044C, YLR134W
RPE
ribulose 5-phosphate 3-
[c]: ru5p-D <==> xu5p-D
YJL121C
epimerase
SERD_L
L-serine deaminase
[c]: ser-L --> nh4 + pyr
YIL168W, YCL064C
SUCD2_u6m
succinate
[m]: q6 + succ <==> fum + q6h2
YKL148C + YMR118C + YLL041C + YDR178W,
dehydrogenase
YKL141W + YLL041C + YJL045W + YDR178W,
(ubiquinone-6),
YKL148C + YKL141W + YLL041C + YLR164W,
mitochondrial
YKL148C + YKL141W + YLL041C + YDR178W
SUCD3-u6m
succinate
[m]: fadh2 + q6 <==> fad + q6h2
YKL148C + YMR118C + YLL041C + YDR178W,
dehydrogenase
YKL141W + YLL041C + YJL045W + YDR178W,
(ubiquinone-6),
YKL148C + YKL141W + YLL041C + YLR164W,
mitochondrial
YKL148C + YKL141W + YLL041C + YDR178W
SUCOASAm
Succinate--CoA ligase
[m]: atp + coa + succ <==> adp + pi + succoa
YOR142W + YGR244C
(ADP-forming)
THRA
threonine aldolase
[c]: thr-L <==> acald + gly
YEL046C
THRS
threonine synthase
[c]: h2o + phom --> pi + thr-L
YCR053W
TKT2
transketolase
[c]: e4p + xu5p-D <==> f6p + g3p
YBR117C, YPR074C
TABLE 8
List of the metabolite abbreviations, the corresponding names of all
the metabolites that participate in the reactions listed in Table 7.
Metabolite Abbreviation
Metabolite Name
1pyr5c
1-Pyrroline-5-carboxylate
3pg
3-Phospho-D-glycerate
3php
3-Phosphohydroxypyruvate
6pgc
6-Phospho-D-gluconate
6pgl
6-phospho-D-glucono-1,5-lactone
acald
Acetaldehyde
accoa
Acetyl-CoA
adp
ADP
akg
2-Oxoglutarate
ala-L
L-Alanine
asp-L
L-Aspartate
aspsa
L-Aspartate 4-semialdehyde
atp
ATP
cit
Citrate
co2
CO2
coa
Coenzyme A
dhap
Dihydroxyacetone phosphate
dhlam
Dihydrolipoamide
e4p
D-Erythrose 4-phosphate
etoh
Ethanol
f6p
D-Fructose 6-phosphate
fad
FAD
fadh2
FADH2
fum
Fumarate
g3p
Glyceraldehyde 3-phosphate
g6p
D-Glucose 6-phosphate
glu-L
L-Glutamate
glu5sa
L-Glutamate 5-semialdehyde
glx
Glyoxylate
gly
Glycine
glyc
Glycerol
glyc3p
sn-Glycerol 3-phosphate
h
H+
h2o
H2O
hom-L
L-Homoserine
icit
Isocitrate
lpam
Lipoamide
mal-L
L-Malate
methf
5,10-Methenyltetrahydrofolate
mlthf
5,10-Methylenetetrahydrofolate
nad
Nicotinamide adenine dinucleotide
nadh
Nicotinamide adenine dinucleotide-reduced
nh4
Ammonium
oaa
Oxaloacetate
orn-L
L-Ornithine
pep
Phosphoenolpyruvate
phom
O-Phospho-L-homoserine
pi
Phosphate
pro-L
L-Proline
pser-L
O-Phospho-L-serine
pyr
Pyruvate
q6
Ubiquinone-6
q6h2
Ubiquinol-6
ru5p-D
D-Ribulose 5-phosphate
sdhlam
S-Succinyldihydrolipoamide
ser-L
L-Serine
succ
Succinate
succoa
Succinyl-CoA
thf
5,6,7,8-Tetrahydrofolate
thr-L
L-Threonine
xu5p-D
D-Xylulose 5-phosphate
Throughout this application various publications have been referenced within parentheses. The disclosures of these publications in their entireties are hereby incorporated by reference in this application in order to more fully describe the state of the art to which this invention pertains.
Although the invention has been described with reference to the disclosed embodiments, those skilled in the art will readily appreciate that the specific examples and studies detailed above are only illustrative of the invention. It should be understood that various modifications can be made without departing from the spirit of the invention. Accordingly, the invention is limited only by the following claims.
1.PublishNumber: US-2010009419-A1
2.Date Publish: 20100114
3.Inventor: BURK MARK J.
BURGARD ANTHONY P.
PHARKYA PRITI
4.Inventor Harmonized: BURK MARK J(US)
BURGARD ANTHONY P(US)
PHARKYA PRITI(US)
5.Country: US
6.Claims:
(en)A non-naturally occurring eukaryotic or prokaryotic organism includes one or more gene disruptions occurring in genes encoding enzymes imparting increased fumarate, malate or acrylate production in the organism when the gene disruption reduces an activity of the enzyme. The one or more gene disruptions confers increased production of acrylate onto the organism. Organisms that produce acrylate have an acrylate pathway that at least one exogenous nucleic acid encoding an acrylate pathway enzyme expressed in a sufficient amount to produce acrylate, the acrylate pathway comprising a decarboxylase. Methods of producing fumarate, malate or acrylate include culturing these organisms.
7.Description:
(en)This application claims the benefit of priority of U.S. Provisional Ser. No. 61/073,348, filed Jun. 17, 2008; U.S. Provisional Ser. No. 61/077,127, filed Jun. 30, 2008; and U.S. Provisional Ser. No. 61/088,628, filed Aug. 13, 2008, each of which is incorporated by reference in their entirety.
BACKGROUND
The present disclosure relates generally to the design of engineered organisms and, more specifically to organisms having selected genotypes for the production of fumarate, malate, and acrylate.
Fumaric acid is used in industrial processes as a raw material in a wide range of chemical syntheses. The presence of a double bond and two carboxyl groups in this compound facilitates its use in making polyesters and other polymers. Some of its industrial applications include manufacturing of synthetic resins and biodegradable polymers. It also finds widespread use as a food acidulant, a dietary supplement and as a beverage ingredient. Fumaric acid is currently derived from maleic anhydride, which is produced by the catalytic oxidation of benzene or butene feedstocks. Even though fumaric acid is approximately 10% more expensive than maleic anhydride, the non-toxic nature of the former and the special properties, such as greater hardness, that it imparts to the polymer structure makes it a good option for polymer industry as compared to maleic anhydride. Recently, two new applications for fumaric acid have been developed: (i) it can be used medicinally for treating a skin condition called psoriasis, and (ii) it can be used as a supplement for cattle feed.
Malic acid is used as an acidulant and taste enhancer in the beverage and food industry. Racemic malic acid is synthesized petrochemically from maleic anhydride whereas enantiometrically pure L-malic acid (used in pharmaceutical production) is produced from fumarate by hydration with fumarase.
Acrylic acid is a large volume petrochemical product. For example, acrylic acid is a commodity monomer intermediate used for the production of polymeric materials such polyacrylic acid, which is a major component of superabsorbant diapers. Acrylic acid also is used for the production of acrylate esters, which are utilized in water-soluble latex coatings, adhesives and inks. Acrylic acid and acrylate esters are manufactured by petrochemical processes such as oxidation of propylene, followed by esterification with alcohols such as methanol, butanol, and 2-ethylhexanol.
Chemicals manufactured from petroleum feedstocks suffer the burden of high and volatile prices, insecure foreign supply chains, and declining reserves (Frost, J. W., Redefining chemical manufacture. Ind. Biotechnol. 1:23-24 (2005)). Therefore, a method of producing large volume chemicals or their intermediates by alternative means that reduce petroleum-based processes and also use less energy- and capital-intensive processes would be beneficial.
Thus, there is a need to gain access to microorganisms having the commercially valuable characteristics of efficiently bio synthesizing fumarate, malate, and acrylate in high yields. The present invention satisfies this need and provides related advantages as well.
SUMMARY OF THE INVENTION
In some embodiments, the present invention provides a non-naturally occurring microbial organism that includes one or more gene disruptions occurring in genes encoding enzymes selected from the group of fumarate reductase (FRD), alcohol dehydrogenase (ADHEr) and lactate dehydrogenase (LDH_D) such that the one or more gene disruptions confers increased production of fumarate onto said non-naturally occurring microbial organism.
In some embodiments, the present invention provides a method for producing fumaric acid that includes culturing a non-naturally occurring microbial organism having one or more gene disruptions occurring in genes encoding enzymes selected from the group of fumarate reductase (FRD), alcohol dehydrogenase (ADHEr) and lactate dehydrogenase (LDH_D) such that the one or more gene disruptions confers increased production of fumarate onto said non-naturally occurring microbial organism.
In some embodiments, the present invention provides a non-naturally occurring microbial organism that includes one or more gene disruptions occurring in genes encoding enzymes selected from a group of fumarate reducatse (FRD), alcohol dehydrogenase (ADHEr), fumarase (FUM) and lactate dehydrogenase (LDH_D), when the gene disruption reduces an activity of the enzyme it confers increased production of malate onto said non-naturally occurring microbial organism.
In some embodiments, the present invention provides a method for producing malic acid that includes culturing a non-naturally occurring microbial organism having one or more gene disruptions occurring in genes encoding enzymes selected from a group of fumarate reducatse (FRD), alcohol dehydrogenase (ADHEr), fumarase (FUM) and lactate dehydrogenase (LDH_D), when the gene disruption reduces an activity of the enzyme it confers increased production of malate onto said non-naturally occurring microbial organism.
In some embodiments, the present invention provides a non-naturally occurring eukaryotic organism, comprising one or more gene disruptions occurring in genes encoding enzymes imparting increased fumarate production in the organism when the gene disruption reduces an activity of the enzyme, whereby the one or more gene disruptions confers increased production of fumarate onto the organism.
In some embodiments, the present invention provides a method for producing fumaric acid that includes culturing a non-naturally occurring eukaryotic organism having one or more gene disruptions occurring in genes encoding an enzyme providing increased fumarate production in the organism when the gene disruption reduces an activity of the enzyme, whereby the one or more gene disruptions confers increased production of fumarate onto the organism.
In some embodiments, the present invention provides a non-naturally occurring eukaryotic organism that includes one or more gene disruptions occurring in genes encoding enzymes imparting increased malate production in the organism when the gene disruption reduces an activity of the enzyme, whereby the one or more gene disruptions confers enhanced production of malate onto the organism.
In some embodiments, the present invention provides a method for producing malic acid that includes culturing a non-naturally occurring eukaryotic organism having one or more gene disruptions occurring in genes encoding enzymes imparting increased malate production to the organism when the gene disruption reduces an activity of the enzyme, whereby the one or more gene disruptions confers increased production of malate onto the organism.
In some embodiments, the present invention provides a non-naturally occurring eukaryotic organism that includes one or more gene disruptions occurring in genes encoding enzymes imparting increased acrylate production in the organism when the gene disruption reduces an activity of the enzyme, whereby the one or more gene disruptions confers increased production of acrylate onto the organism.
In some embodiments, the present invention provides a method for producing acrylic acid that includes culturing a non-naturally occurring eukaryotic organism having one or more gene disruptions occurring in genes encoding enzymes imparting enhanced acrylate production in the organism when the gene disruption reduces an activity of the enzyme, whereby the one or more gene disruptions confers increased production of acrlyate onto the organism.
In some embodiments, the present invention provides a non-naturally occurring microbial organism that includes a microbial organism having an olefin pathway having at least one exogenous nucleic acid encoding an olefin pathway enzyme expressed in a sufficient amount to produce an olefin, the olefin pathway including a decarboxylase.
In some embodiments, the present invention provides a method for producing an olefin that includes culturing a non-naturally occurring microbial organism having an olefin pathway that includes at least one exogenous nucleic acid encoding an olefin pathway enzyme expressed in a sufficient amount to produce an olefin under conditions and for a sufficient period of time to produce an olefin, the olefin pathway including a decarboxylase.
In some embodiments, the present invention provides a non-naturally occurring microbial organism that includes a microbial organism having an acrylate pathway having at least one exogenous nucleic acid encoding an acrylate pathway enzyme expressed in a sufficient amount to produce acrylate, the acrylate pathway including a decarboxylase.
In some embodiments, the present invention provides a method for producing acrylate that includes culturing a non-naturally occurring microbial organism having an acrylate pathway, the pathway includes at least one exogenous nucleic acid encoding an acrylate pathway enzyme expressed in a sufficient amount to produce acrylate under conditions and for a sufficient period of time to produce acrylate, the acrylate pathway including a decarboxylase.
In some embodiments, the present invention provides a method for producing acrylate that includes a) culturing a first non-naturally occurring microbial organism that includes one or more gene disruptions occurring in one or more genes encoding one or more enzymes that enhance fumarate production toin the organism when the one or more genes disruptions reduces an activity of the one or more enzymes, whereby the one or more gene disruptions confers increased production of fumarate onto the non-naturally occurring organism, and b) adding a decarboxylase to the cultured first non-naturally occurring microbial organism, the decarboxylase catalyzing the decarboxylation of fumarate.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows the hypothetical production envelopes of an OptKnock-designed strain contrasted against a typical non-growth-coupled production strain. Note that the potential evolutionary trajectories of the OptKnock strain are fundamentally different in that they will lead to a high producing phenotype.
FIG. 2 shows increased fumarate production characteristics of one strain (black, dashed) compared with those of the wild-type E. coli network (black). At the maximum rate of growth, the wild-type network is not expected to form any fumarate.
FIG. 3 shows increased fumarate production characteristics of another strain (black, dotted) compared with those of the wild-type E. coli network (black). The grey point shows the minimum amount of product formation expected from this strain.
FIG. 4 shows the production curve for still another strain (grey, dashed) compared with the production curve for the wild-type E. coli network (black). Note that this strain design is equivalent to design B if an additional deletion in THD2 is introduced.
FIG. 5 shows the production curve for yet another strain (grey, dashed) compared with the production curve of the wild type E. coli network (black). The black point indicates the minimum amount of product formation expected from this strain.
FIG. 6 shows the production curves for the strains in FIG. 2 (black, dashed), FIG. 3 (black, dotted), FIG. 4 (grey, dashed) and FIG. 5 (grey) compared with each other and with the production characteristics of the wild-type E. coli network (black). Note the reduction in feasible solution space as additional deletions are imposed on the network.
FIG. 7 shows the malate production curve for one strain (light grey) compared with the production curve for the wild type E. coli network (black).
FIG. 8 shows the production curve for a modified malate-producing strain design based on the strain of FIG. 7 , replacing deletion of FRD with deletion of ASPT,(grey) compared with that of the wild-type E. coli network (black).
FIG. 9 shows increased fumarate production characteristics of one strain (black, dotted) compared with those of the wild-type S. cerevisiae network (black). At the maximum rate of growth, the wild-type network is not expected to form any fumarate.
FIG. 10 shows increased fumarate production characteristics of another strain (light gray) compared with those of the wild-type S. cerevisiae network (black). The gray point shows the minimum amount of product formation expected from this strain.
FIG. 11 shows the production curve for yet another strain (dark gray, dashed) compared with the production curve for the wild-type S. cerevisiae network (black). The dark gray point shows the minimum amount of fumarate production expected from this design.
FIG. 12 shows the production curve for still another strain (light gray, dashed) compared with the production curve of the wild type S. cerevisiae network (black). The light gray point indicates the minimum amount of product formation expected from this strain.
FIG. 13 shows the production curves for various strains in FIG. 9 , black, dotted; FIG. 10 , light gray; FIG. 11 dark gray, dashed; and FIG. 12 light gray, dashed, compared with each other and with the production characteristics of the wild-type S. cerevisiae network (black). Note the reduction in feasible solution space as additional deletions are imposed on the network.
FIG. 14 shows the acrylate production curve for one strain (dark gray, dashed) compared with the production curve for the wild type S. cerevisiae network (black).
FIG. 15 shows the acrylate production curve for another strain (black, dotted) compared with the production curve for the wild type S. cerevisiae network (black).
FIG. 16 shows the acrylate production curve for yet another strain (dark gray) compared with the production curve for the wild type S. cerevisiae network (black).
FIG. 17 shows the acrylate production curve for still another strain (light gray) compared with the production curve for the wild type S. cerevisiae network (black).
FIG. 18 shows the acrylate production curve for yet still another strain (light gray, dashed) compared with the production curve for the wild type S. cerevisiae network (black).
FIG. 19 shows the prophetic transformations of a) 1,1- and 1,2-substituted carboxylic acids to terminal olefins catalyzed by a decarboxylase and b) the transformation of a pentadienoic acid to 1,3-butadiene.
FIG. 20 shows a biosynthetic pathway for the direct production of acrylate through decarboxylation of fumarate.
FIG. 21 a shows the prophetic transformation of fumarate to acrylate catalyzed by a decarboxylase.
FIG. 21 b shows the decarboxylation of aconitate to itaconate catalyzed by aconitate decarboxylase.
FIG. 21 c shows the decarboxylation of 4-oxalocrotonate to 2-oxopentenoate catalyzed by 4-oxalocrotonate decarboxylase.
FIG. 21 d shows the decarboxylation of cinnamate derivatives to styrene derivatives catalyzed by a decarboxylase.
DETAILED DESCRIPTION OF THE INVENTION
This invention is directed, in part, to engineered organisms having biosynthetic pathways to fumarate, malate, and acrylate. In some embodiments, the invention utilizes optimization-based approaches based on in silico stoichiometric models of Escherichia coli and Saccharomyces cerevisiae metabolism that identify metabolic designs for increased production of fumarate, malate, and acrylate in these organisms. A bilevel programming framework, OptKnock, is applied within an iterative algorithm to predict multiple sets of gene disruptions, that collectively result in increased production of fumarate, malate, or acrylate. As disclosed herein, various combinations of gene deletions or functional disruptions of genes significantly improve the fumarate, malate, or acrylate production capabilities of E. coli and S. cerevisiae.
Production of acrylate, in particular, involves not only primary metabolic production of fumarate, but also subsequent mono-decarboxylation. Thus, the invention is also directed, in part, to a developing a route to acrylate from fumarate by reaction with a decarboxylase enzyme. The decarboxylase enzyme can be introduced as an exogenous nucleic acid into the same organism that has been engineered for increased fumarate production via gene disruptions, or alternatively through a secondary transformation involving extracellular addition of a decarboxylase to a culture containing over-produced fumarate. Another alternative is to provide a second organism having decarboxylase activity. In such a case, the fumarate-producing organism can be co-cultured or serially cultured with the second organism possessing the requisite decarboxylase.
The engineering designs are equally applicable if an organism other than E. coli or S. cerevisiae is chosen as the production host, even if the organism naturally lacks the activity or exhibits low activity of a subset of the gene products marked for disruption. In those cases, disruptions must only be introduced to eliminate or lessen the enzymatic activities of the gene products that are naturally present in the chosen production host. Production of fumarate, malate, or acrylate for the in silico designs are confirmed by construction of strains having the designed metabolic genotype. These metabolically engineered cells or organisms can also be subjected to adaptive evolution to further augment product production.
In a further embodiment, the invention is directed to an integrated computational and engineering platform for developing metabolically altered microorganism strains having enhanced fumarate, malate, or acrylate producing characteristics. Strains identified via the computational component of the platform are put into actual production by genetically engineering the predicted metabolic alterations which lead to the enhanced production of fumarate, malate, or acrylate. Production of the desired product is optionally coupled to optimal growth of the microorganism. Strains exhibiting increased production of these products can be further subjected to adaptive evolution to further augment product biosynthesis. The levels of product production following adaptive evolution also can be predicted by the computational component of the system where, in this specific embodiment, the elevated product levels are realized following evolution.
Currently, the only organisms known to produce fumarate at a reasonable level are Rhizopus (Tsao et al., Adv. Biochem. Eng. Biotechnol., 65:243-280 (1999); Lee et al., Macromolecular Bioscience, 4:157-164 (1999); Rhodes et al., Appl. Microbiol. 1962, 10(1):9-15; and Rhodes et al., Appl. Microbiol. 7(2):74-80 (1959)). Fumarate production in these organisms utilizes pyruvate carboxylase to fix carbon dioxide, converting pyruvate into oxaloacetate (Kenealy et al., Appl. Environ. Microbiol. 52(1):128-133 (1986)). This is subsequently converted into malate and finally into fumarate. Some reports on fumarate production in Rhizopus have outlined fermentation and culture conditions for obtaining fumarate (Moresi et al., J. Chem. Technol. Biotechnol. 54(3):283-2890 (1992)). Optimum concentrations of metal ions and phosphate have been determined to maximize the fumarate production during the fermentation process (Zhou et al., Appl. Biochem. Biotechnol. 84-86:779-89 (2000)). Another study examined various cassaya bagasse hydrolysates as a cheap carbon source, reporting a yield of 22 g/L of fumarate (Carta et al., Bioresource Technology 68(1):23-28 (1999)). A study of neutralizing agents for fumarate production was also undertaken. It was determined that utilizing CaCO 3 provides the highest fumaric acid weight yield (53.4%) and volumetric productivity (1.03 g/L.hr) (Zhou et al., Bioprocess Biosyst. Eng. 25(3):179-181 (2002)).
However, growing mycelia often form interlocking hyphae mingled with calcium carbonate, resulting in oxygen transfer limitations, thus slowing down the rate of fermentation. Another difficulty involved in fumarate production is the tendency of Rhizopus sporangiospores to grow into mycelial mats or mycelial lumps (Zhou et al., Appl. Biochem. Biotechnol. 84-86:779-89 (2000)), interfering with the function of bafflers and propellers inside a reactor. A rotary biofilm contactor has been utilized in a simultaneous fermentation-adsorption process to obtain yields of 85 g/L of fumarate from 100 g/L of glucose. Finally, R. arrhizus NRR11526 immoblized on a polyurethane sponge was used to facilitate continuous fermentation for fumarate production. Yields of approximately 12.3 g/L of fumaric acid were obtained in this work (Lee et al., Macromolecular Bioscience 4:157-164 (2004)). However, despite the above efforts, the approaches employed have several drawbacks which hinder applicability in commercial settings. Chemical processes remain predominantly used in fumarate production because of (a) the cost benefits of chemical production and (b) the complications associated with maintaining the right size of mycelial particles for fumarate production.
Malic acid production has been reported in a wide range of organisms, including both yeast and bacteria (Jantama, K., et al., Biotechnol Bioeng, 99(5):1140-53 (2008); Moon, S. Y., et al., Biochemical Engineering Journal (2008).). Most recently, malic acid titers of up to 59 g/L with yields of 0.42 mol/mol glucose were reported in Saccharomyces cerevisiae . (Zelle, R. M., et al., Appl Environ Microbiol, 74(9):2766-77 (2008)). This level of malic acid production was achieved by introducing three genetic modifications: (i) overexpression of the native pyruvate carboxylase, (ii) increasing the expression of malate dehydrogenase and retargeting it to cytosol, and (iii) functional expression of a heterologous malate transporter gene. Other yeasts in which malic acid has been produced successfully include Aspergillus flavus, Rhizopus arrhizus , and Zygosaccharomyces rouxii . (Zelle, R. M., et al., Appl Environ Microbiol, 74(9):2766-77 (2008)). The highest malic acid titer has been reported in A. flavus (113 g/L) with malic acid yield at 63% of the maximum theoretical yield on glucose. However, potential aflatoxin production has rendered this organism unusable for the production of food-grade malic acid. Malic acid yields with other yeasts are not high enough to pursue commercial production. (Zelle, R. M., et al., Appl Environ Microbiol, 74(9):2766-77 (2008)). Relatively higher malate yields have been reported in a mutant strain of Escherichia coli C (1.4 mol/mol glucose) which was engineered to inhibit secretion of byproducts such as acetate, lactate, formate, and ethanol. (Jantama, K., et al., Biotechnol Bioeng, 99(5):1140-53 (2008)).
This invention is also directed, in part, to methods for producing olefins by decarboxylation an alpha, beta-unsaturated carboxylic acids as exemplified in FIG. 19 a . The unsaturated carboxylic acid substrate can be of any structural olefin geometry. For example the unsaturated carboxylic acid may be substituted at either the alpha or beta position. Additionally, beta-substituted unsaturated carboxylic acid substrates can have either E or Z olefin geometry. The product will typically be a terminal olefin. Furthermore, the carboxylic acid substrate can be further conjugated as shown in FIG. 19 b , wherein pentadienoic acid is decarboxylated to the commercially valuable commodity chemical 1,3-butadiene. 1,3-butadiene is an important chemical in the manufacture of synthetic rubbers, for example.
In some embodiments this invention is directed to methods of producing acrylic acid involving primary metabolic production of fumaric acid, followed by decarboxylation. FIG. 20 shows a biosynthetic scheme for producing acrylic acid which involves treatment of fumaric acid with a decarboxylase enzyme in a pathway leading directly to acrylate, or alternatively through a secondary transformation involving extracellular addition of a decarboxylase to a culture containing over-produced fumarate.
As shown in FIG. 20 , two moles of acrylic acid are produced from each mole of glucose consumed and carbon is utilized in a very efficient manner. Carbon from 1 mole of glucose provides two moles of phosphoenol pyruvate (PEP) through glycolysis, which then reacts with carbon dioxide (via PEP carboxylase or PEP caboxykinase) to afford a maximum theoretical yield of 2.0 moles of fumaric acid, which upon decarboxylation leads to two moles of acrylic acid. This efficient use of carbon is important for achieving high yields (0.8 g acrylic acid/g glucose) and favorable process economics in the production of acrylic acid from renewable feedstocks. In addition, although the final decarboxylation step leads to release of carbon dioxide, the conversion of phosphoenolpyruvate to oxaloacetate actually consumes one mole of carbon dioxide, leading to an overall process that is CO 2 neutral. The decarboxylation of fumarate to acrylate also will drive the equilibrium between malate and fumarate, thus leading to all carbon being funneled to the desired acrylic acid product.
Production of acrylic acid by fermentation involving renewable feedstocks has been investigated previously, and several designs have been proposed (Straathof, A. J. et al., Appl. Microbiol. Biotechnol., 67:727-34 (2005)). In particular, processes involving conversion of lactate or lactoyl-CoA to acrylate or acryloyl-CoA have been explored, but suffer from unfavorable thermodynamics and undesirably high levels of lactate secretion. Another bioprocess for acrylic acid production proceeds through the intermediate 3-hydroxypropionic acid (3-HP), which is produced first by fermentation and then isolated and dehydrated in a second step under anhydrous conditions (Cameron, D. C. and P. F. Suthers WO0242418).
Such two-step routes to acrylic acid via 3-HP have presented challenges and are still under development. Direct conversion of biomass-derived sugars to acrylic acid is highly desirable due to substantial economic benefits associated with reduction in capital and energy costs relative to multi-step processes.
The maximum theoretical yield of each of the acid products described herein is 2 moles per mole of glucose consumed (see equations 1-3 below), indicating a significant potential for improving the existing biochemical processes further.
C 6 H 12 O 6 +2CO 2 →2C 4 H 4 O 4 +2H 2 O(fumaric acid) equation 1
C 6 H 12 O 6 +2CO 2 →2C 4 H 6 O 5 (malic acid) equation 2
C 6 H 12 O 6 →2C 3 H 4 O 2 +2H 2 O (acrylic acid) equation 3
Many different substrates derived from renewable feedstocks, such as glucose, xylose, arabinose, sorbitol, sucrose, glycerol, or even synthesis gas (a mixture carbon monoxide, hydrogen and carbon dioxide), can serve as carbon and energy sources for a fermentation process. Each of these substrates can be used for biological production of fumarate, malate, or acrylate.
As used herein, the term “non-naturally occurring” when used in reference to a microbial organism or microorganism of the invention is intended to mean that the microbial organism has at least one genetic alteration not normally found in a naturally occurring strain of the referenced species, including wild-type strains of the referenced species. Genetic alterations include, for example, modifications introducing expressible nucleic acids encoding metabolic polypeptides, other nucleic acid additions, nucleic acid deletions and/or other functional disruption of the microbial genetic material. Such modifications include, for example, coding regions and functional fragments thereof, for heterologous, homologous or both heterologous and homologous polypeptides for the referenced species. Additional modifications include, for example, non-coding regulatory regions in which the modifications alter expression of a gene or operon. Exemplary metabolic polypeptides include enzymes or proteins within a cyclohexanone biosynthetic pathway.
As used herein, the term “gene disruption,” or grammatical equivalents thereof, is intended to mean a genetic alteration that renders the encoded gene product inactive. The genetic alteration can be, for example, deletion of the entire gene, deletion of a regulatory sequence required for transcription or translation, deletion of a portion of the gene with results in a truncated gene product or by any of various mutation methods that inactivate the encoded gene product. One particularly useful method of gene disruption is complete gene deletion because it reduces or eliminates the occurrence of genetic reversions in the non-naturally occurring eukaryotic organisms of the invention. The term “gene disruption” is also intended to mean a genetic alteration that lowers the activity of a given gene product relative to its activity in a wild-type organism. This attenuation of activity can be due to, for example, a deletion in a portion of the gene which results in a truncated gene product or any of various mutation methods that render the encoded gene product less active than its natural form, replacement or mutation of the promoter sequence leading to lower or less efficient expression of the gene, culturing the organism under a condition where the gene is less highly expressed than under normal culture conditions, or introducing antisense RNA molecules that interact with complementary mRNA molecules of the gene and alter its expression.
A metabolic modification refers to a biochemical reaction that is altered from its naturally occurring state. Therefore, non-naturally occurring microorganisms can have genetic modifications to nucleic acids encoding metabolic polypeptides or, functional fragments thereof. Exemplary metabolic modifications are disclosed herein.
As used herein, the term “isolated” when used in reference to a microbial organism is intended to mean an organism that is substantially free of at least one component as the referenced microbial organism is found in nature. The term includes a microbial organism that is removed from some or all components as it is found in its natural environment. The term also includes a microbial organism that is removed from some or all components as the microbial organism is found in non-naturally occurring environments. Therefore, an isolated microbial organism is partly or completely separated from other substances as it is found in nature or as it is grown, stored or subsisted in non-naturally occurring environments. Specific examples of isolated microbial organisms include partially pure microbes, substantially pure microbes and microbes cultured in a medium that is non-naturally occurring.
As used herein, the terms “microbial,” “microbial organism” or “microorganism” is intended to mean any organism that exists as a microscopic cell that is included within the domains of archaea, bacteria or eukarya. Therefore, the term is intended to encompass prokaryotic or eukaryotic cells or organisms having a microscopic size and includes bacteria, archaea and eubacteria of all species as well as eukaryotic microorganisms such as yeast and fungi. The term also includes cell cultures of any species that can be cultured for the production of a biochemical.
As used herein the term “parent decarboxylase” refers to both wild-type and previously engineered decarboxylases that serve as a starting point for further optimization of the decarboxylation activity. Optimizations can include not only changes made to the nucleic acid sequence encoding the decarboxylase, but also post-translational modifications to the enzyme product.
As used herein the terms “acrylate” and “acrylic acid” are used interchangeably. One skilled in the art will appreciate that the ionization state of a typical carboxylic acid will depend on the pH of its environment. For example, with a pK a of approximately 4, acrylic acid can be significantly in its ionized acrylate form when the pH is 6 or more. While the final isolated product of any given process can be acrylic acid, the direct product of fermentation will frequently be the corresponding acrylate salt, although this can vary depending on the pH conditions employed. In a similar manner, “fumarate” and “fumaric acid,” “malate” and “malic acid,” and “carboxylate” and “carboxylic acid” are used interchangeably.
As used herein, the term “substantially anaerobic” when used in reference to a culture or growth condition is intended to mean that the amount of oxygen is less than about 10% of saturation for dissolved oxygen in liquid media. The term also is intended to include sealed chambers of liquid or solid medium maintained with an atmosphere of less than about 1% oxygen.
“Exogenous” as it is used herein is intended to mean that the referenced molecule or the referenced activity is introduced into the host microbial organism. The molecule can be introduced, for example, by introduction of an encoding nucleic acid into the host genetic material such as by integration into a host chromosome or as non-chromosomal genetic material such as a plasmid. Therefore, the term as it is used in reference to expression of an encoding nucleic acid refers to introduction of the encoding nucleic acid in an expressible form into the microbial organism. When used in reference to a biosynthetic activity, the term refers to an activity that is introduced into the host reference organism. The source can be, for example, a homologous or heterologous encoding nucleic acid that expresses the referenced activity following introduction into the host microbial organism. Therefore, the term “endogenous” refers to a referenced molecule or activity that is present in the host. Similarly, the term when used in reference to expression of an encoding nucleic acid refers to expression of an encoding nucleic acid contained within the microbial organism. The term “heterologous” refers to a molecule or activity derived from a source other than the referenced species whereas “homologous” refers to a molecule or activity derived from the host microbial organism. Accordingly, exogenous expression of an encoding nucleic acid of the invention can utilize either or both a heterologous or homologous encoding nucleic acid.
The non-naturally occurring microbal organisms of the invention can contain stable genetic alterations, which refers to microorganisms that can be cultured for greater than five generations without loss of the alteration. Generally, stable genetic alterations include modifications that persist greater than 10 generations, particularly stable modifications will persist more than about 25 generations, and more particularly, stable genetic modifications will be greater than 50 generations, including indefinitely.
Those skilled in the art will understand that the genetic alterations, including metabolic modifications exemplified herein, are described with reference to a suitable host organism such as E. coli and their corresponding metabolic reactions or a suitable source organism for desired genetic material such as genes for a desired metabolic pathway. However, given the complete genome sequencing of a wide variety of organisms and the high level of skill in the area of genomics, those skilled in the art will readily be able to apply the teachings and guidance provided herein to essentially all other organisms. For example, the E. coli metabolic alterations exemplified herein can readily be applied to other species by incorporating the same or analogous encoding nucleic acid from species other than the referenced species. Such genetic alterations include, for example, genetic alterations of species homologs, in general, and in particular, orthologs, paralogs or nonorthologous gene displacements.
An ortholog is a gene or genes that are related by vertical descent and are responsible for substantially the same or identical functions in different organisms. For example, mouse epoxide hydrolase and human epoxide hydrolase can be considered orthologs for the biological function of hydrolysis of epoxides. Genes are related by vertical descent when, for example, they share sequence similarity of sufficient amount to indicate they are homologous, or related by evolution from a common ancestor. Genes can also be considered orthologs if they share three-dimensional structure but not necessarily sequence similarity, of a sufficient amount to indicate that they have evolved from a common ancestor to the extent that the primary sequence similarity is not identifiable. Genes that are orthologous can encode proteins with sequence similarity of about 25% to 100% amino acid sequence identity. Genes encoding proteins sharing an amino acid similarity less that 25% can also be considered to have arisen by vertical descent if their three-dimensional structure also shows similarities. Members of the serine protease family of enzymes, including tissue plasminogen activator and elastase, are considered to have arisen by vertical descent from a common ancestor.
Orthologs include genes or their encoded gene products that through, for example, evolution, have diverged in structure or overall activity. For example, where one species encodes a gene product exhibiting two functions and where such functions have been separated into distinct genes in a second species, the three genes and their corresponding products are considered to be orthologs. For the production of a biochemical product, those skilled in the art will understand that the orthologous gene harboring the metabolic activity to be introduced or disrupted is to be chosen for construction of the non-naturally occurring microorganism. An example of orthologs exhibiting separable activities is where distinct activities have been separated into distinct gene products between two or more species or within a single species. A specific example is the separation of elastase proteolysis and plasminogen proteolysis, two types of serine protease activity, into distinct molecules as plasminogen activator and elastase. A second example is the separation of mycoplasma 5′-3′ exonuclease and Drosophila DNA polymerase III activity. The DNA polymerase from the first species can be considered an ortholog to either or both of the exonuclease or the polymerase from the second species and vice versa.
In contrast, paralogs are homologs related by, for example, duplication followed by evolutionary divergence and have similar or common, but not identical functions. Paralogs can originate or derive from, for example, the same species or from a different species. For example, microsomal epoxide hydrolase (epoxide hydrolase I) and soluble epoxide hydrolase (epoxide hydrolase II) can be considered paralogs because they represent two distinct enzymes, co-evolved from a common ancestor, that catalyze distinct reactions and have distinct functions in the same species. Paralogs are proteins from the same species with significant sequence similarity to each other suggesting that they are homologous, or related through co-evolution from a common ancestor. Groups of paralogous protein families include HipA homologs, luciferase genes, peptidases, and others.
A nonorthologous gene displacement is a nonorthologous gene from one species that can substitute for a referenced gene function in a different species. Substitution includes, for example, being able to perform substantially the same or a similar function in the species of origin compared to the referenced function in the different species. Although generally, a nonorthologous gene displacement will be identifiable as structurally related to a known gene encoding the referenced function, less structurally related but functionally similar genes and their corresponding gene products nevertheless will still fall within the meaning of the term as it is used herein. Functional similarity requires, for example, at least some structural similarity in the active site or binding region of a nonorthologous gene product compared to a gene encoding the function sought to be substituted. Therefore, a nonorthologous gene includes, for example, a paralog or an unrelated gene.
Therefore, in identifying and constructing the non-naturally occurring microbial organisms of the invention having cyclohexanone biosynthetic capability, those skilled in the art will understand with applying the teaching and guidance provided herein to a particular species that the identification of metabolic modifications can include identification and inclusion or inactivation of orthologs. To the extent that paralogs and/or nonorthologous gene displacements are present in the referenced microorganism that encode an enzyme catalyzing a similar or substantially similar metabolic reaction, those skilled in the art also can utilize these evolutionally related genes.
Orthologs, paralogs and nonorthologous gene displacements can be determined by methods well known to those skilled in the art. For example, inspection of nucleic acid or amino acid sequences for two polypeptides will reveal sequence identity and similarities between the compared sequences. Based on such similarities, one skilled in the art can determine if the similarity is sufficiently high to indicate the proteins are related through evolution from a common ancestor. Algorithms well known to those skilled in the art, such as Align, BLAST, Clustal W and others compare and determine a raw sequence similarity or identity, and also determine the presence or significance of gaps in the sequence which can be assigned a weight or score. Such algorithms also are known in the art and are similarly applicable for determining nucleotide sequence similarity or identity. Parameters for sufficient similarity to determine relatedness are computed based on well known methods for calculating statistical similarity, or the chance of finding a similar match in a random polypeptide, and the significance of the match determined. A computer comparison of two or more sequences can, if desired, also be optimized visually by those skilled in the art. Related gene products or proteins can be expected to have a high similarity, for example, 25% to 100% sequence identity. Proteins that are unrelated can have an identity which is essentially the same as would be expected to occur by chance, if a database of sufficient size is scanned (about 5%). Sequences between 5% and 24% can represent sufficient homology to conclude that the compared sequences are related. Additional statistical analysis to determine the significance of such matches given the size of the data set can be carried out to determine the relevance of these sequences.
Exemplary parameters for determining relatedness of two or more sequences using the BLAST algorithm, for example, can be as set forth below. Briefly, amino acid sequence alignments can be performed using BLASTP version 2.0.8 (Jan. 5, 1999) and the following parameters: Matrix: 0 BLOSUM62; gap open: 11; gap extension: 1; x_dropoff: 50; expect: 10.0; wordsize: 3; filter: on. Nucleic acid sequence alignments can be performed using BLASTN version 2.0.6 (Sep. 16-1998) and the following parameters: Match: 1; mismatch: −2; gap open: 5; gap extension: 2; x_dropoff: 50; expect: 10.0; wordsize: 11; filter: off. Those skilled in the art will know what modifications can be made to the above parameters to either increase or decrease the stringency of the comparison, for example, and determine the relatedness of two or more sequences.
In some embodiments, the invention provides a non-naturally occurring microbial organism, that includes one or more gene disruptions. The disruptions occur in genes encoding an enzyme that is obligatory to coupling fumarate production to growth of the microorganism when the gene disruption reduces the activity of the enzyme, such that the gene disruptions confer stable growth-coupled production of fumarate onto the non-naturally occurring microorganism. In other embodiments, engineered organisms that include one or more gene disruptions can enhance non-growth coupled production fumarate by linking the production of fumarate to energy generation and/or redox balance.
