English
Tiếng Việt
(en)The present invention provides novel genes encoding Class II acyl-ACP thioesterases and variants thereof that are active on C8, C10, C12, C14, C16, and C18 acyl-ACP substrates. The thioesterases can be introduced into transgenic organisms, including microorganisms and photosynthetic organisms, for producing fatty acids and fatty acid products.
1.ApplicationNumber: US-201514608847-A
1.PublishNumber: US-2015147790-A1
2.Date Publish: 20150528
3.Inventor: ROESSLER PAUL GORDON
ROY GENA
4.Inventor Harmonized: ROESSLER PAUL GORDON(US)
ROY GENA(US)
5.Country: US
6.Claims:
(en)The present invention provides novel genes encoding Class II acyl-ACP thioesterases and variants thereof that are active on C8, C10, C12, C14, C16, and C18 acyl-ACP substrates. The thioesterases can be introduced into transgenic organisms, including microorganisms and photosynthetic organisms, for producing fatty acids and fatty acid products.
7.Description:
(en)CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation application of U.S. application Ser. No. 12/826,592 filed Jun. 29, 2010, now pending; which claims the benefit under 35 USC §119(e) to U.S. Application Ser. No. 61/223,328 filed Jul. 6, 2009 and to U.S. Application Ser. No. 61/221,500 filed Jun. 29, 2009, both now expired. The disclosure of each of the prior applications is considered part of and is incorporated by reference in the disclosure of this application.
REFERENCE TO SEQUENCE LISTING
The instant application contains a Sequence Listing which has been submitted via EFS-Web and is hereby incorporated by reference in its entirety. Said ASCII copy, created on Jan. 26, 2015, is named SGI1230-3_ST25.txt and is 218 KB in size. The aforementioned sequence listing is hereby incorporated by reference in its entirety pursuant to 37 C.F.R. §1.52(e)(5).
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to the production of fatty acids and fatty acid products in transgenic or genetically modified organisms, such as microorganisms and photosynthetic organisms. The invention also relates to genes encoding enzymes that function in the biosynthesis of fatty acids and related products, and in particular to acyl-ACP thioesterases.
2. Background Information
Plants supply most of the oils used in food products, and plant-derived lipids are also used in the manufacture of many non-dietary products, such as lubricants, soaps, detergents, cosmetics, and thickeners. In higher plants, fatty acids are synthesized in plastids and incorporated into triacylglycerols (triglycerides) in the endoplasmic reticulum (ER). In cells that store fats, such as the cells of seeds or nuts, fat droplets bud off of the ER to form lipid bodies within the cytoplasm. These reservoirs of lipids in the form of triglycerides provide an energy resource for germinating seeds.
The diversity of fatty acids produced by plant cells and incorporated into triglycerides can add to the time and cost of purification of fatty acids of particular chain lengths used for particular purposes. Medium chain fatty acids, for example, are used in the manufacture of surface disinfectants, anti-foaming agents, surfactants, lubricants, perfumes, dyes, and flavoring agents, and can be used to produce polymers and fuels. Long chain fatty acids are used in food products as well as detergents, soaps, surfactants, cosmetics, plastics, and lubricants, and can also be used in the production of fuels.
Acyl-acyl carrier protein (ACP) thioesterases are key enzymes in determining the chain lengths of fatty acids produced by a plant. Two families of acyl-ACP thioesterases are present in higher plants, the “Class I” acyl-ACP thioesterases encoded by FatA genes, and responsible for cleaving long chain (for example, C16 and C18) unsaturated fatty acids from acyl-ACP and the “Class II” acyl-ACP thioesterases encoded by FatB genes, that are active on saturated fatty acyl chains and can be specific for medium chain (C8-C14) acyl-ACPs or can be active on both medium and long chain fatty acyl-ACPs. Different acyl-ACP thioesterases have different degrees of chain length specificity, sometimes referred to as the enzyme's “preference” for cleaving a particular length of fatty acid from ACP, and thioesterases are typically most active in cleaving a particular chain length fatty acid while having lesser activity in cleaving one or more other chain length fatty acids. Some Class II (FatB) acyl-ACP thioesterases have binary activity, having a first peak of activity against a specific medium chain length acyl substrate and a second peak of activity against one or more specific long chain length acyl substrates.
The isolation of Class II acyl-ACP thioesterase genes from higher plants with medium chain specificity or having activity on both medium and long chain fatty acids has been described previously. Examples include U.S. Pat. No. 5,298,421, entitled “Plant medium-chain-preferring acyl-ACP thioesterases and related methods”, which describes the isolation of an acyl-ACP thioesterase and the gene that encodes it from the immature seeds of Umbellularia californica. Other patents of interest include U.S. Pat. No. 5,304,481, entitled “Plant thioesterase having preferential hydrolase activity toward C12 acyl-ACP substrate”, U.S. Pat. No. 5,344,771, entitled “Plant thioesterases”, U.S. Pat. No. 5,455,167, entitled “Medium-chain thioesterases in plants”, U.S. Pat. No. 5,512,482, entitled “Plant thioesterases”, U.S. Pat. No. 5,639,790, entitled “Plant medium-chain thioesterases”, U.S. Pat. No. 5,667,997, entitled “C8 and C10 medium-chain thioesterases in plants”, U.S. Pat. No. 5,807,893, entitled “Plant thioesterases and use for modification of fatty acid composition in plant seed oils”, U.S. Pat. No. 5,850,022, entitled “Production of myristate in plant cells”, and U.S. Pat. No. 5,910,631, entitled “Middle chain-specific thioesterase genes from Cuphea lanceolata” , U.S. Pat. No. 5,955,329, entitled “Engineering plant thioesterases for altered substrate specificity”, and U.S. Pat. No. 6,150,512, entitled “Engineering plant thioesterases and disclosure of plant thioesterases having novel substrate specificity”, disclose variants of plant thioesterase genes having altered chain length specificities for the encoded thioesterase enzymes.
Journal articles disclosing Class II chain acyl-ACP thioesterases include Dehesh, K. et al., “Production of high levels of 8:0 and 10:0 fatty acids in transgenic canola by overexpression of Ch FatB2, a thioesterase cDNA from Cuphea hookeriana”, The Plant Journal 9:167-172 (1996), Dehesh, K. et al., “Two novel thioesterases are key determinants of the bimodal distribution of acyl chain length of Cuphea palustris seed oil”, Plant Physiology 110:203-210 (1996), Dehesh, K., et al., “KAS IV: a 3-ketoacyl-ACP synthase from Cuphea sp. is a medium chain specific condensing enzyme”, The Plant Journal 15:383-390 (1998), Dormann, P. et al., “Characterization of two acyl-acyl carrier protein thioesterases from developing Cuphea seeds specific for medium-chain and oleoyl-acyl carrier protein”, Planta 189:425-432 (1993), Filichkin, S., et al., “New FATB thioesterases from a high-laurate Cuphea species: Functional and complementation analyses”, European Journal of Lipid Science and Technology 108:979-990 (2006), Slabaugh, M., et al., “Condensing enzymes from Cuphea wrightii associated with medium chain fatty acid biosynthesis”, The Plant Journal 13:611-620 (1998), Voelker, T., et al., “Fatty acid biosynthesis redirected to medium chains in transgenic oilseed plants”, Science 257:72-74 (1992), Voelker, T., and Davies, M., “Alteration of the specificity and regulation of fatty acid synthesis of Escherichia coli by expression of a plant medium-chain acyl-acyl carrier protein thioesterase”, Journal of Bacteriology 176:7320-7327 (1994).
In addition to synthesizing fatty acids for nonfuel products, microorganisms or photosynthetic organisms can be used to produce fatty acids or fatty acid products for the production of fuels and chemicals such as alcohols or hydrocarbons. In synthesizing fatty acids, these organisms can use atmospheric CO 2 or plant products such as starch, sugars, or cellulose that are themselves based on fixed atmospheric CO 2 as a source of carbon, thereby reducing the net amount of CO 2 generated in the production and use of the fuel or chemical. Increasing the yield and recovery of fatty acids and fatty acid products of a particular chain length from cultured microorganisms and photosynthetic organisms can improve the cost effectiveness of providing a renewable source of a variety of products, including fuel products.
SUMMARY OF THE INVENTION
The invention provides compositions and methods for producing fatty acids and fatty acid products of specific chain lengths for synthesis of a variety of intermediary or final products for various uses, for example, in foods and nutritional products, lubricants, surfactants, chemicals, plastics, soaps, and fuels. Nucleic acid molecules are provided that encode acyl-ACP thioesterases exhibiting a preference for specific acyl chain lengths, such that fatty acid preparations in which a preponderance of the isolated fatty acids are of one or more specific chain lengths can be recovered from cultures of transgenic organisms expressing the exogenous acyl-ACP thioesterase.
A first aspect of the invention provides recombinant or isolated nucleic acid molecules encoding acyl-ACP thioesterases in which the encoded thioesterases include an amino acid sequence having at least 85%, at least 90%, at least 92%, at least 95%, or at least 99% identity with the amino acid sequence from amino acid position 64 to amino acid position 361 of SEQ ID NO:51; at least 98% identity with the amino acid sequence from amino acid position 66 to amino acid position 362 of SEQ ID NO:55; at least 97% identity with the amino acid sequence from amino acid position 65 to amino acid position 360 of SEQ ID NO:59; at least 90% identity with the amino acid sequence from amino acid position 65 to amino acid position 359 of SEQ ID NO:63; at least 98% identity with the amino acid sequence from amino acid position 115 to amino acid position 410 of SEQ ID NO:65; at least 96% identity with the amino acid sequence from amino acid position 65 to amino acid position 356 of SEQ ID NO:69; at least 98% identity with the amino acid sequence from amino acid position 115 to amino acid position 410 of SEQ ID NO:71; at least 96% identity with the amino acid sequence from amino acid position 64 to amino acid position 361 of SEQ ID NO:75; at least 97% identity with the amino acid sequence from amino acid position 65 to amino acid position 360 of SEQ ID NO:79; at least 96% identity with the amino acid sequence from amino acid position 116 to amino acid position 413 of SEQ ID NO:81; at least 96% identity with the amino acid sequence from amino acid position 65 to amino acid position 362 of SEQ ID NO:85; at least 96% identity with the amino acid sequence from amino acid position 64 to amino acid position 361 of SEQ ID NO:89; at least 97% identity with the amino acid sequence from amino acid position 115 to amino acid position 394 of SEQ ID NO:91; at least 97% identity with the amino acid sequence from amino acid position 115 to amino acid position 394 of SEQ ID NO:93; at least 99% identity with the amino acid sequence from amino acid position 115 to amino acid position 394 of SEQ ID NO:95; at least 92% identity with the amino acid sequence from amino acid position 63 to amino acid position 360 of SEQ ID NO:99; or at least 98% identity with the amino acid sequence from amino acid position 115 to amino acid position 393 of SEQ ID NO:101, in which the thioesterase encoded by the isolated nucleic acid molecule has at least the level of activity as the thioesterase encoded by the reference sequence from which it is derived.
In some embodiments, the recombinant or isolated nucleic acid molecule encoding an acyl-ACP thioesterase includes an amino acid sequence having at least 85% identity with the amino acid sequence from amino acid position 33 to amino acid position 361 of SEQ ID NO:51; having at least 98% identity with the amino acid sequence from amino acid position 35 to amino acid position 362 of SEQ ID NO:55; having at least 97% identity with the amino acid sequence from amino acid position 34 to amino acid position 360 of SEQ ID NO:59; having at least 90% identity with the amino acid sequence from amino acid position 34 to amino acid position 359 of SEQ ID NO:63; having at least 98% identity with the amino acid sequence from amino acid position 84 to amino acid position 410 of SEQ ID NO:65; having at least 96% identity with the amino acid sequence from amino acid position 34 to amino acid position 356 of SEQ ID NO:69; having at least 98% identity with the amino acid sequence from amino acid position 84 to amino acid position 410 of SEQ ID NO:71; having at least 96% identity with the amino acid sequence from amino acid position 33 to amino acid position 361 of SEQ ID NO:75; having at least 97% identity with the amino acid sequence from amino acid position 34 to amino acid position 360 of SEQ ID NO:79; having at least 96% identity with the amino acid sequence from amino acid position 85 to amino acid position 413 of SEQ ID NO:81; having at least 96% identity with the amino acid sequence from amino acid position 34 to amino acid position 362 of SEQ ID NO:85; having at least 96% identity with the amino acid sequence from amino acid position 33 to amino acid position 361 of SEQ ID NO:89; having at least 97% identity with the amino acid sequence from amino acid position 84 to amino acid position 394 of SEQ ID NO:91; having at least 97% identity with the amino acid sequence from amino acid position 84 to amino acid position 394 of SEQ ID NO:93; having at least 99% identity with the amino acid sequence from amino acid position 84 to amino acid position 394 of SEQ ID NO:95; having at least 92% identity with the amino acid sequence from amino acid position 33 to amino acid position 360 of SEQ ID NO:99; or having at least 98% identity with the amino acid sequence from amino acid position 84 to amino acid position 393 of SEQ ID NO:101, and has at least the level of activity of the reference thioesterase from which the encoded thioesterase sequence is derived. In some embodiments, the encoded thioesterase shares at least 85%, at least 90%, at least 92%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or at least 99.5% identity with the above provided amino acid sequences, and the thioesterase encoded by the isolated nucleic acid molecule has at least the level of activity of the reference thioesterase from which the sequence is derived.