In other embodiments, the disruptions occur in genes encoding an enzyme obligatory to coupling malate production to growth of the microorganism when the gene disruption reduces the activity of the enzyme, such that the gene disruptions confer stable growth-coupled production of malate onto the non-naturally occurring microorganism. Engineered organisms that include one or more gene disruptions can also enhance non-growth coupled production malate by linking the production of malate to energy generation and/or redox balance.
In other embodiments, the invention provides a non-naturally occurring microbial organism that includes one or more gene disruptions. The disruptions occur in genes encoding an enzyme obligatory to coupling acrylate production to growth of the microorganism when the gene disruption reduces the activity of the enzyme, such that the gene disruptions confer stable growth-coupled production of acrylate onto the non-naturally occurring microorganism. In other embodiments, engineered organisms that include one or more gene disruptions can also enhance non-growth coupled production acrylate by linking the production of acrylate to energy generation and/or redox balance.
In some embodiments, the invention provides a non-naturally occurring prokaryotic organism, that includes one or more gene disruptions. The disruptions occur in genes encoding an enzyme obligatory to coupling fumarate production to growth of the microorganism when the gene disruption reduces the activity of the enzyme, such that the gene disruptions confer stable growth-coupled production of fumarate onto the non-naturally occurring microorganism. In other embodiments, an engineered prokaryotic organism that includes one or more gene disruptions can also enhance non-growth coupled production fumarate by linking the production of fumarate to energy generation and/or redox balance.
In other embodiments, the invention provides a non-naturally occurring prokaryotic organism that includes one or more gene disruptions. The disruptions occur in genes encoding an enzyme obligatory to coupling malate production to growth of the microorganism when the gene disruption reduces the activity of the enzyme, such that the gene disruptions confer stable growth-coupled production of malate onto the non-naturally occurring microorganism. In other embodiments, an engineered prokaryotic organism that includes one or more gene disruptions can also enhance non-growth coupled production malate by linking the production of malate to energy generation and/or redox balance.
In still further embodiments, the invention provides a non-naturally occurring prokaryotic organism that includes one or more gene disruptions. The disruptions occur in genes encoding an enzyme obligatory to coupling acrylate production to growth of the organism when the gene disruption reduces the activity of the enzyme, such that the gene disruptions confer stable growth-coupled production of acrylate onto the non-naturally occurring organism. In other embodiments, an engineered prokaryotic organism that includes one or more gene disruptions can also enhance non-growth coupled production acrylate by linking the production of acrylate to energy generation and/or redox balance.
In some embodiments, the invention provides a non-naturally occurring eurakoytic organism, that includes one or more gene disruptions. The disruptions occur in genes encoding an enzyme obligatory to coupling fumarate production to growth of the organism when the gene disruption reduces the activity of the enzyme, such that the gene disruptions confer stable growth-coupled production of fumarate onto the non-naturally occurring organism. In other embodiments, an engineered eukaryotic organism that includes one or more gene disruptions can also enhance non-growth coupled production fumarate by linking the production of fumarate to energy generation and/or redox balance.
In other embodiments, the invention provides a non-naturally occurring eukaryotic organism that includes one or more gene disruptions. The disruptions occur in genes encoding an enzyme obligatory to coupling malate production to growth of the organism when the gene disruption reduces the activity of the enzyme, such that the gene disruptions confer stable growth-coupled production of malate onto the non-naturally occurring organism. In other embodiments, an engineered eukaryotic organism that includes one or more gene disruptions can also enhance non-growth coupled production malate by linking the production of malate to energy generation and/or redox balance.
In still further embodiments, the invention provides a non-naturally occurring eukaryotic organism that includes one or more gene disruptions. The disruptions occur in genes encoding an enzyme obligatory to coupling acrylate production to growth of the organism when the gene disruption reduces the activity of the enzyme, such that the gene disruptions confer stable growth-coupled production of acrylate onto the non-naturally occurring organism. In other embodiments, an engineered eukaryotic organism that includes one or more gene disruptions can also enhance non-growth coupled production acrylate by linking the production of acrylate to energy generation and/or redox balance.
Further, the present invention provides methods of producing such non-naturally prokaryotic or eukaryotic organisms having stable growth-coupled production of fumarate, malate, or acrylate. For fumarate production, for example, the method includes: (a) identifying in silico a set of metabolic modifications requiring fumarate production during cell growth, and (b) genetically modifying a microorganism to contain the set of metabolic modifications requiring fumarate production.
The engineered organisms described herein are useful not only for enhancing growth-coupled production, but they are also well-suited for enhancing non-growth coupled production because they link the production of fumarate, malate and/or acrylate to energy generation and/or redox balance. Exemplary non-growth coupled production methods include implementing an aerobic growth phase followed by an anaerobic production phase. For example, Vemuri et al. J. Ind. Microbiol. Biotechnol., 6:325-332, (2002) describe a dual-phase process for the production of succinate in E. Coli . A similar non-growth couple production process in a strain of Corynebacterium glutamicum has been described (Okino et al., Appl. Microbiol. Biotechnol. 81:459-464 (2008)).
Another such method involves withholding an essential nutrient from a propagated cell culture, thereby limiting growth, but not precluding production as described in Durner et al., Appl. Environ. Microbiol. 8:3408-3414 (2000). Yet another strategy aimed at decoupling growth from production involves replacing the growth substrate with another compound that is more slowly metabolizable as described in Altamirano et al., Biotechnol. Bioeng. 76:351-360 (2001). Growth decoupled-product formation can also be brought about by specific genetic modifications as described in Blombach et al. Appl. Microbiol. Biotechnol. 79:471-479 (2008).
One computational method for identifying and designing metabolic alterations favoring growth-coupled production of a product is the OptKnock computational framework, Burgard et al., Biotechnol Bioeng, 84:647-657 (2003). OptKnock is a metabolic modeling and simulation program that suggests gene disruption strategies that result in genetically stable microorganisms which overproduce the target product. Specifically, the framework examines the complete metabolic and/or biochemical network of a microorganism in order to suggest genetic manipulations that force the desired biochemical to become an obligatory byproduct of cell growth. By coupling biochemical production with cell growth through strategically placed gene deletions or other functional gene disruption, the growth selection pressures imposed on the engineered strains after long periods of time in a bioreactor lead to improvements in performance as a result of the compulsory growth-coupled biochemical production.
The concept of growth-coupled biochemical production can be visualized in the context of the biochemical production envelopes of a typical metabolic network calculated using an in silico model. These limits are obtained by fixing the uptake rate(s) of the limiting substrate(s) to their experimentally measured value(s) and calculating the maximum and minimum rates of biochemical production at each attainable level of growth. Although exceptions exist, typically the production of a desired biochemical is in direct competition with biomass formation for intracellular resources. Thus, enhanced rates of biochemical production will necessarily result in sub-maximal growth rates. The knockouts suggested by OptKnock are designed to restrict the allowable solution boundaries forcing a change in metabolic behavior from the wild-type strain as depicted in FIG. 1 . Although the actual solution boundaries for a given strain will expand or contract as the substrate uptake rate(s) increase or decrease, each experimental point should lie within its calculated solution boundary. Plots such as these enable one to visualize how close strains are to their performance limits or, in other words, how much room is available for improvement. The OptKnock framework has already been able to identify promising gene deletion strategies for biochemical overproduction, (Burgard et al., Biotechnol Bioeng, 84:647-657 (2003); Pharkya et al., Biotechnol Bioeng, 84:887-899 (2003)) and establishes a systematic framework that will naturally encompass future improvements in metabolic and regulatory modeling frameworks. Lastly, when complete gene deletions are constructed there is a negligible possibility of the designed strains reverting to their wild-type states because the genes selected by OptKnock are completely removed from the genome.
Briefly, OptKnock is a term used herein to refer to a computational method and system for modeling cellular metabolism. The OptKnock program relates to a framework of models and methods that incorporate particular constraints into flux balance analysis (FBA) models. These constraints include, for example, qualitative kinetic information, qualitative regulatory information, and/or DNA microarray experimental data. OptKnock also computes solutions to various metabolic problems by, for example, tightening the flux boundaries derived through flux balance models and subsequently probing the performance limits of metabolic networks in the presence of gene additions or deletions. OptKnock computational framework allows the construction of model formulations that enable an effective query of the performance limits of metabolic networks and provides methods for solving the resulting mixed-integer linear programming problems. The metabolic modeling and simulation methods referred to herein as OptKnock are described in, for example, U.S. patent application Ser. No. 10/043,440, filed Jan. 10, 2002, and in International Patent No. PCT/US02/00660, filed Jan. 10, 2002.
Another computational method for identifying and designing metabolic alterations favoring growth-coupled production of a product is metabolic modeling and simulation system termed SimPheny®. This computational method and system is described in, for example, U.S. patent application Ser. No. 10/173,547, filed Jun. 14, 2002, and in International Patent Application No. PCT/US03/18838, filed Jun. 13, 2003.
SimPheny® is a computational system that can be used to produce a network model in silico and to simulate the flux of mass, energy or charge through the chemical reactions of a biological system to define a solution space that contains any and all possible functionalities of the chemical reactions in the system, thereby determining a range of allowed activities for the biological system. This approach is referred to as constraints-based modeling because the solution space is defined by constraints such as the known stoichiometry of the included reactions as well as reaction thermodynamic and capacity constraints associated with maximum fluxes through reactions. The space defined by these constraints can be interrogated to determine the phenotypic capabilities and behavior of the biological system or of its biochemical components. Analysis methods such as convex analysis, linear programming and the calculation of extreme pathways as described, for example, in Schilling et al., J. Theor. Biol. 203:229-248 (2000); Schilling et al., Biotech. Bioeng. 71:286-306 (2000) and Schilling et al., Biotech. Prog. 15:288-295 (1999), can be used to determine such phenotypic capabilities.
As described above, one constraints-based method used in the computational programs applicable to the invention is flux balance analysis. Flux balance analysis is based on flux balancing in a steady state condition and can be performed as described in, for example, Varma and Palsson, Biotech. Bioeng. 12:994-998 (1994). Flux balance approaches have been applied to reaction networks to simulate or predict systemic properties of, for example, adipocyte metabolism as described in Fell and Small, J. Biochem. 138:781-786 (1986), acetate secretion from E. coli under ATP maximization conditions as described in Majewski and Domach, Biotech. Bioeng. 35:732-738 (1990) or ethanol secretion by yeast as described in Vanrolleghem et al., Biotech. Prog. 12:434-448 (1996). Additionally, this approach can be used to predict or simulate the growth of S. cerevisiae on a variety of single-carbon sources as well as the metabolism of H. influenzae as described in Edwards and Palsson, Proc. Natl. Acad. Sci. 97:5528-5533 (2000), Edwards and Palsson, J. Bio. Chem. 274:17410-17416 (1999) and Edwards et al., Nature Biotech. 19:125-130 (2001).
Once the solution space has been defined, it can be analyzed to determine possible solutions under various conditions. This computational approach is consistent with biological realities because biological systems are flexible and can reach the same result in many different ways. Biological systems are designed through evolutionary mechanisms that have been restricted by fundamental constraints that all living systems must face. Therefore, constraints-based modeling strategy embraces these general realities. Further, the ability to continuously impose further restrictions on a network model via the tightening of constraints results in a reduction in the size of the solution space, thereby enhancing the precision with which physiological performance or phenotype can be predicted.
Given the teachings and guidance provided herein, those skilled in the art will be able to apply various computational frameworks for metabolic modeling and simulation to design and implement growth-coupled production of a biochemical product. Such metabolic modeling and simulation methods include, for example, the computational systems exemplified above as SimPheny® and OptKnock. For simplicity in illustrating the invention, the methods and strains will be described herein with reference to the OptKnock computation framework for modeling and simulation. Those skilled in the art will know how to apply the identification, design and implementation of the metabolic alterations using OptKnock to any of such other metabolic modeling and simulation computational frameworks and methods well known in the art.
The ability of a cell or organism to obligatory couple growth to the production of a biochemical product can be illustrated in the context of the biochemical production limits of a typical metabolic network calculated using an in silico model. These limits are obtained by fixing the uptake rate(s) of the limiting substrate(s) to their experimentally measured value(s) and calculating the maximum and minimum rates of biochemical production at each attainable level of growth. As shown in FIG. 1 , the production of a desired biochemical generally is in direct competition with biomass formation for intracellular resources. Under these circumstances, enhanced rates of biochemical production will necessarily result in sub-maximal growth rates. The knockouts suggested by the above metabolic modeling and simulation programs such as OptKnock are designed to restrict the allowable solution boundaries forcing a change in metabolic behavior from the wild-type strain as depicted in FIG. 1 . Although the actual solution boundaries for a given strain will expand or contract as the substrate uptake rate(s) increase or decrease, each experimental point will lie within its calculated solution boundary. Plots such as these enable accurate predictions of how close the designed strains are to their performance limits which also indicates how much room is available for improvement.
The OptKnock mathematical framework is exemplified herein for pinpointing gene deletions leading to growth-coupled biochemical production as illustrated in FIG. 1 . The procedure builds upon constraint-based metabolic modeling which narrows the range of possible phenotypes that a cellular system can display through the successive imposition of governing physico-chemical constraints, Price et al., Nat Rev Microbiol, 2: 886-97 (2004). As described above, constraint-based models and simulations are well known in the art and generally invoke the optimization of a particular cellular objective, subject to network stoichiometry, to suggest a likely flux distribution.
Briefly, the maximization of a cellular objective quantified as an aggregate reaction flux for a steady state metabolic network comprising a set N={1 . . . , N} of metabolites and a set M={1, . . . , M}of metabolic reactions is expressed mathematically as follows:
maximize
v
cellular
objective
subject
to
∑
j
=
1
M
S
ij
v
j
=
0
,
∀
∈
N
v
substrate
=
v
subsirate_uptake
m
mol
/
gDW
·
hr
∀
∈
{
limiting
substrate
(
s
)
}
v
atp
≥
v
atp_main
m
mol
/
gDW
·
hr
v
j
≥
0
,
∀
∈
{
irrev
.
reactions
}
where S ij is the stoichiometric coefficient of metabolite i in reaction j, v j is the flux of reaction j, V substrate — uptake represents the assumed or measured uptake rate(s) of the limiting substrate(s), and v atp — main is the non-growth associated ATP maintenance requirement. The vector v includes both internal and external fluxes. In this study, the cellular objective is often assumed to be a drain of biosynthetic precursors in the ratios required for biomass formation, Neidhardt, F. C. et al., 2nd ed. 1996, Washington, D.C.: ASM Press. 2 v. (xx, 2822, lxxvi). The fluxes are generally reported per 1 gDW·hr (gram of dry weight times hour) such that biomass formation is expressed as g biomass produced/gDW·hr or l/hr.
The modeling of gene deletions, and thus reaction elimination, first employs the incorporation of binary variables into the constraint-based approach framework, Burgard et al., Biotechnol Bioeng, 74: 364-375 (2001), Burgard et al., Biotechnol Prog, 17: 791-797 (2001). These binary variables,
y
j
=
{
1
,
if
reaction
flux
v
j
is
active
0
,
if
reaction
flux
v
j
is
not
active
,
∀
∈
M
assume a value of 1 if reaction j is active and a value of 0 if it is inactive. The following constraint,
v
j
min
·y
j
≧b
j
≧v
j
next
·y
i
,∀jεM
ensures that reaction flux v j is set to zero only if variable y j is equal to zero. Alternatively, when y j is equal to one, v j is free to assume any value between a lower v j min and an upper v j max bound. Here, v j min and v j max are identified by minimizing and maximizing, respectively, every reaction flux subject to the network constraints described above, Mahadevan et al., Metab Eng, 5: 264-76 (2003).
Optimal gene/reaction knockouts are identified by solving a bilevel optimization problem that chooses the set of active reactions (y j =1) such that an optimal growth solution for the resulting network overproduces the chemical of interest. Schematically, this bilevel optimization problem is illustrated in FIG. 2 . Mathematically, this bilevel optimization problem is expressed as the following bilevel mixed-integer optimization problem:
maximize
y
j
v
chemical
(
OptKnock
)
(
subject
to
v
j
maximize
v
biomass
subject
to
∑
j
=
1
M
S
ij
v
j
=
0
,
∀
∈
N
v
substrate
=
v
substrate_uptake
∀
∈
{
limiting
substrate
(
s
)
}
v
atp
≥
v
atp_main
v
biomass
≥
v
biomass
target
)
v
j
min
·
y
j
≤
v
j
≤
v
j
max
·
y
j
,
∀
j
∈
M
∑
j
∈
M
forward
(
1
-
y
j
)
=
K
y
j
∈
{
0
,
1
}
,
∀
j
∈
M
where v chemical is the production of the desired target product, for example fumarate or other biochemical product, and K is the number of allowable knockouts. Note that setting K equal to zero returns the maximum biomass solution of the complete network, while setting K equal to one identifies the single gene/reaction knockout (y j =0) such that the resulting network involves the maximum overproduction given its maximum biomass yield. The final constraint ensures that the resulting network meets a minimum biomass yield. Burgard et al., Biotechnol Bioeng, 84: 647-57 (2003), provide a more detailed description of the model formulation and solution procedure. Problems containing hundreds of binary variables can be solved in the order of minutes to hours using CPLEX 8.0, GAMS: The Solver Manuals. 2003: GAMS Development Corporation, accessed via the GAMS, Brooke et al., GAMS Development Corporation (1998), modeling environment on an IBM RS6000-270 workstation. The OptKnock framework has already been able to identify promising gene deletion strategies for biochemical overproduction, Burgard et al., Biotechnol Bioeng, 84: 647-57 (2003), Pharkya et al., Biotechnol Bioeng, 84: 887-899 (2003), and establishes a systematic framework that will naturally encompass future improvements in metabolic and regulatory modeling frameworks.
Any solution of the above described bilevel OptKnock problem will provide one set of metabolic reactions to disrupt. Elimination of each reaction within the set or metabolic modification can result in fumarate as an obligatory product during the growth phase of the organism. Because the reactions are known, a solution to the bilevel OptKnock problem also will provide the associated gene or genes encoding one or more enzymes that catalyze each reaction within the set of reactions. Identification of a set of reactions and their corresponding genes encoding the enzymes participating in each reaction is generally an automated process, accomplished through correlation of the reactions with a reaction database having a relationship between enzymes and encoding genes.
Once identified, the set of reactions that are to be disrupted in order to achieve increased fumarate, malate, or acrylate production are implemented in the target cell or organism by functional disruption of at least one gene encoding each metabolic reaction within the set. As described previously, one particularly useful means to achieve functional disruption of the reaction set is by deletion of each encoding gene. However, in some instances, it can be beneficial to disrupt the reaction by other genetic aberrations including, for example, mutation, deletion of regulatory regions such as promoters or cis binding sites for regulatory factors, or by truncation of the coding sequence at any of a number of locations. These latter aberrations, resulting in less than total deletion of the gene set can be useful, for example, when rapid assessments of the product coupling are desired or when genetic reversion is less likely to occur.
To identify additional productive solutions to the above described bilevel OptKnock problem which lead to further sets of reactions to disrupt or metabolic modifications that can result in the growth-coupled production of fumarate, malate, acrylate, or other biochemical products, an optimization method, termed integer cuts, can be implemented. This method proceeds by iteratively solving the OptKnock problem exemplified above with the incorporation of an additional constraint referred to as an integer cut at each iteration. Integer cut constraints effectively prevent the solution procedure from choosing the exact same set of reactions identified in any previous iteration that obligatory couples product biosynthesis to growth. For example, if a previously identified growth-coupled metabolic modification specifies reactions 1, 2, and 3 for disruption, then the following constraint prevents the same reactions from being simultaneously considered in subsequent solutions: y 1 +y 2 +y 3 ≧1. The integer cut method is well known in the art and can be found described in, for example, reference, Burgard et al., Biotechnol Prog, 17:791-797 (2001). As with all methods described herein with reference to their use in combination with the OptKnock computational framework for metabolic modeling and simulation, the integer cut method of reducing redundancy in iterative computational analysis also can be applied with other computational frameworks well known in the art including, for example, SimPheny.
Constraints of the above form preclude identification of larger reaction sets that include previously identified sets. For example, employing the integer cut optimization method above in a further iteration would preclude identifying a quadruple reaction set that specified reactions 1, 2, and 3 for disruption since these reactions had been previously identified. To ensure identification of all possible reaction sets leading to growth-coupled production of a product, a modification of the integer cut method was employed.
Briefly, the modified integer cut procedure begins with iteration ‘zero’ which calculates the maximum production of the desired biochemical at optimal growth for a wild-type network. This calculation corresponds to an OptKnock solution with K equaling 0. Next, single knockouts are considered and the two parameter sets, objstore iter and ystore iter,j , are introduced to store the objective function (v chemical ) and reaction on-off information (y j ), respectively, at each iteration, (y j ). The following constraints are then successively added to the OptKnock formulation at each iteration.
v chemical ≧objstore iter +ε−M·Σ jεystore iter,j =0 y j
In the above equation, ε and M are a small and a large numbers, respectively. In general, ε can be set at about 0.01 and M can be set at about 1000. However, numbers smaller and/or larger then these numbers also can be used. M ensures that the constraint can be binding only for previously identified knockout strategies, while ε ensures that adding knockouts to a previously identified strategy must lead to an increase of at least ε in biochemical production at optimal growth. The approach moves onto double deletions whenever a single deletion strategy fails to improve upon the wild-type strain. Triple deletions are then considered when no double deletion strategy improves upon the wild-type strain, and so on. The end result is a ranked list, represented as desired biochemical production at optimal growth, of distinct deletion strategies that differ from each other by at least one knockout. This optimization procedure as well as the identification of a wide variety of reaction sets that, when disrupted, lead to increased production of a biochemical product are exemplified in detail further below. Given the teachings and guidance provided herein, those skilled in the art will understand that the methods and metabolic engineering designs exemplified herein are applicable to linking cell or microorganism growth to any biochemical product.
Employing the methods exemplified above, one can construct cells and organisms that obligatorily couple the production of a target biochemical product to growth of the cell or organism engineered to harbor the identified genetic alterations. In this regard, metabolic alterations have been identified that obligatorily couple the production of fumarate, malate, or acrylate to organism growth. Prokaryotic or eukaryotic organism strains constructed with the identified metabolic alterations produce elevated levels of fumarate, malate, or acrylate during the exponential growth phase. These strains can be beneficially used for the commercial production of fumarate, malate, or acrylate in continuous fermentation process without being subjected to the negative selective pressures described previously.
As described above, the metabolic alterations also enable non-growth coupled production of fumarate, malate, or acrylate. The invention is described herein with general reference to the metabolic reaction, reactant or product thereof, or with specific reference to one or more genes associated with the referenced metabolic reaction, reactant or product. Unless otherwise expressly stated herein, those skilled in the art will understand that reference to a reaction also constitutes reference to the reactants and products of the reaction. Similarly, unless otherwise expressly stated herein, reference to a reactant or product also references the reaction and that reference to any of these metabolic constitutes also references the gene or genes encoding the enzymes that catalyze the referenced reaction, reactant or product. Likewise, given the well known fields of metabolic biochemistry, enzymology and genomics, reference herein to a gene also constitutes a reference to the corresponding encoded enzyme and the reaction it catalyzes as well as the reactants and products of the reaction.
The methods of the invention provide a set of metabolic modifications that are identified by an in silico method selected from OptKnock. The set of metabolic modifications can include functional disruption of one or more metabolic reactions including, for example, disruption by gene deletion. Exemplary reactions, reaction nomenclature, reactants, products, cofactors and genes encoding enzymes catalyzing a reaction involved in the growth-coupled production of fumarate and malate in E. Coli are set forth in Tables 1, 2, 3, and 4.
The invention provides non naturally occurring microorganisms having increased production of fumarate or malate. Fumarate or malate production can be obligatorily linked to the exponential growth phase of the microorganism by genetically altering the metabolic pathways of the cell. The genetic alterations make fumarate an obligatory product during the growth phase. In some embodiments, fumarate or malate production is not obligatorily linked to growth. In such a case, the production of fumarate or malate takes place during a non-growth phase, for example. Sets of metabolic alterations or transformations that result in elevated levels of fumarate or malate biosynthesis are exemplified in Tables 1 and 2, respectively. Each alteration within a set corresponds to the requisite metabolic reaction that can be functionally disrupted. Functional disruption of all reactions within each set results increased production of fumarate or malate by the engineered strain. The corresponding reactions to the referenced alterations in Tables 1 and 2, and the gene or genes that potentially encode them in E. coli , are set forth in Table 3.
For example, for each strain exemplified in Table 1, the metabolic alterations that can be generated for increased fumarate production are shown in each row. These alterations include the functional disruption of from one to six or more reactions. In particular, 348 strains are exemplified in Table 1 that have non-naturally occurring metabolic genotypes. Each of these non-naturally occurring alterations result in an enhanced level of fumarate production during the exponential growth phase of the microorganism compared to a wild-type strain, under appropriate culture conditions. Appropriate conditions include, for example, those exemplified further below in the Example I such as particular carbon sources or reactant availabilities and/or adaptive evolution.
One such strain design for fumarate production involves deletions in fumarate reductase (FRD), alcohol dehydrogenase (ADHEr), lactate dehydrogenase (LDH_D), and glutamate dehydrogenase (GLUDy). This strain is predicted to have a growth-coupled yield of 1.83 moles of fumarate per mole of glucose consumed and the maximum growth rate is anticipated to be 0.09/hr as shown in FIG. 2 . The deletion of FRD, ADHEr, and LDH_D prevents the formation and secretion of byproducts, namely succinate, ethanol and lactate. The elimination of glutamate dehydrogenase that transaminates alpha-ketoglutarate into glutamate with the utilization of a molecule of NADPH, disrupts a loop of reactions that form and use NADPH for synthesis of amino acids such as alanine and valine. All the disruptions can be implemented sequentially based on the necessity to do so. FIG. 2 shows the growth-coupled fumarate production characteristics of the strain (black, dashed) incorporating these disruptions compared with those of the wild-type E. coli network (black, at the maximum rate of growth, the wild-type network is not expected to form any fumarate.)
Another strain, shown in FIG. 3 , has three common deletions with the strain shown in FIG. 2 and involves elimination of malic enzyme (ME2) and transhydrogenase (THD2) activity additionally. Malic enzyme catalyzes the decarboxylation of malate to form pyruvate with the concomitant reduction of a molecule of NADP to form NADPH. Transhydrogenase catalyzes the oxidation of NADH causing the reduction of NADP into NADPH. The deletion of the NADPH-forming malic enzyme and the membrane-bound proton-translocating transhydrogenase catalyzed by PntAB prevents or reduces the formation of NADPH, thus preventing or reducing carbon from being funneled into amino acids instead of being converted into fumarate. The efficacy of the two latter knockouts for fumarate production can be assessed and implemented sequentially based on the necessity to do so.
The strain of FIG. 3 is expected to have a maximum growth-coupled yield of 1.87 moles of fumarate per mole of glucose consumed at an expected maximum growth rate of 0.08/hr. Note also that the strain is has a minimum theoretical product yield of 0.48 moles per mole of glucose (the grey point on the black, dotted curve). FIG. 3 shows the growth-coupled fumarate production characteristics of the strain (black, dotted) compared with those of the wild-type E. coli network (black). The grey point shows the minimum amount of product formation expected from this strain.
An additional disruption in PFL (pyruvate formate lyase) can improve the theoretical yield of fumarate marginally to 1.89 moles per mole of glucose consumed and the expected growth rate of this strain is 0.07 per hour.
Another strain, shown in FIG. 4 , disrupts the GLCpts mechanism of glucose transport and instead relies on hexokinase activity. This disruption along with disruption of FRD, ADHEr, LDH_D, and ME2 leads to an expected maximum growth rate for the strain at approximately 0.1 per hour. The product yield is expected to be 1.82 moles per mole of glucose consumed. The strain is expected to start producing fumarate once it reaches approximately 36% of its maximum theoretical biomass formation rate. FIG. 4 shows the production curve for this strain (grey, dashed) compared with the production curve for the wild-type E. coli network (black). Note that this strain is equivalent to the strain of FIG. 2 if an additional deletion in THD2 is introduced.
Another strain, shown in FIG. 5 , has deletions in FRD, ADHEr, LDH_D, ME2, THD2 and HEX1. The deletion in HEX1 forces glucose flux through the PTS system, converting an equivalent molar amount of phosphoenolpyruvate (PEP) into pyruvate. To attain a balance of cofactors, the network is forced to convert most of the pyruvate back into PEP through PEP synthase. This is an energy-intensive step and limits the biomass formation in the network. However, the carbon distribution provides PEP to be used by PPCK and subsequent channeling into the reductive TCA cycle. This leads to the very high fumarate yields in the network of up to 1.97 moles per mole of glucose consumed as shown in FIG. 5 . These disruptions reduce the feasible solution space of the mutant network significantly and the strain is expected to have a minimum product yield of at least 1.25 moles per mole of glucose consumed as shown by the black point in FIG. 5 . Although strain is predicted to grow slowly at a rate of approximately 0.02 per hour, the prospect of achieving near maximum theoretical product yields makes this design particularly useful. The strain is expected to secrete very small quantities of acetate and formate. FIG. 5 shows the production curve for the strain (grey, dashed) compared with the production curve of the wild type E. coli network (black). The black point indicates the minimum amount of product formation expected from this strain.
To provide a comparison of the fumarate production characteristics of the four strains discussed above, the production curves are presented on the same plot and compared with those of the wild-type E. coli network as shown in FIG. 6 . Other strains for fumarate production in E. Coli are listed in Table 1. FIG. 6 shows the production curves for the strains in 1) black, dashed, 2) black, dotted, 3) grey, dashed and 4) grey compared with each other and with the production characteristics of the wild-type E. coli network in black. Note the reduction in feasible solution space as additional deletions are imposed on the network.
The anaerobic designs for the formation of malate are described below and utilize disruptions that have already been described for fumarate production. The strain designs for malate production have additional knockouts that preclude fumarate formation in the network.
One strain, shown in FIG. 7 , allows for increased formation of malate by building upon the disruptions in the strain of FIG. 2 . As described above, deletions in ADHEr, LDH_D, FRD, ME2 and THD2 allow for the enhanced formation of either fumarate or malate. An additional deletion in fumarase (FUM) prevents or reduces the conversion of malate into fumarate, leading to increase malate production of 1.86 moles per mole of glucose consumed as shown in FIG. 7 . Small modifications in this strain lead to another high-yielding strain shown in FIG. 8 . Thus, instead of the FRD deletion, this strain has a disruption in aspartase (ASPT). The deletion of ASPT reinforces the effect of the fumarase deletion by preventing the network from converting oxaloacetate into aspartate which can subsequently be transformed into fumarate via aspartase. Without the deletion in ASPT, the strain can produce approximately 1.55 moles of succinate per mole of glucose consumed. This modified strain design with deletions in ADHEr, THD2, LDH_D, ME2, FUM, and ASPT leads to a growth-coupled theoretical yield of 1.85 moles of malate per mole of glucose consumed, shown in FIG. 8 , with an expected growth rate of 0.08 per hour. Each of these strains is expected to have a non-zero minimum rate of malate production. Note the grey and black points in FIGS. 7 and 8 respectively. Several other strains with increased malate yields in E. Coli have been identified and are listed in Table 2.
Based on these strains, the invention also provides a non-naturally occurring microorganism having a set of metabolic modifications coupling fumarate or malate production to growth of the microorganism, the set of metabolic modifications includes disruption of one or more genes selected from the set of genes encoding proteins that include: (a) a fumarate reductase (FRD), an alcohol dehydrogenase (ADHEr), and a lactate dehydrogenase (LDH_D).
Analysis of the strains for fumarate production allows identification of a minimum set of deletions that increase fumarate production in the network. Note that PPCK was assumed to be reversible in the network. Briefly, deletions in fumarate reductase (FRD), alcohol dehydrogenase (ADHEr), and lactate dehydrogenase (LDH_D) prevent the formation of competing byproducts, namely, succinate, ethanol and lactate. The minimum enzyme disruption set based on the aforementioned strains includes disruption of fumarate reductase, alcohol dehydrogenase and lactate dehydrogenase. This corresponds to the following minimal exemplary gene disruption set:
frd (b4151 or b4152 or b4153 or b4154), adhE (b1421), and ldhA (b1380)
Additional disruptions have been identified by the OptKnock framework for the increased formation of fumarate. Note that these disruptions may have been predicted because no regulatory information is accounted for in the metabolic network. Nevertheless, it is predicted that supplementary disruptions or deletions in one or more of the functionalities, namely glutamate dehydrogenase (GLUDy), malic enzyme (ME2), and transhydrogenase (THD2) are useful for increased formation of the diacids of interest. These deletions can be introduced sequentially into E. coli K12. If these deletions/dirsuptions have to be introduced, the minimal set of activities that need to be deleted can be expanded to include the following:
Fumarate reductase, alcohol dehydrogenase, lactate dehydrogenase, and glutamate dehydrogenase, or
Fumarate reductase, alcohol dehydrogenase, lactate dehydrogenase, and malic enzyme, or
Fumarate reductase, alcohol dehydrogenase, lactate dehydrogenase, malic enzyme, and transhydrogenase
Correspondingly, the minimal gene set can be expanded to yield:
frd (b4151 or b4152 or b4153 or b4154), adhE (b1421), ldhA (b1380), and gdhA (b1761), or
frd (b4151 or b4152 or b4153 or b4154), adhE (b1421), ldhA (b1380), and maeB (b2463), or
frd (b4151 or b4152 or b4153 or b4154), adhE (b1421), ldhA (b1380), pntAB (b1602, b1603), and maeB (b2463)
Further improvement in yields can be attained by disrupting one or more of the following functionalities: phosphotransacetylase (PTAr), the PTS mechanism of glucose transport (GLCpts), hexokinase (HEX 1) or pyruvate formate lyase (PFL). Note that all the isozymes capable of carrying out a given activity should be disrupted or deleted given a possibility of the isozymes becoming active due to adaptive evolution. The enzyme disruption set after introducing these auxiliary deletions are listed below:
Fumarate reductase, alcohol dehydrogenase, lactate dehydrogenase, transhydrogenase, malic enzyme, and hexokinase, or
Fumarate reductase, alcohol dehydrogenase, lactate dehydrogenase, malic enzyme, and the PTS transport mechanism of glucose, or
Fumarate reductase, alcohol dehydrogenase, lactate dehydrogenase, transhydrogenase, malic enzyme, and pyruvate formate lyase
The corresponding gene deletion sets are:
frd (b4151 or b4152 or b4153 or b4154), adhE (b1421), ldhA (b1380), pntAB (b1602, b1603), maeB (b2463) and glk (b2388)
frd (b4151 or b4152 or b4153 or b4154), adhE (b1421), ldhA (b1380), maeB (b2463), and pts (b1101 or b2415 or b2416 or b2417)
frd (b4151 or b4152 or b4153 or b4154), adhE (b1421), ldMA (b1380), pntAB (b1602, b1603), maeB (b2463), and pflAB (b0902, b0903)
For homomalate production, a disruption in fumarase (FUM) is utilized in addition to disruptions in alcohol dehydrogenase (ADHEr), lactate dehydrogenase (LDH_D) and fumarate reductase (FRD). Thus, the minimal enzyme deletion set is:
Fumarate reductase, alcohol dehydrogenase, lactate dehydrogenase, and fumarase
The disruption of these activities corresponds to the deletion of the following genes:
frd (b4151 or b4152 or b4153 or b4154), adhE (b1421), ldha (b1380), and fumABC (b1611, b1612, b4122)
An alternative set of enzyme deletions can also enable homomalate production is as follows:
Alcohol dehydrogenase, lactate dehydrogenase, fumarase and L-aspartase
This corresponds to a minimum gene deletion set of:
adhE (b1421), ldhA (b1380), and fumABC (b1611, b1612, b4122) and aspA (b4139)
Thus, in some embodiments, the present invention provides a non-naturally occurring microbial organism that includes one or more gene disruptions occurring in genes encoding enzymes that increase homomalate production when the gene disruption reduces an activity of the enzyme, whereby the one or more gene disruptions confers increased production of homomalate onto said non-naturally occurring microorganism.
However, as explained earlier for fumarate production, disruptions in one or more out of the following reactions, glutamate dehydrogenase (GLUDy), transhydrogenase (THD2) and malic enzyme (ME2), can be useful, yielding the following minimal enzyme sets for deletion:
Fumarate reductase, alcohol dehydrogenase, lactate dehydrogenase, fumarase, and glutamate dehydrogenase, or
Fumarate reductase, alcohol dehydrogenase, lactate dehydrogenase, fumarase, and malic enzyme, or
Fumarate reductase, alcohol dehydrogenase, lactate dehydrogenase, fumarase, transhydrogenase and malic enzyme
Accordingly, the gene deletion sets expand and are listed below:
frd(b4151 or b4152 or b4153 or b4154), adhE (b1421), ldha (b1380),fumABC (b1611, b1612, b4122), and gdhA (b1761), or
frd(b4151 or b4152 or b4153 or b4154), adhE (b1421), ldha (b1380),fumABC (b1611, b1612, b4122), and maeB (b2463), or
frd(b4151 or b4152 or b4153 or b4154), adhE (b1421), ldhA (b1380),fumABC (b1611, b1612, b4122), pntAB (b1602, b1603), and maeB (b2463).
Each of these strains may be supplemented with additional deletions if it is determined that the strain does not sufficiently increase the formation of the product. Alternatively, some other enzymes not known to possess significant activity may become active due to adaptive evolution or random mutagenesis and they will also have to be disrupted as well. For example, succinate dehydrogenase which oxidizes succinate to fumarate and is known to be active only under aerobic conditions may assume significant activity even under anaerobic conditions and may have to be disrupted. However, the list of gene disruption sets provided here serves as a starting point for construction of high-yielding malate and fumarate producing strains.
For fumarate and malate production metabolic modifications in eukarotic organisms sets of metabolic modifications are listed in Table 5. For acrylate production metabolic modifications in eukaryotic organisms can be selected from the set of metabolic modifications listed in Table 6.
The non-naturally occurring eukaryotic organism can have one or more gene disruptions included in a metabolic modification listed in Tables 5 or 6. The one or more gene disruptions can be a deletion. The non-naturally occurring eukaryotic organism of the invention can be selected from a group of eukaryotic organism having a metabolic modification listed in Tables 5 or 6. Non-naturally occurring eukaryotic organisms of the invention include yeast, fungus, or any of a variety of other microorganisms applicable to fermentation processes. Exemplary eukaryotic species include those selected from Saccharomyces cerevisiae, Schizosaccharomyces pombe, Kluyveromyces lactis, Kluyveromyces marxianus, Aspergillus terreus, Aspergillus niger, Rhizopus arrhizus, Rhizopus oryzae , and Pichia pastoris.
The eukaryotic organisms having increased fumarate, malate, or acrylate production are exemplified herein with reference to an S. cerevisiae genetic background. However, with the complete genome sequence available for now more than 550 species (with more than half of these available on public databases such as the NCBI), including 395 microorganism genomes and a variety of yeast, fungi, plant, and mammalian genomes, the identification of an alternate species homolog for one or more genes, including for example, orthologs, paralogs and nonorthologous gene displacements, and the interchange of genetic alterations between organisms is routine and well known in the art. Accordingly, the metabolic alterations enabling increased production of the products described herein with reference to a particular organism such as S. cerevisiae can be readily applied to other microorganisms, especially other eukaryotic organisms. Given the teachings and guidance provided herein, those skilled in the art will know that a metabolic alteration exemplified in one organism can be applied equally to other organisms.
As described previously, homologues can include othologs and/or nonorthologous gene displacements. In some instances, such as when a substitute metabolic pathway exists in the species of interest, functional disruption can be accomplished by, for example, deletion of a paralog that catalyzes a similar, yet non-identical metabolic reaction which replaces the referenced reaction. Because there are differences among metabolic networks between different organisms, those skilled in the art will understand that the actual genes disrupted between different organisms may differ. However, given the teachings and guidance provided herein, those skilled in the art also will understand that the methods of the invention can be applied to all microorganisms to identify the cognate metabolic alterations between organisms and to construct an organism in a species of interest that will enhance the coupling of fumarate, malate, or acrylate biosynthesis to growth.