In some embodiments, the recombinant or isolated nucleic acid molecule encoding an acyl-ACP thioesterase includes an amino acid sequence having at least 85% identity with the amino acid sequence from amino acid position 1 to amino acid position 361 of SEQ ID NO:51; an amino acid sequence having at least 98% identity with the amino acid sequence from amino acid position 1 to amino acid position 362 of SEQ ID NO:55; an amino acid sequence having at least 97% identity with the amino acid sequence from amino acid position 1 to amino acid position 360 of SEQ ID NO:59; an amino acid sequence having at least 90% identity with the amino acid sequence from amino acid position 1 to amino acid position 359 of SEQ ID NO:63; an amino acid sequence having at least 98% identity with the amino acid sequence from amino acid position 53 to amino acid position 410 of SEQ ID NO:65; an amino acid sequence having at least 96% identity with the amino acid sequence from amino acid position 1 to amino acid position 356 of SEQ ID NO:69; an amino acid sequence having at least 98% identity with the amino acid sequence from amino acid position 53 to amino acid position 410 of SEQ ID NO:71; an amino acid sequence having at least 96% identity with the amino acid sequence from amino acid position 1 to amino acid position 361 of SEQ ID NO:75; an amino acid sequence having at least 97% identity with the amino acid sequence from amino acid position 1 to amino acid position 360 of SEQ ID NO:79; an amino acid sequence having at least 96% identity with the amino acid sequence from amino acid position 54 to amino acid position 413 of SEQ ID NO:81; an amino acid sequence having at least 96% identity with the amino acid sequence from amino acid position 1 to amino acid position 362 of SEQ ID NO:85; an amino acid sequence having at least 96% identity with the amino acid sequence from amino acid position 1 to amino acid position 361 of SEQ ID NO:89; an amino acid sequence having at least 97% identity with the amino acid sequence from amino acid position 53 to amino acid position 394 of SEQ ID NO:91; an amino acid sequence having at least 97% identity with the amino acid sequence from amino acid position 53 to amino acid position 394 of SEQ ID NO:93; an amino acid sequence having at least 99% identity with the amino acid sequence from amino acid position 53 to amino acid position 394 of SEQ ID NO:95; an amino acid sequence having at least 92% identity with the amino acid sequence from amino acid position 1 to amino acid position 360 of SEQ ID NO:99; or an amino acid sequence having at least 98% identity with the amino acid sequence from amino acid position 53 to amino acid position 393 of SEQ ID NO:101, and has at least the level of activity of the reference thioesterase from which the encoded thioesterase sequence is derived.
In additional aspects, the invention includes a transgenic organism that carries a recombinant nucleic acid molecule encoding any of the thioesterases provided herein, such as those having at least 85%, at least 87%, at least 90%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identity with amino acid sequences of SEQ ID NO:49, SEQ ID NO:51, SEQ ID NO:53, SEQ ID NO:55, SEQ ID NO:59, SEQ ID NO:61, SEQ ID NO:63, SEQ ID NO:65, SEQ ID NO:67, SEQ ID NO:69, SEQ ID NO:71, SEQ ID NO:73, SEQ ID NO:75, SEQ ID NO:77, SEQ ID NO:79, SEQ ID NO:81, SEQ ID NO:83, SEQ ID NO:85, SEQ ID NO:87, SEQ ID NO:89, SEQ ID NO:91, SEQ ID NO:93, SEQ ID NO:95, SEQ ID NO:97, SEQ ID NO:99, or SEQ ID NO:101. The transgenic organism can be, for example, a plant, a bacterium, a fungus, a chromist, an alga, or a cyanobacterium.
Also included in the invention is a recombinant nucleic acid molecule encoding an acyl-ACP thioesterase that includes an amino acid sequence that has at least 99% identity to the amino acid sequence from amino acid position 65 to 355 of SEQ ID NO:29, in which expression of the thioesterase in a microorganism results in at least 60%, at least 70%, at least 80%, at least 85%, at least 90%, or at least 95% of the free fatty acid isolated from the cells or culture media have a single chain length, such as a C8 chain length. In some embodiments, the thioesterase includes an amino acid sequence that has at least 99% identity to the amino acid sequence from amino acid position 65 to 355 or from amino acid position 34 to 355 of SEQ ID NO:29, SEQ ID NO:8, SEQ ID NO:12, SEQ ID NO:26, SEQ ID NO:33, SEQ ID NO:40, SEQ ID NO:43, or SEQ ID NO:45, or from amino acid position 1 to 323 of SEQ ID NO:38. In some embodiments, the thioesterase includes an amino acid sequence that has at least 99% identity to the amino acid sequence from amino acid position 1 to 355 of SEQ ID NO:29, SEQ ID NO:8, SEQ ID NO:12, SEQ ID NO:22, SEQ ID NO:26, SEQ ID NO:33, SEQ ID NO:40, SEQ ID NO:43, or SEQ ID NO:45. In some embodiments, the thioesterase includes the amino acid sequence from amino acid position 1 to position 355 of SEQ ID NO:29.
In a further aspect, the invention includes an isolated nucleic acid molecule encoding a variant of a plant acyl-ACP thioesterase having increased activity with respect to the native thioesterase it is derived from, in which the variant comprises a mutation of the amino acid corresponding to the amino acid at position 174 of SEQ ID NO:29. In preferred embodiments, expression of the variant acyl-ACP thioesterase encoded by the isolated nucleic acid molecule in a transgenic organism increases the amount of fatty acid product produced by the organism with respect to the amount produced by the organism transformed with the gene encoding the acyl-ACP thioesterase that does not include the mutation at position 174.
In some embodiments, the acyl-ACP thioesterase gene having a mutation at position 174 encodes a variant that has increased activity toward a preferred fatty acyl substrate. In some embodiments, the acyl-ACP thioesterase gene having a mutation at position 174 encodes a variant that has increased activity toward a C8 fatty acyl substrate. In preferred embodiments, the percentage of a C8 fatty acid product to the total fatty acid product produced by a transgenic organism expressing the variant thioesterase is at least 5%, at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, at least 45%, at least 50%, at least 55%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the total fatty acid product produced by the organism.
In some preferred embodiments, the plant acyl-ACP thioesterase is a Class II, or “FatB” acyl-ACP thioesterase. The Class II acyl-ACP thioesterase in some embodiments comprises an amino acid sequence that is at least 65% identical, at least 70% identical, at least 75% identical, at least 80% identical, at least 85% identical, at least 90% identical, or at least 95% identical to amino acids 65 to 355 of SEQ ID NO:29. In some embodiments, a mutation in a variant of a plant acyl-ACP thioesterase changes the amino acid corresponding to position 174 of SEQ ID NO:29 to an uncharged amino acid, which in some embodiments is a branched chain aliphatic amino acid. In some embodiments, the mutation changes the amino acid at position 174 to cysteine, methionine, phenylalanine, valine, leucine, or isoleucine. In some embodiments, the mutation changes a methionine at position 174 to cysteine, phenylalanine, valine, leucine, or isoleucine. In some embodiments, the variant acyl-ACP thioesterase has one, two, three, or more mutations in addition to the mutation at position 174. In an exemplary embodiment, the isolated nucleic acid molecule encodes a variant of a plant acyl-ACP thioesterase that has an isoleucine at position 103 and comprises the mutation M1741. In some embodiments, the variant acyl-ACP thioesterase has one, two, three, or more mutations in addition to the mutation at position 174.
In some embodiments, the isolated nucleic acid molecule encodes a variant of a plant acyl-ACP thioesterase, in which the variant has at least 90% identity or at least 95% identity to the amino acid sequence from amino acid position 65 to 355 of SEQ ID NO:40, SEQ ID NO:43, or SEQ ID NO:45. In exemplary embodiments the isolated nucleic acid molecule comprises a sequence encoding the amino acid sequence from position 65 to 355 of SEQ ID NO:40, SEQ ID NO:43, or SEQ ID NO:45, or from position 34 to 355 of SEQ ID NO:40, SEQ ID NO:43, or SEQ ID NO:45. The isolated nucleic acid molecule in some embodiments comprises SEQ ID NO:39, SEQ ID NO:42, or SEQ ID NO:44.
In additional aspects, the invention includes transgenic organisms that harbor recombinant nucleic acid molecules encoding acyl-ACP thioesterase variants having increased activity as described herein, in which the variants include a mutation at the amino acid position corresponding to amino acid 174 of SEQ ID NO:29. The organisms can be transformed with or carry an exogenous gene encoding a variant acyl-ACP thioesterase that has one, two, three, or more mutations in addition to the mutation at position 174. In some preferred embodiments, a transgenic organism includes an exogenous gene encoding a variant acyl-ACP thioesterase having a mutation at position 174 and an isoleucine at position 103, for example, the transgenic organism may have an isoleucine, methionine, phenylalanine, cysteine, leucine, or valine at position 174 and an isoleucine at position 103. In an exemplary embodiment, the variant thioesterase has an isoleucine at amino acid position 103 and an isoleucine at amino acid position 174. The transgenic organism can be, for example, a plant, a bacterium, a fungus, a chromist, an alga, or a cyanobacterium.
Also included in the invention is a method of producing a fatty acid product (including a fatty acid), in which the method includes culturing cells of an organism having an exogenous nucleic acid molecule encoding any of the Class II acyl-ACP thioesterases disclosed herein, and isolating a fatty acid product from the organism or culture medium. In some embodiments, the organism is a photosynthetic organisms, a prokaryotic organism, a fungal species, or a chromist species (e.g, a member of the Sagenista, Oomycota, Bacillariophyta, Silicoflagellata, Chrysophyta, or Xanthophyta). In some embodiments of the methods, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, at least 45%, or at least 50% of the isolated fatty acid or fatty acid product is a fatty acid or fatty acid product of a specific chain length. In some embodiments of the methods, at least 5%, at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, at least 45%, or at least 50% of the isolated fatty acids or fatty acid products are fatty acids or fatty acid products of two specific chain lengths or three specific chain lengths.
The organism carrying the exogenous acyl-ACP thioesterase gene in some embodiments is a photosynthetic organism, and in some embodiments is an alga, such as a microalga, and can be a eukaryotic alga or a cyanobacterium, for example. The sequence encoding the thioesterase is in some embodiments codon-optimized for expression in the host organism.
The photosynthetic organism can be cultured or grown phototrophically or mixotrophically. The fatty acid or fatty acid product can be isolated from the culture medium, from cells or tissue, or from whole culture, including both the culture medium and cells of the transgenic organism. In some embodiments, the fatty acid or fatty acid product is a triglyceride. The fatty acid or fatty acid product in alternative embodiments is a free fatty acid, a fatty aldehyde, a fatty alcohol, a fatty ester (including a wax ester) or a hydrocarbon, such as an alkane or alkene. In some embodiments, the host organism also includes one or more additional transgenes that encode enzymes used in the biosynthesis of the fatty acid product, such as, for example, an acetyl-CoA carboxylase, a ketoacyl-CoA synthase, a fatty acid elongase, an acyl-CoA synthetase, a fatty acyl-CoA reductase, a fatty aldehyde reductase, an alcohol acetyl transferase, an acyl-CoA alcohol transacylase, an acyltransferase, a wax synthase, an aldehyde decarbonylase, or a fatty acid decarboxylase.
The method can be used to produce fatty acids or fatty acid products such as triglycerides, fatty aldehydes, fatty alcohols, fatty esters, hydrocarbons, or fatty acids. In some embodiments, at least 5%, at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, or at least 40%, at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, or at least 90% of the isolated fatty acids or fatty acid products are one or more of a C8, a C10, a C12, a C14, a C16, or a C18 fatty acid or fatty acid product, such as a free fatty acid or derivative thereof.
A further aspect of the invention is a method of producing a fatty acid product, in which the method includes cultivating an organism containing an exogenous nucleic acid molecule encoding a variant plant acyl-ACP thioesterase having a mutation at the amino acid position corresponding to amino acid 174 of SEQ ID NO:29, and isolating a fatty acid product from the organism or culture medium. The transgenic organism can be, for example, a bacterium or a photosynthetic organism, such as a plant, microalga, or cyanobacterium. In some embodiments, for example, the transgenic organism is a prokaryote, and the method comprises isolating fatty acids from the culture medium. The sequence encoding the plant acyl-ACP thioesterase is codon-optimized for expression in the organism in some preferred embodiments.
In some preferred embodiments, the organism is a microorganism, and a fatty acid or fatty acid product is isolated from the culture medium. In some preferred embodiments, at least 10% of the fatty acid product isolated from the cells or medium is a C8 fatty acid or fatty acid product, and in some preferred embodiments, at least 30%, at least 35%, least 40%, at least 45%, at least 50%, at least 55%, at least 60%, or at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, least 90%, or at least 95%, of the fatty acid or fatty acid product isolated from the cells or culture medium is a C8 fatty acid or fatty acid product. In some embodiments, the fatty acid product isolated from the cells or medium of a culture of a transgenic microorganism is octanoic acid.
Included in the method are embodiments in which the host organism carries an exogenous nucleic acid molecule that encodes a variant of a naturally-occurring medium chain length acyl-ACP thioesterase having a mutation at position 174, in which the variant has enhanced activity towards a C8 acyl substrate with respect to the naturally-occurring thioesterase. In some preferred embodiments, the variant thioesterase having enhanced activity toward a C8 acyl substrate has an isoleucine residue at the amino acid position corresponding to amino acid position 174 of SEQ ID NO:29. In an exemplary embodiment, the variant thioesterase has an isoleucine at amino acid position 103 and an isoleucine at amino acid position 174. In illustrative embodiments, the variant comprises the amino acid sequence from position 65 to amino acid 355 of SEQ ID NO:40, SEQ ID NO:43, or SEQ ID NO:45.
The method can be used to produce fatty acids or fatty acid products such as triglycerides, fatty aldehydes, fatty alcohols, fatty esters, hydrocarbons, or fatty acids. In some embodiments, fatty acids are isolated, and at least 5%, at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, or at least 40%, at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, or at least 90% of the isolated fatty acid products are a C8 fatty acid or fatty acid product, such as a C8 fatty acid or derivative thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 provides an alignment of the deduced amino acid sequence of the wild-type C. aequipetala FatB2 acyl-ACP thioesterase (Ca1FatB2) from a gene assembled by PCR of genomic DNA with the removal of intron sequences (SEQ ID NO:29) and the wild-type gene in which the N-terminal sequence was extended (SEQ ID NO:22). The methionine at position 174 is underlined.
FIGS. 2A-2D are tables showing the amount of C8, C10, C12, C14, C16, and C18 fatty acids produced by bacterial isolates which had been transformed with genes encoding variants of the Ca1FatB2 gene.
FIGS. 3A-3D are tables showing the amount of C8, C10, C12, C14, C16, and C18 fatty acids produced by strains, of bacterial isolates which had been transformed with genes encoding variants of the Ca1FatB2 gene, normalized for cell density.
FIG. 4A depicts graphically the C8 fatty acid production of the isolates of FIGS. 2A-2D that harbor the acyl-ACP thioesterase gene mutated at position 174 (isolates 1-38) or positions 103, 184, and 174 (isolates 39-72).
FIG. 4B depicts graphically the data from FIGS. 3A-3D of C8 fatty acid production normalized to cell density of the same isolates overnight growth.
FIG. 5A is a table showing the amount of C8, C10, C12, C14, C16, and C18 fatty acids produced by bacterial isolates encoding variants of the Ca1FatB2 gene mutated at position 174 (isolates 81, 82, 85, and 86); at positions 174 and 103 (isolates 83 and 84), or at positions 103, 184, and 174 (isolates 79, 80, 87, 88, 89, and 90).
FIG. 5B is a table of the bacterial isolates of FIG. 5A in which the amount of C8, C10, C12, C14, C16, and C18 fatty acids produced by the strains has been normalized for cell density.
FIG. 6 depicts graphically the C8 fatty acid production, normalized for cell density, of the isolates of FIGS. 5A-5B .
FIG. 7 is an alignment of the translated sequence of the 5′ portion of the Ca1FatB2 thioesterase genes cloned in expression constructs. Amino acid positions in the aligned thioesterases corresponding to position 33/34 and position 63/64 are shown in bold.
FIG. 8 provides a graph showing the amount of C8:0, C10:0, C10:1, C12:0, C12:1, C14:0, C14:1, C16:0, C16:1, C18:0, and C18:1 free fatty acids, normalized to cell density, isolated from cultures of E. coli transformed with various Cuphea FatB thioesterase genes.
FIG. 9 provides a graph showing the amount of C8:0, C10:0, C10:1, C12:0, C12:1, C14:0, C14:1, C16:0, C16:1, C18:0, and C18:1 free fatty acids, normalized to cell density, isolated from cultures of E. coli transformed with various Cuphea FatB thioesterase genes.
FIG. 10 provides a graph showing the amount of C8:0, C10:0, C12:0, C14:0, C16:0, C16:1, C18:0, and C18:1 free fatty acids, normalized to cell density, isolated from cultures of E. coli transformed with the Ca1FatB1 thioesterase gene.
FIG. 11 provides a graph showing the amount of C8:0, C10:0, C12:0, C14:0, C16:0, C16:1, C18:0, and C18:1 free fatty acids, normalized to cell density, isolated from cultures of Synechocystis transformed with various Cuphea FatB thioesterase genes.
FIG. 11 provides a graph showing the amount of C8:0, C10:0, C12:0, C14:0, C16:0, C16:1, C18:0, and C18:1 free fatty acids, normalized to cell density, isolated from cultures of Synechocystis transformed with various Cuphea FatB thioesterase genes.
FIG. 12 provides a graph showing the amount of C8:0, C10:0, C12:0, C14:0, C16:0, C16:1, C18:0, and C18:1 free fatty acids, normalized to cell density, isolated from a culture of Synechocystis transformed with the Ca2FatB2 thioesterase gene.
FIG. 13A provides a graph showing the amount of C8:0, C10:0, C12:0, C14:0, C16:0, C16:1, C18:0, and C18:1 free fatty acids isolated from cultures of Synechocystis transformed with various Cuphea FatB thioesterase genes.
FIG. 13B provides a graph of the same data, in which the production values were normalized for cell density.
FIG. 14A depicts the results of gas chromatography analysis of wax ester products extracted from E. coli cells transformed with the Mus musculus wax synthase gene and the Cc1FatB1 thioesterase gene and supplied with decanol.
FIG. 14B depicts the results of gas chromatography analysis of wax ester products extracted from E. coli cells transformed with the Mus musculus wax synthase gene and C. hookeriana thioesterase ChFatB2.
DETAILED DESCRIPTION OF THE INVENTION
Disclosed in the present application are nucleic acid molecules encoding novel plant acyl-ACP thioesterases. Such nucleic acid molecules can be used to transform organisms, such as photosynthetic organisms and prokaryotic organisms, for synthesizing fatty acids and fatty acid products such as fatty aldehydes, fatty alcohols, fatty esters, including wax esters, and hydrocarbons. Also included in the invention are organisms transformed with the nucleic acid molecules provided herein, and methods of making fatty acid products using the organisms transformed with nucleic acid molecules encoding novel acyl-ACP thioesterases.
Elements of the embodiments described herein can be combined to make additional embodiments not specifically described that are also within the scope of the invention. Headings within the application are solely for the convenience of the reader, and do not limit in any way the scope of the invention or its embodiments.
All publications and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention is related. The following terms are defined for purposes of the invention as described herein.
Accession numbers are unique identifiers for a sequence record publicly available at the National Center for Biotechnology Information internet site maintained by the United States National Institutes of Health which can be accessed at ncbi.nlm.nih.gov. The “GenInfo Identifier” (GI) sequence identification number is specific to a nucleotide or amino acid sequence. If a sequence changes in any way, a new GI number is assigned. A Sequence Revision History tool is available to track the various GI numbers, version numbers, and update dates for sequences that appeared in a specific GenBank record. Searching and obtaining nucleic acid or gene sequences or protein sequences based on Accession numbers and GI numbers is well known in the arts of cell biology, biochemistry, molecular biology, and molecular genetics.
The singular form “a”, “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a cell” includes a plurality of cells and reference to “an antibody” includes a plurality of antibodies, etc.
As used herein, the terms “about” or “approximately” when referring to any numerical value are intended to mean a value of plus or minus 10% of the stated value. For example, “about 50 degrees C.” (or “approximately 50 degrees C.”) encompasses a range of temperatures from 45 degrees C. to 55 degrees C., inclusive. Similarly, “about 100 mM” (or “approximately 100 mM”) encompasses a range of concentrations from 90 mM to 110 mM, inclusive. All ranges provided within the application are inclusive of the values of the upper and lower ends of the range.
An “isolated” biomolecule such as an isolated protein or nucleic acid, is a biomolecule removed from the context in which the biomolecule exist in nature. For example, an isolated protein or nucleic acid molecule is removed from the cell or organism with which it is associated in its natural state. An isolated biomolecule can be, in some instances, partially or substantially purified, for example, an isolated nucleic acid molecule can be a nucleic acid sequence that has been excised from the chromosome, genome, or episome that it is integrated into in nature.
A recombinant or “engineered” nucleic acid molecule is a nucleic acid molecule that has been altered through human manipulation. As nonlimiting examples, a recombinant nucleic acid molecule: 1) includes conjoined nucleotide sequences that are not conjoined in nature, 2) has been engineered using molecular cloning techniques such that it lacks one or more nucleotides with respect to the naturally occurring nucleic acid molecule sequence, or 3) has been manipulated using molecular cloning techniques such that it has one or more sequence changes or rearrangements with respect to the naturally occurring nucleic acid sequence. As nonlimiting examples, a cDNA is a recombinant DNA molecule, as is any nucleic acid molecule that has been generated by in vitro polymerase reaction(s), or to which linkers have been attached, or that has been integrated into a vector, such as a cloning vector or expression vector.
A “homolog” of a gene or protein refers to its functional equivalent in another species.
A “variant” of a gene or nucleic acid sequence is a sequence having at least 65% identity with the referenced gene or nucleic acid sequence, and can include one or more base deletions, additions, or substitutions with respect to the referenced sequence. Variants also include chimeric genes that include sequences from two or more sources. A variant can be a naturally-occurring variant or the result of a spontaneous or induced mutation. Induced mutations can be created using methods known in the art for mutagenesis of organisms or cells (for example, using gamma or UV irradiation or chemical mutagens such as 5-bromo deoxyuridine, ethyl methane sulfonate (EMS), methyl methane sulfonate (MMS), diethylsulfate (DES), nitrosoguanidine (NTG), ICR compounds, etc., or can be introduced using genetic engineering techniques, such as gene synthesis, in vivo single strand repair techniques, polymerase-based amplification at error-permissive temperature and/or polymerase-based amplification using primers that incorporate base changes.
A “variant” of a peptide or protein is a peptide or protein sequence that varies at one or more amino acid positions with respect to the reference peptide or protein. A variant can be a naturally-occurring variant or can be the result of spontaneous, induced, or genetically engineered mutation(s) to the nucleic acid molecule encoding the variant peptide or protein. A variant peptide can also be a chemically synthesized variant.
As used herein “thioesterase” includes wild-type thioesterase proteins as well as variants thereof, and “thioesterase gene” refers to any nucleotide sequence encoding a thioesterase, which can be a wild-type thioesterase or a variant thioesterase.
“Exogenous” in the context of a gene or protein is a gene or protein that is not derived from the host organism species.
A “heterologous” gene or nucleic acid sequence is a gene or sequence from a different source than the host organism it is introduced into, or from a different source than another nucleic acid sequence with which is juxtaposed in a nucleic acid construct. For example, a gene of one species introduced into another species may be referred to as a heterologous gene. A promoter linked to a gene not operably linked to the promoter in its natural state in the organism may be referred to as a heterologous promoter.
A gene that is “codon-optimized” for expression in an organism is a gene whose nucleotide sequence has been altered with respect to the original nucleotide sequence, such that one or more codons of the nucleotide sequence has been changed to a different codon that encodes the same amino acid, in which the new codon is used more frequently in genes of the organism of interest than the original codon. The degeneracy of the genetic code provides that all amino acids except for methionine and tryptophan are encoded by more than one codon. For example, arginine, leucine, and serine are encoded by different six different codons; glycine, alanine, valine, threonine, and proline are encoded by four different codons. Many organisms use certain codons to encode a particular amino acid more frequently than others. Without limiting any aspects of the invention to any particular mechanism, it is believed that some tRNAs for a given amino acid are more prevalent than others within a particular organism, and genes requiring a rare tRNA for translation of the encoded protein may be expressed at a low level due in part to a limiting amount of the rare tRNA. Thus, for adequate or optimal levels of expression of an encoded protein, a gene may be “codon-optimized” to change one or more codons to new codons (“preferred codons”) that are among those used more frequently in the genes of the host organism (referred to as the “codon preference” of the organism). As used in the context of the invention, a “codon-optimized” gene or nucleic acid molecule of the invention need not have every codon altered to conform to the codon preference of the intended host organism, nor is it required that altered codons of a “codon-optimized” gene or nucleic acid molecule be changed to the most prevalent codon used by the organism of interest. For example, a codon-optimized gene may have one or more codons changed to codons that are used more frequently that the original codon(s), whether or not they are used most frequently in the organism to encode a particular amino acid.