As described previously and further below, exemplary reactions, reaction nomenclature, reactants, products, cofactors and genes encoding enzymes catalyzing a reaction involved in the increased production of fumarate, malate, and acrylate in S. Cerevisiae are set forth in Tables 5, 6, 7, and 8.
The invention provides non naturally occurring eukaryotic organisms having growth-coupled production of fumarate, malate, or acrylate. Product production can be optionally obligatorily linked to the exponential growth phase of the microorganism by genetically altering the metabolic pathways of the cell. The genetic alterations can make the formation of the desired product obligatory to growth. Sets of metabolic alterations or transformations that result in elevated levels of fumarate, malate, or acrylate biosynthesis are exemplified in Tables 5 and 6, respectively. Each alteration within a set corresponds to the requisite metabolic reaction that should be functionally disrupted. Functional disruption of all reactions within each set results in the obligatory production of fumarate, malate, or acrylate by the engineered strain during the growth phase. The corresponding reactions to the referenced alterations in Tables 5 and 6, and the gene or genes that potentially encode them in S. cerevisiae , are set forth in Table 7.
For example, for each strain exemplified in Table 5, the metabolic alterations that can be generated for increase fumarate or malate production are shown in each row. These alterations include the functional disruption of from one to six or more reactions. In particular, 278 strains are exemplified in Table 5 that have non-naturally occurring metabolic genotypes. Each of these non-naturally occurring alterations result in an enhanced level of fumarate or malate production in the eukaryotic organism compared to a wild-type strain, under appropriate culture conditions. Appropriate conditions include, for example, those exemplified further below in the Example II such as particular carbon sources or reactant availabilities and/or adaptive evolution. Similarly, 495 strains are exemplified in Table 6 that have non-naturally occurring metabolic genotypes. Each of these non-naturally occurring alterations result in an enhanced level of acrylate production during the exponential growth phase of the eukaryotic organism compared to a wild-type strain, under appropriate culture conditions.
Given the teachings and guidance provided herein, those skilled in the art will understand that to disrupt an enzymatic reaction it is necessary to disrupt the catalytic activity of the one or more enzymes involved in the reaction. Disruption can occur by a variety of means including, for example, deletion of an encoding gene or incorporation of a genetic alteration in one or more of the encoding gene sequences as described previously in reference to the disruptions for E. Coli . The encoding genes targeted for disruption can be one, some, or all of the genes encoding enzymes involved in the catalytic activity. For example, where a single enzyme is involved in a targeted catalytic activity disruption can occur by a genetic alteration that reduces or destroys the catalytic activity of the encoded gene product. Similarly, where the single enzyme is multimeric, including heteromeric, disruption can occur by a genetic alteration that reduces or destroys the function of one or all subunits of the encoded gene products. Destruction of activity can be accomplished by loss of the binding activity of one or more subunits in order to form an active complex, by destruction of the catalytic subunit of the multimeric complex or by both. Other functions of multimeric protein association and activity also can be targeted in order to disrupt a metabolic reaction of the invention. Such other functions are well known to those skilled in the art. Further, some or all of the functions of a single polypeptide or multimeric complex can be disrupted according to the invention in order to reduce or abolish the catalytic activity of one or more enzymes involved in a reaction or metabolic modification of the invention. Similarly, some or all of enzymes involved in a reaction or metabolic modification of the invention can be disrupted so long as the targeted reaction is destroyed.
Given the teachings and guidance provided herein, those skilled in the art also will understand that an enzymatic reaction can be disrupted by reducing or eliminating reactions encoded by a common gene and/or by one or more orthologs of that gene exhibiting similar or substantially the same activity. Reduction of both the common gene and all orthologs can lead to complete abolishment of any catalytic activity of a targeted reaction. However, disruption of either the common gene or one or more orthologs can lead to a reduction in the catalytic activity of the targeted reaction sufficient to promote coupling of growth to product biosynthesis. Exemplified herein are both the common genes encoding catalytic activities for a variety of metabolic modifications as well as their orthologs. Those skilled in the art will understand that disruption of some or all of the genes encoding an enzyme of a targeted metabolic reaction can be practiced in the methods of the invention and incorporated into the non-naturally occurring eukaryotic organisms of the invention in order to achieve the growth-coupled product production.
Herein below are described the designs identified for increasing fumarate, malate, and acrylate production in S. cerevisiae . For prediction of the strains, it was assumed that (i) the glucose uptake rate in the network was 10 mmol/gDCW.hr, (ii) a minimum non-growth associated maintenance requirement of 1 mmol/gDCW.hr was imposed upon the network, and
(iii) phosphoenolpyruvate carboxykinase (PPCK) could operate in the carbon-fixing direction towards oxaloacetate. The reversibility of PPCK allows for the fixing of carbon dioxide such that a yield of 2 moles per mole of glucose for each of these products can be attained under microaerobic/anaerobic conditions. More importantly, it allows for production of ATP in the process. The ATP generation accompanying the reverse operability of PPCK supports the energy requirements for biomass formation as well as for product formation and export under anaerobic conditions. Note that the production of fumaric, malic and acrylic acids is otherwise energetically neutral in the S. cerevisiae metabolic network. The native PPCK in S. cerevisiae , encoded by Pckl, plays a key role in gluconeogenesis and operates to consume ATP to form PEP (Haarasilta and Oura, Eur. J. Biochem., 52:1-7 (1975)). Therefore, a heterologous enzyme, for example from Mannheimia succiniciproducens (Lee et al., Appl Environ Microbiol, 72:1939-1948 (2006)), Anaerobiospirillum succiniciproducens (Laivenieks et al., Appl Environ Microbiol, 63:2273-2280 (1997)), or Actinobacillus succinogenes (Kim, P. et al., Appl Environ Microbiol, 70:1238-1241 (2004)) with more favorable kinetics in the desired direction will be introduced into S. cerevisiae . The functioning of the enzyme in the requisite direction may require high concentrations of dissolved carbon dioxide in the fermentation medium. The protein sequences of the PEP carboxykinase enzymes mentioned in the text can be found via the following GenBank accession numbers and are summarized below:
Gene name
Organism
Accession Number
pckA
Mannheimia
YP_089485
succiniciproducens
(GI: 52426348)
pckA
Anaerobiospirillum
O09460
succiniciproducens
(GI: 3122621)
pck
Actinobacillus
ABX39017
succinogenes
(GI: 160415396)
The designs for fumaric and malic acid production, but not for acrylic acid production, use a small supply of oxygen in the network. This is because diacid production in S. cerevisiae is energetically neutral under anaerobic conditions, even upon assuming the reversibility of PPCK. Assuming that the symport of the fumarate or malate dianion is feasible with a proton at moderately low pH values, one additional proton needs to be pumped out to maintain homeostasis. The ATPase in S. cerevisiae uses one ATP for exporting out each proton which makes fumarate and malate production energetically neutral under anaerobic conditions. A limited supply of oxygen therefore provides for favorable energetics that can enable growth and product export. Note that a more favorable proton translocation stoichiometry of the ATPase can render these designs energetically feasible even in the absence of oxygen. It has been recently shown that introducing point mutations into the ATPase encoded by PMA1 in S. cerevisiae can increase or decrease its proton coupling efficiency and in some cases, bring the number of protons excreted per ATP hydrolyzed closer to two (Guerra, G. et al., Biochim Biophys Acta, 1768:2383-2392 (2007)). Alternatively, a non-native ATPase with an increased coupling efficiency can be introduced, as was demonstrated (Morsomme, P. et al., Embo J, 15:5513-5526 (1996)) where a mutated plant ATPase permitted growth of an ATPase-deficient S. cerevisiae strain at a pH of 4.
In some embodiments, microaerobic (substantially anaerobic) designs can be used based on increased formation of the desired product. To examine this, production cones were constructed for each strain by first maximizing and, subsequently minimizing the product yields at different rates of biomass formation feasible in the network. If the rightmost boundary of all possible phenotypes of the mutant network is a single point, it implies that there is a unique optimum yield of the product at the maximum biomass formation rate possible in the network. In other cases, the rightmost boundary of the feasible phenotypes is a vertical line, indicating that at the point of maximum biomass the network can make any amount of the product in the calculated range, including the lowest amount at the bottommost point of the vertical line. Such designs were given a low priority.
The fumarate-production strategies identified by the OptKnock framework were ranked on the basis of their (i) theoretical yields, and (ii) growth-coupled fumarate formation characteristics. All the strains with high product yields involve four or more knockouts because fewer knockouts were found to provide markedly lower yields. Strains with high yields include, for example, those with about 70% or more yield. The engineered strains can include further metabolic modifications aimed at limiting the production of the fumarate precursor, malate that is at the same redox state as fumarate. For example, the fumarase enzyme(s) can be manipulated by using techniques such as directed evolution so that the overall kinetics favors the conversion of malate into fumarate. Another option is to use a fumarase enzyme from any of the Rhizopus species that are known to produce high concentrations of fumarate without malate formation (e.g. fumR from R. oryzae , GenBank accession number: X78576). In another embodiment, one can use the fumarase from Euglena gracilis with a K m value of 0.031 mM for fumaric acid (Shibata et al., J Bacteriol, 164:762-768 1985)). Further, if an additional enzyme activity is introduced into S. cerevisiae to channel fumarate into a different growth-coupled end product, it will drive the metabolism towards fumarate formation and prevent malate formation. A case in point is the production of acrylic acid. The introduction of an appropriate decarboxylase enzyme can shift the equilibrium between malate and fumarate towards fumarate, thus leading to all carbon being funneled to the desired acrylic acid product. Using all the above options will ensure that the conversion of malate into fumarate is at a higher rate than the export of malate via any of the malate transporters.
For the strains that follow, the enzyme names, their abbreviations, and the corresponding reaction stoichiometries are listed in Table 7. The genes that can be mutated in order to prevent the activities of the enzymes identified for disruption are also shown in Table 7. Finally, metabolites names corresponding to the abbreviations in the reaction equations are listed in Table 8.
One strain for fumarate production, shown in FIG. 9 , involves disruptions in glycerol-3-phosphate dehydrogenase (G3PD), pyruvate decarboxylase (PYRDC), mitochondrial fumarase (FUMm), and soluble fumarate reductase (FRDcm). The disruptions in G3PD and PYRDC prevent glycerol secretion and reduce ethanol formation respectively. The disruption in FUMm prevents the carbon flux from being routed into the reductive mitochondrial TCA cycle. The network instead employs the cytosolic TCA cycle reactions to form fumarate. Finally, the disruption in FRDcm prevents the conversion of cytosolic fumarate into succinate. This strain is predicted to have a growth-coupled yield of 1.47 moles of fumarate per mole of glucose consumed and the maximum growth rate is anticipated to be 0.07/hr as shown in FIG. 9 . If required, the sorbitol reductase activity (encoded by YHR104W) can be removed from the network. All the proposed disruptions can be implemented sequentially based on the necessity to do so.
The strain shown in FIG. 10 has four disruptions including malic enzyme (ME1m), pyruvate kinase (PYK), fumarase (FUMm), and soluble fumarate reductase (FRDcm), two of which are the same as those in FIG. 9 . Under microaerobic conditions, this set of disruptions is expected to yield fumarate up to 1.71 moles/mole of glucose consumed. The disruptions in pyruvate kinase and the malic enzyme are targeted at preventing pyruvate formation in the network such that the maximum amount of PEP can be routed into the reductive TCA cycle using the energy-generating PPCK. As explained earlier, the disruptions in mitochondrial fumarase and in the soluble fumarate reductase prevent the carbon flux from being routed into the reductive mitochondrial TCA cycle and prevent further reduction of fumarate into succinate, respectively. With the imposed disruptions, the strain is expected to produce a minimum of 18% of its maximum theoretical yield see gray point in FIG. 10 . The strain is predicted to have a maximum growth rate of 0.045/hr.
The strain in FIG. 11 has an additional disruption in glucose-6-phosphate dehydrogenase as compared to the strain in FIG. 9 . The disruption of G6PDH alters the cofactor balance in the network favorably for fumarate production at the cost of biomass production by preventing the NADPH formation required for biomass synthesis. These disruptions lead to an expected maximum growth rate of approximately 0.041 per hour for the strain as shown in FIG. 11 . The maximum theoretical fumarate yield is 1.79 moles per mole of glucose consumed. The imposed disruptions reduce the feasible phenotypes significantly such that the strain is anticipated to produce a minimum of 84% of its maximum theoretical yield just to grow as shown by the dark gray point in FIG. 11 .
Another strain, shown in FIG. 12 , has an additional disruption in isocitrate dehydrogenase as compared to the strain in FIG. 11 , leading to a marginal increase in the expected maximum theoretical fumarate yield to 1.83 moles per mole of glucose consumed. The rationale is analogous to that explained for the disruption of G6PDH in design. The maximum biomass formation rate is anticipated to decrease from 0.04 per hour to 0.03 per hour.
To provide a comparison of the fumarate production characteristics of the four strains in FIGS. 9-12 , FIG. 13 shows their production curves on the same plot and compares them with those of the wild-type S. cerevisiae network. All the other designs for fumarate production are listed in Table 5. All the designs proposed for fumarate production described above and in Table 5 can be used for malate production under microaerobic conditions by introducing an additional disruption in the cytosolic fumarase gene that will prevent the conversion of malate into fumarate.
The appropriate reactions for acrylate production from fumarate were added to a genome-scale model of S. cerevisiae very similar to the one described in Duarte et al., Genome Res, 14:1298-1309 (2004). Acrylic acid is a monocarboxylic acid and it has been assumed that it is exported by proton symport. This mechanism of acrylate export makes its production energetically feasible even under anaerobic conditions when a reversible PPCK in introduced. Several design strategies for producing acrylic acid were identified, a few of which are described in detail here with the remaining designs listed in Table 6.
One strain for acrylate production, shown in FIG. 14 , has a disruption in pyruvate decarboxylase (PYRDC). Under anaerobic conditions, a disruption in pyruvate decarboxylase reduces ethanol formation significantly. All the carbon flux is instead redirected towards acrylate production which also allows for the regeneration of the NADH generated in the network, leading to a tight coupling with biomass formation in the network. The maximum product yield is predicted to be 1.55 moles per mole of glucose consumed at the highest growth rate of 0.21 per hour.
Another strain, shown in FIG. 15 , has disruptions in pyruvate kinase (PYK) and mitochondrial ATP synthase (ATPSm). The disruption in PYK prevents PEP conversion into pyruvate. The disruption of ATP synthase prevents ATP formation in the mitochondrion, removing the incentive for the network to route carbon flux into the mitochondrion. The product of YRJ121W is directly involved in the formation of F1-ATP synthase (beta subunit), while YMR064W is a translational regulator required for expression of the mitochondrial ATPase subunit 9 in yeast (Saltzgaber-Muller et al., J Biol. Chem. 258:11465-11470 (1983)). Disruption of either of these two genes does not affect viability of the organism, making them good deletion candidates for lowering or eliminating the ATPSm activity. Other genes can also be targeted for elimination of the ATP synthase activity in S. cerevisiae (Tzagoloff and Dieckmann, Microbiol Rev. 54:211-225 (1990)). Under anaerobic conditions, the maximum theoretical acrylate yield of the strain is expected to be 1.55 moles per mole of glucose consumed at the maximum predicted growth rate of 0.21 per hour. In microaerobic conditions, this strain provides a slightly higher acrylate yield at 1.69 moles per mole of glucose and the maximum growth rate of the strain is predicted to be 0.23 per hour.
Another strain, shown in FIG. 16 , has disruptions in malic enzyme (NAD-dependent) (ME1m) and in pyruvate kinase (PYK). These disruptions are geared towards preventing pyruvate formation in the network. Thus, they have a similar effect to the disruption of PYRDC which limits pyruvate formation by preventing its utilization for acetaldehyde and subsequently, ethanol formation. Overall, these two disruptions cause a high flux through PPCK, ultimately leading to a growth-coupled acrylate yield of 1.61 moles per mole of glucose in the network. The strain is calculated to have a maximum growth rate of 0.19 per hour.
Yet another strain, shown in FIG. 17 , has additional disruptions in fumarase (FUMm) and soluble fumarate reductase (FRDcm). These additional disruptions prevent the formation of succinate in the network. The net acrylate yield calculated for this design is 1.62 moles per mole of glucose consumed and the maximum growth rate is predicted to be 0.19 per hour.
Still another strain, shown in FIG. 18 , has additional disruptions in fumarase (FUMm) and soluble fumarate reductase (FRDcm). This strain can be grown in anaerobic conditions leading to acrylate production. The maximum theoretical acrylate yield of the strain is expected to be 1.65 moles per mole of glucose consumed at the maximum predicted growth rate of 0.18 per hour.
Accordingly, the invention also provides a non-naturally occurring eukaryotic organism having a set of metabolic modifications coupling fumarate, malate, or acrylate production to growth of the organism, the set of metabolic modifications includes disruption of one or more genes selected from the set of genes encoding proteins that include: (a) glycerol-3-phosphate dehydrogenase (G3PD), (b) pyruvate decarboxylase (PYRDC), (c) soluble fumarate reductase (FRDcm) and (d) mitochondrial fumarase (FUMm). In other embodiments, the set of metabolic modifications includes disruption of one or more genes selected from the set of genes encoding proteins that include: (a) malic enzyme (ME1m), (b) pyruvate kinase (PYK), (c) soluble fumarate reductase (FRDcm), and (d) mitochondrial fumarase (FUMm).
Based on an analysis of the strains for fumarate production, two alternative minimum set of disruptions can enable growth-coupled fumarate/malate production in the network. Note that PPCK was assumed to be reversible. Briefly, disruptions in glycerol-3-phosphate dehydrogenase (G3PD), pyruvate decarboxylase (PYRDC), soluble fumarate reductase (FRDcm) and mitochondrial fumarase (FUMm) are required for preventing or reducing the formation of competing byproducts, glycerol, ethanol and succinate. An alternative enzyme disruption set entails the removal of malic enzyme (ME1m), pyruvate kinase (PYK), soluble fumarate reductase (FRDcm) and mitochondrial fumarase (FUMm) for coupling fumarate production to growth. These correspond to the following minimal enzyme disruption sets:
Glycerol-3-phosphate dehydrogenase (G3PD), pyruvate decarboxylase (PYRDC), soluble fumarate reductase (FRDcm) and mitochondrial fumarase (FUMm), or Malic enzyme (ME1m), pyruvate kinase (PYK), soluble fumarate reductase (FRDcm) and mitochondrial fumarase (FUMm).
These enzyme disruption sets correspond to the following gene disruption sets: YDL022W (G3PD), YLR044C, YGR087C, YLR134W (isozymes for PYRDC), YPL262W (FUMm), and YEL047C (FRDcm), or YKL029C (ME1m), YOR347c, YAL038W (isozymes for PYK), YPL262W (FUMm), and YEL047C (FRDcm).
Note that all the isozymes capable of carrying out a given activity can be deleted given a possibility of the isozymes becoming active due to adaptive evolution. Further improvement in yields can be attained by deleting one or more of the following functionalities: glucose-6-phosphate dehydrogenase (G6PDH) and cytosolic NADP-dependent isocitrate dehydrogenase (ICDHy). The enzyme disruption sets after introducing these auxiliary disruptions are: Glycerol-3-phosphate dehydrogenase (G3PD), pyruvate decarboxylase (PYRDC), soluble fumarate reductase (FRDcm) and mitochondrial fumarase (FUMm), and glucose-6-phosphate dehydrogenase (G6PDH), or Malic enzyme (ME1m), pyruvate kinase (PYK), soluble fumarate reductase (FRDcm) and mitochondrial fumarase (FUMm), glucose-6-phosphate dehydrogenase (G6PDH) and cytosolic NADP-dependent isocitrate dehydrogenase (ICDHy).
These enzyme sets corresponds to the following gene disruption sets: YDL022W (G3PD), YLR044C, YGR087C, YLR134W (isozymes for PYRDC), YPL262W (FUMm), and YEL047C (FRDcm), YNL241C (G6PDH), or YKL029C (ME1m), YOR347c, YAL038W (isozymes for PYK), YPL262W (FUMm), and YEL047C (FRDcm), YNL241C (G6PDH), and YLR174W (ICDHy).
For malate production, the enzyme disruption sets can be augmented with the disruption of the cytosolic fumarase which is also encoded by YPL262W. Note that YPL262W encodes for both the cytosolic and the mitochondrial fumarases. However, its localization is determined by the N-terminal mitochondrial targeting sequence and its conformation (Sass et al., J Biol. Chem. 278:45109-45116 (2003)).
Acrylate production in S. cerevisiae is feasible under anaerobic conditions assuming the reversibility of PPCK. Three alternative minimum enzyme disruption sets were identified. These entail (i) disruption in pyruvate decarboxylase, or (ii) disruption in malic enzyme in conjunction with a disruption in pyruvate kinase, or (iii) disruptions in pyruvate kinase and mitochondrial ATP synthase. The corresponding gene disruption sets are: YLR044C, YGR087C, YLR134W (PYRDC), or YKL029C (ME1m), YOR347c, YAL038W (PYK), or YOR347c, YAL038W (encode for PYK isozymes), YJR121W and YMR064W or any other combination of genes that eliminates mitochondrial synthase activity.
Each of these minimal sets can be augmented with supplementary disruptions to further enhance the acrylate yields. The auxiliary disruptions include but are not limited to mitochondrial fumarase, soluble fumarate reductase and glycerol-3-phosphate dehydrogenase. The corresponding gene disruptions are: YPL262W (FUMm), and YEL047C (FRDcm) and YDL022W (G3PD).
The disruption of pyruvate decarboxylase is very similar to the disruption of alcohol dehydrogenase in that both are targeted to prevent ethanol formation in the network. The disruption of alcohol dehydrogenase activity can completely eliminate ethanol formation. However, due to the presence of multiple alcohol dehydrogenases and the substrate promiscuity of these dehydrogenases, it can be difficult to completely remove the alcohol dehydrogenase activity. Therefore, PYRDC is included in the minimum enzyme disruption set.
Each of the strains described above can be supplemented with additional disruptions if it is determined that the predicted strain designs do not sufficiently couple the formation of the product with biomass formation. Alternatively, some other enzymes not known to possess significant activity under the growth conditions can become active due to adaptive evolution or random mutagenesis and can also be knocked out. For example, succinate dehydrogenase that oxidizes succinate to fumarate and is known to be active only under aerobic conditions may assume significant activity even under anaerobic conditions and may have to be knocked out. However, the list of gene disruption sets provided here serves as a starting point for construction of high-yielding growth-coupled malate, fumarate and acrylate production strains.
Therefore, the invention provides a method for producing fumaric acid malic acid, or acrylic acid that includes culturing a non-naturally occurring prokaryotic or eukaryotic microbial organism that includes one or more gene disruptions. The disruptions can occur in genes encoding an enzyme obligatory to coupling fumarate or malate production to growth of the microorganism when the gene disruption reduces an activity of the enzyme, such that the disruptions confer stable growth-coupled production of fumarate or malate onto the non-naturally occurring microorganism.
The non-naturally occurring prokaryotic or eukaryotic organisms of the invention can be employed in the growth-coupled production of fumarate, malate, or acrylate. Essentially any quantity, including commercial quantities, can be synthesized using the growth-coupled fumarate, malate, or acrylate producers of the invention. Because the organisms of the invention obligatorily couple fumarate, malate, or acrylate to continuous growth or near-continuous growth processes are particularly useful for biosynthetic production of fumarate, malate, or acrylate. Such continuous and/or near continuous growth processes are described above and exemplified below in the Example I. Continuous and/or near-continuous microorganism growth processes also are well known in the art. Briefly, continuous and/or near-continuous growth processes involve maintaining the microorganism in an exponential growth or logarithmic phase. Procedures include using apparatuses such as the Evolugator™ evolution machine (Evolugate LLC, Gainesville, Fla.), fermentors and the like. Additionally, shake flask fermentation and grown under microaerobic conditions also can be employed. Given the teachings and guidance provided herein those skilled in the art will understand that the growth-coupled fumarate producing microorganisms can be employed in a variety of different settings under a variety of different conditions using a variety of different processes and/or apparatuses well known in the art.
Generally, the continuous and/or near-continuous production of fumarate, malate, or acrylate will include culturing a non-naturally occurring growth-coupled fumarate, malate, or acrylate producing organism of the invention in sufficient nutrients and medium to sustain and/or nearly sustain growth in an exponential phase. Continuous culture under such conditions can be grown, for example, for a day, 2, 3, 4, 5, 6 or 7 days or more. Additionally, continuous cultures can include time durations of 1 week, 2, 3, 4 or 5 or more weeks and up to several months. It is to be understood that the continuous and/or near-continuous culture conditions also can include all time intervals in between these exemplary periods. In particular embodiments, culturing is conducted in a substantially anaerobic culture medium.
Fumarate, malate, or acrylate can be harvested or isolated at any time point during the continuous and/or near-continuous culture period exemplified above. As exemplified below, the longer the microorganisms are maintained in a continuous and/or near-continuous growth phase, the proportionally greater amount of fumarate and malate can be produced.
One consideration for bioprocessing is whether to use a batch or continuous fermentation scheme. One difference between the two schemes that will influence the amount of product produced is the presence of a preparation, lag, and stationary phase for the batch scheme in addition to the exponential growth phase. In contrast, continuous processes are kept in a state of constant exponential growth and, if properly operated, can run for many months at a time. For growth-associated and mixed-growth-associated product formation, continuous processes provide much higher productivities (i.e., dilution rate times cell mass) due to the elimination of the preparation, lag, and stationary phases. For example, given the following reasonable assumptions:
Monod kinetics (i.e., μ=μ m ·S/(K s +S)) μ m =1.0 hr −1
final cell concentration/initial cell concentration=20
t prep +t lag +t stat =5 hr
feed concentration of limiting nutrient >>Ks
increased productivity from a continuous process has been estimated at 8-fold, Shuler et al, Prentice Hall, Inc .: Upper Saddle River, N.J., 245-247.
Despite advantages in productivity, many more batch processes are in operation than continuous processes for a number of reasons. First, for non-growth associated product formation (e.g., penicillin), the productivity of a batch system may significantly exceed that of a continuous process because the latter would have to operate at very low dilution rates. Next, production strains generally have undergone modifications to their genetic material to improve their biochemical or protein production capabilities. These specialized strains are likely to grow less rapidly than their parental complements whereas continuous processes such as those employing chemostats (fermenters operated in continuous mode) impose large selection pressures for the fastest growing cells. Cells containing recombinant DNA or carrying point mutations leading to the desired overproduction phenotype are susceptible to back-mutation into the original less productive parental strain. It also is possible for strains having single gene disruptions to develop compensatory mutations that will tend to restore the wild-type growth phenotype. The faster growing cells usually out-compete their more productive counterparts for limiting nutrients, drastically reducing productivity. Batch processes, on the other hand, limit the number of generations available by not reusing cells at the end of each cycle, thus decreasing the probability of the production strain reverting back to its wild-type phenotype. Finally, continuous processes are more difficult to operate long-term due to potential engineering obstacles such as equipment failure and foreign organism contamination. The consequences of such failures also are much more considerable for a continuous process than with a batch culture.
For small-volume production of specialty chemicals and/or proteins, the productivity increases of continuous processes rarely outweigh the risks associated with strain stability and reliability. However, for the production of large-volume, growth-associated products such as fumarate, the increases in productivity for a continuous process can result in significant economic gains when compared to a batch process. Although the engineering obstacles associated with continuous bioprocess operation would always be present, the strain stability concerns can be overcome through metabolic engineering strategies that reroute metabolic pathways to reduce or avoid negative selective pressures and favor production of the target product during the exponential growth phase.
The invention provides a method for producing fumaric acid, malic acid, or acrylic acid that includes culturing a non-naturally occurring prokaryotic or eukaryotic organism that includes one or more gene disruptions as described above. The disruptions can occur in genes encoding an enzyme obligatory to coupling fumarate, malate, or acrylate production to growth of the microorganism when the gene disruption reduces an activity of the enzyme, such that the disruptions confer increased production of fumarate, malate, or acrylate onto the non-naturally prokaryotic or eukaryotic organism. The gene disruptions can also be non-growth coupled in other embodiments.
In some embodiments, the gene disruption can include a complete gene deletion. In some embodiments other means to disrupt a gene include, for example, frameshifting by omission or addition of oligonucleotides or by mutations that render the gene inoperable. One skilled in the art will recognize the advantages of gene deletions, however, because of the stability it may confer to the non-naturally occurring organism from reverting to its wild-type. In particular, the gene disruptions are selected from the gene set that includes genes detailed herein above.
In order to confirm the computational predictions, the strains can be constructed, evolved, and tested. Gene deletions are introduced into wild-type, haploid S. cerevisiae , for example, by homologous recombination of the gene interrupted by the KanMX cassette, flanked by loxP sites enabling removal and recycling of the resistance marker (Wach et al., PCR - based gene targeting in Saccharomyces cerevisiae , in Yeast Gene Analysis , M. F. Tuite, Editor. 1998, Academic Press: San Diego.). Starting with a loxP-kanMX-loxP sequence on a plasmid, an artificial construct with this sequence flanked by fragments of the gene of interest can be created by PCR using primers containing both 45-50 bp target sequence followed by a region homologous to the above cassette. This linear DNA is transformed into wild-type S. cerevisiae , and recombinants are selected by geneticin resistance. Colonies can be purified and tested for correct double crossover by PCR. To remove the KanMX marker, a plasmid containing the Cre recombinase and bleomycin resistance will be introduced, promoting recombination between the loxP sites (Gueldener, U., et al., A second set of loxP marker cassettes for Cre - mediated multiple gene knockouts in budding yeast , in Nucleic Acids Res. 2002. p. e23.). Finally, the resulting strain can be cured of the Cre plasmid by successive culturing on media without any antibiotic present. The final strain will have a markerless gene deletion, and thus the same method can be used to introduce multiple deletions in the same strain.
The engineered strains can be characterized by measuring the growth rate, the substrate uptake rate, and the product/byproduct secretion rate. Cultures are grown overnight and used as inoculum for a fresh batch culture for which measurements are taken during exponential growth. The growth rate can be determined by measuring optical density using a spectrophotometer (A600). Concentrations of glucose and other organic acid byproducts in the culture supernatant are determined by HPLC using an HPX-87H column (BioRad), and used to calculate uptake and secretion rates. All experiments are performed with triplicate cultures.
The disruption strains are initially expected to exhibit suboptimal growth rates until their metabolic networks have adjusted to their missing functionalities. To assist in this adjustment, the strains are adaptively evolved. By subjecting the strains to adaptive evolution, cellular growth rate becomes the primary selection pressure and the mutant cells are compelled to reallocate their metabolic fluxes in order to enhance their rates of growth. This reprogramming of metabolism has been recently demonstrated for several E. coli mutants that had been adaptively evolved on various substrates to reach the growth rates predicted a priori by an in silico model (Fong and Palsson, Nat Genet, 36:1056-1058 (2004)). Should the OptKnock predictions prove successful; the growth improvements brought about by adaptive evolution will be accompanied by enhanced rates of fumarate, malate or acrylate production. The OptKnock-generated strains are adaptively evolved in triplicate (running in parallel) due to differences in the evolutionary patterns witnessed previously in E. coli ((Fong and Palsson, Nat Genet, 36:1056-1058 (2004); Fong et al., J Bacteriol, 185:6400-6408 (2003); Ibarra et al., Nature 420: 186-189 (2002)) that could potentially result in one strain having superior production qualities over the others. Evolutions will be run for a period of 2-6 weeks, depending upon the rate of growth improvement attained. In general, evolutions will be stopped once a stable phenotype is obtained.
Following the adaptive evolution process, the new strains are characterized again by measuring the growth rate, the substrate uptake rate, and the product/byproduct secretion rate. These results will be compared to the OptKnock predictions by plotting actual growth and production yields along side the production envelopes in the above figures. The most successful OptKnock design/evolution combinations are chosen to pursue further, and are characterized in lab-scale batch and continuous fermentations. The growth-coupled biochemical production concept behind the OptKnock approach should also result in the generation of genetically stable overproducers. Thus, the cultures are maintained in continuous mode for one month to evaluate long-term stability. Periodic samples are taken to ensure that yield and productivity are maintained throughout the experiment.
As will become evident, the teachings contained herein will enable, in a broader sense, the development of methods for decarboxylating alpha, beta-unsaturated carboxylic acids or their salts through the use of naturally occurring or altered decarboxylases. Such alterations can be introduced through a variety of directed and/or adaptive evolution methods.
In some embodiments, the present invention provides a non-naturally occurring microbial organism, that includes a microbial organism having an olefin pathway having at least one exogenous nucleic acid encoding an olefin pathway enzyme expressed in a sufficient amount to produce an olefin. The olefin pathway includes a decarboxylase. In some embodiments, this exogenous nucleic acid is a heterologous nucleic acid. The microbial organism having this decarboxylase can be optionally cultured under substantially anaerobic conditions.
In other embodiments, the present disclosure provides non-naturally occurring microbial organisms having an acrylate pathway that includes at least one exogenous nucleic acid encoding an acrylate pathway enzyme expressed in a sufficient amount to produce acrylate. This acrylate pathway includes a decarboxylase as described herein below. In particular embodiments, the decarboxylase catalyzes fumarate decarboxylation to provide acrylate.
Decarboxylases (also known as carboxy lyases) catalyze the loss of carbon dioxide from an organic compound or a cellular metabolite possessing a carboxylic acid function. Decarboxylases are prevalent in nature and can require either pyridoxal phosphate or pyruvate as a co-factor, although many require no bound co-factors. Over 50 decarboxylase enzymes have been reported and characterized by biochemical and/or analytical methods.
The process in FIGS. 20 and 21A show the decarboxylation of fumaric acid to acrylic acid. Numerous decarboxylase enzymes have been characterized and shown to decarboxylate structurally similar substrates to fumarate( FIGS. 21B-D ). These enzymes are applicable for use in the present invention to decarboxylate fumarate and other unsaturated carboxylic acids, as shown in FIG. 19 . One enzyme with closely related function is aconitate decarboxylase ( FIG. 21B ). This enzyme catalyzes the final step in itaconate biosynthesis in a strain of Candida and also in the filamentous fungus Aspergillus terreus . (Bonnarme et al. J. Bacteriol. 177:3573-3578 (1995); Willke et al. Appl. Microbiol. Biotechnol 56:289-295 (2001)). Aconitate decarboxylase has been purified and characterized from Aspergillus terreus (Dwiarti et al. J. Biosci. Bioeng., 94(1): 29-33 (2002). The gene and protein sequence for the cis-aconitic acid decarboxylase (CAD) enzyme are described in EP2017344 and WO 2009/014437. The protein sequence is listed below along with several close homologs described in EP2017344 and WO2009/014437.
Gene name
GenBankID
Organism
CAD
XP_001209273
Aspergillus terreus
(GI: 115385453)
XP_001217495
Aspergillus terreus
(GI: 115402837)
XP_001209946
Aspergillus terreus
(GI: 115386810)
BAE66063
Aspergillus oryzae
(GI: 83775944)
XP_001393934
Aspergillus niger
(GI: 83775944)
XP_391316
Gibberella zeae
(GI: 46139251)
XP_001389415
Aspergillus niger
(GI: 145230213)
XP_001383451
Pichia stipitis
(GI: 126133853)
YP_891060
Mycobacterium smegmatis
(GI: 118473159)
NP_961187
Mycobacterium avium subsp.
(GI: 41408351)
pratuberculosis
YP_880968
Mycobacterium avium
(GI: 118466464)
ZP_01648681
Salinispora arenicola
(GI: 119882410)
ZP_01648681
Salonispora tropica
(GI: 119882410)
Another enzyme type with similar function is 4-oxalocrotonate decarboxylase ( FIG. 21C ). This enzyme has been isolated from numerous organisms and characterized. Genes encoding this enzyme include dmpH and dmpE in Pseudomonas sp. (strain 600) (Shingler et al. J. Bacteriol. 174:711-724 (1992)), xyIII and xyIII from Pseudomonas putida (Kato et al. Arch. Microbiol. 168:457-463 (1997); Stanley et al. Biochemistry 39:718-726 (2000); Lian et al. J. Am. Chem. Soc. 116, 10403-10411 (1994)) and Reut_B5691 and Reut_B5692 from Ralstonia eutropha JMP134 (Hughes et al. J. Bacteriol. 158:79-83 (1984). The genes encoding the enzyme from Pseudomonas sp. (strain 600) have been cloned and expressed in E. coli (Shingler et al. J. Bacteriol. 174:711-724 (1992)).
Finally, a class of decarboxylases has been characterized that catalyze the conversion of cinnamate (phenylacrylate) and substituted cinnamate derivatives to the corresponding styrene derivatives ( FIG. 21D ). These enzymes are common in a variety of organisms and specific genes encoding these enzymes that have been cloned and expressed in E. coli are: pad I from Saccharomyces cerevisae (Clausen et al. Gene 142:107-112 (1994), pdc from Lactobacillus plantarum (Barthelmebs et al. Appl. Environ. Microbiol. 67, 1063-1069 (2001); Qi et al. Metabolic Engineering 9: 268-276 (2007); Rodriguez et al. J. Agric. Food Chem. 56, 3068-3072 (2008)), pofK (pad) from Klebsiella oxytoca (Hashidoko et al. Biosci. Biotech. Biochem. 58, 217-218 (1994); Uchiyama et al. Biosci. Biotech. Biochem. 72: 116-123 (2008)), and Pedicoccus pentosaceus (Barthelmebs et al. J. Bacteriol. 182: 6724-6731 (2000); Barthelmebs et al. Appl. Environ. Microbiol. 67: 1063-1069 (2001)), and padC from Bacillus subtilis and Bacillus pumilus (Barthelmebs et al. 2001 supra; Qi, et al supra). A ferulic acid decarboxylase from Pseudomonas fluorescens also has been purified and characterized (Huang et al. J. Bacteriol. 176: 5912-5918 (1994)). Importantly, this class of enzymes have been shown to be stable and do not require either exogenous or internally bound co-factors, thus making these enzymes ideally suitable for biotransformations (Sariaslani Annu. Rev. Microbiol. 61: 51-69 (2007)). A summary of genes encoding these various decarboxylases for carrying out the transformations shown in FIGS. 21B-21D are shown below.
Gene name
GenBankID
Organism
dmpH
CAA43228.1
Pseudomonas sp. CF600
(GI: 45685)
dmpE
CAA43225.1
Pseudomonas sp. CF600
(GI: 45682)
xylII
YP_709328.1
Pseudomonas putida
(GI: 111116444)
xylIII
YP_709353.1
Pseudomonas putida
(GI: 111116469)
Reut_B5691
YP_299880.1
Ralstonia eutropha JMP134
(GI: 73539513)
Reut_B5692
YP_299881.1
Ralstonia eutropha JMP134
(GI: 73539514)
pad1
AB368798
Saccharomyces cerevisae
(GI: 188496948)
pdc
U63827
Lactobacillus plantarum
(GI: 1762615)
pofK (pad)
AB330293
Klebsiella oxytoca
(GI: 149941607)
padC
AF017117
Bacillus subtilis
(GI: 2394281)
pad
AJ276891
Pedicoccus pentosaceus
(GI: 11322456)
pad
AJ278683
Bacillus pumilus
(GI: 11691809)
Each of the decarboxylases listed above represents a suitable enzyme for the transformation shown in FIGS. 20 and 21A . If the desired activity or productivity of the enzyme is not observed in the conversion of fumarate to acrylate, or if acrylic acid production inhibits the decarboxylase enzymes, the decarboxylase enzymes can be evolved using known protein engineering methods to achieve the required performance. Importantly, it was shown through the use of chimeric enzymes that the C-terminal region of decarboxylases appears to be responsible for substrate specificity (Barthelmebs et al. (2001) supra). Accordingly, directed evolution experiments to broaden the specificity of decarboxylases in order to gain activity with fumarate can be focused on the C-terminal region of these enzymes.