“Photosynthetic organisms” are any prokaryotic or eukaryotic organisms that can perform photosynthesis. Photosynthetic organisms include higher plants (i.e., vascular plants), bryophytes, algae, and photosynthetic bacteria. The term “algae” includes cyanobacteria (Cyanophyceae), green algae (Chlorophyceae), yellow-green algae (Xanthophyceae), golden algae (Chrysophyceae), brown algae (Phaeophyceae), red algae (Rhodophyceae), diatoms (Bacillariophyceae), and “pico-plankton” (Prasinophyceae and Eustigmatophyceae). Also included in the term algae are members of the taxonomic classes Dinophyceae, Cryptophyceae, Euglenophyceae, Glaucophyceae, and Prymnesiophyceae. Microalgae are unicellular or colonial algae that can be seen as single organisms only with the aid of a microscope. Microalgae include both eukaryotic and prokaryotic algae (e.g., cyanobacteria). Photosynthetic bacteria include cyanobacteria, green sulfur bacteria, purple sulfur bacteria, purple nonsulfur bacteria, and green nonsulfur bacteria.
A “plant acyl-ACP thioesterase” is an acyl-ACP thioesterase derived from a plant species, which includes species of higher plants, ferns, and mosses, for example, bryophyte, pteridophyte, cycadophyte, ginkgophyte, pinophyte, gnetophyte, and magnoliophyte species.
A “fatty acid product” includes a fatty acid, a fatty aldehyde, a fatty alcohol, a fatty ester (including a wax ester), a triglyceride, a hydrocarbon, or any other fatty acid derivatives.
A “C8 fatty acid” or a “C8 fatty acid product” is a fatty acid or a fatty acid product having an acyl chain of 8 carbons. An example of a saturated C8 fatty acid is octanoic acid, also called caprylic acid.
A “C10 fatty acid” or a “C10 fatty acid product” is a fatty acid or a fatty acid product having an acyl chain of 10 carbons. An example of a C10 fatty acid is decanoic acid, also known as capric acid.
A “C12 fatty acid” or a “C12 fatty acid product” is a fatty acid or a fatty acid product having an acyl chain of 12 carbons. An example of a C12 fatty acid is dodecanoic acid, also known as lauric acid.
A “C14 fatty acid” or a “C14 fatty acid product” is a fatty acid or a fatty acid product having an acyl chain of 14 carbons. An example of a C14 fatty acid is tetradecanoic acid, also known as myristic acid.
A “C16 fatty acid” or a “C16 fatty acid product” is a fatty acid or a fatty acid product having an acyl chain of 16 carbons. An example of a C14 fatty acid is hexadecanoic acid, also known as palmitic acid.
A “C18 fatty acid” or a “C18 fatty acid product” is a fatty acid or a fatty acid product having an acyl chain of 18 carbons. An example of a C18 fatty acid is octadecanoic acid, also known as stearic acid.
A “C8 preferring” acyl-ACP thioesterase is an acyl-ACP thioesterase having higher activity on a C8 acyl-ACP substrate (e.g., octanoyl-ACP) than on any other chain length substrate. Analogously, a “C10 preferring” acyl-ACP thioesterase is an acyl-ACP thioesterase having higher activity on a C10 acyl-ACP substrate (e.g., decanoyl-ACP) than on any other chain length substrate, a “C12 preferring” acyl-ACP thioesterase is an acyl-ACP thioesterase having higher activity on a C12 acyl-ACP substrate (e.g., dodecanoyl-ACP) than on any other chain length substrate, a “C14 preferring” acyl-ACP thioesterase is an acyl-ACP thioesterase having higher activity on a C14 acyl-ACP substrate (e.g., tetradecanoyl-ACP) than on any other chain length substrate, a “C16 preferring” acyl-ACP thioesterase is an acyl-ACP thioesterase having higher activity on a C16 acyl-ACP substrate (e.g., hexadecanoyl-ACP) than on any other chain length substrate, and a “C18 preferring” acyl-ACP thioesterase is an acyl-ACP thioesterase having higher activity on a C18 acyl-ACP substrate (e.g., octadecanoyl-ACP) than on any other chain length substrate.
An acyl-ACP thioesterase with “binary activity” is a thioesterase that has a preference for one or more medium chain length acyl-ACP substrates as well as a preference for one or more long chain length acyl-ACP substrates.
A “medium chain length” fatty acid or fatty acid product is a fatty acid or fatty acid product having an acyl chain length of from 8-14 carbons.
A “long chain length” fatty acid or fatty acid product is a fatty acid or fatty acid product having an acyl chain length of greater than 14 carbons.
The degree of amino acid or nucleic acid sequence identity can be determined by various computer programs for aligning the sequences to be compared based on designated program parameters. For example, sequences can be aligned and compared using the local homology algorithm of Smith & Waterman, Adv. Appl. Math. 2:482 (1981), the homology alignment algorithm of Needleman & Wunsch, J. Mol. Biol. 48:443 (1970), or the search for similarity method of Pearson & Lipman, Proc. Nat'l. Acad. Sci. USA 85:2444 (1988), and can be aligned and compared based on visual inspection or can use computer programs for the analysis (for example, GAP, BESTFIT, FASTA, and TFASTA in the Wisconsin Genetics Software Package, Genetics Computer Group, 575 Science Dr., Madison, Wis.).
The BLAST algorithm, described in Altschul et al., J. Mol. Biol. 215:403-410 (1990), is publicly available through software provided by the National Center for Biotechnology Information (at the web address www.ncbi.nlm.nih.gov). This algorithm identifies high scoring sequence pairs (HSPs) by identifying short words of length W in the query sequence, which either match or satisfy some positive-valued threshold score T when aligned with a word of the same length in a database sequence. T is referred to as the neighborhood word score threshold (Altschul et al., supra.). Initial neighborhood word hits act as seeds for initiating searches to find longer HSPs containing them. The word hits are then extended in both directions along each sequence for as far as the cumulative alignment score can be increased. Cumulative scores are calculated using, for nucleotide sequences, the parameters M (reward score for a pair of matching residues; always >0) and N (penalty score for mismatching residues; always <0). For amino acid sequences, a scoring matrix is used to calculate the cumulative score. Extension of the word hits in each direction are halted when: the cumulative alignment score falls off by the quantity X from its maximum achieved value; the cumulative score goes to zero or below due to the accumulation of one or more negative-scoring residue alignments; or the end of either sequence is reached. For determining the percent identity of an amino acid sequence or nucleic acid sequence, the default parameters of the BLAST programs can be used. For analysis of amino acid sequences, the BLASTP defaults are: word length (W), 3; expectation (E), 10; and the BLOSUM62 scoring matrix. For analysis of nucleic acid sequences, the BLASTN program defaults are word length (W), 11; expectation (E), 10; M=5; N=−4; and a comparison of both strands. The TBLASTN program (using a protein sequence to query nucleotide sequence databases) uses as defaults a word length (W) of 3, an expectation (E) of 10, and a BLOSUM 62 scoring matrix. (see Henikoff & Henikoff, Proc. Natl. Acad. Sci. USA 89:10915 (1989)).
In addition to calculating percent sequence identity, the BLAST algorithm also performs a statistical analysis of the similarity between two sequences (see, e.g., Karlin & Altschul, Proc. Nat'l. Acad. Sci. USA 90:5873-5787 (1993)). The smallest sum probability (P(N)), provides an indication of the probability by which a match between two nucleotide or amino acid sequences would occur by chance. For example, a nucleic acid is considered similar to a reference sequence if the smallest sum probability in a comparison of the test nucleic acid to the reference nucleic acid is less than about 0.1, preferably less than about 0.01, and more preferably less than about 0.001.
Nucleic Acid Molecules Encoding Class II Thioesterases
Provided herein are new thioesterase FatB genes from various Cuphea species. As detailed in the examples, the native or wild-type FatB genes Ca1FatB2 (SEQ ID NO:21), Cc1FatB1 (SEQ ID NO:48), Ca1FatB1 (SEQ ID NO:52), Ci1FatB1 (SEQ ID NO:56), Cl1FatB1 (SEQ ID NO:60), Cl1FatB2 (SEQ ID NO:64), Cp1FatB1 (SEQ ID NO:66), Cl2FatB1 (SEQ ID NO:70), Cl2FatB2 (SEQ ID NO:72), Cl3FatB1 (SEQ ID NO:76), Cl3FatB2 (SEQ ID NO:80), Cd1FatB l (SEQ ID NO:82), Cl4FatB1 (SEQ ID NO:86), Cl4FatB2 (SEQ ID NO:90), Cl4FatB3 (SEQ ID NO:92), Ca2FatB1 (SEQ ID NO:94), Ca2FatB2 (SEQ ID NO:96), and Ca2FatB3 (SEQ ID NO:100), have been reconstructed using primer-based amplification (i.e., polymerase chain reaction, or PCR) and gene walking such that, based on homology with other plant thioesterases, it is estimated that all of the protein-encoding sequence except for sequences encoding approximately ten to fifteen amino acids of the N-terminuses have been determined. The deduced amino acid sequences of the encoded proteins are provided as SEQ ID NO:22 (Ca1FatB2), SEQ ID NO:49 (Cc1FatB1), SEQ ID NO:53 (Ca1FatB1), SEQ ID NO:57 (Ci1FatB1), SEQ ID NO:61 (Cl1FatB1), SEQ ID NO:65 (Cl1FatB2), SEQ ID NO:67 (Cp1FatB), SEQ ID NO:71 (Cl2FatB1), SEQ ID NO:73 (Cl2FatB2), SEQ ID NO:77 (Cl3FatB1), SEQ ID NO:81 (Cl3FatB2), SEQ ID NO:83 (Cd1FatB1), SEQ ID NO:87 (Cl4FatB1), SEQ ID NO:91 (Cl4FatB2), SEQ ID NO:93 (Cl4FatB3), SEQ ID NO:95 (Ca2FatB1), SEQ ID NO:97 (Ca2FatB2), and SEQ ID NO:101 (Ca2FatB3). Protein-encoding sequences of gene constructs for the expression of thioesterases based on some of these genes and the deduced amino acid sequences are provided in Table 4. The nucleotide and amino acid sequences disclosed herein are reference sequences when referring to variants based on those sequences. A reference thioesterase is a thioesterase having the sequence of the reference sequence.
The invention includes isolated or recombinant nucleic acid molecules encoding Class II thioesterases having at least at least 85%, at least 90%, at least 95%, or at least 99% identity with the amino acid sequence from amino acid position 1 to amino acid position 361 of SEQ ID NO:51; an amino acid sequence having at least 98% identity with the amino acid sequence from amino acid position 1 to amino acid position 362 of SEQ ID NO:55; an amino acid sequence having at least 97% identity with the amino acid sequence from amino acid position 1 to amino acid position 360 of SEQ ID NO:59; an amino acid sequence having at least 90% identity with the amino acid sequence from amino acid position 1 to amino acid position 359 of SEQ ID NO:63; an amino acid sequence having at least 98% identity with the amino acid sequence from amino acid position 53 to amino acid position 410 of SEQ ID NO:65; an amino acid sequence having at least 96% identity with the amino acid sequence from amino acid position 1 to amino acid position 356 of SEQ ID NO:69; an amino acid sequence having at least 98% identity with the amino acid sequence from amino acid position 53 to amino acid position 410 of SEQ ID NO:71; an amino acid sequence having at least 96% identity with the amino acid sequence from amino acid position 1 to amino acid position 361 of SEQ ID NO:75; an amino acid sequence having at least 97% identity with the amino acid sequence from amino acid position 1 to amino acid position 360 of SEQ ID NO:79; an amino acid sequence having at least 96% identity with the amino acid sequence from amino acid position 54 to amino acid position 413 of SEQ ID NO:81; an amino acid sequence having at least 96% identity with the amino acid sequence from amino acid position 1 to amino acid position 362 of SEQ ID NO:85; an amino acid sequence having at least 96% identity with the amino acid sequence from amino acid position 1 to amino acid position 361 of SEQ ID NO:89; an amino acid sequence having at least 97% identity with the amino acid sequence from amino acid position 53 to amino acid position 394 of SEQ ID NO:91; an amino acid sequence having at least 97% identity with the amino acid sequence from amino acid position 53 to amino acid position 394 of SEQ ID NO:93; an amino acid sequence having at least 99% identity with the amino acid sequence from amino acid position 53 to amino acid position 394 of SEQ ID NO:95; an amino acid sequence having at least 92% identity with the amino acid sequence from amino acid position 1 to amino acid position 360 of SEQ ID NO:99; or an amino acid sequence having at least 98% identity with the amino acid sequence from amino acid position 53 to amino acid position 393 of SEQ ID NO:101, in which the expressed protein encoded by the nucleic acid molecule has thioesterase activity. In some embodiments, the expressed thioesterase has at least the level of activity against an acyl-ACP substrate as the reference thioesterase from which the encoded thioesterase sequence is derived.
Also contemplated are nucleic acid molecules encoding acyl-ACP thioesterases with mature polypeptide sequences having at least 85%, 87%, 90%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity to the sequences of a mature thioesterase as disclosed herein, in which the thioesterases have N-terminal sequences that differ from the wild-type thioesterases from which they are derived. Thioesterase genes from plants such as Cuphea encode transit peptides. The cleavage site for removal of the transit peptide upon import of thioesterases into chloroplasts is hypothesized to be between positions 33 and 34 of SEQ ID NO:29 (Mayer and Shanklin BMC Plant Biology 7:1 (2007); see FIG. 1 and FIG. 7 ). As the transit peptide of plant thioesterases for import of the enzymes into plastids is not necessary for the activity of a thioesterase expressed in a prokaryotic organism, in many embodiments thioesterase genes designed for expression in prokaryotes, as exemplified in the Examples herein, do not encode all or a portion of a transit peptide.
In some embodiments, the recombinant or isolated nucleic acid molecule encoding an acyl-ACP thioesterase includes an amino acid sequence having at least 85%, at least 90%, at least 95%, or at least 99% identity with the amino acid sequence from amino acid position 33 to amino acid position 361 of SEQ ID NO:51; having at least 98% identity with the amino acid sequence from amino acid position 35 to amino acid position 362 of SEQ ID NO:55; having at least 97% identity with the amino acid sequence from amino acid position 34 to amino acid position 360 of SEQ ID NO:59; having at least 90% identity with the amino acid sequence from amino acid position 34 to amino acid position 359 of SEQ ID NO:63; having at least 98% identity with the amino acid sequence from amino acid position 84 to amino acid position 410 of SEQ ID NO:65; having at least 96% identity with the amino acid sequence from amino acid position 34 to amino acid position 356 of SEQ ID NO:69; having at least 98% identity with the amino acid sequence from amino acid position 84 to amino acid position 410 of SEQ ID NO:71; having at least 96% identity with the amino acid sequence from amino acid position 33 to amino acid position 361 of SEQ ID NO:75; having at least 97% identity with the amino acid sequence from amino acid position 34 to amino acid position 360 of SEQ ID NO:79; having at least 96% identity with the amino acid sequence from amino acid position 85 to amino acid position 413 of SEQ ID NO:81; having at least 96% identity with the amino acid sequence from amino acid position 34 to amino acid position 362 of SEQ ID NO:85; having at least 96% identity with the amino acid sequence from amino acid position 33 to amino acid position 361 of SEQ ID NO:89; having at least 97% identity with the amino acid sequence from amino acid position 84 to amino acid position 394 of SEQ ID NO:91; having at least 97% identity with the amino acid sequence from amino acid position 84 to amino acid position 394 of SEQ ID NO:93; having at least 99% identity with the amino acid sequence from amino acid position 84 to amino acid position 394 of SEQ ID NO:95; having at least 92% identity with the amino acid sequence from amino acid position 33 to amino acid position 360 of SEQ ID NO:99; or having at least 98% identity with the amino acid sequence from amino acid position 84 to amino acid position 393 of SEQ ID NO:101, and has at least the level of activity of the reference thioesterase from which the encoded thioesterase sequence is derived. In some embodiments, the encoded thioesterase shares at least 85%, at least 90%, at least 92%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or at least 99.5% identity with the above provided amino acid sequences, and the thioesterase encoded by the isolated nucleic acid molecule has at least the level of activity of the reference thioesterase from which the sequence is derived.
In some embodiments of the invention, a nucleic acid molecule may encode acyl-ACP thioesterases having a transit peptide sequence derived from one or more different acyl-ACP thioesterases, or from one or more proteins other than thioesterases that are imported into plastids. For example, in some embodiments in which a thioesterase gene is transformed into a eukaryotic photosynthetic organism for the production of a fatty acid product, the acyl-ACP thioesterase gene can encode a thioesterase that is at least 85%, at least 90%, at least 92%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or at least 99.5% identical to a thioesterase disclosed herein, while optionally including a sequence encoding any functional plastid transit peptide, such as a chloroplast transit peptide having an amino acid sequence that is less than 95% identical, less than 90% identical, less than 80% identical, less than 70% identical, less than 60% identical, less than 50% identical, less than 40% identical, less than 30% identical or less than 20% identical to sequences of the reference thioesterase precursor transit peptide. The transit peptide operably linked to the mature acyl-ACP thioesterase protein is in some embodiments from a chloroplast-directed protein from the species to be used as a transgenic host in the methods of the invention.
Furthermore, plant Class II thioesterases having deletions of the N-terminal amino acids extending to and including the amino acid corresponding to amino acid 65 of SEQ ID NO:29 (see FIG. 7 ), in which the thioesterase encoded by the isolated nucleic acid molecule has thioesterase activity. In preferred embodiments the encoded thioesterase has at least the level of activity as the reference thioesterase.
The invention includes, in exemplary embodiments, nucleic acid molecules encoding a thioesterase comprising an amino acid sequences having at least 96% identity to the amino acid sequence of SEQ ID NO:75, or from amino acid 64 to amino acid 361 of SEQ ID NO:75; or at least 92% identity to the amino acid sequence of SEQ ID NO:99 or from amino acid 64 to amino acid 361 of SEQ ID NO:99, in which the encoded thioesterase has a C10 acyl substrate preference, a C16 acyl substrate preference, or a binary preference for C10 and C16 acyl substrates. In illustrative examples expression of nucleic acid molecules encoding a thioesterase in a transgenic prokaryotic organism results in at least 20%, at least 30%, at least 35%, at least 40%, at least 45%, at least 50%, or at least 60% of the free fatty acids produced by or isolated from the prokaryotic organism being C10 and/or C16 fatty acids. In some embodiments, a nucleic acid molecule has at least 96% identity to the amino acid sequence of SEQ ID NO:75, or from amino acid 64 to amino acid 361 of SEQ ID NO:75; or at least 92% identity to the amino acid sequence of SEQ ID NO:99 or from amino acid 64 to amino acid 361 of SEQ ID NO:99, and expression of the thioesterase in a transgenic photosynthetic organism results in at least 20%, at least 30%, or at least 40%, of the free fatty acids produced by or isolated from the prokaryotic organism being C10 fatty acids.
In some embodiments, a nucleic acid molecule encodes a thioesterase having binary substrate preference, for example, the encoded thioesterase having at least 96% identity to SEQ ID NO:75 or at least 92% identity to SEQ ID NO:99, or a portion thereof, in some embodiments has a preference for one or more C10 substrates and one or more C16 substrates.
In another example, the invention includes nucleic acid molecules encoding a thioesterase comprising an amino acid sequences having at least 92% identity to from amino acid 63 to amino acid 360 of SEQ ID NO:99 or at least 99% identity to from amino acid 65 to amino acid 360 of SEQ ID NO:29, and the encoded thioesterase has a C8 acyl substrate preference. In some embodiments, a nucleic acid molecule encodes a thioesterase comprising an amino acid sequences having at least 92% identity to from amino acid 63 to amino acid 360 of SEQ ID NO:95 and expression of the thioesterase in a transgenic prokaryotic organism results in at least 20%, at least 30%, at least 35%, at least 40%, at least 45%, or at least 50% of the free fatty acids produced by or isolated from the prokaryotic organism being C8 and/or C10 fatty acids. In some embodiments, a nucleic acid molecule has at least 92% identity to from amino acid 63 to amino acid 360 of SEQ ID NO:99 or at least 99% identity to from amino acid 65 to amino acid 360 of SEQ ID NO:29, and expression of the thioesterase in a transgenic photosynthetic organism results in at least 20%, at least 30%, at least 35%, at least 40%, at least 45%, or at least 50% of the free fatty acids produced by or isolated from the prokaryotic organism being C8 fatty acids.
In other examples, the invention includes nucleic acid molecules encoding a thioesterase comprising an amino acid sequences having at least 85%, at least 90%, at least 92%, at least 95%, or at least 99% identity with the amino acid sequence from amino acid position 64 to amino acid position 361 of SEQ ID NO:51; at least 98% identity with the amino acid sequence from amino acid position 66 to amino acid position 362 of SEQ ID NO:55; at least 97% identity with the amino acid sequence from amino acid position 65 to amino acid position 360 of SEQ ID NO:59; at least 90% identity with the amino acid sequence from amino acid position 65 to amino acid position 359 of SEQ ID NO:63; at least 98% identity with the amino acid sequence from amino acid position 115 to amino acid position 410 of SEQ ID NO:65; at least 96% identity with the amino acid sequence from amino acid position 65 to amino acid position 356 of SEQ ID NO:69; at least 98% identity with the amino acid sequence from amino acid position 115 to amino acid position 410 of SEQ ID NO:71; at least 96% identity with the amino acid sequence from amino acid position 64 to amino acid position 361 of SEQ ID NO:75; at least 97% identity with the amino acid sequence from amino acid position 65 to amino acid position 360 of SEQ ID NO:79; at least 96% identity with the amino acid sequence from amino acid position 116 to amino acid position 413 of SEQ ID NO:81; at least 96% identity with the amino acid sequence from amino acid position 65 to amino acid position 362 of SEQ ID NO:85; at least 96% identity with the amino acid sequence from amino acid position 64 to amino acid position 361 of SEQ ID NO:89; at least 97% identity with the amino acid sequence from amino acid position 115 to amino acid position 394 of SEQ ID NO:91; at least 97% identity with the amino acid sequence from amino acid position 115 to amino acid position 394 of SEQ ID NO:93; at least 99% identity with the amino acid sequence from amino acid position 115 to amino acid position 394 of SEQ ID NO:95; at least 92% identity with the amino acid sequence from amino acid position 63 to amino acid position 360 of SEQ ID NO:99; or at least 98% identity with the amino acid sequence from amino acid position 115 to amino acid position 393 of SEQ ID NO:101, in which the encoded thioesterase has a C12, C14, and/or C16 acyl substrate preference. In some examples, the encoded acyl-ACP thioesterase has a C14 and/or C16 substrate preference. In illustrative examples expression of nucleic acid molecules encoding a thioesterase in a transgenic prokaryotic organism results in at least 20%, at least 30%, at least 35%, at least 40%, at least 45%, at least 50%, or at least 60% of the free fatty acids produced by or isolated from the prokaryotic organism being C12, C14 and/or C16 fatty acids.
An acyl-ACP thioesterase, such any of those disclosed herein, can be tested for its ability to direct synthesis of fatty acids or fatty acid products that are produced by transgenic organisms transformed with the nucleic acid molecules. Provided in the examples are descriptions of transforming host organisms with recombinant nucleic acid molecules encoding acyl-ACP thioesterases and recovering fatty acid products to determine the amount of fatty acid products of different chain lengths produced by the transgenic host.
Assays of a thioesterase can also be performed using lysates of transgenic organisms such as E. coli that are transformed with expression constructs that include the acyl-ACP thioesterase gene. Such assays can use labeled acyl substrates (see, for example, U.S. Pat. No. 5,667,997, incorporated herein by reference). An acyl-ACP thioesterase can also be partially or substantially purified prior to performing an assay; for example, the thioesterase can be expressed with an affinity tag (for example, a His tag) for affinity purification prior to performing the assay (Dehesh et al. Plant Physiol 110: 203-210 (1996), incorporated herein by reference).
The nucleic acid molecules encoding acyl-ACP thioesterases can be used to transform prokaryotic organisms or photosynthetic organisms, such as plants or algae, for the production of fatty acid products in the organisms. In some preferred embodiments, the sequence encoding the Class II thioesterase is codon-optimized for expression in the host organism. Codons can be optimized by methods such as those provided in U.S. Pat. No. 7,135,290, incorporated herein by reference. A codon usage database is available at the world wide web site kazusa.or.jp/codon/. Preferred codon usage can also be determined by a practitioner based on gene sequences entered in databases such as Genbank (ncbi.nlm.nih.gov/GenBank/), or a subset of genes of the organism (for example, highly expressed genes).
In some embodiments, the transgenic organism that includes a thioesterase gene of the invention is a bacterium, such as, but not limited to, an Acetobacter, Acinetobacter, Arthrobacter, Bacillus, Brevibacterium, Chromatium, Chlorobium, Clostridium, Corynebacterium, Deinococcus, Delftia, Desulfovibrio, Enterococcus, Escherichia, Kineococcus, Klebsiella, Lactobacillus, Lactococcus, Micrococcus, Mycobacterium, Jeotgalicoccus, Paenibacillus, Propionibacter, Pseudomonas, Rhodopseudomonas, Rhodobacter, Rhodococcus, Rhodospirillium, Rhodomicrobium, Salmonella, Serratia, Shewanella, Stenotrophomonas, Streptomyces, Streptococcus, Vibrio, or Zymomonas species.