Some of the decarboxylases can exhibit higher activity on the cis-isomer of fumarate known as maleate. Fumarate can be converted to maleate by maleate cis-trans isomerase encoded by the maiA gene from Alcaligenes faecalis (Hatakeyama, et al., Biochem. Biophys. Research Comm. 239, 74-79 (1997)) or similar genes that can be identified by sequence homology including those from Geobacillus stearothermophilus and Ralstonia pickettii 12D. Additional maleate cis-trans isomerase enzymes are encoded by the enzymes whose amino acid sequences are described (SEQ ID NO: 1-4) in U.S. Pat. No. 6,133,014, which is incorporated by reference in its entirety. Useful GenBank information for some of these isomerases is shown below.
Gene name
GenBankID
Organism
maiA
BAA23002.1
Alcaligenes faecalis
(GI: 2575787)
maiA
BAA77296
Geobacillus
(GI: 4760466)
stearothermophilus
Rpic12DDRAFT_0600
ZP_02009633
Ralstonia pickettii 12D
(GI: 153888491)
The exogenous nucleic acid encoding the decarboxylase can come from another organism such as those described above, thus providing a heterologous nucleic acid. Alternatively, in the case of a microbial organism that already has a native decarboxylase capable of decarboxylating fumarate, additional copies of the decarboxylase can be introduced to increase its expression. In addition to incorporating a decarboxylase, a non-naturally occurring microbial organism will have certain energy requirements for growth and maintenance as outlined below.
Engineering the capability for fumarate decarboxylation into Escherichia coli , for example, results in a redox-balanced pathway for the production of acrylate from carbohydrates. Provided that symport of the acrylate monoanion is the predominant means of product export, the pathway as depicted in FIG. 20 can be energetically negative because the high energy phosphate bond contained in each PEP molecule gained from glycolysis will be lost upon conversion to oxaloacetate by PEP carboxylase, a native E. coli enzyme that is functional during growth on carbohydrates.
This energetic limitation can be remedied by either supplying a limited amount of an external electron acceptor such as oxygen or nitrate to enable energy generation via respiration, or by at least two strain engineering strategies provided herein below. Either strain engineering method ensures that the pathway for production of acrylate via fumarate decarboxylase generates sufficient energy to support cell growth and maintenance under anaerobic or aerobic conditions. Although the non-naturally occurring microbial organism can be grown under aerobic or anaerobic conditions, a substantially anaerobic culture medium is preferred. The two exemplary designs described below can be implemented in order to generate the requisite energy for growth and maintenance under anaerobic conditions.
In one embodiment, a non-naturally occurring microbial organism can include an exogenous nucleic acid encoding at least one malic enzyme to supply the requisite energy for growth and maintenance. Malic enzymes for this purpose can include, without limitation, malic enzyme (NAD-dependent) and malic enzyme (NADP-dependent). For example, one of the native E. coli malic enzymes (Takeo, K., J. Biochem. 66:379-387 (1969)) or a similar non-native enzyme with higher activity can be expressed to enable the conversion of pyruvate and CO 2 to malate. By fixing carbon to pyruvate as opposed to PEP, malic enzyme enables the high-energy phosphate bond from PEP to be conserved by pyruvate kinase whereby ATP is generated in the formation of pyruvate or by the phosphotransferase system for glucose transport. Although malic enzyme is typically assumed to operate in the direction of pyruvate formation from malate, overexpression of the NAD-dependent enzyme, encoded by maeA, has been demonstrated to increase succinate production in E. coli while restoring the lethal Δpfl-ΔldhA phenotype under anaerobic conditions by operating in the carbon-fixing direction (Stols and Donnelly, Appl Environ Microbiol 63:2695-2701 (1997)). Thus, in some embodiments the non-naturally occurring microbial organism can include an exogenous nucleic acid providing a gene such as maeA. A similar observation was made upon overexpressing the malic enzyme from Ascaris suum in E. coli (Stols et al., Appl Biochem. Biotechnol 63-65:153-158 (1997)). The second E. coli malic enzyme, encoded by maeB, is NADP-dependent and also decarboxylates oxaloacetate and other alpha-keto acids (Iwakura et al., J. Biochem. 85:1355-1365 (1979)) Therefore, in other embodiments the non-naturally occurring microbial organism can include an exogenous nucleic acid providing a gene such as maeB. The relevant malic enzyme gene information is shown below.
Gene name
Organism
Accession Number
maeA
E. coli
NP_415996
(GI: 90111281)
maeB
E. coli
NP_416958
(GI: 16130388)
NAD-ME
Ascaris suum
P27443
(GI: 126732)
Another option for providing an energetically favorable pathway involves introducing a reversible phosphoenolpyruvate kinase (PPCK) enzyme, which unlike PEP carboxylase, can generate one ATP per phosphoenolpyruvate molecule converted to oxaloacetate. In some embodiments, the non-naturally occurring microbial organism can also include an exogenous nucleic acid encoding a phosphoenolpyruvate carboxykinase. PEP carboxykinase is known to produce oxaloacetate from PEP in rumen bacteria such as Mannheimia succiniciproducens (Hong et al., Nat Biotechnol 22:1275-1281 (2004)) However, the role of PEP carboxykinase, encoded by pck, in producing oxaloacetate in E. coli is believed to be minor as compared to PEP carboxylase, possibly due to the higher K m for bicarbonate of PEP carboxykinase (Kim et al., Appl Environ Microbiol 70:1238-1241 (2004)) Nevertheless, activity of the native E. coli PEP carboxykinase from PEP towards oxaloacetate has been recently demonstrated in ppc mutants of E. coli K-12 (Kwon et al., J. Microbiol. Biotechnol. 16:1448-1452 (2006)). These strains exhibited no growth defects and had increased succinate production at high NaHCO 3 concentrations. In addition, examples of non-native PEP carboxykinase genes that have been cloned and shown to function in E. coli include those from M. succiniciproducens (Lee et al., Gene. Biotechnol. Bioprocess Eng. 7:95-99 (2002)), Anaerobiospirillum succiniciproducens (Laivenieks et al. Appl Environ Microbiol 63:2273-2280 (1997)), and Actinobacillus succinogenes (Kim et al., Appl Environ Microbiol 70:1238-1241 (2004)). The relevant PEP carboxykinase gene information is shown below.
Gene
name
Organism
Accession Number
pck
E. coli
NP_417862
(GI: 16131280)
pckA
Mannheimia succiniciproducens
YP_089485
(GI: 52426348)
pckA
Anaerobiospirillum succiniciproducens
O09460
(GI: 3122621)
pck
Actinobacillus succinogenes
ABX39017
(GI: 160415396)
In addition to the supplying the requisite energy as described above, the formation of acrylate can also be optimized by modifying the non-naturally occurring microbial organism's metabolic production of fumarate. Toward this end, the non-naturally occurring microbial organism can include one or more gene disruptions in addition to the inserted nucleic acid sequences outline above. Gene disruptions can result from, for example, single nucleotide insertion or deletions, stable mutations, and complete gene deletions. Exemplary pathway designs are described below.
The non-naturally occurring microbial organisms that synthesize acrylate can be produced by introducing expressible nucleic acids encoding one or more of the enzymes or proteins participating in one or more acrylate biosynthetic pathways. Depending on the host microbial organism chosen for biosynthesis, nucleic acids for some or all of a particular acrylate biosynthetic pathway can be expressed. For example, if a chosen host is deficient in one or more enzymes or proteins for a desired biosynthetic pathway, then expressible nucleic acids for the deficient enzyme(s) or protein(s) are introduced into the host for subsequent exogenous expression. Alternatively, if the chosen host exhibits endogenous expression of some pathway genes, but is deficient in others, then an encoding nucleic acid is needed for the deficient enzyme(s) or protein(s) to achieve acrylate biosynthesis. Thus, a non-naturally occurring microbial organism of the invention can be produced by introducing exogenous enzyme or protein activities to obtain a desired biosynthetic pathway or a desired biosynthetic pathway can be obtained by introducing one or more exogenous enzyme or protein activities that, together with one or more endogenous enzymes or proteins, produces a desired product such as acrylate.
Depending on the acrylate biosynthetic pathway constituents of a selected host microbial organism, the non-naturally occurring microbial organisms of the invention will include at least one exogenously expressed acrylate pathway-encoding nucleic acid and up to all encoding nucleic acids for one or more acrylate biosynthetic pathways. For example, acrylate biosynthesis can be established in a host deficient in a pathway enzyme or protein through exogenous expression of the corresponding encoding nucleic acid. In a host deficient in all enzymes or proteins of an acrylate pathway, exogenous expression of all enzyme or proteins in the pathway can be included, although it is understood that all enzymes or proteins of a pathway can be expressed even if the host contains at least one of the pathway enzymes or proteins. For example, exogenous expression of all enzymes or proteins in a pathway for production of acrylate can be included, such as a decarboxylase.
Given the teachings and guidance provided herein, those skilled in the art will understand that the number of encoding nucleic acids to introduce in an expressible form will, at least, parallel the acrylate pathway deficiencies of the selected host microbial organism. Therefore, a non-naturally occurring microbial organism of the invention can have one, two, three, four, up to all nucleic acids encoding the enzymes or proteins constituting an acrylate biosynthetic pathway disclosed herein. In some embodiments, the non-naturally occurring microbial organisms also can include other genetic modifications that facilitate or optimize acrylate biosynthesis or that confer other useful functions onto the host microbial organism. One such other functionality can include, for example, augmentation of the synthesis of one or more of the acrylate pathway precursors such as fumarate.
Generally, a host microbial organism is selected such that it produces the precursor of an acrylate pathway, either as a naturally produced molecule or as an engineered product that either provides de novo production of a desired precursor or increased production of a precursor naturally produced by the host microbial organism. For example, fumarate is produced naturally in a host organism such as E. coli . A host organism can be engineered to increase production of a precursor, as disclosed herein. In addition, a microbial organism that has been engineered to produce a desired precursor can be used as a host organism and further engineered to express enzymes or proteins of an acrylate pathway.
In some embodiments, a non-naturally occurring microbial organism of the invention is generated from a host that contains the enzymatic capability to synthesize acrylate. In this specific embodiment it can be useful to increase the synthesis or accumulation of an acrylate pathway product to, for example, drive acrylate pathway reactions toward acrylate production. Increased synthesis or accumulation can be accomplished by, for example, overexpression of nucleic acids encoding one or more of the above-described acrylate pathway enzymes or proteins. Over expression the enzyme or enzymes and/or protein or proteins of the acrylate pathway can occur, for example, through exogenous expression of the endogenous gene or genes, or through exogenous expression of the heterologous gene or genes. Therefore, naturally occurring organisms can be readily generated to be non-naturally occurring microbial organisms of the invention, for example, producing acrylate, through overexpression of one, two, three, four, five, that is, up to all nucleic acids encoding acrylate biosynthetic pathway enzymes or proteins. In addition, a non-naturally occurring organism can be generated by mutagenesis of an endogenous gene that results in an increase in activity of an enzyme in the acrylate biosynthetic pathway.
In particularly useful embodiments, exogenous expression of the encoding nucleic acids is employed. Exogenous expression confers the ability to custom tailor the expression and/or regulatory elements to the host and application to achieve a desired expression level that is controlled by the user. However, endogenous expression also can be utilized in other embodiments such as by removing a negative regulatory effector or induction of the gene's promoter when linked to an inducible promoter or other regulatory element. Thus, an endogenous gene having a naturally occurring inducible promoter can be up-regulated by providing the appropriate inducing agent, or the regulatory region of an endogenous gene can be engineered to incorporate an inducible regulatory element, thereby allowing the regulation of increased expression of an endogenous gene at a desired time. Similarly, an inducible promoter can be included as a regulatory element for an exogenous gene introduced into a non-naturally occurring microbial organism.
It is understood that, in methods of the invention, any of the one or more exogenous nucleic acids can be introduced into a microbial organism to produce a non-naturally occurring microbial organism of the invention. The nucleic acids can be introduced so as to confer, for example, an acrylate biosynthetic pathway onto the microbial organism. Alternatively, encoding nucleic acids can be introduced to produce an intermediate microbial organism having the biosynthetic capability to catalyze some of the required reactions to confer acrylate biosynthetic capability. For example, a non-naturally occurring microbial organism having an acrylate biosynthetic pathway can comprise at least one exogenous nucleic acids encoding desired enzymes or proteins, such as a decarboxylase, and the like.
In addition to the biosynthesis of acrylate as described herein, the non-naturally occurring microbial organisms and methods of the invention also can be utilized in various combinations with each other and with other microbial organisms and methods well known in the art to achieve product biosynthesis by other routes. For example, one alternative to produce acrylate other than use of the acrylate producers is through addition of another microbial organism capable of converting an acrylate pathway intermediate to acrylate. One such procedure includes, for example, the fermentation of a microbial organism that produces an acrylate pathway intermediate. The acrylate pathway intermediate can then be used as a substrate for a second microbial organism that converts the acrylate pathway intermediate to acrylate. The acrylate pathway intermediate can be added directly to another culture of the second organism or the original culture of the acrylate pathway intermediate producers can be depleted of these microbial organisms by, for example, cell separation, and then subsequent addition of the second organism to the fermentation broth can be utilized to produce the final product without intermediate purification steps.
In other embodiments, the non-naturally occurring microbial organisms and methods of the invention can be assembled in a wide variety of subpathways to achieve biosynthesis of, for example, acrylate. In these embodiments, biosynthetic pathways for a desired product of the invention can be segregated into different microbial organisms, and the different microbial organisms can be co-cultured to produce the final product. In such a biosynthetic scheme, the product of one microbial organism is the substrate for a second microbial organism until the final product is synthesized. For example, the biosynthesis of acrylate can be accomplished by constructing a microbial organism that contains biosynthetic pathways for conversion of one pathway intermediate to another pathway intermediate or the product. Alternatively, acrylate also can be biosynthetically produced from microbial organisms through co-culture or co-fermentation using two organisms in the same vessel, where the first microbial organism produces a fumarate intermediate and the second microbial organism converts the intermediate to acrylate.
Microorganisms capable of directly producing acrylate are constructed by introducing genes encoding decarboxylase enzymes into the strains engineered as described above for maximal fumarate production. The following example describes the creation of a microbial organism that can produce acrylic acid from renewable feedstocks such as glucose or sucrose.
To generate an E. coli strain engineered to produce acrylate or acrylic acid, nucleic acids encoding the decarboxylase enzymes are cloned and expressed in E. coli capable of overproducing fumarate using well known molecular biology techniques and recombinant and detection methods well known in the art. Such methods are described in, for example, Sambrook et al., Molecular Cloning: A Laboratory Manual , Third Ed., Cold Spring Harbor Laboratory, New York (2001); and Ausubel et al., Current Protocols in Molecular Biology , John Wiley and Sons, Baltimore, Md. (1999).
An acrylate producing strain is constructed, by cloning the individual phenylacrylic acid decarboxylase genes pad1 (AB368798), pdc (U63827), pofK (AB330293), padC (AF017117), pad (AJ276891), and pad (AJ278683) into pZA33 or pZE13 vectors (Expressys, Ruelzheim, Germany) under the IPTG-titratable PA1/lacO promoter. The plasmids are transformed into the fumarate overproducing E. coli strain using standard methods such as electroporation. The resulting genetically engineered organism is cultured in glucose-containing medium following procedures well known in the art (see, for example, Sambrook et al., supra, 2001). Expression of the decarboxylase genes are corroborated using methods well known in the art for determining polypeptide expression or enzymatic activity, including for example, Northern blots, PCR amplification of mRNA, immunoblotting, and the like. Enzymatic activities of the expressed enzymes are confirmed using assays specific for the individual activities. The ability of the engineered E. coli strain to produce acrylic acid is confirmed using HPLC, gas chromatography-mass spectrometry (GCMS) and/or liquid chromatography-mass spectrometry (LCMS).
Microbial strains engineered to have a functional acrylic acid synthesis pathway are further augmented by optimization for efficient utilization of the pathway. Briefly, the engineered strain is assessed to determine whether exogenous genes are expressed at a rate limiting level. Flux analysis using 13 C-labeled glucose is performed to assess bottlenecks in the system. Expression is increased for enzymes produced at low levels and that limit the flux through the pathway by, for example, introduction of additional gene copy numbers or changes to the promoter and ribosome binding sites.
To generate better acrylate producers, metabolic modeling is utilized to optimize growth conditions. Modeling is also used to design gene knockouts that additionally optimize utilization of the pathway, as described above. Modeling analysis allows reliable predictions of the effects on cell growth of shifting the metabolism towards more efficient production of acrylic acid. Adaptive evolution is performed to improve both growth and production characteristics (Fong and Palsson, Nat. Genet. 36:1056-1058 (2004)). Based on the results, subsequent rounds of modeling, genetic engineering and adaptive evolution can be applied to the acrylic acid producer to further increase production.
For large-scale production of acrylic acid, the above organism is cultured in a fermenter using a medium known in the art to support growth of the organism under anaerobic conditions. Fermentations are performed in either a batch, fed-batch or continuous manner. Anaerobic conditions are maintained by first sparging the medium with nitrogen and then sealing the culture vessel, for example, flasks can be sealed with a septum and crimp-cap. Microaerobic conditions also can be utilized by providing a small hole in the septum for limited aeration. The pH of the medium is maintained in the optimum range by addition of acids such as H 2 SO 4 or bases such as NaOH or Na 2 CO 3 . The growth rate is determined by measuring optical density using a spectrophotometer (600 nm) and the glucose uptake rate by monitoring carbon source depletion over time. Byproducts such as undesirable alcohols, organic acids, and residual glucose can be quantified by HPLC (Shimadzu, Columbia Md.), for example, using an Aminex® series of HPLC columns (for example, HPX-87 series) (BioRad, Hercules Calif.), using a refractive index detector for glucose and alcohols, and a UV detector for organic acids (Lin et al., Biotechnol. Bioeng. 775-779 (2005)).
E. coli and other microorganisms are known to possess fatty acid and organic acid degradation pathways that could lead to acrylate degradation. While fermentative production of acrylic acid under anaerobic conditions should not be accompanied by degradation, should product degradation be observed, the pathways responsible for product degradation will be deleted.
Given the teachings and guidance provided herein, those skilled in the art will understand that a wide variety of combinations and permutations exist for the non-naturally occurring microbial organisms and methods of the invention together with other microbial organisms, with the co-culture of other non-naturally occurring microbial organisms having subpathways and with combinations of other chemical and/or biochemical procedures well known in the art to produce acrylate.
Sources of encoding nucleic acids for an acrylate pathway enzyme or protein can include, for example, any species where the encoded gene product is capable of catalyzing the referenced reaction. Such species include both prokaryotic and eukaryotic organisms including, but not limited to, bacteria, including archaea and eubacteria, and eukaryotes, including yeast, plant, insect, animal, and mammal, including human. Exemplary species for such sources include, for example, Escherichia coli, Candida albicans, Candida boidinii, Aspergillus terreus, Pseudomonas sp. CF600, Pseudomonas putida, Ralstonia eutropha JMP 134, Saccharomyces cerevisae, Lactobacillus plantarum, Klebsiella oxytoca, Bacillus subtilis, Bacillus pumilus, Pedicoccus pentosaceus , as well as other exemplary species disclosed herein or available as source organisms for corresponding genes. However, with the complete genome sequence available for now more than 550 species (with more than half of these available on public databases such as the NCBI), including 395 microorganism genomes and a variety of yeast, fungi, plant, and mammalian genomes, the identification of genes encoding the requisite acrylate biosynthetic activity for one or more genes in related or distant species, including for example, homologues, orthologs, paralogs and nonorthologous gene displacements of known genes, and the interchange of genetic alterations between organisms is routine and well known in the art. Accordingly, the metabolic alterations enabling biosynthesis of acrylate described herein with reference to a particular organism such as E. coli can be readily applied to other microorganisms, including prokaryotic and eukaryotic organisms alike. Given the teachings and guidance provided herein, those skilled in the art will know that a metabolic alteration exemplified in one organism can be applied equally to other organisms.
In some instances, such as when an alternative acrylate biosynthetic pathway exists in an unrelated species, acrylate biosynthesis can be conferred onto the host species by, for example, exogenous expression of a paralog or paralogs from the unrelated species that catalyzes a similar, yet non-identical metabolic reaction to replace the referenced reaction. Because certain differences among metabolic networks exist between different organisms, those skilled in the art will understand that the actual gene usage between different organisms can differ. However, given the teachings and guidance provided herein, those skilled in the art also will understand that the teachings and methods of the invention can be applied to all microbial organisms using the cognate metabolic alterations to those exemplified herein to construct a microbial organism in a species of interest that will synthesize acrylate.
Host microbial organisms can be selected from, and the non-naturally occurring microbial organisms generated in, for example, bacteria, yeast, fungus or any of a variety of other microorganisms applicable to fermentation processes. Exemplary bacteria include species selected from Escherichia coli, Klebsiella oxytoca, Anaerobiospirillum succiniciproducens, Actinobacillus succinogenes, Mannheimia succiniciproducens, Rhizobium etli, Bacillus subtilis, Corynebacterium glutamicum, Gluconobacter oxydans, Zymomonas mobilis, Lactococcus lactis, Lactobacillus plantarum, Streptomyces coelicolor, Clostridium acetobutylicum, Pseudomonas fluorescens , and Pseudomonas putida . Exemplary yeasts or fungi include species selected from Saccharomyces cerevisiae, Schizosaccharomyces pombe, Kluyveromyces lactis, Kluyveromyces marxianus, Aspergillus terreus, Aspergillus niger and Pichia pastoris. E. coli is a particularly useful host organism since it is a well characterized microbial organism suitable for genetic engineering. Other particularly useful host organisms include yeast such as Saccharomyces cerevisiae.
Methods for constructing and testing the expression levels of a non-naturally occurring acrylate-producing host can be performed, for example, by recombinant and detection methods well known in the art. Such methods can be found described in, for example, Sambrook et al., Molecular Cloning: A Laboratory Manual , Third Ed., Cold Spring Harbor Laboratory, New York (2001); and Ausubel et al., Current Protocols in Molecular Biology , John Wiley and Sons, Baltimore, Md. (1999).
Exogenous nucleic acid sequences involved in a pathway for production of acrylate can be introduced stably or transiently into a host cell using techniques well known in the art including, but not limited to, conjugation, electroporation, chemical transformation, transduction, transfection, and ultrasound transformation. For exogenous expression in E. coli or other prokaryotic cells, some nucleic acid sequences in the genes or cDNAs of eukaryotic nucleic acids can encode targeting signals such as an N-terminal mitochondrial or other targeting signal, which can be removed before transformation into prokaryotic host cells, if desired. For example, removal of a mitochondrial leader sequence led to increased expression in E. coli (Hoffmeister et al., J. Biol. Chem. 280:4329-4338 (2005)). For exogenous expression in yeast or other eukaryotic cells, genes can be expressed in the cytosol without the addition of leader sequence, or can be targeted to mitochondrion or other organelles, or targeted for secretion, by the addition of a suitable targeting sequence such as a mitochondrial targeting or secretion signal suitable for the host cells. Thus, it is understood that appropriate modifications to a nucleic acid sequence to remove or include a targeting sequence can be incorporated into an exogenous nucleic acid sequence to impart desirable properties. Furthermore, genes can be subjected to codon optimization with techniques well known in the art to achieve optimized expression of the proteins.
An expression vector or vectors can be constructed to include one or more acrylate biosynthetic pathway encoding nucleic acids as exemplified herein operably linked to expression control sequences functional in the host organism. Expression vectors applicable for use in the microbial host organisms of the invention include, for example, plasmids, phage vectors, viral vectors, episomes and artificial chromosomes, including vectors and selection sequences or markers operable for stable integration into a host chromosome. Additionally, the expression vectors can include one or more selectable marker genes and appropriate expression control sequences. Selectable marker genes also can be included that, for example, provide resistance to antibiotics or toxins, complement auxotrophic deficiencies, or supply critical nutrients not in the culture media. Expression control sequences can include constitutive and inducible promoters, transcription enhancers, transcription terminators, and the like which are well known in the art. When two or more exogenous encoding nucleic acids are to be co-expressed, both nucleic acids can be inserted, for example, into a single expression vector or in separate expression vectors. For single vector expression, the encoding nucleic acids can be operationally linked to one common expression control sequence or linked to different expression control sequences, such as one inducible promoter and one constitutive promoter. The transformation of exogenous nucleic acid sequences involved in a metabolic or synthetic pathway can be confirmed using methods well known in the art. Such methods include, for example, nucleic acid analysis such as Northern blots or polymerase chain reaction (PCR) amplification of mRNA, or immunoblotting for expression of gene products, or other suitable analytical methods to test the expression of an introduced nucleic acid sequence or its corresponding gene product. It is understood by those skilled in the art that the exogenous nucleic acid is expressed in a sufficient amount to produce the desired product, and it is further understood that expression levels can be optimized to obtain sufficient expression using methods well known in the art and as disclosed herein.
In some embodiments, a method for producing acrylate, includes culturing a non-naturally occurring microbial organism having an acrylate pathway. The pathway includes at least one exogenous nucleic acid encoding an acrylate pathway enzyme expressed in a sufficient amount to produce acrylate under conditions and for a sufficient period of time to produce acrylate. Ideally, the non-naturally occurring microbial organism is in a substantially anaerobic culture medium as described above.
The acrylate pathway includes a decarboxylase gene introduced into an organism that is engineered to produce high levels of fumaric acid under anaerobic conditions from carbon substrates such as glucose or sucrose. Expression of active decarboxylases for the production of chemicals previously has been demonstrated in E. coli (Sariaslani, F. S., Annu. Rev. Microbiol. 61:51-69 (2007)). In this scenario, decarboxylation of fumaric acid occurs intracellularly and acrylate is produced directly and is secreted from the cell and recovered through standard methods employed for acid separation and purification.
One challenge with direct acrylate production could be the known cellular toxicity of acrylic acid and acrylate salts (Straathof et al., Appl. Microbiol. Biotechnol. 67:727-734 (2005)). Selection of an appropriate production organism involves detailed acrylate toxicity assessment in order to determine inherent levels of tolerance. In addition, adaptive evolution methods are applied to the production host to increase tolerance to acrylate up to the required levels of acrylate (e.g., 5-10% final titers). Previous studies have found evolution to be useful for increasing tolerance of microorganisms to organic acids (Steiner 2003; Patnaik 2002). It has been estimated that production of at least 50 g/L acrylate should be possible through fermentation processes (Straathof et al., Appl. Microbiol. Biotechnol. 67, 727-734 (2005)). Should the toxicity of acrylate prove too high for effective production (the world wide web at toxnet.nlm.nih.gov/cgi-bin/sis/search/r?dbs+hsdb:@term+@rn+@rel+79-10-7 indicates that toxicity to bacteria is low), a second approach involves primary production and secretion of fumarate into a fermentation broth, followed by secondary addition of separately produced decarboxylase enzyme. This approach allows effective conversion of fumarate to acrylate without concern for cell viability. Subsequent processing will be the same as above, involving separation and purification of acrylic acid directly from the broth with no need to separate or isolate fumaric acid prior to treatment with decarboxylase.
An alternative to this production mode is to engineer a decarboxylase enzyme so that it is secreted from the fumarate-producing cell, in which case acrylate production occurs in the same vessel as fumarate production. This approach is particularly effective if decarboxylase enzyme production and secretion are subject to inducible programming (e.g., using a temperature sensitive promoter) such that the enzyme is produced and secreted into the broth following completion of fumarate production.
Thus, in some embodiments, the present invention provides a method for producing acrylate, that includes culturing a first non-naturally occurring microbial organism having one or more gene disruptions. Again, the one or more gene disruptions can occur in one or more genes encoding one or more enzymes obligatory to coupling fumarate production to growth of the microorganism when the disruptions reduce an activity of the enzymes such that the disruptions confer stable growth-coupled production of fumarate. Finally, one adds a decarboxylase to the cultured first non-naturally occurring microbial organism, said decarboxylase catalyzing the decarboxylation of fumarate.
In some embodiments, the decarboxylase is expressed in a second non-naturally occurring microbial organism. In such an instance, the first and second non-naturally occurring microbial organisms can be co-cultured. Additionally, the decarboxylase can also be secreted by a second non-naturally occurring microbial organism which still allows for the first and second microbial organisms to be co-cultured.
Suitable purification and/or assays to test for the production of acrylate can be performed using well known methods. Suitable replicates such as triplicate cultures can be grown for each engineered strain to be tested. For example, product and byproduct formation in the engineered production host can be monitored. The final product and intermediates, and other organic compounds, can be analyzed by methods such as HPLC (High Performance Liquid Chromatography), GC-MS (Gas Chromatography-Mass Spectroscopy) and LC-MS (Liquid Chromatography-Mass Spectroscopy) or other suitable analytical methods using routine procedures well known in the art. The release of product in the fermentation broth can also be tested with the culture supernatant. Byproducts and residual glucose can be quantified by HPLC using, for example, a refractive index detector for glucose and alcohols, and a UV detector for organic acids (Lin et al., Biotechnol. Bioeng. 90:775-779 (2005)), or other suitable assay and detection methods well known in the art. The individual enzyme or protein activities from the exogenous DNA sequences can also be assayed using methods well known in the art.
The acrylate can be separated from other components in the culture using a variety of methods well known in the art. Such separation methods include, for example, extraction procedures as well as methods that include continuous liquid-liquid extraction, pervaporation, membrane filtration, membrane separation, reverse osmosis, electrodialysis, distillation, crystallization, centrifugation, extractive filtration, ion exchange chromatography, size exclusion chromatography, adsorption chromatography, and ultrafiltration. All of the above methods are well known in the art.
Any of the non-naturally occurring microbial organisms described herein can be cultured to produce and/or secrete the biosynthetic products of the invention. For example, the acrylate producers can be cultured for the biosynthetic production of acrylate.
For the production of acrylate, the recombinant strains are cultured in a medium with carbon source and other essential nutrients. It is highly desirable to maintain anaerobic conditions in the fermenter to reduce the cost of the overall process. Such conditions can be obtained, for example, by first sparging the medium with nitrogen and then sealing the flasks with a septum and crimp-cap. For strains where growth is not observed anaerobically, microaerobic conditions can be applied by perforating the septum with a small hole for limited aeration. Exemplary anaerobic conditions have been described previously and are well-known in the art. Exemplary aerobic and anaerobic conditions are described, for example, in U.S. patent application Ser. No. 11/891,602, filed Aug. 10, 2007. Fermentations can be performed in a batch, fed-batch or continuous manner, as disclosed herein.
If desired, the pH of the medium can be maintained at a desired pH, in particular neutral pH, such as a pH of around 7 by addition of a base, such as NaOH or other bases, or acid, as needed to maintain the culture medium at a desirable pH. The growth rate can be determined by measuring optical density using a spectrophotometer (600 nm), and the glucose uptake rate by monitoring carbon source depletion over time.
The growth medium can be, for example, any carbohydrate source which can supply a source of carbon to the non-naturally occurring microorganism. Such sources include, for example, sugars such as glucose, xylose, arabinose, galactose, mannose, fructose and starch. Other sources of carbohydrate include, for example, renewable feedstocks and biomass. Exemplary types of biomasses that can be used as feedstocks in the methods of the invention include cellulosic biomass, hemicellulosic biomass and lignin feedstocks or portions of feedstocks. Such biomass feedstocks contain, for example, carbohydrate substrates useful as carbon sources such as glucose, xylose, arabinose, galactose, mannose, fructose and starch. Given the teachings and guidance provided herein, those skilled in the art will understand that renewable feedstocks and biomass other than those exemplified above also can be used for culturing the microbial organisms of the invention for the production of acrylate.
In addition to renewable feedstocks such as those exemplified above, the acrylate microbial organisms of the invention also can be modified for growth on syngas as its source of carbon. In this specific embodiment, one or more proteins or enzymes are expressed in the acrylate producing organisms to provide a metabolic pathway for utilization of syngas or other gaseous carbon source.
Synthesis gas, also known as syngas or producer gas, is the major product of gasification of coal and of carbonaceous materials such as biomass materials, including agricultural crops and residues. Syngas is a mixture primarily of H 2 and CO and can be obtained from the gasification of any organic feedstock, including but not limited to coal, coal oil, natural gas, biomass, and waste organic matter. Gasification is generally carried out under a high fuel to oxygen ratio. Although largely H 2 and CO, syngas can also include CO 2 and other gases in smaller quantities. Thus, synthesis gas provides a cost effective source of gaseous carbon such as CO and, additionally, CO 2 .
The Wood-Ljungdahl pathway catalyzes the conversion of CO and H 2 to acetyl-CoA and other products such as acetate. Organisms capable of utilizing CO and syngas also generally have the capability of utilizing CO 2 and CO 2 /H 2 mixtures through the same basic set of enzymes and transformations encompassed by the Wood-Ljungdahl pathway. H 2 -dependent conversion of CO 2 to acetate by microorganisms was recognized long before it was revealed that CO also could be used by the same organisms and that the same pathways were involved. Many acetogens have been shown to grow in the presence of CO 2 and produce compounds such as acetate as long as hydrogen is present to supply the necessary reducing equivalents (see for example, Drake, Acetogenesis , pp. 3-60 Chapman and Hall, New York, (1994)). This can be summarized by the following equation:
2CO 2 +4H 2 +nADP+nPi →CH 3 COOH+2H 2 O+ nATP
Hence, non-naturally occurring microorganisms possessing the Wood-Ljungdahl pathway can utilize CO 2 and H 2 mixtures as well for the production of acetyl-CoA and other desired products.
The Wood-Ljungdahl pathway is well known in the art and consists of 12 reactions which can be separated into two branches: (1) methyl branch and (2) carbonyl branch. The methyl branch converts syngas to methyl-tetrahydrofolate (methyl-THF) whereas the carbonyl branch converts methyl-THF to acetyl-CoA. The reactions in the methyl branch are catalyzed in order by the following enzymes or proteins: ferredoxin oxidoreductase, formate dehydrogenase, formyltetrahydrofolate synthetase, methenyltetrahydrofolate cyclodehydratase, methylenetetrahydrofolate dehydrogenase and methylenetetrahydrofolate reductase. The reactions in the carbonyl branch are catalyzed in order by the following enzymes or proteins: cobalamide corrinoid/iron-sulfur protein, methyltransferase, carbon monoxide dehydrogenase, acetyl-CoA synthase, acetyl-CoA synthase disulfide reductase and hydrogenase. Following the teachings and guidance provided herein for introducing a sufficient number of encoding nucleic acids to generate an acrylate pathway, those skilled in the art will understand that the same engineering design also can be performed with respect to introducing at least the nucleic acids encoding the Wood-Ljungdahl enzymes or proteins absent in the host organism. Therefore, introduction of one or more encoding nucleic acids into the microbial organisms of the invention such that the modified organism contains the complete Wood-Ljungdahl pathway will confer syngas utilization ability.
Accordingly, given the teachings and guidance provided herein, those skilled in the art will understand that a non-naturally occurring microbial organism can be produced that secretes the biosynthesized compounds of the invention when grown on a carbon source such as a carbohydrate. Such compounds include, for example, acrylate and any of the intermediate metabolites in the acrylate pathway. All that is required is to engineer in one or more of the required enzyme or protein activities to achieve biosynthesis of the desired compound or intermediate including, for example, inclusion of some or all of the acrylate biosynthetic pathways. Accordingly, the invention provides a non-naturally occurring microbial organism that produces and/or secretes acrylate when grown on a carbohydrate or other carbon source and produces and/or secretes any of the intermediate metabolites shown in the acrylate pathway when grown on a carbohydrate or other carbon source. The acrylate producing microbial organisms of the invention can initiate synthesis from an intermediate, for example, fumarate.
The non-naturally occurring microbial organisms of the invention are constructed using methods well known in the art as exemplified herein to exogenously express at least one nucleic acid encoding an acrylate pathway enzyme or protein in sufficient amounts to produce acrylate. It is understood that the microbial organisms of the invention are cultured under conditions sufficient to produce acrylate. Following the teachings and guidance provided herein, the non-naturally occurring microbial organisms of the invention can achieve biosynthesis of acrylate resulting in intracellular concentrations between about 0.1-200 mM or more. Generally, the intracellular concentration of acrylate is between about 3-150 mM, particularly between about 5-125 mM and more particularly between about 8-100 mM, including about 10 mM, 20 mM, 50 mM, 80 mM, or more. Intracellular concentrations between and above each of these exemplary ranges also can be achieved from the non-naturally occurring microbial organisms of the invention.
The fumarate, malate, or acrylate can be separated from other components in the culture using a variety of methods well known in the art. Such separation methods include, for example, extraction procedures as well as methods that include continuous liquid-liquid extraction, pervaporation, membrane filtration, membrane separation, reverse osmosis, electrodialysis, distillation, crystallization, centrifugation, extractive filtration, ion exchange chromatography, size exclusion chromatography, adsorption chromatography, and ultrafiltration. All of the above methods are well known in the art.
Any of the non-naturally occurring microbial organisms described herein can be cultured to produce and/or secrete the biosynthetic products of the invention. For example, the fumarate, malate, or acrylate producers can be cultured for the biosynthetic production of fumarate, malate, or acrylate.
For the production of fumarate, malate, or acrylate, the recombinant strains are cultured in a medium with carbon source and other essential nutrients. It is highly desirable to maintain anaerobic conditions in the fermenter to reduce the cost of the overall process. Such conditions can be obtained, for example, by first sparging the medium with nitrogen and then sealing the flasks with a septum and crimp-cap. For strains where growth is not observed anaerobically, microaerobic conditions can be applied by perforating the septum with a small hole for limited aeration. Exemplary anaerobic conditions have been described previously and are well-known in the art. Exemplary aerobic and anaerobic conditions are described, for example, in U.S. patent application Ser. No. 11/891,602, filed Aug. 10, 2007. Fermentations can be performed in a batch, fed-batch or continuous manner, as disclosed herein.
If desired, the pH of the medium can be maintained at a desired pH, in particular neutral pH, such as a pH of around 7 by addition of a base, such as NaOH or other bases, or acid, as needed to maintain the culture medium at a desirable pH. The growth rate can be determined by measuring optical density using a spectrophotometer (600 nm), and the glucose uptake rate by monitoring carbon source depletion over time.
The growth medium can include, for example, any carbohydrate source which can supply a source of carbon to the non-naturally occurring microorganism. Such sources include, for example, sugars such as glucose, xylose, arabinose, galactose, mannose, fructose and starch. Other sources of carbohydrate include, for example, renewable feedstocks and biomass. Exemplary types of biomasses that can be used as feedstocks in the methods of the invention include cellulosic biomass, hemicellulosic biomass and lignin feedstocks or portions of feedstocks. Such biomass feedstocks contain, for example, carbohydrate substrates useful as carbon sources such as glucose, xylose, arabinose, galactose, mannose, fructose and starch. Given the teachings and guidance provided herein, those skilled in the art will understand that renewable feedstocks and biomass other than those exemplified above also can be used for culturing the microbial organisms of the invention for the production of fumarate, malate, or acrylate.
In addition to renewable feedstocks such as those exemplified above, the fumarate, malate, or acrylate microbial organisms of the invention also can be modified for growth on syngas as its source of carbon. In this specific embodiment, one or more proteins or enzymes are expressed in the fumarate, malate, or acrylate producing organisms to provide a metabolic pathway for utilization of syngas or other gaseous carbon source.
Synthesis gas, also known as syngas or producer gas, is the major product of gasification of coal and of carbonaceous materials such as biomass materials, including agricultural crops and residues. Syngas is a mixture primarily of H 2 and CO and can be obtained from the gasification of any organic feedstock, including but not limited to coal, coal oil, natural gas, biomass, and waste organic matter. Gasification is generally carried out under a high fuel to oxygen ratio. Although largely H 2 and CO, syngas can also include CO 2 and other gases in smaller quantities. Thus, synthesis gas provides a cost effective source of gaseous carbon such as CO and, additionally, CO 2 .
The Wood-Ljungdahl pathway catalyzes the conversion of CO and H 2 to acetyl-CoA and other products such as acetate. Organisms capable of utilizing CO and syngas also generally have the capability of utilizing CO 2 and CO 2 /H 2 mixtures through the same basic set of enzymes and transformations encompassed by the Wood-Ljungdahl pathway. H 2 -dependent conversion of CO 2 to acetate by microorganisms was recognized long before it was revealed that CO also could be used by the same organisms and that the same pathways were involved. Many acetogens have been shown to grow in the presence of CO 2 and produce compounds such as acetate as long as hydrogen is present to supply the necessary reducing equivalents (see for example, Drake, Acetogenesis , pp. 3-60 Chapman and Hall, New York, (1994)). This can be summarized by the following equation:
2CO 2 +4H 2 +nADP+nPi →CH 3 COOH+2H 2 O+ nATP
Hence, non-naturally occurring microorganisms possessing the Wood-Ljungdahl pathway can utilize CO 2 and H 2 mixtures as well for the production of acetyl-CoA and other desired products.