A photosynthetic organism transformed with the nucleic acid molecule that encodes a thioesterase gene can be a plant, such as but not limited to a higher plant, or can be an alga. Higher plants considered for use in the invention include, without limitation, Arabidopsis thaliana, Arachis hypogaea, Avena sativa, Brassica species (e.g., Brassica napus, Brassica campestris, Brassica juncea ), Camelina sativa, Carthamus tinctorius, Cocos nucifera, Crambe ahyssiraica, Cuphea species, Elaeis species (e.g., Elaeis guineensis, Elaeis oleifera ), Gossypium hirsutum, Glycine max, Helianthus annuulus, Jatropha species, Cucurbita pepo, Oryza satvia, Sesamum indicum, Simmondsia chinensis, Theobroma cacao, Ricinus communis, and Zea mays.
Algae that can be used in the methods of the invention can be any algae, and can include microalgae, such as but not limited to, Achnanthes, Amphiprora, Amphora, Ankistrodesmus, Asteromonas, Boekelovia, Borodinella, Botryococcus, Bracteococcus, Chaetoceros, Carteria, Chlamydomonas, Chlorococcum, Chlorogonium, Chlorella, Chroomonas, Chrysosphaera, Cricosphaera, Crypthecodinium, Cryptomonas, Cyclotella, Dunaliella, Ellipsoidon, Emiliania, Eremosphaera, Ernodesmius, Euglena, Franceia, Fragilaria, Gloeothamnion, Haematococcus, Halocafeteria, Hymenomonas, Isochrysis, Lepocinclis, Micractinium, Monoraphidium, Nannochloris, Nannochloropsis, Navicula, Neochloris, Nephrochloris, Nephroselmis, Nitzschia, Ochromonas, Oedogonium, Oocystis, Ostreococcus, Pavlova, Parachlorella, Pascheria, Phaeodactylum, Phagus, Platymonas, Pleurochrysis, Pleurococcus, Prototheca, Pseudochlorella, Pyramimonas, Pyrobotrys, Scenedesmus, Schizochytrium, Skeletonema, Spyrogyra, Stichococcus, Tetraselmis, Thraustochytrium, Viridiella, or Volvox species.
In some embodiments, photosynthetic bacteria, including for example, green sulfur bacteria, purple sulfur bacteria, green nonsulfur bacteria, purple nonsulfur bacteria, or cyanobacteria are used for producing a fatty acid product. Cyanobacterial species that can be used for production of fatty acid products include, without limitation, Agmenellum, Anabaena, Anabaenopsis, Anacystis, Aphanizomenon, Arthrospira, Asterocapsa, Borzia, Calothrix, Chamaesiphon, Chlorogloeopsis, Chroococcidiopsis, Chroococcus, Crinalium, Cyanobacterium, Cyanobium, Cyanocystis, Cyanospira, Cyanothece, Cylindrospermopsis, Cylindrospermum, Dactylococcopsis, Dermocarpella, Fischerella, Fremyella, Geitleria, Geitlerinema, Gloeobacter, Gloeocapsa, Gloeothece, Halospirulina, Iyengariella, Leptolyngbya, Limnothrix, Lyngbya, Microcoleus, Microcystis, Myxosarcina, Nodularia, Nostoc, Nostochopsis, Oscillatoria, Phormidium, Planktothrix, Pleurocapsa, Prochlorococcus, Prochloron, Prochlorothrix, Pseudanabaena, Rivularia, Schizothrix, Scytonema, Spirulina, Stanieria, Starria, Stigonema, Symploca, Synechococcus, Synechocystis, Tolypothrix, Trichodesmium, Tychonema, or Xenococcus species.
In addition to photosynthetic microorganisms, non-photosynthetic microorganisms such as fungi, and nonalgal stamenophiles can be transformed with one or more thioesterase genes as disclosed herein for producing fatty acid products. For example, oleaginous yeasts, including but not limited to Aspergillus niger, Yarrowia lypolytica, Cryptococcus curvatus, Cryptococcus terricolus, Candida species, Lipomyces starkeyi, Lipomyces lipofer, Endomycopsis vernalis, Rhodotorula glutinis, and Rhodotorula gracilis can also be hosts transformed with thioesterase genes as disclosed herein. Other fungi, including but not limited to species of Aspergillus, Trichoderma, Neurospora, Fusarium, Humicola, Rhizomucor, Kluyveromyces, Pichia, Mucor, Myceliophtora, Penicillium, Phanerochaete, Chrysosporium, Saccharomyces, and Schizosaccharomyces, are also considered as transgenic hosts expressing thioesterase genes as disclosed herein for use in making fatty acid products. Labyrinthulomycete species (e.g., Thraustichytrium, Ulkenia, and Schizochytrium species) can also be transformed with a thioesterase gene in the practice of the invention.
Production of Fatty Acid Products
In another aspect, the invention provides a method of producing a fatty acid or a fatty acid product, in which the method includes cultivating an organism having an exogenous nucleic acid molecule that includes a sequence encoding an acyl-ACP thioesterase as disclosed herein, and isolating a fatty acid or a fatty acid product from the organism or culture medium. The transgenic host organism can be a bacterium, alga, cyanobacterium, or plant as provided herein, and the sequence encoding the plant acyl-ACP thioesterase in some embodiments is codon-optimized for expression in the host organism.
The methods can be used for the production and isolation of a fatty acid product such as a triglyceride, a fatty aldehyde, a fatty alcohol, a fatty ester, or a hydrocarbon such as an alkene or alkane. In some embodiments, the methods include isolation of fatty acid products that include one or more of a C8, C10, C12, C14, C16, or C18 fatty acid product. In some embodiments, the methods include isolation of fatty acid products that include one or more of a C8 or C10 fatty acid product. In some exemplary embodiments, one or more fatty acids (free fatty acids) are isolated using the methods of the invention, such as, for example, one or more of a C8 fatty acid or a C10 fatty acid.
In some preferred embodiments expression of an acyl-ACP thioesterase gene as provided herein in a transgenic organism results in at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, or at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the isolated fatty acid products isolated from the organism and/or culture medium being a single chain length fatty acid product. For example, in some embodiments, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, or at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the isolated fatty acid products from an organism expressing an exogenous acyl-ACP thioesterase of the invention is a C8, a C10, a C12, a C14, a C16, or a C18 fatty acid product. In some preferred embodiments, the isolated fatty acid products are fatty acids, and at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, or at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the fatty acids isolated from the organism and/or the growth medium is a C8 or a C10 free fatty acid.
In some embodiments, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, or at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the isolated fatty acid products from an organism expressing an exogenous acyl-ACP thioesterase of the invention are fatty acid products or two or more chain lengths, such as two or more of a C8, a C10, a C12, a C14, a C16, or a C18 fatty acid product. In some preferred embodiments, the fatty acid products are fatty acids, and at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, or at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the fatty acids isolated from the organism and/or the growth medium are fatty acids of a specific chain length, such as two or more of C8, C10, C12, C14, C16, or C18 fatty acids.
In some embodiments, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, or at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the isolated fatty acid products from an organism expressing an exogenous acyl-ACP thioesterase of the invention are fatty acid products or two or more chain lengths, such as two or more of a C12, a C14, a C16, or a C18 fatty acid product. In some preferred embodiments, the fatty acid products are fatty acids, and at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, or at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the fatty acids isolated from the organism and/or the growth medium are fatty acids of a specific chain length, such as two or more of C12, C14, C16, or C18 fatty acids. In some preferred embodiments, the fatty acid products are fatty acids, and at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, or at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the fatty acids isolated from the organism and/or the growth medium are fatty acids of a specific chain length, such as C14 and C16 fatty acids.
Nucleic acid molecules used in the methods of the invention include those disclosed herein.
In some embodiments of the invention, the transgenic organism is transformed with a nucleic acid molecule that encodes a thioesterase having 96% or greater identity with amino acids 64 to 361 of SEQ ID NO:75 or 92% or greater identity with amino acids 64 to 361 of SEQ ID NO:99, and at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, or at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the fatty acid products isolated from the transgenic organism and/or medium from culturing of a transgenic organism are C10 fatty acid products, such as but not limited to a C10 fatty acid, C10 fatty aldehyde, or C10 fatty alcohol, or a wax ester, alkene, or alkane.
In some embodiments of the invention, the transgenic organism is transformed with a nucleic acid molecule that encodes a thioesterase having 96% or greater identity with amino acids 64 to 361 of SEQ ID NO:75, or to amino acids 64 to 361 of SEQ ID NO:99, and at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, or at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the fatty acid products isolated from the transgenic organism and/or medium from culturing of a transgenic organism are C16 fatty acid products, such as but not limited to a C16 fatty acid, C16 fatty aldehyde, or C16 fatty alcohol, or a wax ester, alkene, or alkane.
In some examples, a transgenic organism is transformed with a nucleic acid molecule that encodes a thioesterase having 92% or greater identity with amino acid 63 to amino acid 360 of SEQ ID NO:99, and at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, or at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the isolated fatty acid products are a C8 and/or a C10 fatty acid product. In some examples, a transgenic organism is transformed with a nucleic acid molecule that encodes a thioesterase having 92% or greater identity with amino acid 63 to amino acid 360 of SEQ ID NO:99, and at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, or at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the isolated fatty acid products are a C8 fatty acid product, such as but not limited to a C8 fatty acid, C8 fatty aldehyde, or C8 fatty alcohol, or a wax ester, alkene, or alkane.
In further examples, a transgenic organism is transformed with a nucleic acid molecule that encodes a thioesterase having at least 85%, at least 90%, at least 92%, at least 95%, or at least 99% identity with the amino acid sequence from amino acid position 64 to amino acid position 361 of SEQ ID NO:51; at least 98% identity with the amino acid sequence from amino acid position 66 to amino acid position 362 of SEQ ID NO:55; at least 97% identity with the amino acid sequence from amino acid position 65 to amino acid position 360 of SEQ ID NO:59; at least 90% identity with the amino acid sequence from amino acid position 65 to amino acid position 359 of SEQ ID NO:63; at least 98% identity with the amino acid sequence from amino acid position 115 to amino acid position 410 of SEQ ID NO:65; at least 96% identity with the amino acid sequence from amino acid position 65 to amino acid position 356 of SEQ ID NO:69; at least 98% identity with the amino acid sequence from amino acid position 115 to amino acid position 410 of SEQ ID NO:71; at least 96% identity with the amino acid sequence from amino acid position 64 to amino acid position 361 of SEQ ID NO:75; at least 97% identity with the amino acid sequence from amino acid position 65 to amino acid position 360 of SEQ ID NO:79; at least 96% identity with the amino acid sequence from amino acid position 116 to amino acid position 413 of SEQ ID NO:81; at least 96% identity with the amino acid sequence from amino acid position 65 to amino acid position 362 of SEQ ID NO:85; at least 96% identity with the amino acid sequence from amino acid position 64 to amino acid position 361 of SEQ ID NO:89; at least 97% identity with the amino acid sequence from amino acid position 115 to amino acid position 394 of SEQ ID NO:91; at least 97% identity with the amino acid sequence from amino acid position 115 to amino acid position 394 of SEQ ID NO:93; at least 99% identity with the amino acid sequence from amino acid position 115 to amino acid position 394 of SEQ ID NO:95; at least 92% identity with the amino acid sequence from amino acid position 63 to amino acid position 360 of SEQ ID NO:99; or at least 98% identity with the amino acid sequence from amino acid position 115 to amino acid position 393 of SEQ ID NO:101, and at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, or at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the isolated fatty acid products are a C12, C14, C16 and/or a C18 fatty acid product. In some examples, a transgenic organism is transformed with a nucleic acid molecule that encodes a thioesterase and at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, or at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the isolated fatty acid products are a C12, a C14, a C16, or a C18 fatty acid product, such as but not limited to a fatty acid, fatty aldehyde, or fatty alcohol, or a wax ester, alkene, or alkane. For example, the isolated fatty acid products from culturing a transgenic organism may be at least 50%, at least 60%, at least 70%, at least 80%, or at least 90% C14 and/or C16 fatty acid products.
The transgenic organism is in some embodiments a photosynthetic organism, such as, for example, a microalga. In some embodiments, the transgenic organism is a prokaryote.
In some illustrative embodiments, the method includes isolating fatty acid products from the culture medium, in which at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, or at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the fatty acid products isolated from the organism or the growth medium are fatty acid products of a specific chain length.
Production of Medium Chain Fatty Acid Products
As set forth in the Examples, a new Class II thioesterase gene from Cuphea aequipetala, denoted Ca1FatB2, has been isolated. The sequence of the putative mature form of the enzyme is provided in FIG. 1 as SEQ ID NO:29. The invention provides a method of producing a C8 fatty acid product in which the method includes culturing a photosynthetic organism that includes an exogenous nucleic acid molecule encoding a medium chain length acyl-ACP thioesterase that is at least 90% identical to amino acids 65 to 355 of SEQ ID NO:29 and isolating a fatty acid product from the organism or culture medium, in which at least 5% of the isolated fatty acid product is a C8 fatty acid product. The method includes the use of transgenic host organisms that include an exogenous nucleic acid molecule encoding a medium chain acyl-ACP thioesterase that is at least 90% identical to amino acids 34 to 355 of SEQ ID NO:29. A nucleic acid molecule used in these methods encodes a Class II medium chain plant acyl-ACP thioesterase or a variant thereof.
Nucleic acid molecules used in the methods of the invention encode acyl-ACP thioesterases having at least 90% identity to amino acids 65 to 355 of SEQ ID NO:29, in which expression of the thioesterase-encoding sequences in a photosynthetic transgenic organism results in production of a population of fatty acid products in the cells or growth media in which at least 5% of the fatty acid products isolated from the cells or growth media is a C8 fatty acid product. In some embodiments, a nucleic acid molecule used in the methods of the invention encodes an acyl-ACP thioesterase having at least 90% identity to amino acids 34 to 355 of SEQ ID NO:29. Using the methods of the invention, the percentage of a C8 fatty acid product, such as, for example, octanoic acid, in the recovered fatty acids is, for example, 5% or greater, 10% or greater, 15% or greater, 20% or greater, 25% or greater, 30% or greater, 35% or greater, 40% or greater, 45% or greater, 50% or greater, 55% or greater, 60% or greater, 65% or greater, 70% or greater, 75% or greater, or 80% or greater. In some preferred embodiments, the percentage of octanoic acid or another C8 fatty acid product in the fatty acids or fatty acid products recovered from the cultured cells and/or the culture medium is 85% or greater, such as 86%, 87%, between 87% and 90%, between 90% and 93%, between 93% and 95%, between 95% and 97%, between 97% and 98%, between 98% and 99%, or between 99% and 100%.
As detailed in Example 3, the Cuphea aequipetala FatB2 coding sequence has been reconstructed using PCR and gene walking such that, based on homology with other plant thioesterases, it is estimated that all but approximately ten to fifteen amino acids of the N-terminus have been determined. This sequence of the C. aequipetala FatB2 coding sequence (SEQ ID NO:22) is provided in FIG. 1 . As evident in the figure, SEQ ID NO:22 and SEQ ID NO:29 are identical from amino acid position 2 to amino acid position 355. (SEQ ID NO:22 includes additional amino acids −43 to −1, considered to be amino acids included in the chloroplast transit peptide, that are not present in SEQ ID NO:29.) Thus, reference to any amino acid sequences between amino acid position 2 and amino acid 355 of SEQ ID NO:22 are interchangeable with the same sequences of SEQ ID NO:29 and vice versa.
The acyl-ACP thioesterase variants encoded by the nucleic acid molecules carried by transgenic host organisms may have N-terminal or C-terminal regions that differ from the wild-type thioesterase from which they are derived. With regard to the N-terminus, it is noted that acyl-ACP thioesterases of higher plants, such as the acyl-ACP thioesterase of C. aequipetala, are synthesized as precursor proteins that are transported into plastids, where the enzymes function in fatty acid biosynthesis. The site within the precursor protein sequence at which cleavage of the N-terminal transit peptide occurs has not been empirically determined.
The examples provided herein confirm that the transit peptide (including amino acids -43 through -1 of SEQ ID NO:22 in FIG. 1 ) is not necessary for the activity of a thioesterase expressed in a prokaryotic organism. Example 4 further demonstrates that thioesterase activity is not reduced by additional deletion of amino acids 1 to 33 of the putative mature thioesterase (SEQ ID NO:29). Plant medium chain thioesterases having deletions of the N-terminal amino acids extending to the amino acid corresponding to amino acid 64 of SEQ ID NO:22 have been shown to be active (see, for example, U.S. Pat. 5,667,997). Thus, the invention recognizes that N-terminal deletions of up to amino acid 64 (referencing SEQ ID NO:22 and SEQ ID NO:29, FIG. 1 ) of a medium chain acyl-ACP thioesterase are useful in the methods of the invention. The invention therefore includes methods of producing a fatty acid product in which a transgenic organism used to synthesize the fatty acid product is transformed with a gene encoding an acyl-ACP thioesterase having a deletion in its N-terminal region, in which the acyl-ACP thioesterase is at least 90% identical to amino acids 65-355 of SEQ ID NO:29.
In some embodiments of the invention, a nucleic acid molecule may encode acyl-ACP thioesterases having a transit peptide sequence derived from a different acyl-ACP thioesterase, or from a protein other than a thioesterase that is imported into plastids. For example, in some embodiments in which a thioesterase gene is transformed into a eukaryotic photosynthetic organism for the production of a fatty acid product, the acyl-ACP thioesterase gene can encode a thioesterase that is at least 90% identical to amino acids 65 to 355 of SEQ ID NO:29, while including a sequence encoding a transit peptide having an amino acid sequence that is less than 90% identical, less than 80% identical, less than 70% identical, less than 60% identical, less than 50% identical, less than 40% identical or less than 30% identical to sequences of the thioesterase precursor of SEQ ID NO:22. The transit peptide operably linked to the mature acyl-ACP thioesterase protein is in some embodiments from a chloroplast-directed protein from the species to be used as a transgenic host in the methods of the invention.
Also demonstrated in examples herein is the ability to introduce variations into the sequence of the C-terminal portion of a medium chain acyl-ACP thioesterase without significant loss of activity (see Example 2). Thus the invention includes variants of acyl-ACP thioesterases that terminate at amino acid 355, that include a C-terminal sequence of a different acyl-ACP thioesterase, or that have one or more amino acids that differ from any known acyl-ACP thioesterase, so long as there is no substantial detrimental effect on the activity of the thioesterase with regard to its C8 specificity and activity level.
The examples further disclose genes encoding variant acyl-ACP thioesterases having one, two, or three mutations with respect to the wild-type sequence (SEQ ID NO:29), in which the mutants retain the C8 specificity of the wild-type molecule, and where expression of a variant results in recovery of as great or a greater amount of C8 fatty acid from the culture as results from expression of the wild-type thioesterase. In some embodiments, then, a nucleic acid molecule used in the methods of the invention encodes an acyl-ACP thioesterase having between 90% and 95% identity, between 95% and 97% identity, between 97% and 98% identity, between 98% and 99% identity, between 99% and 99.5% identity, or between 99.5% and 100% identity to amino acids 65 to 355 of SEQ ID NO:29, while retaining at least the level of activity toward a C8 acyl substrate of the thioesterase of SEQ ID NO:29. In some embodiments of the methods a nucleic acid molecule encodes an acyl-ACP thioesterase having between 90% and 95% identity, between 95% and 97% identity, between 97% and 98% identity, between 98% and 99% identity, between 99% and 99.5% identity, or between 99.5% and 100% identity to amino acids 34 to 355 of SEQ ID NO:29, while retaining at least the level of activity toward a C8 acyl substrate of the thioesterase of SEQ ID NO:29.
In some embodiments, a nucleic acid molecule used in the methods of the invention encodes an acyl-ACP thioesterase having between 90% and 95% identity, between 95% and 98% identity, between 98% and 99% identity, between 99% and 99.5% identity, or between 99.5% and 100% identity to amino acids 65 to 355 of SEQ ID NO:29, in which expression of the acyl-ACP thioesterase in a transgenic organism results in production of at least the level of a C8 fatty acid produced by the transgenic organism expressing the thioesterase of SEQ ID NO:29. In some embodiments of the methods a nucleic acid molecule encodes an acyl-ACP thioesterase having between 90% and 95% identity, between 95% and 97% identity, between 97% and 98% identity, between 98% and 99% identity, between 99% and 99.5% identity, or between 99.5% and 100% identity to amino acids 34 to 355 of SEQ ID NO:29, and expression of the acyl-ACP thioesterase in a transgenic organism results in production of at least the level of a C8 fatty acid produced by the transgenic organism expressing the thioesterase of SEQ ID NO:29.
For any variants of an acyl-ACP thioesterase, such as variants of the acyl-ACP thioesterase of SEQ ID NO:22 or SEQ ID NO:29, the nucleic acid molecule encoding a variant acyl-ACP thioesterase can be tested for its ability to direct synthesis of a high proportion of C8 fatty acids or C8 fatty acid products, that are produced by the organisms and can be isolated from higher plants or cultures of algae transformed with the nucleic acid molecules. Provided in the examples are descriptions of transforming host organisms with recombinant nucleic acid molecules encoding acyl-ACP thioesterases and recovering fatty acid products to determine the amount of fatty acid products of different chain lengths produced by the transgenic host.
Assays of a thioesterase can also be performed using lysates of transgenic organisms such as E. coli that are transformed with expression constructs that include the acyl-ACP thioesterase gene and its activity determined using labeled acyl substrates (see, for example, U.S. Pat. No. 5,667,997, incorporated herein by reference). An acyl-ACP thioesterase variant can also be partially or substantially purified prior to performing an assay; for example, the thioesterase or thioesterase variant can be expressed with an affinity tag (for example, a His tag) for affinity purification prior to performing the assay (Dehesh et al. Plant Physiol 110: 203-210 (1996), incorporated herein by reference).
In some preferred embodiments, a nucleic acid molecule used in the methods of the invention encodes a plant B-type acyl-ACP thioesterase or a variant thereof, in which the encoded B-type acyl-ACP thioesterase comprises an amino acid sequence that is at least 95%, at least 97%, at least 98%, at least 99%, or at least 99.5% identical to amino acids 65 to 355 of SEQ ID NO:29. In some embodiments, the nucleic acid molecule encodes SEQ ID NO:8, SEQ ID NO:12, SEQ ID NO:22, SEQ ID NO:26, SEQ ID NO:33, SEQ ID NO:40, SEQ ID NO:43, or SEQ ID NO:45, or a thioesterase having any combination of the mutations provided in Table 2, the table provided in FIGS. 3A-3D , or the table provided in FIGS. 5A-5B . In some embodiments, the nucleic acid molecule comprises a sequence that encodes at least amino acids 65-355 of SEQ ID NO:29. In some preferred embodiments, a nucleic acid molecule according to the invention encodes a plant B-type acyl-ACP thioesterase or a variant thereof, in which the encoded B-type acyl-ACP thioesterase comprises an amino acid sequence that is at least 95%, at least 97%, at least 98%, at least 99%, or at least 99.5% identical to amino acids 34 to 355 of SEQ ID NO:29. In some embodiments, the nucleic acid molecule encodes SEQ ID NO:8, SEQ ID NO:12, SEQ ID NO:22, SEQ ID NO:26, SEQ ID NO:33, SEQ ID NO:40, SEQ ID NO:43, or SEQ ID NO:45, or a thioesterase having any combination of the mutations provided in Table 2, the table provided in FIGS. 3A-3D , or the table provided in FIGS. 5A-5B . In some embodiments, the nucleic acid molecule comprises a sequence that encodes at least amino acids 34-355 SEQ ID NO:29. In some embodiments, the nucleic acid molecule comprises a sequence that encodes SEQ ID NO:29.
The nucleic acid molecules encoding acyl-ACP thioesterases can be used to transform photosynthetic organisms, such as plants or algae, for the production of C8-enriched fatty acid products in the organisms. In some preferred embodiments, the sequence encoding the medium chain length fatty acid is codon-optimized for expression in the host organism. Codons can be optimized by methods such as those provided in U.S. Pat. No. 7,135,290, incorporated herein by reference. A codon usage database is available at the world wide web site kazusa.or.jp/codon/. Preferred codon usage can also be determined by a practitioner based on gene sequences entered in databases such as Genbank (ncbi.nlm.nih.gov/GenBank/), or a subset of genes of the organism (for example, highly expressed genes).
A photosynthetic organism transformed with the nucleic acid molecule that encodes a thioesterase gene can be a plant, such as but not limited to a higher plant, or can be an alga. Higher plants considered for use in the invention include, without limitation, Arabidopsis thaliana, Arachis hypogaea, Avena sativa, Brassica species (e.g., Brassica napus, Brassica campestris, Brassica juncea ), Camelina sativa, Carthamus tinctorius, Cocos nucifera, Crambe abyssinica, Cuphea species, Elaeis species (e.g., Elaeis guineensis, Elaeis oleifera ), Gossypium hirsutum, Glycine max, Helianthus annuulus, Jatropha species, Cucurbita pepo, Oryza satvia, Sesamum indicum, Simmondsia chinensis, Theobroma cacao, Ricinus communis, and Zea mays.
Algae that can be used in the methods of the invention can be any algae, and can include microalgae, such as but not limited to, Achnanthes, Amphiprora, Amphora, Ankistrodesmus, Asteromonas, Boekelovia, Borodinella, Botryococcus, Bracteococcus, Chaetoceros, Carteria, Chlamydomonas, Chlorococcum, Chlorogonium, Chlorella, Chroomonas, Chrysosphaera, Cricosphaera, Crypthecodinium, Cryptomonas, Cyclotella, Dunaliella, Ellipsoidon, Emiliania, Eremosphaera, Ernodesmius, Euglena, Franceia, Fragilaria, Gloeothamnion, Haematococcus, Halocafeteria, Hymenomonas, Isochrysis, Lepocinclis, Micractinium, Monoraphidium, Nannochloris, Nannochloropsis, Navicula, Neochloris, Nephrochloris, Nephroselmis, Nitzschia, Ochromonas, Oedogonium, Oocystis, Ostreococcus, Pavlova, Parachlorella, Pascheria, Phaeodactylum, Phagus, Platymonas, Pleurochrysis, Pleurococcus, Prototheca, Pseudochlorella, Pyramimonas, Pyrobotrys, Scenedesmus, Schizochytrium, Skeletonema, Spyrogyra, Stichococcus, Tetraselmis, Thalassiosira, Viridiella, or Volvox species.