The Wood-Ljungdahl pathway is well known in the art and consists of 12 reactions which can be separated into two branches: (1) methyl branch and (2) carbonyl branch. The methyl branch converts syngas to methyl-tetrahydrofolate (methyl-THF) whereas the carbonyl branch converts methyl-THF to acetyl-CoA. The reactions in the methyl branch are catalyzed in order by the following enzymes or proteins: ferredoxin oxidoreductase, formate dehydrogenase, formyltetrahydrofolate synthetase, methenyltetrahydrofolate cyclodehydratase, methylenetetrahydrofolate dehydrogenase and methylenetetrahydrofolate reductase. The reactions in the carbonyl branch are catalyzed in order by the following enzymes or proteins: methyltetrahydrofolate:corrinoid protein methyltransferase (for example, AcsE), corrinoid iron-sulfur protein, nickel-protein assembly protein (for example, AcsF), ferredoxin, acetyl-CoA synthase, carbon monoxide dehydrogenase and nickel-protein assembly protein (for example, CooC). Following the teachings and guidance provided herein for introducing a sufficient number of encoding nucleic acids to generate a fumarate, malate, or acrylate pathway, those skilled in the art will understand that the same engineering design also can be performed with respect to introducing at least the nucleic acids encoding the Wood-Ljungdahl enzymes or proteins absent in the host organism. Therefore, introduction of one or more encoding nucleic acids into the microbial organisms of the invention such that the modified organism contains the complete Wood-Ljungdahl pathway will confer syngas utilization ability.
Accordingly, given the teachings and guidance provided herein, those skilled in the art will understand that a non-naturally occurring microbial organism can be produced that secretes the biosynthesized compounds of the invention when grown on a carbon source such as a carbohydrate. Such compounds include, for example, fumarate, malate, or acrylate and any of the intermediate metabolites in the fumarate, malate, or acrylate pathway. All that is required is to engineer in one or more of the required enzyme or protein activities to achieve biosynthesis of the desired compound or intermediate including, for example, inclusion of some or all of the fumarate, malate, or acrylate biosynthetic pathways. Accordingly, the invention provides a non-naturally occurring microbial organism that produces and/or secretes fumarate, malate, or acrylate when grown on a carbohydrate or other carbon source and produces and/or secretes any of the intermediate metabolites shown in the fumarate, malate, or acrylate pathway when grown on a carbohydrate or other carbon source. The fumarate, malate, or acrylate producing microbial organisms of the invention can initiate synthesis from any of the aforementioned intermediates.
The non-naturally occurring microbial organisms of the invention are constructed using methods well known in the art as exemplified herein to exogenously express at least one nucleic acid encoding a fumarate, malate, or acrylate pathway enzyme or protein in sufficient amounts to produce fumarate, malate, or acrylate. It is understood that the microbial organisms of the invention are cultured under conditions sufficient to produce fumarate, malate, or acrylate. Following the teachings and guidance provided herein, the non-naturally occurring microbial organisms of the invention can achieve biosynthesis of fumarate, malate, or acrylate resulting in intracellular concentrations between about 0.1-200 mM or more. Generally, the intracellular concentration of fumarate, malate, or acrylate is between about 3-200 mM, particularly between about 10-175 mM and more particularly between about 50-150 mM, including about 50 mM, 75 mM, 100 mM, 125 mM, or more. Intracellular concentrations between and above each of these exemplary ranges also can be achieved from the non-naturally occurring microbial organisms of the invention.
In some embodiments, culture conditions include anaerobic or substantially anaerobic growth or maintenance conditions. Exemplary anaerobic conditions have been described previously and are well known in the art. Exemplary anaerobic conditions for fermentation processes are described herein and are described, for example, in U.S. patent application Ser. No. 11/891,602, filed Aug. 10, 2007. Any of these conditions can be employed with the non-naturally occurring microbial organisms as well as other anaerobic conditions well known in the art. Under such anaerobic conditions, the fumarate, malate, or acrylate producers can synthesize fumarate, malate, or acrylate at intracellular concentrations of 5-10 mM or more as well as all other concentrations exemplified herein. It is understood that, even though the above description refers to intracellular concentrations, fumarate, malate, or acrylate producing microbial organisms can produce fumarate, malate, or acrylate intracellularly and/or secrete the product into the culture medium.
The culture conditions can include, for example, liquid culture procedures as well as fermentation and other large scale culture procedures. As described herein, particularly useful yields of the biosynthetic products of the invention can be obtained under anaerobic or substantially anaerobic culture conditions.
As described herein, one exemplary growth condition for achieving biosynthesis of fumarate, malate, or acrylate includes anaerobic culture or fermentation conditions. In certain embodiments, the non-naturally occurring microbial organisms of the invention can be sustained, cultured or fermented under anaerobic or substantially anaerobic conditions. Briefly, anaerobic conditions refers to an environment devoid of oxygen. Substantially anaerobic conditions include, for example, a culture, batch fermentation or continuous fermentation such that the dissolved oxygen concentration in the medium remains between 0 and 10% of saturation. Substantially anaerobic conditions also includes growing or resting cells in liquid medium or on solid agar inside a sealed chamber maintained with an atmosphere of less than 1% oxygen. The percent of oxygen can be maintained by, for example, sparging the culture with an N 2 /CO 2 mixture or other suitable non-oxygen gas or gases.
The culture conditions described herein can be scaled up and grown continuously for manufacturing of fumarate, malate, or acrylate. Exemplary growth procedures include, for example, fed-batch fermentation and batch separation; fed-batch fermentation and continuous separation, or continuous fermentation and continuous separation. All of these processes are well known in the art. Fermentation procedures are particularly useful for the biosynthetic production of commercial quantities of fumarate, malate, or acrylate. Generally, and as with non-continuous culture procedures, the continuous and/or near-continuous production of fumarate, malate, or acrylate can include culturing a non-naturally occurring fumarate, malate, or acrylate producing organism of the invention in sufficient nutrients and medium to sustain and/or nearly sustain growth in an exponential phase. Continuous culture under such conditions can include, for example, 1 day, 2, 3, 4, 5, 6 or 7 days or more. Additionally, continuous culture can include 1 week, 2, 3, 4 or 5 or more weeks and up to several months. Alternatively, organisms of the invention can be cultured for hours, if suitable for a particular application. It is to be understood that the continuous and/or near-continuous culture conditions also can include all time intervals in between these exemplary periods. It is further understood that the time of culturing the microbial organism of the invention is for a sufficient period of time to produce a sufficient amount of product for a desired purpose.
Fermentation procedures are well known in the art. Briefly, fermentation for the biosynthetic production of fumarate, malate, or acrylate can be utilized in, for example, fed-batch fermentation and batch separation; fed-batch fermentation and continuous separation, or continuous fermentation and continuous separation. Examples of batch and continuous fermentation procedures are well known in the art.
In addition to the above fermentation procedures using the fumarate, malate, or acrylate producers of the invention for continuous production of substantial quantities of fumarate, malate, or acrylate, the fumarate, malate, or acrylate producers also can be, for example, simultaneously subjected to chemical synthesis procedures to convert the product to other compounds or the product can be separated from the fermentation culture and sequentially subjected to chemical conversion to convert the product to other compounds, if desired.
Directed evolution is a powerful approach that involves the introduction of mutations targeted to a specific gene in order to improve and/or alter the properties of an enzyme. Improved and/or altered enzymes can be identified through the development and implementation of sensitive high-throughput screening assays that allow the automated screening of many enzyme variants (e.g., >10 4 ). Iterative rounds of mutagenesis and screening typically are performed to afford an enzyme with optimized properties. Computational algorithms that can help to identify areas of the gene for mutagenesis also have been developed and can significantly reduce the number of enzyme variants that need to be generated and screened.
Numerous directed evolution technologies have been developed (for reviews, see Hibbert et al., Biomol. Eng 22:11-19 (2005); Huisman et al., Biocatalysis in the pharmaceutical and biotechnology industries, pp. 717-742 (2007) CRC Press, R. N. Patel, Ed.); Otten et al., Biomol. Eng 22:1-9 (2005); and Sen et al., Appl Biochem. Biotechnol 143:212-223 (2007).) to be effective at creating diverse variant libraries and these methods have been successfully applied to the improvement of a wide range of properties across many enzyme classes.
Enzyme characteristics that have been improved and/or altered by directed evolution technologies include, for example, selectivity/specificity—for conversion of non-natural substrates; temperature stability—for robust high temperature processing; pH stability—for bioprocessing under lower or higher pH conditions; substrate or product tolerance—so that high product titers can be achieved; binding (K m )—broadens substrate binding to include non-natural substrates; inhibition (K i )—to remove inhibition by products, substrates, or key intermediates; activity (kcat)—increases enzymatic reaction rates to achieve desired flux; expression levels -increases protein yields and overall pathway flux; oxygen stability—for operation of air sensitive enzymes under aerobic conditions; and anaerobic activity—for operation of an aerobic enzyme in the absence of oxygen.
The following exemplary methods have been developed for the mutagenesis and diversification of genes to target desired properties of specific enzymes. Any of these can be used to alter/optimize activity of a decarboxylase enzyme.
EpPCR (Pritchard et al., J. Theor. Biol. 234:497-509 (2005).) introduces random point mutations by reducing the fidelity of DNA polymerase in PCR reactions by the addition of Mn 2+ ions, by biasing dNTP concentrations, or by other conditional variations. The five step cloning process to confine the mutagenesis to the target gene of interest involves: 1) error-prone PCR amplification of the gene of interest; 2) restriction enzyme digestion; 3) gel purification of the desired DNA fragment; 4) ligation into a vector; 5) transformation of the gene variants into a suitable host and screening of the library for improved performance. This method can generate multiple mutations in a single gene simultaneously, which can be useful. A high number of mutants can be generated by EpPCR, so a high-throughput screening assay or a selection method (especially using robotics) is useful to identify those with desirable characteristics.
Error-prone Rolling Circle Amplification (epRCA) (Fujii et al., Nucl. Acids Res 32:e145 (2004); and Fujii et al., Nat. Protoc. 1:2493-2497 (2006).) has many of the same elements as epPCR except a whole circular plasmid is used as the template and random 6-mers with exonuclease resistant thiophosphate linkages on the last 2 nucleotides are used to amplify the plasmid followed by transformation into cells in which the plasmid is re-circularized at tandem repeats. Adjusting the Mn 2+ concentration can vary the mutation rate somewhat. This technique uses a simple error-prone, single-step method to create a full copy of the plasmid with 3-4 mutations/kbp. No restriction enzyme digestion or specific primers are required. Additionally, this method is typically available as a kit.
DNA or Family Shuffling (Stemmer, W. P., Proc Natl Acad Sci U.S.A. 91:10747-10751 (1994); and Stemmer, W. P., Nature 370:389-391 (1994).) typically involves digestion of 2 or more variant genes with nucleases such as Dnase I or EndoV to generate a pool of random fragments that are reassembled by cycles of annealing and extension in the presence of DNA polymerase to create a library of chimeric genes. Fragments prime each other and recombination occurs when one copy primes another copy (template switch). This method can be used with >1 kbp DNA sequences. In addition to mutational recombinants created by fragment reassembly, this method introduces point mutations in the extension steps at a rate similar to error-prone PCR. The method can be used to remove deleterious random neutral mutations that might confer antigenicity.
Staggered Extension (StEP) (Zhao et al., Nat. Biotechnol 16:258-261 (1998).) entails template priming followed by repeated cycles of 2 step PCR with denaturation and very short duration of annealing/extension (as short as 5 sec). Growing fragments anneal to different templates and extend further, which is repeated until full-length sequences are made. Template switching means most resulting fragments have multiple parents. Combinations of low-fidelity polymerases (Taq and Mutazyme) reduce error-prone biases because of opposite mutational spectra.
In Random Priming Recombination (RPR) random sequence primers are used to generate many short DNA fragments complementary to different segments of the template. (Shao et al., Nucleic Acids Res 26:681-683 (1998).) Base misincorporation and mispriming via epPCR give point mutations. Short DNA fragments prime one another based on homology and are recombined and reassembled into full-length by repeated thermocycling. Removal of templates prior to this step assures low parental recombinants. This method, like most others, can be performed over multiple iterations to evolve distinct properties. This technology avoids sequence bias, is independent of gene length, and requires very little parent DNA for the application.
In Heteroduplex Recombination linearized plasmid DNA is used to form heteroduplexes that are repaired by mismatch repair. (Volkov et al., Nucleic Acids Res 27:e18 (1999); and Volkov et al., Methods Enzymol. 328:456-463 (2000).) The mismatch repair step is at least somewhat mutagenic. Heteroduplexes transform more efficiently than linear homoduplexes. This method is suitable for large genes and whole operons.
Random Chimeragenesis on Transient Templates (RACHITT) (Coco et al., Nat. Biotechnol 19:354-359 (2001).) employs Dnase I fragmentation and size fractionation of ssDNA. Homologous fragments are hybridized in the absence of polymerase to a complementary ssDNA scaffold. Any overlapping unhybridized fragment ends are trimmed down by an exonuclease. Gaps between fragments are filled in, and then ligated to give a pool of full-length diverse strands hybridized to the scaffold (that contains U to preclude amplification). The scaffold then is destroyed and is replaced by a new strand complementary to the diverse strand by PCR amplification. The method involves one strand (scaffold) that is from only one parent while the priming fragments derive from other genes; the parent scaffold is selected against. Thus, no reannealing with parental fragments occurs. Overlapping fragments are trimmed with an exonuclease. Otherwise, this is conceptually similar to DNA shuffling and StEP. Therefore, there should be no siblings, few inactives, and no unshuffled parentals. This technique has advantages in that few or no parental genes are created and many more crossovers can result relative to standard DNA shuffling.
Recombined Extension on Truncated templates (RETT) entails template switching of unidirectionally growing strands from primers in the presence of unidirectional ssDNA fragments used as a pool of templates. (Lee et al., J. Molec. Catalysis 26:119-129 (2003).) No DNA endonucleases are used. Unidirectional ssDNA is made by DNA polymerase with random primers or serial deletion with exonuclease. Unidirectional ssDNA are only templates and not primers. Random priming and exonucleases don't introduce sequence bias as true of enzymatic cleavage of DNA shuffling/RACHITT. RETT can be easier to optimize than StEP because it uses normal PCR conditions instead of very short extensions. Recombination occurs as a component of the PCR steps—no direct shuffling. This method can also be more random than StEP due to the absence of pauses.
In Degenerate Oligonucleotide Gene Shuffling (DOGS) degenerate primers are used to control recombination between molecules; (Bergquist et al., Methods Mol. Biol. 352:191-204 (2007); Bergquist et al., Biomol. Eng 22:63-72 (2005); Gibbs et al., Gene 271:13-20 (2001).) This can be used to control the tendency of other methods such as DNA shuffling to regenerate parental genes. This method can be combined with random mutagenesis (epPCR) of selected gene segments. This can be a good method to block the reformation of parental sequences. No endonucleases are needed. By adjusting input concentrations of segments made, one can bias towards a desired backbone. This method allows DNA shuffling from unrelated parents without restriction enzyme digests and allows a choice of random mutagenesis methods.
Incremental Truncation for the Creation of Hybrid Enzymes (ITCHY) creates a combinatorial library with 1 base pair deletions of a gene or gene fragment of interest. (Ostermeier et al., Proc Natl Acad Sci U. S. A 96:3562-3567 (1999); Ostermeier et la., Nat. Biotechnol 17:1205-1209 (1999).) Truncations are introduced in opposite direction on pieces of 2 different genes. These are ligated together and the fusions are cloned. This technique does not require homology between the 2 parental genes. When ITCHY is combined with DNA shuffling, the system is called SCRATCHY (see below). A major advantage of both is no need for homology between parental genes; for example, functional fusions between an E. coli and a human gene were created via ITCHY. When ITCHY libraries are made, all possible crossovers are captured.
Thio-Incremental Truncation for the Creation of Hybrid Enzymes (THIO-ITCHY) is almost the same as ITCHY except that phosphothioate dNTPs are used to generate truncations. (Lutz et al., Nucleic Acids Res 29:E16 (2001).) Relative to ITCHY, THIO-ITCHY can be easier to optimize, provide more reproducibility, and adjustability.
SCRATCHY-ITCHY combined with DNA shuffling is a combination of DNA shuffling and ITCHY; therefore, allowing multiple crossovers. (Lutz et al. 2001, Proc Natl Acad Sci U.S.A. 98:11248-11253 (2001).) SCRATCHY combines the best features of ITCHY and DNA shuffling. Computational predictions can be used in optimization. SCRATCHY is more effective than DNA shuffling when sequence identity is below 80%.
In Random Drift Mutagenesis (RNDM) mutations made via epPCR followed by screening/selection for those retaining usable activity. (Bergquist et al., Biomol. Eng 22:63-72 (2005).) Then, these are used in DOGS to generate recombinants with fusions between multiple active mutants or between active mutants and some other desirable parent. Designed to promote isolation of neutral mutations; its purpose is to screen for retained catalytic activity whether or not this activity is higher or lower than in the original gene. RNDM is usable in high throughput assays when screening is capable of detecting activity above background. RNDM has been used as a front end to DOGS in generating diversity. The technique imposes a requirement for activity prior to shuffling or other subsequent steps; neutral drift libraries are indicated to result in higher/quicker improvements in activity from smaller libraries. Though published using epPCR, this could be applied to other large-scale mutagenesis methods.
Sequence Saturation Mutagenesis (SeSaM) is a random mutagenesis method that: 1) generates pool of random length fragments using random incorporation of a phosphothioate nucleotide and cleavage; this pool is used as a template to 2) extend in the presence of “universal” bases such as inosine; 3) replication of a inosine-containing complement gives random base incorporation and, consequently, mutagenesis. (Wong et al., Biotechnol J 3:74-82 (2008); Wong et al., Nucleic Acids Res 32:e26 (2004); and Wong et al., Anal. Biochem. 341:187-189 (2005).) Using this technique it can be possible to generate a large library of mutants within 2-3 days using simple methods. This is very non-directed compared to mutational bias of DNA polymerases. Differences in this approach makes this technique complementary (or alternative) to epPCR.
In Synthetic Shuffling, overlapping oligonucleotides are designed to encode “all genetic diversity in targets” and allow a very high diversity for the shuffled progeny. (Ness et al., Nat. Biotechnol 20:1251-1255 (2002).) In this technique, one can design the fragments to be shuffled. This aids in increasing the resulting diversity of the progeny. One can design sequence/codon biases to make more distantly related sequences recombine at rates approaching more closely related sequences and it doesn't require possessing the template genes physically.
Nucleotide Exchange and Excision Technology NexT exploits a combination of dUTP incorporation followed by treatment with uracil DNA glycosylase and then piperidine to perform endpoint DNA fragmentation. (Muller et al., Nucleic Acids Res 33:e117 (2005).) The gene is reassembled using internal PCR primer extension with proofreading polymerase. The sizes for shuffling are directly controllable using varying dUPT::dTTP ratios. This is an end point reaction using simple methods for uracil incorporation and cleavage. One can use other nucleotide analogs such as 8-oxo-guanine with this method. Additionally, the technique works well with very short fragments (86 bp) and has a low error rate. Chemical cleavage of DNA means very few unshuffled clones.
In Sequence Homology-Independent Protein Recombination (SHIPREC) a linker is used to facilitate fusion between 2 distantly/unrelated genes; nuclease treatment is used to generate a range of chimeras between the two. Result is a single crossover library of these fusions. (Sieber et al., Nat. Biotechnol 19:456-460 (2001).) This produces a limited type of shuffling; mutagenesis is a separate process. This technique can create a library of chimeras with varying fractions of each of 2 unrelated parent genes. No homology is needed. SHIPREC was tested with a heme-binding domain of a bacterial CP450 fused to N-terminal regions of a mammalian CP450; this produced mammalian activity in a more soluble enzyme.
In Gene Site Saturation Mutagenesis (GSSM) the starting materials are a supercoiled dsDNA plasmid with insert and 2 primers degenerate at the desired site for mutations. (Kretz et al., Methods Enzymol. 388:3-11 (2004).) Primers carry the mutation of interest and anneal to the same sequence on opposite strands of DNA; mutation in the middle of the primer and ˜20 nucleotides of correct sequence flanking on each side. The sequence in the primer is NNN or NNK (coding) and MNN (noncoding) (N=all 4, K=G, T, M=A, C). After extension, DpnI is used to digest dam-methylated DNA to eliminate the wild-type template. This technique explores all possible amino acid substitutions at a given locus (i.e., one codon). The technique facilitates the generation of all possible replacements at one site with no nonsense codons and equal or near-equal representation of most possible alleles. It does not require prior knowledge of structure, mechanism, or domains of the target enzyme. If followed by shuffling or Gene Reassembly, this technology creates a diverse library of recombinants containing all possible combinations of single-site up-mutations. The utility of this technology combination has been demonstrated for the successful evolution of over 50 different enzymes, and also for more than one property in a given enzyme.
Combinatorial Cassette Mutagenesis (CCM) involves the use of short oligonucleotide cassettes to replace limited regions with a large number of possible amino acid sequence alterations. (Reidhaar-Olson et al., Methods Enzymol. 208:564-586 (1991); and Reidhaar-Olson et al., Science 241:53-57 (1988).) Simultaneous substitutions at 2 or 3 sites are possible using this technique. Additionally, the method tests a large multiplicity of possible sequence changes at a limited range of sites. It has been used to explore the information content of lambda repressor DNA-binding domain.
Combinatorial Multiple Cassette Mutagenesis (CMCM) is essentially similar to CCM except it is employed as part of a larger program: 1) Use of epPCR at high mutation rate to 2) ID hot spots and hot regions and then 3) extension by CMCM to cover a defined region of protein sequence space. (Reetz et al., Angew. Chem. Int. Ed Engl. 40:3589-3591 (2001).) As with CCM, this method can test virtually all possible alterations over a target region. If used along with methods to create random mutations and shuffled genes, it provides an excellent means of generating diverse, shuffled proteins. This approach was successful in increasing, by 51-fold, the enantioselectivity of an enzyme.
In the Mutator Strains technique conditional ts mutator plasmids allow increases of 20- to 4000-X in random and natural mutation frequency during selection and to block accumulation of deleterious mutations when selection is not required. (Selifonova et al., Appl Environ Microbiol 67:3645-3649 (2001).) This technology is based on a plasmid-derived mutD5 gene, which encodes a mutant subunit of DNA polymerase III. This subunit binds to endogenous DNA polymerase III and compromises the proofreading ability of polymerase III in any of the strain that harbors the plasmid. A broad-spectrum of base substitutions and frameshift mutations occur. In order for effective use, the mutator plasmid should be removed once the desired phenotype is achieved; this is accomplished through a temperature sensitive origin of replication, which allows plasmid curing at 41° C. It should be noted that mutator strains have been explored for quite some time (e.g., see Winter and coworkers, J. Mol. Biol. 260:359-3680 (1996). In this technique very high spontaneous mutation rates are observed. The conditional property minimizes non-desired background mutations. This technology could be combined with adaptive evolution to enhance mutagenesis rates and more rapidly achieve desired phenotypes.
“Look-Through Mutagenesis (LTM) is a multidimensional mutagenesis method that assesses and optimizes combinatorial mutations of selected amino acids.” (Rajpal et al., Proc Natl Acad Sci U.S.A 102:8466-8471 (2005.) Rather than saturating each site with all possible amino acid changes, a set of 9 is chosen to cover the range of amino acid R-group chemistry. Fewer changes per site allows multiple sites to be subjected to this type of mutagenesis. A >800-fold increase in binding affinity for an antibody from low nanomolar to picomolar has been achieved through this method. This is a rational approach to minimize the number of random combinations and should increase the ability to find improved traits by greatly decreasing the numbers of clones to be screened. This has been applied to antibody engineering, specifically to increase the binding affinity and/or reduce dissociation. The technique can be combined with either screens or selections.
Gene Reassembly is a DNA shuffling method that can be applied to multiple genes at one time or to creating a large library of chimeras (multiple mutations) of a single gene. (on the world-wide web at verenium.com/Pages/Technology/EnzymeTech/TechEnzyTGR.html) Typically this technology is used in combination with ultra-high-throughput screening to query the represented sequence space for desired improvements. This technique allows multiple gene recombination independent of homology. The exact number and position of cross-over events can be pre-determined using fragments designed via bioinformatic analysis. This technology leads to a very high level of diversity with virtually no parental gene reformation and a low level of inactive genes. Combined with GSSM, a large range of mutations can be tested for improved activity. The method allows “blending” and “fine tuning” of DNA shuffling, e.g. codon usage can be optimized.
In Silico Protein Design Automation PDA is an optimization algorithm that anchors the structurally defined protein backbone possessing a particular fold, and searches sequence space for amino acid substitutions that can stabilize the fold and overall protein energetics. (Hayes et al., Proc Natl Acad Sci U.S.A. 99:15926-15931 (2002).) This technology allows in silico structure-based entropy predictions in order to search for structural tolerance toward protein amino acid variations. Statistical mechanics is applied to calculate coupling interactions at each position—structural tolerance toward amino acid substitution is a measure of coupling. Ultimately, this technology is designed to yield desired modifications of protein properties while maintaining the integrity of structural characteristics. The method computationally assesses and allows filtering of a very large number of possible sequence variants (10 50 ). Choice of sequence variants to test is related to predictions based on most favorable thermodynamics and ostensibly only stability or properties that are linked to stability can be effectively addressed with this technology. The method has been successfully used in some therapeutic proteins, especially in engineering immunoglobulins. In silico predictions avoid testing extraordinarily large numbers of potential variants. Predictions based on existing three-dimensional structures are more likely to succeed than predictions based on hypothetical structures. This technology can readily predict and allow targeted screening of multiple simultaneous mutations, something not possible with purely experimental technologies due to exponential increases in numbers.
Iterative Saturation Mutagenesis (ISM) involves 1) Use knowledge of structure/function to choose a likely site for enzyme improvement. 2) Saturation mutagenesis at chosen site using Stratagene QuikChange (or other suitable means). 3) Screen/select for desired properties. 4) With improved clone(s), start over at another site and continue repeating. (Reetz et al., Nat. Protoc. 2:891-903 (2007); and Reetz et al., Angew. Chem. Int. Ed Engl. 45:7745-7751 (2006).) This is a proven methodology assures all possible replacements at a given position are made for screening/selection.
Any of the aforementioned methods for mutagenesis can be used alone or in any combination. Additionally, any one or combination of the directed evolution methods can be used in conjunction with adaptive evolution techniques.
To generate better producers, metabolic modeling can be utilized to optimize growth conditions. Modeling can also be used to design gene disruptions that additionally optimize utilization of the pathway (see, for example, U.S. patent publications US 2002/0012939, US 2003/0224363, US 2004/0029149, US 2004/0072723, US 2003/0059792, US 2002/0168654 and US 2004/0009466, and U.S. Pat. No. 7,127,379). Modeling analysis allows reliable predictions of the effects on cell growth of shifting the metabolism towards more efficient production of fumarate, malate, or acrylate.
Another computational method for identifying and designing metabolic alterations favoring biosynthetic production of a product is a metabolic modeling and simulation system termed SimPheny®. This computational method and system is described in, for example, U.S. publication 2003/0233218, filed Jun. 14, 2002, and in International Patent Application No. PCT/US03/18838, filed Jun. 13, 2003. SimPheny® is a computational system that can be used to produce a network model in silico and to simulate the flux of mass, energy or charge through the chemical reactions of a biological system to define a solution space that contains any and all possible functionalities of the chemical reactions in the system, thereby determining a range of allowed activities for the biological system. This approach is referred to as constraints-based modeling because the solution space is defined by constraints such as the known stoichiometry of the included reactions as well as reaction thermodynamic and capacity constraints associated with maximum fluxes through reactions. The space defined by these constraints can be interrogated to determine the phenotypic capabilities and behavior of the biological system or of its biochemical components.
These computational approaches are consistent with biological realities because biological systems are flexible and can reach the same result in many different ways. Biological systems are designed through evolutionary mechanisms that have been restricted by fundamental constraints that all living systems must face. Therefore, constraints-based modeling strategy embraces these general realities. Further, the ability to continuously impose further restrictions on a network model via the tightening of constraints results in a reduction in the size of the solution space, thereby enhancing the precision with which physiological performance or phenotype can be predicted.
Given the teachings and guidance provided herein, those skilled in the art will be able to apply various computational frameworks for metabolic modeling and simulation to design and implement biosynthesis of a desired compound in host microbial organisms. Such metabolic modeling and simulation methods include, for example, the computational systems exemplified above as SimPheny® and OptKnock. For illustration of the invention, some methods are described herein with reference to the OptKnock computation framework for modeling and simulation. Those skilled in the art will know how to apply the identification, design and implementation of the metabolic alterations using OptKnock to any of such other metabolic modeling and simulation computational frameworks and methods well known in the art.
The methods described above will provide one set of metabolic reactions to disrupt. Elimination of each reaction within the set or metabolic modification can result in a desired product as an obligatory product during the growth phase of the organism. Because the reactions are known, a solution to the bilevel OptKnock problem also will provide the associated gene or genes encoding one or more enzymes that catalyze each reaction within the set of reactions. Identification of a set of reactions and their corresponding genes encoding the enzymes participating in each reaction is generally an automated process, accomplished through correlation of the reactions with a reaction database having a relationship between enzymes and encoding genes.
Once identified, the set of reactions that are to be disrupted in order to achieve production of a desired product are implemented in the target cell or organism by functional disruption of at least one gene encoding each metabolic reaction within the set. One particularly useful means to achieve functional disruption of the reaction set is by deletion of each encoding gene. However, in some instances, it can be beneficial to disrupt the reaction by other genetic aberrations including, for example, mutation, deletion of regulatory regions such as promoters or cis binding sites for regulatory factors, or by truncation of the coding sequence at any of a number of locations. These latter aberrations, resulting in less than total deletion of the gene set can be useful, for example, when rapid assessments of the coupling of a product are desired or when genetic reversion is less likely to occur.
To identify additional productive solutions to the above described bilevel OptKnock problem which lead to further sets of reactions to disrupt or metabolic modifications that can result in the biosynthesis, including growth-coupled biosynthesis of a desired product, an optimization method, termed integer cuts, can be implemented. This method proceeds by iteratively solving the OptKnock problem exemplified above with the incorporation of an additional constraint referred to as an integer cut at each iteration. Integer cut constraints effectively prevent the solution procedure from choosing the exact same set of reactions identified in any previous iteration that obligatorily couples product biosynthesis to growth. For example, if a previously identified growth-coupled metabolic modification specifies reactions 1, 2, and 3 for disruption, then the following constraint prevents the same reactions from being simultaneously considered in subsequent solutions. The integer cut method is well known in the art and can be found described in, for example, Burgard et al., Biotechnol. Prog. 17:791-797 (2001). As with all methods described herein with reference to their use in combination with the OptKnock computational framework for metabolic modeling and simulation, the integer cut method of reducing redundancy in iterative computational analysis also can be applied with other computational frameworks well known in the art including, for example, SimPheny®.
The methods exemplified herein allow the construction of cells and organisms that biosynthetically produce a desired product, including the obligatory coupling of production of a target biochemical product to growth of the cell or organism engineered to harbor the identified genetic alterations. Therefore, the computational methods described herein allow the identification and implementation of metabolic modifications that are identified by an in silico method selected from OptKnock or SimPheny®. The set of metabolic modifications can include, for example, addition of one or more biosynthetic pathway enzymes and/or functional disruption of one or more metabolic reactions including, for example, disruption by gene deletion.
It is understood that modifications which do not substantially affect the activity of the various embodiments of this invention are also included within the definition of the invention provided herein. Accordingly, the following examples are intended to illustrate but not limit the present invention.
Example I
Microorganisms Having Growth-coupled Production of Fumarate
This Example describes the construction in silico designed strains for the increased production of fumarate in E. Coli.
Escherichia coli K-12 MG1655 serves as the wild-type strain into which the deletions are introduced. The strains are constructed by incorporating in-frame deletions using homologous recombination via the λ Red recombinase system of Datsenko and Wanner. (Datsenko and Wanner, Proc Natl Acad Sci U.S.A., 97(12):6640-5 (2000).) The approach involves replacing a chromosomal sequence (i.e., the gene targeted for removal) with a selectable antibiotic resistance gene, which itself is later removed. Knockouts are integrated one by one into the recipient strain. No antibiotic resistance markers will remain after each deletion allowing accumulation of multiple mutations in each target strain. The deletion technology completely removes the gene targeted for removal so as to substantially reduce the possibility of the constructed mutants reverting back to the wild-type.
As described further below, one exemplary growth condition for achieving biosynthesis of fumarate/malate includes anaerobic culture or fermentation conditions. In certain embodiments, the non-naturally occurring microbial organisms of the invention can be sustained, cultured or fermented under anaerobic or substantially anaerobic conditions. Briefly, anaerobic conditions refers to an environment devoid of oxygen. Substantially anaerobic conditions include, for example, a culture, batch fermentation or continuous fermentation such that the dissolved oxygen concentration in the medium remains between 0 and 10% of saturation. Substantially anaerobic conditions also includes growing or resting cells in liquid medium or on solid agar inside a sealed chamber maintained with an atmosphere of less than 1% oxygen. The percent of oxygen can be maintained by, for example, sparging the culture with an N 2 /CO 2 mixture or other suitable non-oxygen gas or gases.
The engineered strains are characterized by measuring the growth rate, the substrate uptake rate, and the product/byproduct secretion rate. Cultures are grown overnight and used as inoculum for a fresh batch culture for which measurements are taken during exponential growth. The growth rate is determined by measuring optical density using a spectrophotometer (A600). Concentrations of glucose, fumarate, malate, and other organic acid byproducts in the culture supernatant are determined by HPLC using an HPX-87H column (BioRad), and are used to calculate uptake and secretion rates. All experiments are performed with triplicate cultures.
The knockout strains can exhibit suboptimal growth rates until their metabolic networks have adjusted to their missing functionalities. To enable this adjustment, the strains are adaptively evolved. By subjecting the strains to adaptive evolution, cellular growth rate becomes the primary selection pressure and the mutant cells are compelled to reallocate their metabolic fluxes in order to enhance their rates of growth. This reprogramming of metabolism has been recently demonstrated for several E. coli mutants that had been adaptively evolved on various substrates to reach the growth rates predicted a priori by an in silico model. (Fong and Palsson, Nat Genet, 36(10):1056-8 (2004).)
Should the OptKnock predictions prove successful; the growth improvements brought about by adaptive evolution will be accompanied by enhanced rates of fumarate and/or malate production. The OptKnock-generated strains are adaptively evolved in triplicate (running in parallel) due to differences in the evolutionary patterns witnessed previously in E. coli (Fong and Palsson, Nat Genet, 36(10):1056-8 (2004); Fong et al., J Bacteriol, 185(21):6400-6408 (2003); Ibarra et al., Nature 420:186-189 (2002)) that could potentially result in one strain having superior production qualities over the others. Evolutions are run for a period of 2-6 weeks, depending upon the rate of growth improvement attained. In general, evolutions are stopped once a stable phenotype is obtained.
The adaptive evolution procedure involves maintaining the cells in prolonged exponential growth by the serial passage of batch cultures into fresh medium before the stationary phase is attained. Briefly, one procedure allows cells to reach mid-exponential growth (A 600 =0.5) before being diluted and passed to fresh medium (i.e., M9 minimal media with 2 g/L carbon source). This process is repeated, allowing for about 500 generations for each culture. Culture samples are taken, frozen with liquid nitrogen, and the optical culture density recorded for each day throughout the course of the evolutions. The conditions required for each evolution are summarized on table 7. The evolutions are performed in triplicate (i.e., 18 evolutions total) due to differences in the evolutionary patterns witnessed previously Donnelly et al., Appl Biochem Biotechnol 70-72: 187-98 (1998); Vemuri et al., Appl Environ Microbiol 68:1715-27 (2002), that could potentially result in one strain having superior production qualities over the others. The adaptive evolution step can take up to about two months or more. The adaptive evolution step also can be less than two months depending on the strain design, for example.
Another process can evolve cells using automation technology and is commercially available by Evolugate, LLC (Gainesville, Fla.) under a service contract. The procedure employs the Evolugator™ evolution machine which results in significant time and effort savings over non-automated evolution techniques. Cells are maintained in prolonged exponential growth by the serial passage of batch cultures into fresh medium before the stationary phase is attained. By automating optical density measurement and liquid handling, the Evolugator can perform serial transfer at high rates using large culture volumes, thus approaching the efficiency of a chemostat for evolution of cell fitness 25 . In contrast to a chemostat, which maintains cells in a single vessel, the machine operates by moving from one “reactor” to the next in subdivided regions of a spool of tubing, thus eliminating any selection for wall-growth. Culture samples are taken, frozen with liquid nitrogen, and the optical culture density recorded each day throughout the course of the evolutions. The Evolugator is used for each strain until a stable growth rate is achieved. Growth rate improvements of nearly 50% have been observed in two weeks using this device. The above-described strains are adaptively evolved in triplicate (running in parallel). At ten day intervals, culture samples are taken from the Evolugator, purified on agar plates, and cultured in triplicate as discussed above to assess strain physiology.
Following the adaptive evolution process, the new strains are again characterized by measuring the growth rate, the substrate uptake rate, and the product/byproduct secretion rate. These results are compared to the OptKnock predictions by plotting actual growth and production yields along side the production envelopes. The most successful OptKnock design/evolution combinations are chosen to pursue further, and is characterized in lab-scale batch and continuous fermentations. The growth-coupled biochemical production concept behind the OptKnock approach should also result in the generation of genetically stable overproducers. Thus, the cultures can be maintained in continuous mode for one month to evaluate long-term stability. Periodic samples will be taken to ensure that yield and productivity are maintained throughout the experiment.
Example II
Microorganisms having Growth-Coupled Production of Fumarate
This Example describes the construction in silico designed strains for the increased production of fumarate in S. cerevisiae.
Gene deletions are introduced into wild-type, haploid S. cerevisiae by homologous recombination of the gene interrupted by the KanMX cassette, flanked by loxP sites enabling removal and recycling of the resistance marker (Wach, A., et al., PCR - based gene targeting in Saccharomyces cerevisiae , in Yeast Gene Analysis , M. F. Tuite, Editor. 1998, Academic Press: San Diego.). Starting with a loxP-kanMX-loxP sequence on a plasmid, an artificial construct with this sequence flanked by fragments of the gene of interest will be created by PCR using primers containing both 45-50 bp target sequence followed by a region homologous to the above cassette. This linear DNA will be transformed into wild-type S. cerevisiae , and recombinants will be selected by geneticin resistance. Colonies will be purified and tested for correct double crossover by PCR. To remove the KanMX marker, a plasmid containing the Cre recombinase and bleomycin resistance will be introduced, promoting recombination between the loxP sites (Gueldener et al., Nucleic Acids Res. 30:e23 (2002)). Finally, the resulting strain can be cured of the Cre plasmid by successive culturing on media without any antibiotic present. The final strain will have a markerless gene deletion, and thus the same method can be used to introduce multiple deletions in the same strain.
As described further below, one exemplary growth condition for achieving biosynthesis of fumarate includes anaerobic culture or fermentation conditions. In certain embodiments, the non-naturally occurring eukaryotic organism of the invention can be sustained, cultured or fermented under anaerobic or substantially anaerobic conditions. Briefly, anaerobic conditions refer to an environment devoid of oxygen. Substantially anaerobic conditions include, for example, a culture, batch fermentation or continuous fermentation such that the dissolved oxygen concentration in the medium remains between 0 and 10% of saturation. One skilled in the art will recognize substantially anaerobic conditions include microaerobic conditions. Substantially anaerobic conditions also includes growing or resting cells in liquid medium or on solid agar inside a sealed chamber maintained with an atmosphere of less than 1% oxygen. The percent of oxygen can be maintained by, for example, sparging the culture with an N 2 /CO 2 mixture or other suitable non-oxygen gas or gases.
The engineered strains are characterized by measuring the growth rate, the substrate uptake rate, and the product/byproduct secretion rate. Cultures are grown overnight and used as inoculum for a fresh batch culture for which measurements are taken during exponential growth. The growth rate is determined by measuring optical density using a spectrophotometer (A600). Concentrations of glucose, fumarate, malate, and other organic acid byproducts in the culture supernatant are determined by HPLC using an HPX-87H column (BioRad), and are used to calculate uptake and secretion rates. All experiments are performed with triplicate cultures.
The knockout strains can exhibit suboptimal growth rates until their metabolic networks have adjusted to their missing functionalities. To enable this adjustment, the strains are adaptively evolved. By subjecting the strains to adaptive evolution, cellular growth rate becomes the primary selection pressure and the mutant cells are compelled to reallocate their metabolic fluxes in order to enhance their rates of growth. This reprogramming of metabolism has been recently demonstrated for several E. coli mutants that had been adaptively evolved on various substrates to reach the growth rates predicted a priori by an in silico model. (Fong and Palsson, Nat Genet, 36:1056-1058 (2004).) These teachings can be applied to S. cerevisiae.
Should the OptKnock predictions prove successful; the growth improvements brought about by adaptive evolution will be accompanied by enhanced rates of fumarate production, and further strains can be engineered in a similar matter to optimize malate or acrylate production. The OptKnock-generated strains are adaptively evolved in triplicate (running in parallel) due to differences in the evolutionary patterns witnessed previously in E. coli (Fong and Palsson, Nat Genet, 36:1056-1058 (2004); Fong et al., J Bacteriol, 185:6400-6408 (2003); Ibarra et al., Nature 420:186-189 (2002)) that could potentially result in one strain having superior production qualities over the others. Evolutions are run for a period of 2-6 weeks, depending upon the rate of growth improvement attained. In general, evolutions are stopped once a stable phenotype is obtained.
The adaptive evolution procedure involves maintaining the cells in prolonged exponential growth by the serial passage of batch cultures into fresh medium before the stationary phase is attained. Briefly, one procedure allows cells to reach mid-exponential growth (A 600 =0.5) before being diluted and passed to fresh medium (i.e., M9 minimal media with 2 g/L carbon source). This process is repeated, allowing for about 500 generations for each culture. Culture samples are taken, frozen with liquid nitrogen, and the optical culture density recorded for each day throughout the course of the evolutions. The evolutions are performed in triplicate due to differences in the evolutionary patterns witnessed previously Donnelly et al., Appl Biochem Biotechnol 70-72: 187-98 (1998); Vemuri et al., Appl Environ Microbiol 68:1715-27 (2002), that could potentially result in one strain having superior production qualities over the others. The adaptive evolution step can take up to about two months or more. The adaptive evolution step also can be less than two months depending on the strain design, for example.
Another process can evolve cells using automation technology and is commercially available by Evolugate, LLC (Gainesville, Fla.) under a service contract. The procedure employs the Evolugator™ evolution machine which results in significant time and effort savings over non-automated evolution techniques. Cells are maintained in prolonged exponential growth by the serial passage of batch cultures into fresh medium before the stationary phase is attained. By automating optical density measurement and liquid handling, the Evolugator can perform serial transfer at high rates using large culture volumes, thus approaching the efficiency of a chemostat for evolution of cell fitness. In contrast to a chemostat, which maintains cells in a single vessel, the machine operates by moving from one “reactor” to the next in subdivided regions of a spool of tubing, thus eliminating any selection for wall-growth. Culture samples are taken, frozen with liquid nitrogen, and the optical culture density recorded each day throughout the course of the evolutions. The Evolugator is used for each strain until a stable growth rate is achieved. Growth rate improvements of nearly 50% have been observed in two weeks using this device. The above-described strains are adaptively evolved in triplicate (running in parallel). At ten day intervals, culture samples are taken from the Evolugator, purified on agar plates, and cultured in triplicate as discussed above to assess strain physiology.
Following the adaptive evolution process, the new strains are again characterized by measuring the growth rate, the substrate uptake rate, and the product/byproduct secretion rate. These results are compared to the OptKnock predictions by plotting actual growth and production yields along side the production envelopes. The most successful OptKnock design/evolution combinations are chosen to pursue further, and is characterized in lab-scale batch and continuous fermentations. The growth-coupled biochemical production concept behind the OptKnock approach should also result in the generation of genetically stable overproducers. Thus, the cultures can be maintained in continuous mode for one month to evaluate long-term stability. Periodic samples will be taken to ensure that yield and productivity are maintained throughout the experiment.
Example III
Acrylate Biosynthesis
This Example describes the generation of a microbial organism capable of producing acrylate using a decarboxylase metabolic pathway.
Escherichia coli is used as a target organism to engineer a decarboxylase pathway ( FIG. 1 ), and testing growth and acrylate production from glucose. E. coli provides a good model for developing a non-naturally occurring microorganism capable of producing acrylate, from glucose since it is amenable to genetic manipulation and is known to be capable of producing various products, like ethanol, effectively under anaerobic conditions from glucose.
To generate an E. coli strain engineered to produce primary alcohol, nucleic acids encoding proteins and enzymes required for the acrylate production pathway via fumarate decarboxylation as described above, are expressed in E. coli using well known molecular biology techniques (see, for example, Sambrook, supra, 2001; Ausubel supra, 1999; Roberts et al., supra, 1989). The pad1 gene (AB368798), encoding a decarboxylase under anaerobic conditions, are cloned into the pZE13 vector under the PA1/lacO promoter. The of plasmid is transformed into E. coli strain MG1655 to express the enzyme aconitate decarboxylase required for decarboxylation of fumarate to acrylate.
The engineered production organism containing a decarboxylase enzyme is grown in a 10 L bioreactor sparged with an N 2 /CO 2 mixture, using 5 L broth containing 5 g/L potassium phosphate, 2.5 g/L ammonium chloride, 0.5 g/L magnesium sulfate, and 30 g/L corn steep liquor, and an initial glucose concentration of 20 g/L. As the cells grow and utilize the glucose, additional 70% glucose is fed into the bioreactor at a rate approximately balancing glucose consumption. The temperature of the bioreactor is maintained at 30 degrees C. Growth continues for approximately 24 hours, until acrylate reaches a concentration of between 10-200 g/L, with the cell density being between 5 and 50 g/L. Upon completion of the cultivation period, the fermenter contents are passed through a cell separation unit (e.g., centrifuge) to remove cells and cell debris, and the fermentation broth and acrylate is separated from the broth and purified by standard methods for organic acid recovery.
Example IV
Acrylate from Biologically Produced Fumarate
Escherichia coli K-12 MG1655 is used as one reference wild-type strain into which the deletions are introduced. The knockouts are integrated, for example, one-by-one into the recipient strain allowing the accumulation of several deletions. The deletion methodology completely removes the gene targeted for removal so as to avoid the possibility of the constructed mutants reverting back to their wild-type.
The strains are constructed by incorporating in-frame deletions using homologous recombination by well known methods such as the λ Red recombinase system (Datsenko and Wanner, Proc Natl Acad Sci U.S.A., 97:6640-6645 (2000)). The approach involves replacing a chromosomal sequence (i.e., the gene targeted for removal) with a selectable antibiotic resistance gene, which itself is later removed. The knockouts are integrated sequentially into the recipient strain. Antibiotic resistance markers are removed after each deletion, thus allowing accumulation of multiple mutations in each target strain.
An organism engineered for high level fumarate production is grown in a 10 L bioreactor sparged with an N 2 /CO 2 mixture, using 5 L broth containing 5 g/L potassium phosphate, 2.5 g/L ammonium chloride, 0.5 g/L magnesium sulfate, and 30 g/L corn steep liquor, and an initial glucose concentration of 20 g/L. As the cells grow and utilize the glucose, additional 70% glucose is fed into the bioreactor at a rate approximately balancing glucose consumption. The temperature of the bioreactor is maintained at 30 degrees C. Growth continues for approximately 24 hours, until fumarate reaches a concentration of between 10-200 g/L, with the cell density being between 5 and 50 g/L. Upon completion of the cultivation period, a decarboxylase enzyme is added either directly to the fermenter or after initial removal of cells and cell debris. After agitating for the required length of time required for complete conversion of fumarate to acrylate, the acrylate is recovered as described above.
TABLE 1
The list of all strains identified by OptKnock that are most likely to provide increased
fumarate yields in E. Coli.
1.
ACKr
ADHEr
AKGD
ASNS2
ATPS4r
LDH_D
2.
ACKr
ADHEr
AKGD
ATPS4r
CBMK2
LDH_D
3.
ACKr
ADHEr
AKGD
ATPS4r
GLUDy
LDH_D
4.
ACKr
ADHEr
AKGD
ATPS4r
LDH_D
5.
ACKr
ADHEr
AKGD
ATPS4r
LDH_D
RPE
6.
ACKr
ADHEr
AKGD
ATPS4r
LDH_D
TAL
7.
ACKr
ADHEr
AKGD
ATPS4r
LDH_D
TKT1
8.
ACKr
ADHEr
AKGD
ATPS4r
LDH_D
TKT2
9.
ACKr
ADHEr
ASNS2
ATPS4r
LDH_D
SUCOAS
10.
ACKr
ADHEr
ASNS2
LDH_D
ME2
SUCD4
11.
ACKr
ADHEr
ATPS4r
CBMK2
LDH_D
SUCOAS
12.
ACKr
ADHEr
ATPS4r
GLUDy
LDH_D
SUCOAS
13.
ACKr
ADHEr
ATPS4r
LDH_D
PDH
PFLi
14.
ACKr
ADHEr
ATPS4r
LDH_D
RPE
SUCOAS
15.
ACKr
ADHEr
ATPS4r
LDH_D
SUCOAS
16.
ACKr
ADHEr
ATPS4r
LDH_D
SUCOAS
TAL
17.
ACKr
ADHEr
ATPS4r
LDH_D
SUCOAS
TKT1
18.
ACKr
ADHEr
ATPS4r
LDH_D
SUCOAS
TKT2
19.
ACKr
ADHEr
CBMK2
FRD2
LDH_D
ME2
THD2
20.
ACKr
ADHEr
CBMK2
LDH_D
ME2
SUCD4
21.
ACKr
ADHEr
FRD2
G5SD
LDH_D
ME2
THD2
22.
ACKr
ADHEr
FRD2
GLCpts
GLUDy
LDH_D
ME2
23.
ACKr
ADHEr
FRD2
GLU5K
LDH_D
ME2
THD2
24.
ACKr
ADHEr
FRD2
LDH_D
ME2
PFLi
THD2
25.
ACKr
ADHEr
FRD2
LDH_D
ME2
THD2
26.
ACKr
ADHEr
GLCpts
GLUDy
LDH_D
ME2
SUCD4
27.
ACKr
ADHEr
GLCpts
LDH_D
ME2
SUCD4
28.
ACKr
ADHEr
GLUDy
LDH_D
ME2
SUCD4
29.
ACKr
ADHEr
LDH_D
ME2
SUCD4
30.
ACKr
AKGD
ASNS2
ATPS4r
31.
ACKr
AKGD
ASNS2
ATPS4r
CBMK2
32.
ACKr
AKGD
ASNS2
ATPS4r
GLUDy
33.
ACKr
AKGD
ASNS2
ATPS4r
RPE
34.
ACKr
AKGD
ASNS2
ATPS4r
TAL
35.
ACKr
AKGD
ASNS2
ATPS4r
TKT1
36.
ACKr
AKGD
ASNS2
ATPS4r
TKT2
37.
ACKr
AKGD
ATPS4r
38.
ACKr
AKGD
ATPS4r
CBMK2
39.
ACKr
AKGD
ATPS4r
CBMK2
GLUDy
40.
ACKr
AKGD
ATPS4r
CBMK2
RPE
41.
ACKr
AKGD
ATPS4r
CBMK2
TAL
42.
ACKr
AKGD
ATPS4r
CBMK2
TKT1
43.
ACKr
AKGD
ATPS4r
CBMK2
TKT2
44.
ACKr
AKGD
ATPS4r
GLUDy
45.
ACKr
AKGD
ATPS4r
GLUDy
RPE
46.
ACKr
AKGD
ATPS4r
GLUDy
TAL
47.
ACKr
AKGD
ATPS4r
GLUDy
TKT1
48.
ACKr
AKGD
ATPS4r
GLUDy
TKT2
49.
ACKr
AKGD
ATPS4r
PPCK
PYK
50.
ACKr
AKGD
ATPS4r
RPE
51.
ACKr
AKGD
ATPS4r
TAL
52.
ACKr
AKGD
ATPS4r
TKT1
53.
ACKr
AKGD
ATPS4r
TKT2
54.
ACKr
ASNS2
ATPS4r
CBMK2
SUCOAS
55.
ACKr
ASNS2
ATPS4r
GLUDy
SUCOAS
56.
ACKr
ASNS2
ATPS4r
RPE
SUCOAS
57.
ACKr
ASNS2
ATPS4r
SUCOAS
58.
ACKr
ASNS2
ATPS4r
SUCOAS
TAL
59.
ACKr
ASNS2
ATPS4r
SUCOAS
TKT1
60.
ACKr
ASNS2
ATPS4r
SUCOAS
TKT2
61.
ACKr
ATPS4r
CBMK2
GLUDy
SUCOAS
62.
ACKr
ATPS4r
CBMK2
RPE
SUCOAS
63.
ACKr
ATPS4r
CBMK2
SUCOAS
64.
ACKr
ATPS4r
CBMK2
SUCOAS
TAL
65.
ACKr
ATPS4r
CBMK2
SUCOAS
TKT1
66.
ACKr
ATPS4r
CBMK2
SUCOAS
TKT2
67.
ACKr
ATPS4r
FUM
PPCK
68.
ACKr
ATPS4r
GLUDy
RPE
SUCOAS
69.
ACKr
ATPS4r
GLUDy
SUCOAS
70.
ACKr
ATPS4r
GLUDy
SUCOAS
TAL
71.
ACKr
ATPS4r
GLUDy
SUCOAS
TKT1
72.
ACKr
ATPS4r
GLUDy
SUCOAS
TKT2
73.
ACKr
ATPS4r
MDH
PPCK
74.
ACKr
ATPS4r
PDH
PFLi
75.
ACKr
ATPS4r
PPCK
PYK
SUCOAS
76.
ACKr
ATPS4r
RPE
SUCOAS
77.
ACKr
ATPS4r
SUCOAS
78.
ACKr
ATPS4r
SUCOAS
TAL
79.
ACKr
ATPS4r
SUCOAS
TKT1
80.
ACKr
ATPS4r
SUCOAS
TKT2
81.
ACKr
FRD2
ME1x
ME2
PYK
82.
ACKr
ME1x
ME2
PYK
SUCD4
83.
ADHEr
AKGD
ASNS2
ATPS4r
LDH_D
PTAr
84.
ADHEr
AKGD
ATPS4r
CBMK2
LDH_D
PTAr
85.
ADHEr
AKGD
ATPS4r
GLUDy
LDH_D
PTAr
86.
ADHEr
AKGD
ATPS4r
LDH_D
PTAr
87.
ADHEr
AKGD
ATPS4r
LDH_D
PTAr
RPE
88.
ADHEr
AKGD
ATPS4r
LDH_D
PTAr
TAL
89.
ADHEr
AKGD
ATPS4r
LDH_D
PTAr
TKT1
90.
ADHEr
AKGD
ATPS4r
LDH_D
PTAr
TKT2
91.
ADHEr
ALAR
ASNS2
LDH_D
ME2
PRO1z
SUCD4
92.
ADHEr
ALAR
CBMK2
GLUDy
LDH_D
PRO1z
SUCD4
93.
ADHEr
ALAR
CBMK2
LDH_D
ME2
PRO1z
SUCD4
94.
ADHEr
ALAR
FUM
LDH_D
PRO1z
SUCD4
95.
ADHEr
ALAR
G5SD
LDH_D
ME2
PRO1z
SUCD4
96.
ADHEr
ALAR
GLCpts
LDH_D
ME2
PRO1z
SUCD4
97.
ADHEr
ALAR
GLU5K
LDH_D
ME2
PRO1z
SUCD4
98.
ADHEr
ALAR
GLUDy
LDH_D
ME2
PRO1z
SUCD4
99.
ADHEr
ALAR
GLUDy
LDH_D
PRO1z
SUCD4
100.
ADHEr
ALAR
GLUDy
LDH_D
PRO1z
SUCD4
THD2
101.
ADHEr
ALAR
LDH_D
ME2
PRO1z
SUCD4
102.
ADHEr
ALAR
LDH_D
ME2
PRO1z
SUCD4
THD2
103.
ADHEr
ASNS2
ATPS4r
LDH_D
PDH
PFLi
104.
ADHEr
ASNS2
ATPS4r
LDH_D
PTAr
SUCOAS
105.
ADHEr
ASNS2
CBMK2
FRD2
G5SD
GLUDy
LDH_D
106.
ADHEr
ASNS2
CBMK2
FRD2
G5SD
LDH_D
ME2
107.
ADHEr
ASNS2
CBMK2
FRD2
GLU5K
GLUDy
LDH_D
108.
ADHEr
ASNS2
CBMK2
FRD2
GLU5K
LDH_D
ME2
109.
ADHEr
ASNS2
CBMK2
FRD2
LDH_D
ME2
110.
ADHEr
ASNS2
DAAD
LDH_D
ME2
PRO1z
SUCD4
111.
ADHEr
ASNS2
FRD2
G5SD
GLUDy
LDH_D
112.
ADHEr
ASNS2
FRD2
G5SD
GLUDy
LDH_D
ME2
113.
ADHEr
ASNS2
FRD2
G5SD
GLUDy
LDH_D
THD2
114.
ADHEr
ASNS2
FRD2
G5SD
LDH_D
ME2
115.
ADHEr
ASNS2
FRD2
G5SD
LDH_D
ME2
THD2
116.
ADHEr
ASNS2
FRD2
GLU5K
GLUDy
LDH_D
117.
ADHEr
ASNS2
FRD2
GLU5K
GLUDy
LDH_D
ME2
118.
ADHEr
ASNS2
FRD2
GLU5K
GLUDy
LDH_D
THD2
119.
ADHEr
ASNS2
FRD2
GLU5K
LDH_D
ME2
120.
ADHEr
ASNS2
FRD2
GLU5K
LDH_D
ME2
THD2
121.
ADHEr
ASNS2
FRD2
LDH_D
ME2
122.
ADHEr
ASNS2
FRD2
LDH_D
ME2
123.
ADHEr
ASNS2
G5SD
GLUDy
LDH_D
PRO1z
SUCD4
124.
ADHEr
ASNS2
G5SD
LDH_D
ME2
SUCD4
THD2
125.
ADHEr
ASNS2
GLU5K
GLUDy
LDH_D
PRO1z
SUCD4
126.
ADHEr
ASNS2
GLU5K
LDH_D
ME2
SUCD4
THD2
127.
ADHEr
ASNS2
LDH_D
ME2
PTAr
SUCD4
128.
ADHEr
ATPS4r
CBMK2
LDH_D
PDH
PFLi
129.
ADHEr
ATPS4r
CBMK2
LDH_D
PTAr
SUCOAS
130.
ADHEr
ATPS4r
G5SD
LDH_D
PDH
PFLi
131.
ADHEr
ATPS4r
GLU5K
LDH_D
PDH
PFLi
132.
ADHEr
ATPS4r
GLUDy
LDH_D
PDH
PFLi
133.
ADHEr
ATPS4r
GLUDy
LDH_D
PTAr
SUCOAS
134.
ADHEr
ATPS4r
LDH_D
NADH12
PFLi
THD2
135.
ADHEr
ATPS4r
LDH_D
PDH
PFLi
136.
ADHEr
ATPS4r
LDH_D
PDH
PFLi
PTAr
137.
ADHEr
ATPS4r
LDH_D
PDH
PFLi
RPE
138.
ADHEr
ATPS4r
LDH_D
PDH
PFLi
TAL
139.
ADHEr
ATPS4r
LDH_D
PDH
PFLi
TKT1
140.
ADHEr
ATPS4r
LDH_D
PDH
PFLi
TKT2
141.
ADHEr
ATPS4r
LDH_D
PTAr
RPE
SUCOAS
142.
ADHEr
ATPS4r
LDH_D
PTAr
SUCOAS
143.
ADHEr
ATPS4r
LDH_D
PTAr
SUCOAS
TAL
144.
ADHEr
ATPS4r
LDH_D
PTAr
SUCOAS
TKT1
145.
ADHEr
ATPS4r
LDH_D
PTAr
SUCOAS
TKT2
146.
ADHEr
CBMK2
DAAD
GLUDy
LDH_D
PRO1z
SUCD4
147.
ADHEr
CBMK2
DAAD
LDH_D
ME2
PRO1z
SUCD4
148.
ADHEr
CBMK2
FRD2
G5SD
LDH_D
ME2
149.
ADHEr
CBMK2
FRD2
GLCpts
GLUDy
LDH_D
ME2
150.
ADHEr
CBMK2
FRD2
GLCpts
LDH_D
ME2
151.
ADHEr
CBMK2
FRD2
GLU5K
LDH_D
ME2
152.
ADHEr
CBMK2
FRD2
GLUDy
LDH_D
153.
ADHEr
CBMK2
FRD2
GLUDy
LDH_D
ME2
154.
ADHEr
CBMK2
FRD2
GLUDy
LDH_D
ME2
THD2
155.
ADHEr
CBMK2
FRD2
GLUDy
LDH_D
THD2
156.
ADHEr
CBMK2
FRD2
LDH_D
ME2
157.
ADHEr
CBMK2
FRD2
LDH_D
ME2
PFLi
THD2
158.
ADHEr
CBMK2
FRD2
LDH_D
ME2
PTAr
THD2
159.
ADHEr
CBMK2
FRD2
LDH_D
ME2
THD2
160.
ADHEr
CBMK2
GLUDy
LDH_D
ME2
PRO1z
SUCD4
161.
ADHEr
CBMK2
GLUDy
LDH_D
ME2
SUCD4
THD2
162.
ADHEr
CBMK2
GLUDy
LDH_D
PRO1z
SUCD4
163.
ADHEr
CBMK2
GLUDy
LDH_D
PRO1z
SUCD4
THD2
164.
ADHEr
CBMK2
LDH_D
ME2
PTAr
SUCD4
165.
ADHEr
CBMK2
LDH_D
ME2
SUCD4
THD2
166.
ADHEr
DAAD
FUM
LDH_D
PRO1z
SUCD4
167.
ADHEr
DAAD
G5SD
LDH_D
ME2
PRO1z
SUCD4
168.
ADHEr
DAAD
GLCpts
LDH_D
ME2
PRO1z
SUCD4
169.
ADHEr
DAAD
GLU5K
LDH_D
ME2
PRO1z
SUCD4
170.
ADHEr
DAAD
GLUDy
LDH_D
ME2
PRO1z
SUCD4
171.
ADHEr
DAAD
GLUDy
LDH_D
PRO1z
SUCD4
172.
ADHEr
DAAD
GLUDy
LDH_D
PRO1z
SUCD4
THD2
173.
ADHEr
DAAD
LDH_D
ME2
PRO1z
SUCD4
174.
ADHEr
DAAD
LDH_D
ME2
PRO1z
SUCD4
THD2
175.
ADHEr
FDH2
GLUDy
LDH_D
NADH12
NADH6
PRO1z
176.
ADHEr
FDH2
LDH_D
ME2
NADH12
NADH6
THD2
177.
ADHEr
FRD2
FUM
LDH_D
178.
ADHEr
FRD2
FUM
LDH_D
MDH
PYK
179.
ADHEr
FRD2
G5SD
GLCpts
LDH_D
ME2
180.
ADHEr
FRD2
G5SD
LDH_D
ME2
181.
ADHEr
FRD2
G5SD
LDH_D
ME2
PTAr
THD2
182.
ADHEr
FRD2
GLCpts
GLU5K
LDH_D
ME2
183.
ADHEr
FRD2
GLCpts
GLUDy
LDH_D
ME2
184.
ADHEr
FRD2
GLCpts
GLUDy
LDH_D
ME2
PTAr
185.
ADHEr
FRD2
GLCpts
LDH_D
ME1x
ME2
PYK
186.
ADHEr
FRD2
GLCpts
LDH_D
ME2
187.
ADHEr
FRD2
GLU5K
LDH_D
ME2
188.
ADHEr
FRD2
GLU5K
LDH_D
ME2
PTAr
THD2
189.
ADHEr
FRD2
GLUDy
HEX1
LDH_D
ME2
THD2
190.
ADHEr
FRD2
GLUDy
HEX1
LDH_D
THD2
191.
ADHEr
FRD2
GLUDy
LDH_D
192.
ADHEr
FRD2
GLUDy
LDH_D
ME2
193.
ADHEr
FRD2
GLUDy
LDH_D
ME2
PFLi
THD2
194.
ADHEr
FRD2
GLUDy
LDH_D
ME2
THD2
195.
ADHEr
FRD2
GLUDy
LDH_D
THD2
196.
ADHEr
FRD2
HEX1
LDH_D
ME2
THD2
197.
ADHEr
FRD2
LDH_D
ME2
198.
ADHEr
FRD2
LDH_D
ME2
PFLi
PTAr
THD2
199.
ADHEr
FRD2
LDH_D
ME2
PFLi
THD2
200.
ADHEr
FRD2
LDH_D
ME2
PTAr
THD2
201.
ADHEr
FRD2
LDH_D
ME2
THD2
202.
ADHEr
FRD2
ME1x
ME2
PYK
203.
ADHEr
GLCpts
GLUDy
LDH_D
ME2
PRO1z
SUCD4
204.
ADHEr
GLCpts
GLUDy
LDH_D
ME2
PTAr
SUCD4
205.
ADHEr
GLCpts
LDH_D
ME1x
ME2
PYK
SUCD4
206.
ADHEr
GLCpts
LDH_D
ME2
PTAr
SUCD4
207.
ADHEr
GLU5K
LDH_D
208.
ADHEr
GLUDy
HEX1
LDH_D
ME2
SUCD4
THD2
209.
ADHEr
GLUDy
HEX1
LDH_D
PRO1z
SUCD4
THD2
210.
ADHEr
GLUDy
LDH_D
ME2
PRO1z
SUCD4
211.
ADHEr
GLUDy
LDH_D
ME2
PRO1z
SUCD4
THD2
212.
ADHEr
GLUDy
LDH_D
ME2
PTAr
SUCD4
213.
ADHEr
GLUDy
LDH_D
ME2
SUCD4
THD2
214.
ADHEr
GLUDy
LDH_D
PRO1z
SUCD4
215.
ADHEr
GLUDy
LDH_D
PRO1z
SUCD4
THD2
216.
ADHEr
GLUDy
LDH_D
SUCOAS
TKT2
217.
ADHEr
HEX1
LDH_D
ME2
SUCD4
THD2
218.
ADHEr
LDH_D
ME2
PTAr
SUCD4
219.
ADHEr
LDH_D
ME2
SUCD4
THD2
220.
ADHEr
THD2
221.
AKGD
ASNS2
ATPS4r
CBMK2
PTAr
222.
AKGD
ASNS2
ATPS4r
GLUDy
PTAr
223.
AKGD
ASNS2
ATPS4r
PTAr
224.
AKGD
ASNS2
ATPS4r
PTAr
RPE
225.
AKGD
ASNS2
ATPS4r
PTAr
TAL
226.
AKGD
ASNS2
ATPS4r
PTAr
TKT1
227.
AKGD
ASNS2
ATPS4r
PTAr
TKT2
228.
AKGD
ATPS4r
CBMK2
GLUDy
PTAr
229.
AKGD
ATPS4r
CBMK2
PTAr
230.
AKGD
ATPS4r
CBMK2
PTAr
RPE
231.
AKGD
ATPS4r
CBMK2
PTAr
TAL
232.
AKGD
ATPS4r
CBMK2
PTAr
TKT1
233.
AKGD
ATPS4r
CBMK2
PTAr
TKT2
234.
AKGD
ATPS4r
GLUDy
PTAr
235.
AKGD
ATPS4r
GLUDy
PTAr
RPE
236.
AKGD
ATPS4r
GLUDy
PTAr
TAL
237.
AKGD
ATPS4r
GLUDy
PTAr
TKT1
238.
AKGD
ATPS4r
GLUDy
PTAr
TKT2
239.
AKGD
ATPS4r
PPCK
PTAr
PYK
240.
AKGD
ATPS4r
PTAr
241.
AKGD
ATPS4r
PTAr
RPE
242.
AKGD
ATPS4r
PTAr
TAL
243.
AKGD
ATPS4r
PTAr
TKT1
244.
AKGD
ATPS4r
PTAr
TKT2
245.
ALAR
FUM
PRO1z
SUCD4
246.
ASNS2
ATPS4r
CBMK2
PTAr
SUCOAS
247.
ASNS2
ATPS4r
FRD2
PFLi
248.
ASNS2
ATPS4r
GLUDy
PTAr
SUCOAS
249.
ASNS2
ATPS4r
PDH
PFLi
250.
ASNS2
ATPS4r
PTAr
RPE
SUCOAS
251.
ASNS2
ATPS4r
PTAr
SUCOAS
252.
ASNS2
ATPS4r
PTAr
SUCOAS
TAL
253.
ASNS2
ATPS4r
PTAr
SUCOAS
TKT1
254.
ASNS2
ATPS4r
PTAr
SUCOAS
TKT2
255.
ATPS4r
CBMK2
FRD2
PFLi
256.
ATPS4r
CBMK2
GLUDy
PTAr
SUCOAS
257.
ATPS4r
CBMK2
PDH
PFLi
258.
ATPS4r
CBMK2
PTAr
RPE
SUCOAS
259.
ATPS4r
CBMK2
PTAr
SUCOAS
260.
ATPS4r
CBMK2
PTAr
SUCOAS
TAL
261.
ATPS4r
CBMK2
PTAr
SUCOAS
TKT1
262.
ATPS4r
CBMK2
PTAr
SUCOAS
TKT2
263.
ATPS4r
FBA
FRD2
GLUDy
PFLi
264.
ATPS4r
FBA
FRD2
PFLi
265.
ATPS4r
FDH2
PTAr
THD5
266.
ATPS4r
FRD2
G5SD
PFLi
267.
ATPS4r
FRD2
GLU5K
PFLi
268.
ATPS4r
FRD2
GLUDy
PFK
PFLi
269.
ATPS4r
FRD2
GLUDy
PFLi
270.
ATPS4r
FRD2
GLUDy
PFLi
PGI
271.
ATPS4r
FRD2
GLUDy
PFLi
TPI
272.
ATPS4r
FRD2
ME1x
ME2
PYK
273.
ATPS4r
FRD2
ME2
PFLi
THD2
274.
ATPS4r
FRD2
PFK
PFLi
275.
ATPS4r
FRD2
PFLi
276.
ATPS4r
FRD2
PFLi
PGI
277.
ATPS4r
FRD2
PFLi
PPCK
PYK
278.
ATPS4r
FRD2
PFLi
TPI
279.
ATPS4r
FUM
PPCK
PTAr
280.
ATPS4r
G5SD
PDH
PFLi
281.
ATPS4r
GLCpts
ME1x
ME2
PYK
282.
ATPS4r
GLU5K
PDH
PFLi
283.
ATPS4r
GLUDy
PDH
PFLi
284.
ATPS4r
GLUDy
PTAr
RPE
SUCOAS
285.
ATPS4r
GLUDy
PTAr
SUCOAS
286.
ATPS4r
GLUDy
PTAr
SUCOAS
TAL
287.
ATPS4r
GLUDy
PTAr
SUCOAS
TKT1
288.
ATPS4r
GLUDy
PTAr
SUCOAS
TKT2
289.
ATPS4r
MDH
PPCK
PTAr
290.
ATPS4r
ME1x
ME2
PYK
SUCD4
291.
ATPS4r
ME2
NADH12
PFLi
THD2
292.
ATPS4r
PDH
PFLi
293.
ATPS4r
PDH
PFLi
PPCK
PYK
294.
ATPS4r
PDH
PFLi
PTAr
295.
ATPS4r
PDH
PFLi
RPE
296.
ATPS4r
PDH
PFLi
TAL
297.
ATPS4r
PDH
PFLi
TKT1
298.
ATPS4r
PDH
PFLi
TKT2
299.
ATPS4r
PPCK
PTAr
PYK
SUCOAS
300.
ATPS4r
PTAr
RPE
SUCOAS
301.
ATPS4r
PTAr
SUCOAS
302.
ATPS4r
PTAr
SUCOAS
TAL
303.
ATPS4r
PTAr
SUCOAS
TKT1
304.
ATPS4r
PTAr
SUCOAS
TKT2
305.
CBMK2
PGDH
TKT1
306.
DAAD
FUM
PRO1z
SUCD4
307.
EDA
FRD2
FUM
MDH
PYK
308.
EDA
FRD2
ME1x
ME2
PYK
309.
EDA
FUM
MDH
PYK
SUCD4
310.
EDA
ME1x
ME2
PYK
SUCD4
311.
ENO
FUM
SUCD4
312.
FRD2
FUM
313.
FRD2
FUM
G6PDHy
MDH
PYK
314.
FRD2
FUM
GLCpts
MDH
PYK
315.
FRD2
FUM
MDH
PGDHY
PYK
316.
FRD2
FUM
MDH
PGL
PYK
317.
FRD2
FUM
MDH
PYK
318.
FRD2
G6PDHy
ME1x
ME2
PYK
319.
FRD2
GLCpts
ME1x
ME2
PYK
320.
FRD2
GLUDy
ME1x
ME2
PYK
321.
FRD2
MDH
ME1x
ME2
322.
FRD2
ME1x
ME2
PFLi
PYK
323.
FRD2
ME1x
ME2
PGDHY
PYK
324.
FRD2
ME1x
ME2
PGL
PYK
325.
FRD2
ME1x
ME2
PTAr
PYK
326.
FRD2
ME1x
ME2
PYK
327.
FRD2
ME1x
ME2
PYK
RPE
328.
FRD2
ME1x
ME2
PYK
TKT2
329.
FUM
G6PDHy
MDH
PYK
SUCD4
330.
FUM
GLCpts
MDH
PYK
SUCD4
331.
FUM
GLUDy
PRO1z
SUCD4
332.
FUM
MDH
PGDHY
PYK
SUCD4
333.
FUM
MDH
PGL
PYK
SUCD4
334.
FUM
MDH
SUCD4
335.
FUM
ME2
SUCD4
336.
FUM
PGM
SUCD4
337.
FUM
PPCK
SUCD4
338.
G6PDHy
ME1x
ME2
PYK
SUCD4
339.
GLCpts
ME1x
ME2
PYK
SUCD4
340.
GLUDy
ME1x
ME2
PYK
SUCD4
341.
MDH
ME1x
ME2
SUCD4
342.
ME1x
ME2
PFLi
PYK
SUCD4
343.
ME1x
ME2
PGDHY
PYK
SUCD4
344.
ME1x
ME2
PGL
PYK
SUCD4
345.
ME1x
ME2
PTAr
PYK
SUCD4
346.
ME1x
ME2
PYK
RPE
SUCD4
347.
ME1x
ME2
PYK
SUCD4
348.
ME1x
ME2
PYK
SUCD4
TKT2
TABLE 2
The list of all strains identified by OptKnock that are most likely to
provide increased malate yields in E. Coli . Note that some of the
malate production strategies overlap with the fumarate production
strains.
1.
AKGD
ATPS4r
PTAr
2.
ACKr
AKGD
ATPS4r
3.
ACKr
ATPS4r
SUCOAS
4.
ATPS4r
PTAr
SUCOAS
5.
ATPS4r
PDH
PFLi
6.
ATPS4r
FRD2
PFLi
7.
LDH_D
PFK
SUCOAS
8.
ADHEr
FRD2
GLUDy
LDH_D
9.
ADHEr
FRD2
LDH_D
ME2
10.
ACKr
AKGD
ATPS4r
GLUDy
11.
AKGD
ATPS4r
GLUDy
PTAr
12.
ATPS4r
GLUDy
PTAr
SUCOAS
13.
ACKr
ATPS4r
GLUDy
SUCOAS
14.
AKGD
ATPS4r
PTAr
TKT2
15.
ACKr
AKGD
ATPS4r
TKT2
16.
ATPS4r
PTAr
SUCOAS
TKT2
17.
ACKr
ATPS4r
SUCOAS
TKT2
18.
ATPS4r
FUM
GLUDy
PFLi
19.
ACKr
AKGD
ATPS4r
RPE
20.
AKGD
ATPS4r
PTAr
RPE
21.
ACKr
ATPS4r
RPE
SUCOAS
22.
ATPS4r
PTAr
RPE
SUCOAS
23.
ACKr
AKGD
ATPS4r
TKT1
24.
AKGD
ATPS4r
PTAr
TAL
25.
AKGD
ATPS4r
PTAr
TKT1
26.
ACKr
AKGD
ATPS4r
TAL
27.
AKGD
ATPS4r
CBMK2
PTAr
28.
ACKr
AKGD
ATPS4r
CBMK2
29.
ACKr
ATPS4r
SUCOAS
TAL
30.
ATPS4r
PTAr
SUCOAS
TAL
31.
ACKr
ATPS4r
SUCOAS
TKT1
32.
ATPS4r
PTAr
SUCOAS
TKT1
33.
ACKr
AKGD
ASNS2
ATPS4r
34.
AKGD
ASNS2
ATPS4r
PTAr
35.
ATPS4r
CBMK2
PTAr
SUCOAS
36.
ACKr
ATPS4r
CBMK2
SUCOAS
37.
ACKr
ASNS2
ATPS4r
SUCOAS
38.
ASNS2
ATPS4r
PTAr
SUCOAS
39.
ATPS4r
FRD2
PFLi
PGI
40.
ATPS4r
FRD2
PFK
PFLi
41.
ATPS4r
FRD2
PFLi
TPI
42.
ATPS4r
FBA
FRD2
PFLi
43.
FRD2
ME1x
ME2
PYK
44.
ME1x
ME2
PYK
SUCD4
45.
ATPS4r
FRD2
GLUDy
PFLi
46.
ATPS4r
GLUDy
PDH
PFLi
47.
ACKr
ATPS4r
PDH
PFLi
48.
ATPS4r
PDH
PFLi
PTAr
49.
ATPS4r
PDH
PFLi
TKT2
50.
ATPS4r
PDH
PFLi
RPE
51.
ATPS4r
PDH
PFLi
TAL
52.
ATPS4r
PDH
PFLi
TKT1
53.
ATPS4r
CBMK2
PDH
PFLi
54.
ATPS4r
GLU5K
PDH
PFLi
55.
ATPS4r
G5SD
PDH
PFLi
56.
ASNS2
ATPS4r
PDH
PFLi
57.
ASPT
ATPS4r
FUM
PFLi
58.
ATPS4r
CBMK2
FRD2
PFLi
59.
ATPS4r
FRD2
GLU5K
PFLi
60.
ATPS4r
FRD2
G5SD
PFLi
61.
ASNS2
ATPS4r
FRD2
PFLi
62.
ADHEr
ATPS4r
FUM
GLUDy
63.
MDH
ME1x
ME2
SUCD4
64.
FRD2
MDH
ME1x
ME2
65.
ATPS4r
MDH
PPCK
PTAr
66.
ACKr
ATPS4r
MDH
PPCK
67.
ADHEr
FRD2
LDH_D
ME2
THD2
68.
ADHEr
FRD2
GLUDy
LDH_D
THD2
69.
ADHEr
FRD2
GLUDy
LDH_D
ME2
70.
ADHEr
CBMK2
FRD2
GLUDy
LDH_D
71.
ADHEr
LDH_D
ME2
SUCD4
THD2
72.
ADHEr
FUM
GLUDy
LDH_D
SUCD4
73.
ADHEr
ASPT
FUM
GLUDy
LDH_D
74.
ADHEr
FRD2
GLCpts
LDH_D
ME2
75.
ADHEr
GLUDy
LDH_D
PRO1z
SUCD4
76.
ADHEr
CBMK2
FRD2
LDH_D
ME2
77.
ADHEr
FRD2
GLU5K
LDH_D
ME2
78.
ADHEr
FRD2
G5SD
LDH_D
ME2
79.
ADHEr
ASNS2
FRD2
LDH_D
ME2
80.
ADHEr
FUM
GLUDy
LDH_D
NADH6
81.
ADHEr
ASPT
FUM
LDH_D
ME2
82.
FRD2
GLCpts
ME1x
ME2
PYK
83.
GLCpts
ME1x
ME2
PYK
SUCD4
84.
ACKr
ADHEr
LDH_D
ME2
SUCD4
85.
ADHEr
LDH_D
ME2
PTAr
SUCD4
86.
ADHEr
FRD2
ME1x
ME2
PYK
87.
FRD2
ME1x
ME2
PGL
PYK
88.
FRD2
G6PDHy
ME1x
ME2
PYK
89.
FRD2
ME1x
ME2
PGDHY
PYK
90.
EDA
ME1x
ME2
PYK
SUCD4
91.
EDA
FRD2
ME1x
ME2
PYK
92.
ME1x
ME2
PGDHY
PYK
SUCD4
93.
ME1x
ME2
PGL
PYK
SUCD4
94.
G6PDHy
ME1x
ME2
PYK
SUCD4
95.
ACKr
AKGD
ATPS4r
PPCK
PYK
96.
AKGD
ATPS4r
PPCK
PTAr
PYK
97.
FRD2
ME1x
ME2
PFLi
PYK
98.
ACKr
ATPS4r
PPCK
PYK
SUCOAS
99.
ATPS4r
PPCK
PTAr
PYK
SUCOAS
100.
FRD2
ME1x
ME2
PTAr
PYK
101.
ACKr
ME1x
ME2
PYK
SUCD4
102.
ME1x
ME2
PTAr
PYK
SUCD4
103.
ACKr
FRD2
ME1x
ME2
PYK
104.
ACKr
AKGD
ATPS4r
GLUDy
TKT2
105.
AKGD
ATPS4r
GLUDy
PTAr
TKT2
106.
ATPS4r
GLUDy
PTAr
SUCOAS
TKT2
107.
ACKr
ATPS4r
GLUDy
SUCOAS
TKT2
108.
AKGD
ATPS4r
GLUDy
PTAr
RPE
109.
ACKr
AKGD
ATPS4r
GLUDy
RPE
110.
ATPS4r
GLUDy
PTAr
RPE
SUCOAS
111.
ACKr
ATPS4r
GLUDy
RPE
SUCOAS
112.
AKGD
ATPS4r
GLUDy
PTAr
TAL
113.
ACKr
AKGD
ATPS4r
GLUDy
TAL
114.
AKGD
ATPS4r
GLUDy
PTAr
TKT1
115.
ACKr
AKGD
ATPS4r
GLUDy
TKT1
116.
ATPS4r
FRD2
PFLi
PPCK
PYK
117.
ATPS4r
GLUDy
PTAr
SUCOAS
TKT1
118.
ACKr
ATPS4r
GLUDy
SUCOAS
TKT1
119.
ACKr
ATPS4r
GLUDy
SUCOAS
TAL
120.
ATPS4r
GLUDy
PTAr
SUCOAS
TAL
121.
ACKr
AKGD
ATPS4r
CBMK2
GLUDy
122.
AKGD
ATPS4r
CBMK2
GLUDy
PTAr
123.
ACKr
AKGD
ASNS2
ATPS4r
GLUDy
124.
AKGD
ASNS2
ATPS4r
GLUDy
PTAr
125.
ATPS4r
CBMK2
GLUDy
PTAr
SUCOAS
126.
ACKr
ATPS4r
CBMK2
GLUDy
SUCOAS
127.
ASNS2
ATPS4r
GLUDy
PTAr
SUCOAS
128.
ACKr
ASNS2
ATPS4r
GLUDy
SUCOAS
129.
ATPS4r
FUM
GLUDy
PFLi
TKT2
130.
ATPS4r
FUM
ME2
PFLi
THD2
131.
ACKr
AKGD
ATPS4r
CBMK2
TKT2
132.
AKGD
ATPS4r
CBMK2
PTAr
TKT2
133.
ATPS4r
ME2
NADH12
PFLi
THD2
134.
ATPS4r
FUM
GLUDy
PFLi
RPE
135.
AKGD
ASNS2
ATPS4r
PTAr
TKT2
136.
ACKr
AKGD
ASNS2
ATPS4r
TKT2
137.
ACKr
ATPS4r
CBMK2
SUCOAS
TKT2
138.
ATPS4r
CBMK2
PTAr
SUCOAS
TKT2
139.
ATPS4r
FUM
GLUDy
PFLi
TKT1
140.
ATPS4r
FUM
GLUDy
PFLi
TAL
141.
ACKr
ASNS2
ATPS4r
SUCOAS
TKT2
142.
ASNS2
ATPS4r
PTAr
SUCOAS
TKT2
143.
ATPS4r
CBMK2
FUM
GLUDy
PFLi
144.
ACKr
ATPS4r
FUM
GLUDy
PFLi
145.
ATPS4r
FUM
GLUDy
PFLi
PTAr
146.
ACKr
AKGD
ATPS4r
CBMK2
RPE
147.
AKGD
ATPS4r
CBMK2
PTAr
RPE
148.
ATPS4r
FUM
GLU5K
GLUDy
PFLi
149.
ATPS4r
FUM
G5SD
GLUDy
PFLi
150.
ASNS2
ATPS4r
FUM
GLUDy
PFLi
151.
AKGD
ASNS2
ATPS4r
PTAr
RPE
152.
ACKr
AKGD
ASNS2
ATPS4r
RPE
153.
ACKr
ATPS4r
CBMK2
RPE
SUCOAS
154.
ATPS4r
CBMK2
PTAr
RPE
SUCOAS
155.
ASNS2
ATPS4r
PTAr
RPE
SUCOAS
156.
ACKr
ASNS2
ATPS4r
RPE
SUCOAS
157.
AKGD
ATPS4r
CBMK2
PTAr
TAL
158.
AKGD
ATPS4r
CBMK2
PTAr
TKT1
159.
ACKr
AKGD
ATPS4r
CBMK2
TAL
160.
ACKr
AKGD
ATPS4r
CBMK2
TKT1
161.
ACKr
AKGD
ASNS2
ATPS4r
TAL
162.
AKGD
ASNS2
ATPS4r
PTAr
TKT1
163.
AKGD
ASNS2
ATPS4r
PTAr
TAL
164.
ACKr
AKGD
ASNS2
ATPS4r
TKT1
165.
ACKr
ATPS4r
CBMK2
SUCOAS
TKT1
166.
ACKr
ATPS4r
CBMK2
SUCOAS
TAL
167.
ATPS4r
CBMK2
PTAr
SUCOAS
TKT1
168.
ATPS4r
CBMK2
PTAr
SUCOAS
TAL
169.
AKGD
ASNS2
ATPS4r
CBMK2
PTAr
170.
ACKr
AKGD
ASNS2
ATPS4r
CBMK2
171.
ACKr
ASNS2
ATPS4r
SUCOAS
TAL
172.
ASNS2
ATPS4r
PTAr
SUCOAS
TKT1
173.
ASNS2
ATPS4r
PTAr
SUCOAS
TAL
174.
ACKr
ASNS2
ATPS4r
SUCOAS
TKT1
175.
ACKr
ASNS2
ATPS4r
CBMK2
SUCOAS
176.
ASNS2
ATPS4r
CBMK2
PTAr
SUCOAS
177.
ATPS4r
GLCpts
ME1x
ME2
PYK
178.
ATPS4r
FRD2
ME2
PFLi
THD2
179.
ME1x
ME2
PFLi
PYK
SUCD4
180.
FRD2
GLUDy
ME1x
ME2
PYK
181.
GLUDy
ME1x
ME2
PYK
SUCD4
182.
FRD2
ME1x
ME2
PYK
TKT2
183.
ME1x
ME2
PYK
SUCD4
TKT2
184.
ATPS4r
FRD2
GLUDy
PFLi
PGI
185.
ATPS4r
FRD2
GLUDy
PFLi
TPI
186.
ATPS4r
FBA
FRD2
GLUDy
PFLi
187.
ATPS4r
FRD2
GLUDy
PFK
PFLi
188.
ATPS4r
PDH
PFLi
PPCK
PYK
189.
ME1x
ME2
PYK
RPE
SUCD4
190.
FRD2
ME1x
ME2
PYK
RPE
191.
ATPS4r
FRD2
ME1x
ME2
PYK
192.
ATPS4r
ME1x
ME2
PYK
SUCD4
193.
FUM
GLUDy
ME1x
ME2
PYK
194.
ASPT
ATPS4r
FUM
PFLi
PGI
195.
FRD2
ME1x
ME2
PYK
TKT1
196.
ME1x
ME2
PYK
SUCD4
TAL
197.
ME1x
ME2
PYK
SUCD4
TKT1
198.
FRD2
ME1x
ME2
PYK
TAL
199.
ASPT
ATPS4r
FUM
PFLi
TPI
200.
ASPT
ATPS4r
FUM
PFK
PFLi
TABLE 3
A list of all the reaction stoichiometries and the associated genes known to be
associated with the reactions identified for deletion in the strains listed in Tables 1 and 2.
Reaction
Abbreviation
Reaction Name
Reaction Stoichiometry
Associated genes
ACKr
Acetate kinase
[c]: ac + atp <==> actp + adp
(b3115 or b2296 or b1849)
ADHEr
Alcohol dehydrogenase
[c]: accoa + (2) h + (2) nadh <==> coa +
(b0356 or b1478 or b1241)
etoh + (2) nad
AKGD
Alpha-ketoglutarate
[c]: akg + coa + nad --> co2 + nadh + succoa
(b0116 and b0726 and b0727)
dehydrogenase
ALAR
Alanine racemase
[c]: ala-L <==> ala-D
b4053
ASNS2
Asparagine synthetase
[c]: asp-L + atp + nh4 --> amp + asn-L + h + ppi
b3744
ASPT
L-aspartase
[c]: asp-L --> fum + nh4
b4139
ATPS4r
ATP synthase
adp[c] + (4) h[p] + pi[c] <==> atp[c] +
(((b3736 and b3737 and b3738)
(3) h[c] + h2o[c]
and (b3731 and b3732 and b3733
and b3734 and b3735)) or ((b3736
and b3737 and b3738) and (b3731
and b3732 and b3733 and b3734 and
b3735) and b3739))
CBMK2
Carbamate kinase
[c]: atp + co2 + nh4 --> adp + cbp + (2) h
(b0521 or b0323 or b2874)
DAAD
D-amino acid
[c]: ala-D + fad + h2o --> fadh2 + nh4 + pyr
b1189
dehydrogenase
EDA
2-dehydro-3-deoxy-
[c]: 2ddg6p --> g3p + pyr
b1850
phosphogluconate
aldolase
ENO
Enolase
[c]: 2pg <==> h2o + pep
b2779
FBA
Fructose-bis-phosphate
[c]: fdp <==> dhap + g3p
(b2097 or b2925 or b1773)
aldolase
FRD
Fumarate reductase
[c]: fum + mq18 --> mqn8 + succ
(b4151 and b4152 and b4153 and
b4154)
FUM
Fumarase
[c]: fum + h2o <==> mal-L
(b1612 or b4122 or b1611)
G5SD
Glutamate-5-
[c]: glu5p + h + nadph --> glu5sa + nadp + pi
b0243
semialdehyde
dehyrogenase
G6PDHy
Glucose-6-phosphate
[c]: g6p + nadp <==> 6pgl + h + nadph
b1852
dehydrogenase
GLCpts
D-glucose transport via
glc-D[e] + pep[c] --> g6p[c] + pyr[c]
((b2417 and b1101 and b2415 and
PTS mechanism
b2416) or (b1817 and b1818 and
b1819 and b2415 and b2416) or
(b2417 and b1621 and b2415 and
b2416))
GLU5K
Gluatmate-5-kinase
[c]: atp + glu-L --> adp + glu5p
b0242
GLUDy
Glutamate
[c]: glu-L + h2o + nadp <==> akg + h + nadph + nh4
b1761
dehydrogenase
HEX1
Hexokinase
[c]: atp + glc-D --> adp + g6p + h
b2388
LDH_D
Lactate dehydrogenase
[c]: lac-D + nad <==> h + nadh + pyr
b1380 or b2133
MDH
Malate dehydrogenase
[c]: mal-L + nad <==> h + nadh + oaa
b3236
ME1x
Malic enzyme (NAD)
[c]: mal-L + nad --> co2 + nadh + pyr
b1479
ME2
Malic enzyme (NADP)
[c]: mal-L + nadp --> co2 + nadph + pyr
b2463
NADH12
NADH dehydrogenase
[c]: h + nadh + ubq8 -->
b1109
(ubiquinone-8)
nad + ubq8h2
NADH6
NADH dehydrogenase
(4.5) h[c] + nadh[c] + ubq8[c] --> (3.5) h[e] +
(b2276 and b2277 and b2278 and
(ubiquinone-8 and 3.5
nad[c] + ubq8h2[c]
b2279 and b2280 and b2281 and
protons)
b2282 and b2283 and b2284 and
b2285 and b2286 and b2287 and
b2288)
PDH
Pyruvate dehydrogenase
[c]: coa + nad + pyr --> accoa + co2 + nadh
((b0114 and b0115 and b0116) or (b0116
and b0726 and b0727) or (b0116 and
b2903 and b2904 and b2905))
PFK
Phosphofructokinase
[c]: atp + f6p --> adp + fdp + h
(b3916 or b1723)
PFLi
Pyruvate formate lyase
[c]: coa + pyr --> accoa + for
(((b0902 and b0903) and b2579) or
(b0902 and b0903) or (b0902 and
b3114) or (b3951 and b3952))
PGDH
Phosphogluconate
[c]: 6pgc + nadp --> co2 + nadph + ru5p-D
b2029
dehyrogenase
PGDHY
Phosphogluconate
[c]: 6pgc --> 2ddg6p + h2o
b1851
dehydratase
PGI
Glucose-6-phosphate
[c]: g6p <==> f6p
b4025
isomerase
PGL
6-
[c]: 6pgl + h2o --> 6pgc + h
b0767
Phosphogluconolactonase
PGM
Phosphoglycerate mutase
[c]: 3pg <==> 2pg
b3612
PPC
Phosphoenolpyruvate
[c]: co2 + h2o + pep --> h + oaa + pi
b3956
carboxylase
PPCK
Phosphoenolpyruvate
[c]: atp + oaa --> adp + co2 + pep
b3403
carboxykinase
PRO1z
Proline oxidase
[c]: fad + pro-L --> 1pyr5c + fadh2 + h
b1014
PTAr
Phosphotransacetylase
[c]: accoa + pi <==> actp + coa
b2297
PYK
Pyruvate kinase
[c]: adp + h + pep --> atp + pyr
(b1854 or b1676)
RPE
Ribulose-5-phosphate-5-
[c]: ru5p-D <==> xu5p-D
(b4301 or b3386)
epimerase
SUCD4
Succinate dehydrogenase
[c]: fadh2 + ubq8 <==> fad + ubq8h2
(b0721 and b0722 and b0723 and
b0724
SUCOAS
Succinyl-CoA synthetase
[c]: atp + coa + succ <==> adp + pi + succoa
(b0728 and b0729)
TAL
Transaldoalse
[c]: g3p + s7p <==> e4p + f6p
(b2464 or b0008)
THD2
NADP transhydrogenase
(2) h[e] + nadh[c] + nadp[c] --> (2) h[c] +
(b1602 and b1603)
nad[c] + nadph[c]
THD5
NAD transhydrogenase
[c]: nad + nadph --> nadh + nadp
(b3962 or (b1602 and b1603))
TKT1
Transketolase
[c]: r5p + xu5p-D <==> g3p + s7p
(b2935 or b2465)
TKT2
Transketolase
[c]: e4p + xu5p-D <==> f6p + g3p
(b2935 or b2465)
TPI
Triosephosphate
[c]: dhap <==> g3p
b3919
isomerase
VALTA
Valine transaminase
[c]: akg + val-L <==> 3mob + glu-L
b3770
TABLE 4
List of the metabolite abbreviations, the corresponding names and
locations of all the metabolites that participate in the reactions listed
in Table 3.
Metabolite
Abbreviation
Compartment
Metabolite Name
13dpg
Cytosol
3-Phospho-D-glyceroyl phosphate
1pyr5c
Cytosol
1-Pyrroline-5-carboxylate
2ddg6p
Cytosol
2-Dehydro-3-deoxy-D-gluconate
6-phosphate
2pg
Cytosol
D-Glycerate 2-phosphate
3mob
Cytosol
3-Methyl-2-oxobutanoate
3pg
Cytosol
3-Phospho-D-glycerate
6pgc
Cytosol
6-Phospho-D-gluconate
6pgl
Cytosol
6 phospho-D-glucono-1,5-lactone
ac
Cytosol
Acetate
accoa
Cytosol
Acetyl-CoA
actp
Cytosol
Acetyl phosphate
adp
Cytosol
Adenosine diphosphate
akg
Cytosol
2-Oxoglutarate
ala-D
Cytosol
D-alanine
ala-L
Cytosol
L-alanine
amp
Cytosol
Adenosine monophosphate
asn-L
Cytosol
L-asparagine
asp-L
Cytosol
L-aspartate
atp
Cytosol
Adenosine triphosphate
cbp
Cytosol
Carbamoyl phosphate
co2
Cytosol
Carbon dioxide
coa
Cytosol
Coenzyme A
dha
Cytosol
Dihydroxyacetone
dhap
Cytosol
Dihydroxyacetone phosphate
e4p
Cytosol
D-Erythrose 4-phosphate
etoh
Cytosol
Ethanol
f6p
Cytosol
D-Fructose 6-phosphate
fad
Cytosol
Flavin adenine dinucleotide
fadh2
Cytosol
Flavin adenine dinucleotide-reduced
fdp
Cytosol
D-Fructose 1,6-bisphosphate
for
Cytosol
Formate
fum
Cytosol
Fumarate
g3p
Cytosol
Glyceraldehyde 3-phosphate
g6p
Cytosol
D-Glucose 6-phosphate
glc-D[e]
Extra-organism
D-Glucose
glu5p
Cytosol
L-glutamate 5-phosphate
glu5sa
Cytosol
L-glutamate 5-semialdehyde
glu-L
Cytosol
L-Glutamate
h
Cytosol
H +
h[e]
Extra-organism
H +
h2o
Cytosol
Water
lac-D
Cytosol
D-Lactate
mal-L
Cytosol
L-Malate
mql-8
Cytosol
Menaquinol-8
mqn-8
Cytosol
Menaquinone-8
nad
Cytosol
Nicotinamide adenine dinucleotide
nadh
Cytosol
Nicotinamide adenine
dinucleotide-reduced
nadp
Cytosol
Nicotinamide adenine dinucleotide
phosphate
nadph
Cytosol
Nicotinamide adenine dinucleotide
phosphate-reduced
nh4
Cytosol
Ammonium
o2
Cytosol
Oxygen
oaa
Cytosol
Oxaloacetate
pep
Cytosol
Phosphoenolpyruvate
pi
Cytosol
Phosphate
ppi
Cytosol
Diphosphate
pyr
Cytosol
Pyruvate
r5p
Cytosol
alpha-D-Ribose 5-phosphate
ru5p-D
Cytosol
D-Ribulose 5-phosphate
s7p
Cytosol
Sedoheptulose 7-phosphate
succ
Cytosol
Succinate
succoa
Cytosol
Succinyl-CoA
ubq8
Cytosol
Ubiquinone-8
ubq8h2
Cytosol
Ubiquinol-8
val-L
Cytosol
L-valine
xu5p-D
Cytosol
D-Xylulose 5-phosphate
TABLE 5
The list of all strains identified by OptKnock that are most likely to provide increased
fumarate yields in S. Cerevisiae under microaerobic culture conditions. These same designs can
be used for malate production if the cytosolic fumarase (FUM) is deleted additionally.
1
FRDm
FUM
2
ME1m
PYK
FRDm
FUMm
3
ME1m
G3PDm
PYK
SUCD3-u6m
4
G3PDm
GLY3PP
SUCD3-u6m
ALCD2x
5
GLY3PP
FRDm
FUMm
ALCD2x
6
G3PD
FRDm
FUMm
ALCD2x
7
G3PD
G3PD1irm
SUCD3-u6m
ALCD2x
8
G3PD
G3PDm
SUCD3-u6m
ALCD2x
9
G3PDm
PYK
MDHm
SUCD3-
u6m
10
PYK
FRDm
FUMm
MDHm
11
G3PD
G3PDm
SUCD3-u6m
PYRDC
12
G3PDm
GLY3PP
SUCD3-u6m
PYRDC
13
GLY3PP
FRDm
FUMm
PYRDC
14
G3PD
FRDm
FUMm
PYRDC
15
G3PD
G3PD1irm
SUCD3-u6m
PYRDC
16
G3PDm
SUCD3-u6m
PYRDC
ATPtm-
3H
17
FRDm
FUMm
PYRDC
ATPtm-
3H
18
ATPSm
FRDm
FUMm
PYRDC
19
G3PDm
ATPSm
SUCD3-u6m
PYRDC
20
FRDm
FUMm
ALCD2x
ATPtm-
3H
21
G3PDm
SUCD3-u6m
ALCD2x
ATPtm-
3H
22
ATPSm
FRDm
FUMm
ALCD2x
23
G3PDm
ATPSm
SUCD3-u6m
ALCD2x
24
ME1m
FRDm
FUMm
PYRDC
25
ME1m
G3PDm
SUCD3-u6m
PYRDC
26
G3PDm
MDHm
SUCD3-u6m
PYRDC
27
FRDm
FUMm
MDHm
PYRDC
28
ME1m
G3PDm
SUCD3-u6m
ALCD2x
29
ME1m
FRDm
FUMm
ALCD2x
30
G3PDm
MDHm
SUCD3-u6m
ALCD2x
31
FRDm
FUMm
MDHm
ALCD2x
32
ASPTA1
G3PDm
GLY3PP
SUCD3-
u6m
33
ASPTA1
G3PD
FRDm
FUMm
34
ASPTA1
GLY3PP
FRDm
FUMm
35
ASPTA1
G3PD
G3PDm
SUCD3-
u6m
36
ASPTA1
G3PD
G3PD1irm
SUCD3-
u6m
37
G3PDm
GLY3PP
HSK
SUCD3-
u6m
38
G3PDm
GLY3PP
SUCD3-u6m
THRS
39
G3PD
FRDm
FUMm
THRS
40
GLY3PP
HSK
FRDm
FUMm
41
G3PD
G3PDm
HSK
SUCD3-u6m
42
G3PD
G3PD1irm
HSK
SUCD3-u6m
43
G3PD
G3PD1irm
SUCD3-u6m
THRS
44
GLY3PP
FRDm
FUMm
THRS
45
G3PD
HSK
FRDm
FUMm
46
G3PD
G3PDm
SUCD3-u6m
THRS
47
G3PD
FRDm
FUMm
PGL
48
G3PD
FRDm
FUMm
PGDH
49
G3PD
G3PD1irm
SUCD3-u6m
PGDH
50
G3PD
G3PDm
SUCD3-u6m
PGDH
51
G3PDm
GLY3PP
SUCD3-u6m
G6PDH
52
G3PD
G3PDm
SUCD3-u6m
G6PDH
53
G3PDm
GLY3PP
SUCD3-u6m
PGL
54
G3PDm
GLY3PP
SUCD3-u6m
PGDH
55
GLY3PP
FRDm
FUMm
G6PDH
56
G3PD
G3PDm
SUCD3-u6m
PGL
57
G3PD
G3PD1irm
SUCD3-u6m
PGL
58
GLY3PP
FRDm
FUMm
PGL
59
GLY3PP
FRDm
FUMm
PGDH
60
G3PD
G3PD1irm
SUCD3-u6m
G6PDH
61
G3PD
FRDm
FUMm
G6PDH
62
G3PD
G3PDm
SUCD3-u6m
TKT1
63
G3PDm
GLY3PP
SUCD3-u6m
TKT1
64
G3PD
FRDm
FUMm
TKT1
65
G3PD
G3PD1irm
SUCD3-u6m
TKT1
66
GLY3PP
FRDm
FUMm
TKT1
67
G3PDm
GLY3PP
SUCD3-u6m
RPE
68
G3PD
G3PDm
SUCD3-u6m
RPE
69
GLY3PP
FRDm
FUMm
RPE
70
G3PD
G3PD1irm
SUCD3-u6m
RPE
71
G3PD
FRDm
FUMm
RPE
72
G3PDm
SERD_L
PGI
SUCD3-
u6m
73
SERD_L
PGI
FRDm
FUMm
74
GLY3PP
FRDm
FUMm
THRA
75
G3PD
FRDm
FUMm
THRA
76
G3PDm
GLY3PP
SUCD3-u6m
THRA
77
G3PD
G3PDm
SUCD3-u6m
THRA
78
G3PD
G3PD1irm
SUCD3-u6m
THRA
79
ALATA_L
ASPTA1
SUCOASAm
PSP_L
80
ALATA_L
ASPTA1
PSERT
PDHcm
81
ALATA_L
ASPTA1
AKGDbm
PGCD
82
ALATA_L
ASPTA1
SUCOASAm
PSERT
83
ALATA_L
ASPTA1
SUCOASAm
PGCD
84
ALATA_L
ASPTA1
AKGDam
PSERT
85
ALATA_L
ASPTA1
AKGDbm
PSERT
86
ALATA_L
ASPTA1
PSP_L
PDHcm
87
ALATA_L
ASPTA1
AKGDbm
PSP_L
88
ALATA_L
ASPTA1
PGCD
PDHcm
89
ALATA_L
ASPTA1
AKGDam
PSP_L
90
ALATA_L
ASPTA1
AKGDam
PGCD
91
ASPTA1
ICL
SUCOASAm
PSP_L
92
ASPTA1
SUCOASAm
AGT
PSP_L
93
ASPTA1
SUCOASAm
AGT
PSERT
94
ASPTA1
SUCOASAm
AGT
PGCD
95
ASPTA1
ICL
SUCOASAm
PSERT
96
ASPTA1
ICL
SUCOASAm
PGCD
97
ASPTA1
AGT
PSP_L
PDHcm
98
ASPTA1
ICL
AKGDbm
PSP_L
99
ASPTA1
AKGDam
AGT
PSP_L
100
ASPTA1
AGT
PGCD
PDHcm
101
ASPTA1
AKGDbm
AGT
PGCD
102
ASPTA1
AKGDbm
AGT
PSERT
103
ASPTA1
ICL
PGCD
PDHcm
104
ASPTA1
ICL
AKGDbm
PGCD
105
ASPTA1
AGT
PSERT
PDHcm
106
ASPTA1
ICL
PSP_L
PDHcm
107
ASPTA1
ICL
AKGDam
PSERT
108
ASPTA1
ICL
AKGDam
PSP_L
109
ASPTA1
ICL
PSERT
PDHcm
110
ASPTA1
AKGDbm
AGT
PSP_L
111
ASPTA1
ICL
AKGDam
PGCD
112
ASPTA1
AKGDam
AGT
PSERT
113
ASPTA1
AKGDam
AGT
PGCD
114
ASPTA1
ICL
AKGDbm
PSERT
115
GLY3PP
HSDxi
FRDm
FUMm
116
G3PD
HSDxi
FRDm
FUMm
117
G3PD
G3PDm
HSDxi
SUCD3-
u6m
118
G3PD
G3PD1irm
HSDxi
SUCD3-
u6m
119
G3PDm
GLY3PP
HSDxi
SUCD3-
u6m
120
G3PDm
FUm
SUCD1rm
SUCD3-
u6m
121
G3PDm
FUm
FUMm
SUCD3-
u6m
122
G3PDm
MDH
NADH2-u6cm
NADH2-
u6m
123
ASPTA1
ME1m
PSERT
PDHm
PYK
124
ASPTA1
ME1m
PSP_L
PDHm
PYK
125
ASPTA1
ME1m
PGCD
PDHm
PYK
126
ASPTA1
ME1m
ME2m
PSP_L
PYK
127
ASPTA1
ME1m
ME2m
PGCD
PYK
128
ASPTA1
ME1m
ME2m
PSERT
PYK
129
ASPTA1
ORNTA
ME1m
PSP_L
PYK
130
ASPTA1
ORNTA
ME1m
PGCD
PYK
131
ASPTA1
ORNTA
ME1m
PSERT
PYK
132
ASPTA1
ME1m
PRO1xm
PSP_L
PYK
133
ASPTA1
ME1m
P5CDm
PSERT
PYK
134
ASPTA1
ME1m
P5CDm
PSP_L
PYK
135
ASPTA1
ME1m
PRO1xm
PGCD
PYK
136
ASPTA1
ME1m
P5CDm
PGCD
PYK
137
ASPTA1
ME1m
PRO1xm
PSERT
PYK
138
ASPTA1m
ME1m
PSP_L
PDHm
PYK
139
ASPTA1m
ME1m
PSERT
PDHm
PYK
140
ASPTA1m
ME1m
PGCD
PDHm
PYK
141
ASPTA1m
ME1m
PRO1xm
PSP_L
PYK
142
ASPTA1m
ME1m
P5CDm
PGCD
PYK
143
ASPTA1m
ME1m
PRO1xm
PGCD
PYK
144
ASPTA1m
ME1m
PRO1xm
PSERT
PYK
145
ASPTA1m
ME1m
P5CDm
PSERT
PYK
146
ASPTA1m
ME1m
P5CDm
PSP_L
PYK
147
ASPTA1m
ME1m
PSERT
PDHcm
PYK
148
ASPTA1m
ME1m
SUCOASAm
PSERT
PYK
149
ASPTA1m
ME1m
AKGDam
PSP_L
PYK
150
ASPTA1m
ME1m
AKGDbm
PSERT
PYK
151
ASPTA1m
ME1m
SUCOASAm
PGCD
PYK
152
ASPTA1m
ME1m
AKGDam
PGCD
PYK
153
ASPTA1m
ME1m
SUCOASAm
PSP_L
PYK
154
ASPTA1m
ME1m
AKGDam
PSERT
PYK
155
ASPTA1m
ME1m
PSP_L
PDHcm
PYK
156
ASPTA1m
ME1m
PGCD
PDHcm
PYK
157
ASPTA1m
ME1m
AKGDbm
PGCD
PYK
158
ASPTA1m
ME1m
AKGDbm
PSP_L
PYK
159
ASPTA1m
ORNTA
ME1m
PSP_L
PYK
160
ASPTA1m
ORNTA
ME1m
PGCD
PYK
161
ASPTA1m
ORNTA
ME1m
PSERT
PYK
162
ME1m
ME2m
ACONTm
PSP_L
PYK
163
ME1m
ME2m
ACONTm
PGCD
PYK
164
ME1m
ME2m
ACONTm
PSERT
PYK
165
ASPTA1m
ME1m
ME2m
PSP_L
PYK
166
ASPTA1m
ME1m
ME2m
PGCD
PYK
167
ASPTA1m
ME1m
ME2m
PSERT
PYK
168
ME1m
ME2m
ICDHy
PSERT
PYK
169
ME1m
ME2m
ACONT
PSERT
PYK
170
ME1m
ME2m
ACONT
PSP_L
PYK
171
ME1m
ME2m
ICDHy
PSP_L
PYK
172
ME1m
ME2m
ICDHy
PGCD
PYK
173
ME1m
ME2m
ACONT
PGCD
PYK
174
ME1m
ME2m
ICDHxm
PSP_L
PYK
175
ME1m
ME2m
ICDHxm
PGCD
PYK
176
ME1m
ME2m
ICDHxm
PSERT
PYK
177
ME1m
ME2m
G3PDm
PYK
SUCD3-
u6m
178
ME1m
ME2m
PYK
FRDm
FUMm
179
ME1m
PYK
FRDm
FUMm
PGDH
180
ME1m
G3PDm
PYK
SUCD3-u6m
PGDH
181
ME1m
PYK
FRDm
FUMm
PGL
182
ME1m
PYK
FRDm
FUMm
G6PDH
183
ME1m
G3PDm
PYK
SUCD3-u6m
PGL
184
ME1m
G3PDm
PYK
SUCD3-u6m
G6PDH
185
ME1m
G3PDm
PYK
SUCD3-u6m
TKT1
186
ME1m
PYK
FRDm
FUMm
TKT1
187
ME1m
G3PDm
PYK
SUCD3-u6m
RPE
188
ME1m
PYK
FRDm
FUMm
RPE
189
ME1m
PYK
FRDm
FUMm
TKT2
190
ME1m
G3PDm
PYK
SUCD3-u6m
TKT2
191
ME1m
ME2m
PSP_L
PYK
PGDH
192
ME1m
ME2m
PSERT
PYK
PGDH
193
ME1m
ME2m
PGCD
PYK
PGDH
194
ME1m
ME2m
PSERT
PYK
PGL
195
ME1m
ME2m
PSERT
PYK
G6PDH
196
ME1m
ME2m
PGCD
PYK
PGL
197
ME1m
ME2m
PSP_L
PYK
PGL
198
ME1m
ME2m
PSP_L
PYK
G6PDH
199
ME1m
ME2m
PGCD
PYK
G6PDH
200
ME1m
ME2m
PSERT
PYK
TKT1
201
ME1m
ME2m
PGCD
PYK
TKT1
202
ME1m
ME2m
PSP_L
PYK
TKT1
203
ME1m
ME2m
PSERT
PYK
RPE
204
ME1m
ME2m
PSP_L
PYK
RPE
205
ME1m
ME2m
PGCD
PYK
RPE
206
ME1m
ME2m
PSP_L
PYK
TKT2
207
ME1m
ME2m
PSERT
PYK
TKT2
208
ME1m
ME2m
PGCD
PYK
TKT2
209
ATPSm
FRDm
FUMm
PGDH
PYRDC
210
G3PDm
ATPSm
SUCD3-u6m
PGDH
PYRDC
211
ATPSm
FRDm
FUMm
G6PDH
PYRDC
212
G3PDm
ATPSm
SUCD3-u6m
PGL
PYRDC
213
ATPSm
FRDm
FUMm
PGL
PYRDC
214
G3PDm
ATPSm
SUCD3-u6m
G6PDH
PYRDC
215
G3PDm
ATPSm
SUCD3-u6m
TKT1
PYRDC
216
ATPSm
FRDm
FUMm
TKT1
PYRDC
217
G3PDm
SUCD3-u6m
PGL
PYRDC
ATPtm-
3H
218
FRDm
FUMm
PGDH
PYRDC
ATPtm-
3H
219
G3PDm
SUCD3-u6m
PGDH
PYRDC
ATPtm-
3H
220
G3PDm
SUCD3-u6m
G6PDH
PYRDC
ATPtm-
3H
221
FRDm
FUMm
PGL
PYRDC
ATPtm-
3H
222
FRDm
FUMm
G6PDH
PYRDC
ATPtm-
3H
223
G3PDm
SUCD3-u6m
TKT1
PYRDC
ATPtm-
3H
224
FRDm
FUMm
TKT1
PYRDC
ATPtm-
3H
225
G3PDm
ATPSm
SUCD3-u6m
RPE
PYRDC
226
ATPSm
FRDm
FUMm
RPE
PYRDC
227
G3PDm
SUCD3-u6m
RPE
PYRDC
ATPtm-
3H
228
FRDm
FUMm
RPE
PYRDC
ATPtm-
3H
229
G3PDm
ATPSm
SUCD3-u6m
TKT2
PYRDC
230
ATPSm
FRDm
FUMm
TKT2
PYRDC
231
FRDm
FUMm
TKT2
PYRDC
ATPtm-
3H
232
G3PDm
SUCD3-u6m
TKT2
PYRDC
ATPtm-
3H
233
ME2m
FRDm
FUMm
ALCD2x
ATPtm-
3H
234
ME2m
G3PDm
SUCD3-u6m
ALCD2x
ATPtm-
3H
235
ME1m
ME2m
MTHFD
SERD_L
PYK
G6PDH
236
ME1m
ME2m
MTHFD
SERD_L
PYK
PGL
237
ME1m
ME2m
MTHFD
SERD_L
PYK
PGDH
238
ASPTA1
GHMT2
ME1m
SERD_L
PDHm
PYK
239
ORNTA
ME1m
MTHFD
SERD_L
PYK
G6PDH
240
G3PD
FRDm
FUm
PYRDC
241
G3PD
FRDm
FUMmPGDH
PYRDC
242
G3PD
FRDm
FUMmPGL
PYRDC
243
G3PD
G3PD1irm
SUCD3-u6m
G6PDH
PYRDC
244
G3PD
G3PDm
SUCD3-u6m
PGL
PYRDC
245
G3PD
G3PD1irm
SUCD3-u6m
PGDH
PYRDC
246
G3PD
FRDm
FUMm
G6PDH
PYRDC
247
G3PD
G3PDm
SUCD3-u6m
G6PDH
PYRDC
248
G3PD
G3PD1irm
SUCD3-u6m
PGL
PYRDC
249
G3PD
G3PDm
SUCD3-u6m
PGDH
PYRDC
250
G3PD
G3PDm
SUCD3-u6m
TKT1
PYRDC
251
G3PD
G3PD1irm
SUCD3-u6m
TKT1
PYRDC
252
G3PD
FRDm
FUMm
TKT1
PYRDC
253
G3PD
G3PD1irm
SUCD3-u6m
RPE
PYRDC
254
G3PD
G3PDm
SUCD3-u6m
RPE
PYRDC
255
G3PD
FRDm
FUMm
RPE
PYRDC
256
G3PD
G3PD1irm
SUCD3-u6m
TKT2
PYRDC
257
G3PD
G3PDm
SUCD3-u6m
TKT2
PYRDC
258
G3PD
FRDm
FUMm
TKT2
PYRDC
259
ASPTA1
G3PD
G3PD1irm
SUCD3-
PYRDC
u6m
260
ASPTA1
G3PD
G3PDm
SUCD3-
PYRDC
u6m
261
ASPTA1
G3PD
FRDm
FUMm
PYRDC
262
G3PD
G3PD1irm
HSDxi
SUCD3-u6m
PYRDC
263
G3PD
G3PDm
HSDxi
SUCD3-u6m
PYRDC
264
G3PD
HSDxi
FRDm
FUMm
PYRDC
265
G3PD
G3PD1irm
SUCD3-u6m
ALCD2x
PYRDC
266
G3PD
G3PDm
SUCD3-u6m
ALCD2x
PYRDC
267
G3PD
FRDm
FUMmALCD2x
PYRDC
268
ACONT
GLUDC
G3PD
PYRDC
ALDD2y
269
ICDHyG3PD
G3PD1irm
SUCD3-u6m
PGL
PYRDC
270
ICDHyG3PD
FRDm
FUMm
G6PDH
PYRDC
271
ACONT
G3PD
G3PD1irm
SUCD3-
PGL
PYRDC
u6m
272
ACONT
G3PD
FRDm
FUMm
PGDH
PYRDC
273
ACONT
G3PD
G3PD1irm
SUCD3-
G6PDH
PYRDC
u6m
274
ICDHyG3PD
G3PDm
SUCD3-u6m
G6PDH
PYRDC
275
ACONT
G3PD
FRDm
FUMm
G6PDH
PYRDC
276
ACONT
G3PD
G3PDm
SUCD3-
G6PDH
PYRDC
u6m
277
ACONT
G3PD
G3PDm
SUCD3-
PGDH
PYRDC
u6m
278
ICDHyG3PD
G3PDm
SUCD3-u6m
PGL
PYRDC
TABLE 6
The list of all strains identified by OptKnock that are most likely to provide increased
acrylate yields in S. cerevisiae under anaerobic conditions.
1
PYRDC
2
ALCD2x
3
ATPtm-3H
4
ATPSm
5
ME1m
6
PDHm
PYRDC
7
ME1m
PYK
8
ATPSm
ATPS
9
ME1m
ATPS
10
ATPS
ATPtm-3H
11
PDHm
ATPtm-3H
12
PDHm
ALCD2x
13
PDHm
ATPSm
14
PSERT
ALCD2x
15
PSP_L
ALCD2x
16
PGCD
ALCD2x
17
ALCD2x
ATPS
18
PYRDC
IPPSm
19
PGCD
PYRDC
20
PSP_L
PYRDC
21
PSERT
PYRDC
22
PYRDC
ATPS
23
PGCD
ATPSm
24
PSP_L
ATPSm
25
PSERT
ATPSm
26
PSERT
ATPtm-3H
27
PGCD
ATPtm-3H
28
PSP_L
ATPtm-3H
29
ME1m
PDHm
30
ME1m
PGCD
31
ME1m
PSP_L
32
ME1m
PSERT
33
GLU5K
PYRDC
34
GHMT2m
ATPSm
35
ATPtm-3H
IPPSm
36
ALCD2x
IPPSm
37
ATPSm
IPPSm
38
PYK
ATPSm
39
ORNTA
ATPtm-3H
40
MDHm
DHORD4u
41
G3PDm
SUCD3-u6m
ALCD2x
42
G3PDm
ATPSm
SUCD3-u6m
43
GLU5K
PDHm
PYRDC
44
PDHm
PYRDC
IPPS
45
G3PDm
SUCD3-u6m
ATPtm-3H
46
ME1m
G3PDm
SUCD3-u6m
47
PGCD
PDHm
ATPSm
48
PSP_L
PDHm
ATPSm
49
PSERT
PDHm
ATPSm
50
PSERT
PDHm
ALCD2x
51
PGCD
PDHm
ALCD2x
52
PSP_L
PDHm
ALCD2x
53
PDHm
PYK
ATPSm
54
ME1m
PSP_L
PYK
55
ME1m
PSERT
PYK
56
ME1m
PGCD
PYK
57
G3PDm
SUCD3-u6m
PYRDC
58
PSERT
PDHm
ATPtm-3H
59
PSP_L
PDHm
ATPtm-3H
60
PGCD
PDHm
ATPtm-3H
61
PGCD
ATPSm
ALCD2x
62
PSP_L
ATPSm
ALCD2x
63
PSERT
ATPSm
ALCD2x
64
ME2m
ATPSm
ATPS
65
ME1m
PGCD
PDHm
66
ME1m
PSERT
PDHm
67
ME1m
PSP_L
PDHm
68
ME2m
ATPS
ATPtm-3H
69
ME2m
PYRDC
ATPS
70
ORNTA
ATPS
ATPtm-3H
71
GHMT2m
PDHm
ATPSm
72
ACONT
ATPS
ATPtm-3H
73
ICDHyATPS
ATPtm-3H
74
GHMT2
ATPS
ATPtm-3H
75
ME1m
PSP_L
ALCD2x
76
ME1m
PGCD
ALCD2x
77
ME1m
PSERT
ALCD2x
78
ASPTA1m
ATPS
ATPtm-3H
79
FTHFLm
PYK
ATPSm
80
MTHFDm
PYK
ATPSm
81
MTHFCm
PYK
ATPSm
82
MTHFC
ATPS
ATPtm-3H
83
GHMT2
ALCD2x
ATPS
84
PSP_L
PYRDC
IPPSm
85
PSERT
PYRDC
IPPSm
86
PGCD
PYRDC
IPPSm
87
ICDHy
PYRDC
ATPS
88
ACONT
PYRDC
ATPS
89
PGCD
ATPSm
IPPSm
90
PSP_L
ATPSm
IPPSm
91
PSERT
ATPSm
IPPSm
92
ORNTA
PYRDC
ATPS
93
PGCD
ATPtm-3H
IPPSm
94
PSERT
ATPtm-3H
IPPSm
95
PSP_L
ATPtm-3H
IPPSm
96
GLU5K
ALCD2x
ATPS
97
ALCD2x
ATPS
IPPS
98
GLU5K
PYRDC
IPPSm
99
GLU5K
PGCD
PYRDC
100
GLU5K
PSP_L
PYRDC
101
GLU5K
PSERT
PYRDC
102
GLU5K
PYRDC
ATPS
103
ORNTA
PGCD
ATPtm-3H
104
ORNTA
PSERT
ATPtm-3H
105
ORNTA
PSP_L
ATPtm-3H
106
PYK
ATPSm
ATPtm-3H
107
ASPTA1m
PSERT
ATPtm-3H
108
ASPTA1m
PSP_L
ATPtm-3H
109
ASPTA1m
PGCD
ATPtm-3H
110
PYK
ATPSm
IPPSm
111
GHMT2
GHMT2m
ALCD2x
112
MTHFC
PSP_L
ATPtm-3H
113
MTHFC
PGCD
ATPtm-3H
114
MTHFC
PSERT
ATPtm-3H
115
GHMT2m
ATPSm
IPPSm
116
GHMT2
GHMT2m
ATPtm-3H
117
GHMT2
GHMT2m
PYRDC
118
GHMT2m
PYK
ATPSm
119
GLU5K
GHMT2m
ATPSm
120
G5SD
G5SD2
PYRDC
121
GHMT2m
ATPSm
ALCD2x
122
ORNTA
ATPtm-3H
IPPSm
123
MTHFC
GHMT2m
ALCD2x
124
MTHFC
GHMT2m
ATPtm-3H
125
ME2m
ICDHym
ATPtm-3H
126
ME2m
ACONTm
ATPtm-3H
127
GLU5K
ALCD2x
THRA
128
ASPTA1m
THRA
ATPtm-3H
129
GHMT2
ME1m
GHMT2m
130
PSERT
MDHm
DHORD4u
131
PSP_L
MDHm
DHORD4u
132
PGCD
MDHm
DHORD4u
133
ME1m
MTHFC
GHMT2m
134
MDHm
DHORD4u
ATPS
135
PDHm
MDHm
DHORD4u
136
MDHm
DHORD4u
IPPSm
137
ORNTA
MDHm
DHORD4u
138
MDHm
DHORD4u
ALDD2y
139
ASPTA1m
MDHm
DHORD4u
140
MDHm
NADH2-u6m
SUCD3-u6m
141
TPI
MDH
DHORD4u
142
MDH
DHORD4u
ATPS
143
FUM
SUCD1rm
ATPS
144
FUM
FUMmATPS
145
TPI
FUM
SUCD1rm
146
TPI
FUM
FUMm
147
G3PDm
PDHm
SUCD3-u6m
PYRDC
148
GLU5K
G3PDm
SUCD3-u6m
ALCD2x
149
G3PDm
SUCD3-u6m
ALCD2x
IPPS
150
GLU5K
PDHm
PYRDC
IPPS
151
G5SD
G5SD2
PDHm
PYRDC
152
ASPTA1m
ACONTm
PDHm
PYRDC
153
ME1m
G3PDm
PYK
SUCD3-u6m
154
ORNTA
G3PDm
SUCD3-u6m
ATPtm-3H
155
ME2m
G3PDm
SUCD3-u6m
ATPtm-3H
156
ICDHy
G3PDm
SUCD3-u6m
ATPtm-3H
157
ACONT
G3PDm
SUCD3-u6m
ATPtm-3H
158
GHMT2
G3PDm
SUCD3-u6m
ATPtm-3H
159
ASPTA1m
G3PDm
SUCD3-u6m
ATPtm-3H
160
MTHFC
G3PDm
SUCD3-u6m
ATPtm-3H
161
ME2m
G3PDm
SUCD3-u6m
PYRDC
162
ME1m
ME2m
PGCD
PYK
163
ME1m
ME2m
PSP_L
PYK
164
ME1m
ME2m
PSERT
PYK
165
PDHm
PYK
ATPSm
IPPSm
166
ORNTA
ME1m
PSP_L
PYK
167
ORNTA
ME1m
PSERT
PYK
168
ORNTA
ME1m
PGCD
PYK
169
ICDHy
G3PDm
SUCD3-u6m
PYRDC
170
ACONT
G3PDm
SUCD3-u6m
PYRDC
171
ORNTA
G3PDm
SUCD3-u6m
PYRDC
172
ORNTA
PGCD
PDHm
ATPtm-3H
173
ORNTA
PSERT
PDHm
ATPtm-3H
174
ORNTA
PSP_L
PDHm
ATPtm-3H
175
ME1m
PGCD
PYK
ATPSm
176
ME1m
PSERT
PYK
ATPSm
177
ME1m
PSP_L
PYK
ATPSm
178
G3PD
G3PD1irm
ATPSm
SUCD3-u6m
179
MTHFD
PSP_L
PDHm
ALCD2x
180
MTHFD
PGCD
PDHm
ALCD2x
181
MTHFD
PSERT
PDHm
ALCD2x
182
ME1m
G3PD
G3PD1irm
SUCD3-u6m
183
MTHFC
PSP_L
PDHm
ALCD2x
184
MTHFC
PSERT
PDHm
ALCD2x
185
MTHFC
PGCD
PDHm
ALCD2x
186
ASPTA1m
PSP_L
PDHm
ALCD2x
187
ASPTA1m
PGCD
PDHm
ALCD2x
188
ASPTA1m
PSERT
PDHm
ALCD2x
189
ME2m
PGCD
PDHm
ATPtm-3H
190
ME2m
PSERT
PDHm
ATPtm-3H
191
ME2m
PSP_L
PDHm
ATPtm-3H
192
ME1m
MTHFC
PSP_L
PYK
193
ME1m
MTHFC
PSERT
PYK
194
ME1m
MTHFC
PGCD
PYK
195
ASPTA1m
PGCD
ATPSm
ALCD2x
196
ASPTA1m
PSERT
ATPSm
ALCD2x
197
ASPTA1m
PSP_L
ATPSm
ALCD2x
198
GHMT2
PSP_L
PDHm
ATPtm-3H
199
GHMT2
PGCD
PDHm
ATPtm-3H
200
GHMT2
PSERT
PDHm
ATPtm-3H
201
ASPTA1m
PGCD
PDHm
ATPtm-3H
202
ASPTA1m
PSERT
PDHm
ATPtm-3H
203
ASPTA1m
PSP_L
PDHm
ATPtm-3H
204
ACONT
PSP_L
PDHm
ATPtm-3H
205
ACONT
PSERT
PDHm
ATPtm-3H
206
ACONT
PGCD
PDHm
ATPtm-3H
207
ICDHyPSP_L
PDHm
ATPtm-3H
208
ICDHyPGCD
PDHm
ATPtm-3H
209
ICDHyPSERT
PDHm
ATPtm-3H
210
MTHFC
PSP_L
PDHm
ATPtm-3H
211
MTHFC
PGCD
PDHm
ATPtm-3H
212
MTHFC
PSERT
PDHm
ATPtm-3H
213
GLU5K
G3PDm
SUCD3-u6m
PYRDC
214
G3PD
G3PD1irm
SUCD3-u6m
ATPtm-3H
215
GHMT2
GHMT2m
PDHm
ATPtm-3H
216
MTHFDm
PYK
ATPSm
IPPSm
217
MTHFCm
PYK
ATPSm
IPPSm
218
FTHFLm
PYK
ATPSm
IPPSm
219
ME2m
PSP_L
ALCD2x
ATPtm-3H
220
ME2m
PSERT
ALCD2x
ATPtm-3H
221
ME2m
PGCD
ALCD2x
ATPtm-3H
222
GHMT2
GHMT2m
PDHm
ALCD2x
223
ME2m
MTHFC
ATPS
ATPtm-3H
224
ME2m
MTHFC
PYRDC
ATPS
225
GLU5K
GHMT2m
PDHm
ATPSm
226
ORNTA
ACONT
ATPS
ATPtm-3H
227
ORNTA
ICDHyATPS
ATPtm-3H
228
ORNTA
ICDHy
PYRDC
ATPS
229
ORNTA
ACONT
PYRDC
ATPS
230
ASPTA1m
FTHFLm
PYK
ATPSm
231
ASPTA1m
MTHFDm
PYK
ATPSm
232
ASPTA1m
MTHFCm
PYK
ATPSm
233
ORNTA
MTHFC
ATPS
ATPtm-3H
234
GHMT2
GHMT2m
PDHm
ATPSm
235
MTHFC
PSERT
PYK
ATPSm
236
MTHFC
PGCD
PYK
ATPSm
237
MTHFC
PSP_L
PYK
ATPSm
238
GHMT2
ICDHyATPS
ATPtm-3H
239
GHMT2
ACONT
ATPS
ATPtm-3H
240
G3PD
G3PD1irm
SUCD3-u6m
PYRDC
241
FTHFLr
PSERT
PYK
ATPSm
242
FTHFLr
PSP_L
PYK
ATPSm
243
FTHFLr
PGCD
PYK
ATPSm
244
ACONT
PSERT
ALCD2x
ATPtm-3H
245
ICDHyPSP_L
ALCD2x
ATPtm-3H
246
ACONT
PGCD
ALCD2x
ATPtm-3H
247
ICDHyPGCD
ALCD2x
ATPtm-3H
248
ICDHyPSERT
ALCD2x
ATPtm-3H
249
ACONT
PSP_L
ALCD2x
ATPtm-3H
250
ICDHyPYK
ATPSm
ATPtm-3H
251
ACONT
PYK
ATPSm
ATPtm-3H
252
ICDHyMTHFC
ATPS
ATPtm-3H
253
ACONT
MTHFC
ATPS
ATPtm-3H
254
ORNTA
PGCD
ALCD2x
ATPtm-3H
255
ORNTA
PSERT
ALCD2x
ATPtm-3H
256
ORNTA
PSP_L
ALCD2x
ATPtm-3H
257
MTHFDm
PSP_L
PYK
ATPSm
258
FTHFLm
PGCD
PYK
ATPSm
259
MTHFCm
PSP_L
PYK
ATPSm
260
MTHFDm
PSERT
PYK
ATPSm
261
MTHFDm
PGCD
PYK
ATPSm
262
MTHFCm
PGCD
PYK
ATPSm
263
MTHFCm
PSERT
PYK
ATPSm
264
FTHFLm
PSERT
PYK
ATPSm
265
FTHFLm
PSP_L
PYK
ATPSm
266
MTHFD
MTHFD2
ATPS
ATPtm-3H
267
ORNTA
PYK
ATPSm
ATPtm-3H
268
ASPTA1m
MTHFC
ATPS
ATPtm-3H
269
MTHFC
PYK
ATPSm
ATPtm-3H
270
ICDHyGLY3PP
PYRDC
ATPS
271
ACONT
GLY3PP
PYRDC
ATPS
272
ICDHyG3PD
PYRDC
ATPS
273
ACONT
G3PD
PYRDC
ATPS
274
MTHFC
GHMT2m
PDHm
ATPtm-3H
275
MTHFC
GHMT2m
PDHm
ALCD2x
276
GHMT2
PSERT
ALCD2x
ATPS
277
GHMT2
PGCD
ALCD2x
ATPS
278
GHMT2
PSP_L
ALCD2x
ATPS
279
FTHFLr
PYK
ATPSm
ATPtm-3H
280
PYK
ATPSm
ATPtm-3H
IPPSm
281
ACONT
MTHFC
PYRDC
ATPS
282
ICDHyMTHFC
PYRDC
ATPS
283
ORNTA
MTHFC
PYRDC
ATPS
284
GHMT2
FTHFCLm
ALCD2x
ATPS
285
GHMT2
THFATm
ALCD2x
ATPS
286
GHMT2
ALCD2x
ATPS
IPPS
287
ORNTA
PDHm
THRA
ATPtm-3H
288
GLU5K
PSERT
PYRDC
IPPSm
289
GLU5K
PGCD
PYRDC
IPPSm
290
GLU5K
PSP_L
PYRDC
IPPSm
291
ASPTA1m
ORNTA
PYRDC
ATPS
292
ORNTA
PGCD
ATPtm-3H
IPPSm
293
ORNTA
PSERT
ATPtm-3H
IPPSm
294
ORNTA
PSP_L
ATPtm-3H
IPPSm
295
PGCD
PYK
ATPSm
ATPtm-3H
296
PSP_L
PYK
ATPSm
ATPtm-3H
297
PSERT
PYK
ATPSm
ATPtm-3H
298
ASPTA1m
PSERT
ATPtm-3H
IPPSm
299
ASPTA1m
PGCD
ATPtm-3H
IPPSm
300
ASPTA1m
PSP_L
ATPtm-3H
IPPSm
301
ME1m
G3PD
MDHm
SUCD3-u6m
302
MTHFC
PGCD
ATPtm-3H
IPPSm
303
MTHFC
PSP_L
ATPtm-3H
IPPSm
304
MTHFC
PSERT
ATPtm-3H
IPPSm
305
GHMT2
PSERT
ALCD2x
ATPtm-3H
306
GHMT2
PSP_L
ALCD2x
ATPtm-3H
307
GHMT2
PGCD
ALCD2x
ATPtm-3H
308
G3PD
MDHm
SUCD3-u6m
PYRDC
309
GHMT2
GHMT2m
ALCD2x
ATPtm-3H
310
GLU5K
PSP_L
ALCD2x
ATPS
311
GLU5K
PSERT
ALCD2x
ATPS
312
GLU5K
PGCD
ALCD2x
ATPS
313
PSERT
PDHm
MDHm
DHORD4u
314
PSP_L
PDHm
MDHm
DHORD4u
315
PGCD
PDHm
MDHm
DHORD4u
316
GLU5K
PSP_L
ALCD2x
PYRDC
317
GLU5K
PGCD
ALCD2x
PYRDC
318
GLU5K
PSERT
ALCD2x
PYRDC
319
GLU5K
ALCD2x
ATPS
IPPS
320
PSP_L
ALCD2x
ATPS
IPPS
321
PGCD
ALCD2x
ATPS
IPPS
322
PSERT
ALCD2x
ATPS
IPPS
323
ASPTA1m
PYK
ATPSm
ATPtm-3H
324
GHMT2
ME1m
GHMT2m
PDHm
325
MTHFD
G3PD
PYRDC
ATPS
326
MTHFD
GLY3PP
PYRDC
ATPS
327
G5SD
G5SD2
ALCD2x
ATPS
328
ACONT
ICDHxm
PYK
ATPSm
329
ICDHxm
ICDHyPYK
ATPSm
330
ASPTA1m
ACONTm
ALCD2x
ATPS
331
ASPTA1m
G5SD2
ALCD2x
ATPS
332
G5SD
G5SD2
PYRDC
IPPSm
333
G5SD
G5SD2
PSP_L
PYRDC
334
G5SD
G5SD2
PSERT
PYRDC
335
G5SD
G5SD2
PGCD
PYRDC
336
MTHFC
G3PD
PYRDC
ATPS
337
MTHFC
GLY3PP
PYRDC
ATPS
338
G5SD
G5SD2
PYRDC
ATPS
339
GLU5K
GHMT2m
ATPSm
ALCD2x
340
GHMT2
GHMT2m
ATPtm-3H
IPPSm
341
GHMT2m
PYK
ATPSm
ATPtm-3H
342
G3PD
MDHm
SUCD3-u6m
ALCD2x
343
ASPTA1m
MTHFC
PGCD
ATPtm-3H
344
ASPTA1m
MTHFC
PSERT
ATPtm-3H
345
ASPTA1m
MTHFC
PSP_L
ATPtm-3H
346
ASPTA1m
ME2m
PSP_L
ATPtm-3H
347
ASPTA1m
ME2m
PSERT
ATPtm-3H
348
ASPTA1m
ME2m
PGCD
ATPtm-3H
349
GHMT2m
PYK
ATPSm
IPPSm
350
GLU5K
GHMT2m
ATPSm
IPPSm
351
ME2m
ICDHym
PGCD
ATPtm-3H
352
ME2m
ACONTm
PSP_L
ATPtm-3H
353
ME2m
ICDHym
PSP_L
ATPtm-3H
354
ME2m
ACONTm
PSERT
ATPtm-3H
355
ME2m
ACONTm
PGCD
ATPtm-3H
356
ME2m
ICDHym
PSERT
ATPtm-3H
357
MTHFD
MTHFD2
GHMT2m
ALCD2x
358
MTHFD
MTHFD2
PSP_L
ATPtm-3H
359
MTHFD
MTHFD2
PSERT
ATPtm-3H
360
MTHFD
MTHFD2
PGCD
ATPtm-3H
361
GHMT2
GHMT2m
ATPSm
IPPSm
362
GHMT2m
PYK
ATPSm
ALCD2x
363
ME1m
MTHFC
GHMT2m
PDHm
364
THFATm
PYK
ATPtm-3H
IPPSm
365
FTHFCLm
PYK
ATPtm-3H
IPPSm
366
ACONT
GHMT2m
PYK
ATPSm
367
ICDHyGHMT2m
PYK
ATPSm
368
GHMT2
ORNTA
GHMT2m
ATPtm-3H
369
GHMT2
THFATm
GHMT2m
PYRDC
370
GHMT2
FTHFCLm
GHMT2m
PYRDC
371
ME2m
GLU5K
ACONTm
PYRDC
372
ME2m
GLU5K
ICDHym
PYRDC
373
MTHFD
MTHFD2
GHMT2m
ATPtm-3H
374
MTHFD
MTHFD2
GHMT2m
PYRDC
375
G5SD2
GHMT2m
PYK
ATPSm
376
GLU5K
GHMT2m
PYK
ATPSm
377
ASPTA1m
GHMT2m
PYK
ATPSm
378
MTHFD
MTHFD2
GHMT2m
ATPSm
379
G5SD
G5SD2
GHMT2m
ATPSm
380
MTHFC
GHMT2m
ATPtm-3H
IPPSm
381
ASPTA1m
ACONTm
GHMT2m
ATPSm
382
MTHFC
GHMT2m
ALCD2x
IPPSm
383
ME2m
MTHFC
PYK
ATPSm
384
ASPTA1m
G5SD2
GHMT2m
ATPSm
385
G5SD2
MTHFD
GHMT2m
ATPSm
386
ME2m
FTHFLr
PYK
ATPSm
387
THFATm
PYK
TKT2
ATPtm-3H
388
FTHFCLm
PYK
TKT2
ATPtm-3H
389
ORNTA
THFATm
PYK
ATPtm-3H
390
ORNTA
FTHFCLm
PYK
ATPtm-3H
391
ASPTA1m
FTHFCLm
PYK
ATPtm-3H
392
ASPTA1m
THFATm
PYK
ATPtm-3H
393
ORNTA
MTHFC
GHMT2m
ATPtm-3H
394
PDHm
ATPSm
MDHm
PPND
395
MTHFC
THFATm
PYK
ATPtm-3H
396
FTHFCLm
MTHFC
PYK
ATPtm-3H
397
GHMT2
THFATm
PYK
ATPtm-3H
398
GHMT2
FTHFCLm
PYK
ATPtm-3H
399
GHMT2
ORNTA
FTHFCLm
ALCD2x
400
GHMT2
ORNTA
THFATm
ALCD2x
401
G5SD
G5SD2
ALCD2x
THRA
402
PSP_L
MDHm
DHORD4u
IPPSm
403
PSERT
MDHm
DHORD4u
IPPSm
404
PGCD
MDHm
DHORD4u
IPPSm
405
ORNTA
PSERT
MDHm
DHORD4u
406
ORNTA
PSP_L
MDHm
DHORD4u
407
ORNTA
PGCD
MDHm
DHORD4u
408
GHMT2
ORNTA
ME1m
GHMT2m
409
ME1m
MTHFD
MTHFD2
GHMT2m
410
PSERT
MDHm
DHORD4u
ALDD2y
411
PGCD
MDHm
DHORD4u
ALDD2y
412
PSP_L
MDHm
DHORD4u
ALDD2y
413
ASPTA1m
PGCD
MDHm
DHORD4u
414
ASPTA1m
PSP_L
MDHm
DHORD4u
415
ASPTA1m
PSERT
MDHm
DHORD4u
416
PGCD
MDHm
NADH2-u6m
SUCD3-u6m
417
PSERT
MDHm
NADH2-
SUCD3-u6m
u6m
418
PSP_L
MDHm
NADH2-u6m
SUCD3-u6m
419
PYK
MDHm
DHORD4u
ATPS
420
MDHm
NADH2-u6m
SUCD3-u6m
ATPS
421
PDHm
MDHm
DHORD4u
ALDD2y
422
GHMT2
GHMT2m
MDHm
DHORD4u
423
ORNTA
PDHm
MDHm
DHORD4u
424
ASPTA1m
PDHm
MDHm
DHORD4u
425
PDHm
MDHm
NADH2-u6m
SUCD3-u6m
426
ORNTA
MDHm
DHORD4u
IPPSm
427
MDHm
DHORD4u
ALDD2y
IPPSm
428
ASPTA1m
MDHm
DHORD4u
IPPSm
429
MDHm
NADH2-u6m
SUCD3-u6m
IPPSm
430
MTHFC
GHMT2m
MDHm
DHORD4u
431
ORNTA
MDHm
DHORD4u
ALDD2y
432
ME2m
ICDHym
MDHm
DHORD4u
433
ME2m
ACONTm
MDHm
DHORD4u
434
ORNTA
MDHm
NADH2-
SUCD3-u6m
u6m
435
ASPTA1m
MDHm
DHORD4u
ALDD2y
436
MDHm
NADH2-u6m
SUCD3-u6m
ALDD2y
437
ASPTA1m
MDHm
NADH2-
SUCD3-u6m
u6m
438
PSERT
TPI
MDH
DHORD4u
439
PSP_L
TPI
MDH
DHORD4u
440
PGCD
TPI
MDH
DHORD4u
441
TPI
MDH
DHORD4u
THRA
442
PDHm
TPI
MDH
DHORD4u
443
TPI
FDH
MDH
DHORD4u
444
TPI
MDH
NADH2-u6m
SUCD3-u6m
445
G3PDm
TPI
MDH
NADH2-
u6m
446
G3PD1irm
TPI
MDH
NADH2-
u6m
447
GLYCLm
PGI
MDH
DHORD4u
448
GHMT2
PGI
MDH
DHORD4u
449
GHMT2m
PGI
MDH
DHORD4u
450
G3PD1irm
PGI
MDH
NADH2-
u6m
451
G3PDm
PGI
MDH
NADH2-
u6m
452
MDH
DHORD4u
ATPS
ALDD2y
453
ME2m
MDH
DHORD4u
ATPS
454
ICDHy
MDH
DHORD4u
ATPS
455
ACONT
MDH
DHORD4u
ATPS
456
GHMT2
MDH
DHORD4u
ATPS
457
ORNTA
MDH
DHORD4u
ATPS
458
MTHFC
MDH
DHORD4u
ATPS
459
MDH
NADH2-
SUCD3-u6m
ATPS
u6m
460
G3PD1irm
MDH
NADH2-u6m
ATPS
461
G3PDm
MDH
NADH2-u6m
ATPS
462
ASPTA1
FUM
FUMmATPS
463
PSERT
TPI
FUM
FUMm
464
PSP_L
TPI
FUM
FUMm
465
PGCD
TPI
FUM
FUMm
466
G3PDm
FUM
FUMm
SUCD3-u6m
467
G3PDm
FUM
SUCD1rm
SUCD3-u6m
468
G3PDm
MDH
SUCD3-u6m
DHORD4u
469
G3PDm
MDH
NADH2-u6m
SUCD3-u6m
470
ASPTA1
TPI
FUM
FUMm
471
FTHFLr
TPI
FUM
FUMm
472
MTHFC
TPI
FUM
FUMm
473
GHMT2
TPI
FUM
FUMm
474
GLU5K
G3PDm
PDHm
SUCD3-u6m
PYRDC
475
G3PDm
PDHm
SUCD3-u6m
PYRDC
IPPS
476
GLU5K
G3PDm
SUCD3-u6m
ALCD2x
IPPS
477
G5SD
G5SD2
G3PDm
SUCD3-u6m
ALCD2x
478
ASPTA1m
ACONTm
G3PDm
SUCD3-u6m
ALCD2x
479
G3PDm
NADH2-u6cm
NADH2-
DHORD4u
ALCD2x
u6m
480
G3PD
PDHm
MDHm
SUCD3-u6m
PYRDC
481
G5SD
G5SD2
PDHm
PYRDC
IPPS
482
G3PDm
ATPSm
NADH2-
NADH2-
DHORD4u
u6cm
u6m
483
ASPTA1m
ACONTm
PDHm
PYRDC
IPPS
484
ASPTA1m
ICDHxm
ICDHym
PDHm
PYRDC
485
ORNTA
MTHFC
G3PDm
SUCD3-u6m
ATPtm-3H
486
G3PD
PDHm
MDHm
SUCD3-u6m
ALCD2x
487
ME2m
MTHFD
G3PDm
SUCD3-u6m
ATPtm-3H
488
GHMT2
ME2m
G3PDm
SUCD3-u6m
ATPtm-3H
489
ACONT
MTHFC
G3PDm
SUCD3-u6m
ATPtm-3H
490
ICDHyMTHFC
G3PDm
SUCD3-u6m
ATPtm-3H
491
MTHFD
MTHFD2
G3PDm
SUCD3-u6m
ATPtm-3H
492
ASPTA1m
GHMT2
G3PDm
SUCD3-u6m
ATPtm-3H
493
ASPTA1m
MTHFC
G3PDm
SUCD3-u6m
ATPtm-3H
494
MTHFD
G3PDm
GHMT2m
SUCD3-u6m
ATPtm-3H
495
G3PDm
NADH2-u6cm
NADH2-
DHORD4u
ATPtm-3H
u6m
TABLE 7
A list of all the reaction stoichiometries and the associated genes known to be
associated with the reactions identified for disruption in the strains listed in Tables 5 and 6. [c]
refers to cytosol and [m] refers to mitochondrion, indicating the organelle where the reaction
takes place
Reaction
Abbreviation
Reaction Name
Reaction Stoichiometry
Associated genes
ACONT
aconitase
[c]: cit <==> icit
YLR304C
ACONTm
aconitate hydratase
[m]: cit <==> icit
YJL200C, YLR304C
AGT
alanine-glyoxylate
[c]: ala-L + glx <==> gly + pyr
YFL030W
transaminase
AKGDam
oxoglutarate
[m]: akg + h + lpam <==> co2 + sdhlam
YIL125W, YDR148C, YFL018C
dehydrogenase
(lipoamide)
AKGDbm
oxoglutarate
[m]: coa + sdhlam --> dhlam + succoa
YIL125W, YDR148C, YFL018C
dehydrogenase
(dihydrolipoamide S-
succinyltransferase)
ALATA_L
L-alanine transaminase
[c]: akg + ala-L <==> glu-L + pyr
YDR111C
ALCD2x
alcohol dehydrogenase
[c]: etoh + nad <==> acald + h + nadh
YGL256W, YMR303C, YDL168W,
(ethanol: NAD)
YOL086C, YBR145W
ASPTA1
aspartate transaminase
[c]: akg + asp-L <==> glu-L + oaa
YLR027C
ASPTA1m
aspartate transaminase,
[m]: akg + asp-L <==> glu-L + oaa
YKL106W
mitochondrial
ATPSm
ATP synthase,
adp[m] + (3) h[c] + pi[m] --> atp[m] +
YBL099W + YPL078C +
mitochondrial
(2) h[m] + h2o[m]
YDL004W + YDR377W + YOL077W-
A + YJR121W + YDR322C-
A + Q0080 + YBR039W + YDL181W +
Q0130 + YKL016C +
YDR298C + YML081C-
A + YPL271W + Q0085 + YPR020W + YLR295C,
YBL099W + YDL004W + YPL078C +
YDR377W + YJR121W +
Q0080 + YBR039W + YDL181W + YKL016C +
Q0130 + YDR298C + YML081C-
A + YPL271W + Q0085 + YLR295C
ATPtm-3H
ADP/ATP transporter,
adp[c] + atp[m] + (3) h[c] --> adp[m] +
YBL030C, YBR085W, YMR056C
mitochondrial
atp[c] + (3) h[m]
FRDcm
fumarate reductase,
fadh2[m] + fum[c] --> fad[m] + succ[c]
YEL047C
cytosolic/mitochondrial
FRDm
fumarate reductase
[m]: fadh2 + fum --> fad + succ
YJR051W
FUMm
fumarase, mitochondrial
[m]: fum + h2o <==> mal-L
YPL262W
G3PD
Glycerol-3-phosphate
[c]: dhap + h + nadh --> glyc3p + nad
YDL022W
dehydrogenase (NAD)
G3PD1irm
glycerol-3-phosphate
[m]: dhap + h + nadh --> glyc3p + nad
YOL059W
dehydrogenase (NAD),
mitochondrial
G3PDm
glycerol-3-phosphate
[m]: fad + glyc3p --> dhap + fadh2
YIL155C
dehydrogenase
G6PDH
glucose 6-phosphate
[c]: g6p + nadp --> 6pgl + h + nadph
YNL241C
dehydrogenase
GHMT2
glycine
[c]: ser-L + thf --> gly + h2o + mlthf
YLR058C
hydroxymethyltransferase
GLY3PP
glycerol-3-phosphatase
[c]: glyc3p + h2o --> glyc + pi
YER062C, YIL053W
HSDxi
homoserine
[c]: aspsa + h + nadh --> hom-L + nad
YJR139C
dehydrogenase
(NADH), irreversible
HSK
homoserine kinase
[c]: atp + hom-L --> adp + h + phom
YHR025W
ICDHxm
Isocitrate
[m]: icit + nad --> akg + co2 + nadh
YOR136W + YNL037C
dehydrogenase (NAD+)
ICDHy
isocitrate
[c]: icit + nadp <==> akg + co2 + nadph
YLR174W
dehydrogenase (NADP)
ICL
Isocitrate lyase
[c]: icit --> glx + succ
YER065C
MDH
malate dehydrogenase
[c]: mal-L + nad <==> h + nadh + oaa
YOL126C
MDHm
malate dehydrogenase,
[m]: mal-L + nad <==> h + nadh + oaa
YKL085W
mitochondrial
ME1m
malic enzyme (NAD),
[m]: mal-L + nad --> co2 + nadh + pyr
YKL029C
mitochondrial
ME2m
malic enzyme (NADP),
[m]: mal-L + nadp --> co2 + nadph + pyr
YKL029C
mitochondrial
MTHFD
methylenetetrahydrofolate
[c]: mlthf + nadp <==> methf + nadph
YGR204W
dehydrogenase
(NADP)
NADH2-u6cm
NADH dehydrogenase,
h[c] + nadh[c] + q6[m] --> nad[c] + q6h2[m]
YMR145C, YDL085W
cytosolic/mitochondrial
ORNTA
ornithine transaminase
[c]: akg + orn-L --> glu-L + glu5sa
YLR438W
P5CDm
1-pyrroline-5-
[m]: 1pyr5c + (2) h2o + nad --> glu-L + h + nadh
carboxylate
dehydrogenase,
mitochondrial
PDHcm
part of pyruvate
[m]: dhlam + nad --> h + lpam + nadh
YIL125W, YDR148C, YFL018C
dehydrogenase
(dihydrolipoamide
dehydrogenase)
PDHm
pyruvate
[m]: coa + nad + pyr --> accoa + co2 + nadh
YER178W + YBR221C, YNL071W,
dehydrogenase,
YFL018C
mitochondrial
PGCD
phosphoglycerate
[c]: 3pg + nad --> 3php + h + nadh
YIL074C, YER081W
dehydrogenase
PGDH
phosphogluconate
[c]: 6pgc + nadp --> co2 + nadph + ru5p-D
YHR183W, YGR256W
dehydrogenase
PGL
6-
[c]: 6pgl + h2o --> 6pgc + h
YNR034W, YGR248W, YHR163W
phosphogluconolactonase
PRO1xm
proline oxidase (NAD),
[m]: nad + pro-L --> 1pyr5c + (2) h + nadh
YLR142W
mitochondrial
PSERT
phosphoserine
[c]: 3php + glu-L --> akg + pser-L
YOR184W
transaminase
PSP_L
phosphoserine
[c]: h2o + pser-L --> pi + ser-L
YGR208W
phosphatase (L-serine)
PYK
pyruvate kinase
[c]: adp + h + pep --> atp + pyr
YAL038W, YOR347C
PYRDC
pyruvate decarboxylase
[c]: h + pyr --> acald + co2
YGR087C, YLR044C, YLR134W
RPE
ribulose 5-phosphate 3-
[c]: ru5p-D <==> xu5p-D
YJL121C
epimerase
SERD_L
L-serine deaminase
[c]: ser-L --> nh4 + pyr
YIL168W, YCL064C
SUCD2_u6m
succinate
[m]: q6 + succ <==> fum + q6h2
YKL148C + YMR118C + YLL041C + YDR178W,
dehydrogenase
YKL141W + YLL041C + YJL045W + YDR178W,
(ubiquinone-6),
YKL148C + YKL141W + YLL041C + YLR164W,
mitochondrial
YKL148C + YKL141W + YLL041C + YDR178W
SUCD3-u6m
succinate
[m]: fadh2 + q6 <==> fad + q6h2
YKL148C + YMR118C + YLL041C + YDR178W,
dehydrogenase
YKL141W + YLL041C + YJL045W + YDR178W,
(ubiquinone-6),
YKL148C + YKL141W + YLL041C + YLR164W,
mitochondrial
YKL148C + YKL141W + YLL041C + YDR178W
SUCOASAm
Succinate--CoA ligase
[m]: atp + coa + succ <==> adp + pi + succoa
YOR142W + YGR244C
(ADP-forming)
THRA
threonine aldolase
[c]: thr-L <==> acald + gly
YEL046C
THRS
threonine synthase
[c]: h2o + phom --> pi + thr-L
YCR053W
TKT2
transketolase
[c]: e4p + xu5p-D <==> f6p + g3p
YBR117C, YPR074C
TABLE 8
List of the metabolite abbreviations, the corresponding names of all
the metabolites that participate in the reactions listed in Table 7.
Metabolite Abbreviation
Metabolite Name
1pyr5c
1-Pyrroline-5-carboxylate
3pg
3-Phospho-D-glycerate
3php
3-Phosphohydroxypyruvate
6pgc
6-Phospho-D-gluconate
6pgl
6-phospho-D-glucono-1,5-lactone
acald
Acetaldehyde
accoa
Acetyl-CoA
adp
ADP
akg
2-Oxoglutarate
ala-L
L-Alanine
asp-L
L-Aspartate
aspsa
L-Aspartate 4-semialdehyde
atp
ATP
cit
Citrate
co2
CO2
coa
Coenzyme A
dhap
Dihydroxyacetone phosphate
dhlam
Dihydrolipoamide
e4p
D-Erythrose 4-phosphate
etoh
Ethanol
f6p
D-Fructose 6-phosphate
fad
FAD
fadh2
FADH2
fum
Fumarate
g3p
Glyceraldehyde 3-phosphate
g6p
D-Glucose 6-phosphate
glu-L
L-Glutamate
glu5sa
L-Glutamate 5-semialdehyde
glx
Glyoxylate
gly
Glycine
glyc
Glycerol
glyc3p
sn-Glycerol 3-phosphate
h
H+
h2o
H2O
hom-L
L-Homoserine
icit
Isocitrate
lpam
Lipoamide
mal-L
L-Malate
methf
5,10-Methenyltetrahydrofolate
mlthf
5,10-Methylenetetrahydrofolate
nad
Nicotinamide adenine dinucleotide
nadh
Nicotinamide adenine dinucleotide-reduced
nh4
Ammonium
oaa
Oxaloacetate
orn-L
L-Ornithine
pep
Phosphoenolpyruvate
phom
O-Phospho-L-homoserine
pi
Phosphate
pro-L
L-Proline
pser-L
O-Phospho-L-serine
pyr
Pyruvate
q6
Ubiquinone-6
q6h2
Ubiquinol-6
ru5p-D
D-Ribulose 5-phosphate
sdhlam
S-Succinyldihydrolipoamide
ser-L
L-Serine
succ
Succinate
succoa
Succinyl-CoA
thf
5,6,7,8-Tetrahydrofolate
thr-L
L-Threonine
xu5p-D
D-Xylulose 5-phosphate
Throughout this application various publications have been referenced within parentheses. The disclosures of these publications in their entireties are hereby incorporated by reference in this application in order to more fully describe the state of the art to which this invention pertains.
Although the invention has been described with reference to the disclosed embodiments, those skilled in the art will readily appreciate that the specific examples and studies detailed above are only illustrative of the invention. It should be understood that various modifications can be made without departing from the spirit of the invention. Accordingly, the invention is limited only by the following claims.
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