In some embodiments, photosynthetic bacteria, including for example, green sulfur bacteria, purple sulfur bacteria, green nonsulfur bacteria, purple nonsulfur bacteria, or cyanobacteria are used for producing a C8 fatty acid product. Cyanobacterial species that can be used for production of C8 fatty acid products include, without limitation, Agmenellum, Anabaena, Anabaenopsis, Anacystis, Aphanizomenon, Arthrospira, Asterocapsa, Borzia, Calothrix, Chamaesiphon, Chlorogloeopsis, Chroococcidiopsis, Chroococcus, Crinalium, Cyanobacterium, Cyanobium, Cyanocystis, Cyanospira, Cyanothece, Cylindrospermopsis, Cylindrospermum, Dactylococcopsis, Dermocarpella, Fischerella, Fremyella, Geitleria, Geitlerinema, Gloeobacter, Gloeocapsa, Gloeothece, Halospirulina, Iyengariella, Leptolyngbya, Limnothrix, Lyngbya, Microcoleus, Microcystis, Myxosarcina, Nodularia, Nostoc, Nostochopsis, Oscillatoria, Phormidium, Planktothrix, Pleurocapsa, Prochlorococcus, Prochloron, Prochlorothrix, Pseudanabaena, Rivularia, Schizothrix, Scytonema, Spirulina, Stanieria, Starria, Stigonema, Symploca, Synechococcus, Synechocystis, Tolypothrix, Trichodesmium, Tychonema, or Xenococcus species.
In another aspect the invention provides an isolated nucleic acid molecule that encodes a variant of a plant acyl-ACP thioesterase, in which the variant has a mutation at the amino acid corresponding to amino acid position 174 of SEQ ID NO:29 in which the variant has activity as high as or higher than the thioesterase from which the variant was derived. For example, in preferred embodiments, culturing of a transgenic organism that carries the variant gene in some embodiments allows isolation of as great or a greater amount of a fatty acid product of a specific chain length than does culturing of a transgenic organism that carries the native thioesterase gene. In preferred embodiments, expression of the variant in a transgenic host organism allows for isolation of fatty acid products of a specific chain length, in which the percentage of fatty acid products of a specific chain length to total fatty acid products isolated is at least as high as the percentage of fatty acid products of a specific chain length to total fatty acid products isolated from a host organism carrying the native gene.
In some preferred embodiments of the invention, the percentage of octanoic acid present in the population of fatty acids secreted by a prokaryotic organism transformed with a nucleic acid molecule encoding a variant of SEQ ID NO:29 having a mutation at position 174 is 55% or greater, 60% or greater, 65% or greater, 70% or greater, 75% or greater, or 80% or greater. In some preferred embodiments of the invention, the percentage of octanoic acid present in the population of fatty acids secreted by a prokaryotic organism transformed with a nucleic acid molecule encoding a variant of SEQ ID NO:29 having a mutation at position 174 is 85% or greater, such as 86%, 87%, between 87% and 90%, between 90% and 93%, between 93% and 95%, between 95% and 100%, between 95% and 97%, or between 97% and 100%. For example, in some embodiments expression of a variant of the acyl-ACP thioesterase of SEQ ID NO:29 in a bacterium or cyanobacterium results in secretion of a population of fatty acids enriched for octanoic acid.
The amino acid position corresponding to amino acid 174 of SEQ ID NO:29 refers to the amino acid position of an acyl-ACP thioesterase amino acid sequence that would align with amino acid 174 of SEQ ID NO:29 if the sequence of interest and SEQ ID NO:29 were aligned for maximum homology. Such alignments of Class II thioesterase sequences can be seen, for example, in U.S. Pat. No. 6,150,512 at FIG. 1 . The terms “amino acid position 174”, “position 174”, or “consensus position 174” or similar nomenclature all refer to the consensus position for an acyl-ACP thioesterase corresponding to amino acid position 174 of SEQ ID NO:29 (and of SEQ ID NO:22, see FIG. 1 ) when the sequence is aligned with SEQ ID NO:29 (and, optionally, the sequences of other plant acyl-ACP thioesterases) for maximal sequence matches. Analogously, references to other amino acid positions, such as but not limited to, position 34, 35, 64, 65, 67, 103, 184, 355, etc., refer to numbered positions of the thioesterase sequences provided herein, including SEQ ID NO:22 and SEQ ID NO:29 ( FIG. 1 ). These positions can be translated to numbered positions of other thioesterase genes as provided in patents, patent applications, publications, and gene and protein databases by aligning the sequence of SEQ ID NO:22 or SEQ ID NO:29 with the published, documented, or discovered thioesterase sequence for maximum homology.
In contrast to other acyl-ACP thioesterse mutants that have been isolated, the variants described in Examples 4-7 having an amino acid substitution at position 174 have increased activity while the chain length preference of the thioesterase has not been shifted from one acyl chain length to another acyl chain length. Isolation of a variant having a mutation at position 174 having increased activity was surprising not only because no previously identified acyl-ACP thioesterase mutants have exhibited increased activity, but also because the active site for Class II acyl-ACP thioesterases had been identified as being located more than 100 amino acids away from position 174, using SEQ ID NO:29 reference numbering (see FIG. 1 ), in the area of amino acid residues 293-297 and 304 (see, for example, U.S. Pat. No. 6,150,512).
A mutation at consensus position 174 can be a mutation that changes the amino acid of the naturally-occurring or wild-type gene at that consensus position to any other amino acid. In some embodiments, in which the naturally-occurring or wild-type gene has a methionine residue at amino acid position 174, the mutation can change M174 to any other amino acid, for example, glycine, proline, alanine, valine, leucine, isoleucine, phenylalamine, tyrosine, tryptophan, cysteine, serine, threonine, glutamine, asparagine, lysine, arginine, histidine, glutamate, or aspartate. In some embodiments, a mutation at position 174 changes the amino acid at position 174 of an acyl-ACP thioesterase to an uncharged amino acid, which can be, for example, any of glycine, proline, alanine, valine, leucine, isoleucine, phenylalamine, tyrosine, tryptophan, cysteine, methionine, serine, threonine, glutamine, or asparagine. In some embodiments, the mutation changes the amino acid at position 174 to methionine, leucine, phenylalanine, valine, cysteine, or isoleucine. In some embodiments, the mutation changes the amino acid at position 174 to valine or isoleucine.
Alignment of native plant Class II (FatB-encoded) acyl ACP thioesterases reveals that the amino acid at the position that corresponds to amino acid position 174 of SEQ ID NO:29 is typically a methionine residue. (This position is most often designated as a position between about residue 220 and about residue 250 for thioesterase amino acid sequences that number the first residue of the precursor protein as residue 1.) For example, plant acyl-ACP thioesterases having a methionine at the position corresponding to position 174 of SEQ ID NO:29 include FatB-encoded thioesterases of Cuphea species, such as but not limited to those encoded by Cuphea calophylla FatB genes (e.g., ABB71579, ABB71580, and ABB71581), Cuphea hookeriana FatB1 (Q39513), Cuphea hookeriana FatB1-1 (AAC72882), Cuphea hookeriana FatB2 (AAC49269), Cuphea hookeriana FatB3 (AAC72881), the Cuphea hookeriana 16:0-ACP thioesterase (AAC48990), Cuphea palustris FatB1(AAC49179 and 2208474A), Cuphea palustris FatB2 (AAC49180 and 2208474B), Cuphea wrightii FatB1 (AAC49783) and Cuphea wrightii FatB2 (AAC49784), and Cuphea lanceolata Class II thioesterases (e.g., AAE24875, CAA02760, CAA02766, CAA02765, CAA54060, CAC19934, and CAC19933). Also included are the Class II thioesterases of Diploknema butyracea (e.g., AAX51636), Brassica napus (e.g., ABH11710) and Brassica juncea (e.g., ABI18986). Other Class II thioesterases having a methionine at position 174 are those of Camellia oleifera (e.g., ACQ57190, ACQ63293, ACQ57188, ACQ57189, and ACQ57187), Helianthus annuus (e.g., AAB88824, AAQ08202, AAX19387, AAX19386, AAX19385, AAX19384, AAX19383, AAX19382, AAX19381, AAX19380, AAX19379, AAX19378, AAX19377, CAC80371, and CAC80370), and Jatropha curcas (e.g., ABU96744), as well as Madhuca longifolia FatB (AAX51637), Myristica fragrans FatB2 (AAB71729), Populus tomentosa FatB (ABC47311), Ricinus communis FatB genes (e.g., ABV54795, EEF47013, EEF51750, and EEF36100), Umbellularia califonica FatB genes (M941159, AAC49001, and Q41635), Ulmus Americana FatB (AAB71731), and thioesterases of Arabidopsis thaliana (e.g, AAF22899 and CAA85388). The numbers in parentheses are Genbank accession numbers of representative protein sequences. This list is not intended to be exhaustive, but nonetheless demonstrates that a large number of Class II acyl-ACP thioesterases have a methionine at the amino acid position corresponding to amino acid position 174 of SEQ ID NO:29, indicating that the residue is highly conserved among Class II acyl-ACP thioesterases, and strongly suggesting that its functional role is also conserved.
The invention includes plant FatB acyl-ACP thioesterase genes encoding variant thioesterases, in which the methionine residue corresponding to position 174 of SEQ ID NO:29 is mutated to an uncharged amino acid. In these embodiments, the variant thioesterases preferably have higher activity against an acyl-ACP substrate than the thioesterases encoded by the wild-type genes. The encoded FatB acyl-ACP thioesterases can be of any chain length specificity, such as, for example, C8, C10, C12, C14, C16, or C18. Included in the invention is a plant FatB acyl-ACP thioesterase gene encoding a variant thioesterase in which the methionine at position 174 in the wild-type thioesterase is mutated to leucine, phenylalanine, valine, cysteine, or isoleucine. In some embodiments, a variant plant acyl-ACP thioesterase comprises the mutation M1741, wherein the methionine at position 174 is replaced with isoleucine.
In these embodiments variant thioesterase genes having an M1741 mutation may be variants of any plant FatB (Class II) acyl-ACP thioesterase gene that encodes a methionine at the position corresponding to position 174 of SEQ ID NO:29, including but not limited to genes of any of the Class II thioesterases listed above, including variants thereof having at least 85% identity to the amino acid sequence from about position 65 to about position 355 (using the numbering of SEQ ID NO:29 as a reference) of the thioesterase amino acid sequence of Class II thioesterase genes. The thioesterase genes can have any acyl chain length specificity. Illustrative examples of such thioesterase genes include, for example, an Arabidopsis thaliana FatB thioesterase gene, a Cuphea aequipetala FatB thioesterase gene, a Cuphea calophylla FatB thioesterase gene, a Cuphea hookeriana FatB thioesterase gene, a Cuphea lanceolata FatB thioesterase gene, a Cuphea palustris FatB thioesterase gene, a Cuphea wrightii FatB thioesterase gene, a Diploknema butyracea FatB thioesterase gene, a Brassica napus or Brassica juncea FatB thioesterase gene, a Camellia oleifera FatB thioesterase gene, a Helianthus annuus FatB thioesterase gene, a Jatropha curcas FatB thioesterase gene, a Madhuca longifolia FatB gene,a Myristica fragrans FatB2, a Populus tomentosa FatB gene, a Ricinus communis FatB gene, an Umbellularia californica FatB gene, and an Umbellularia californica FatB gene. The variants having an M1741 mutation can have one or more additional amino acid substitutions with respect to the wild type genes from which they are derived, or can be N-terminally deleted or have variant carboxy termini, provided that the variants have a higher thioesterase activity than the wild-type sequence from which they are derived. The variants having an M1741 mutation in some embodiments are between 80% and 85% identical, between 85% and 90% identical, between 90 and 95% identical, between 95% and 97% identical, between 97% and 99% identical, or between 99% and 100% identical to the wild type mature acyl-ACP thioesterase sequence at the amino acid level from about the amino acid position corresponding to position 65 of SEQ ID NO:29 to about the amino acid position corresponding to position 355 of SEQ ID NO:29. A variant acyl-ACP encoded by a nucleic acid molecule of the invention in some embodiments includes an isoleucine at the amino acid position corresponding to amino acid 103 of SEQ ID NO:29 in addition to the M1741 mutation.
In other embodiments, a variant acyl-ACP thioesterase has an isoleucine at position 103 and the amino acid at position 174 is phenylalanine, cysteine, leucine, or valine.
The invention includes an isolated nucleic acid molecule that encodes a variant plant Class II acyl-ACP thioesterase having at least 80%, at least 85%, at least 90%, or at least 95% identity to the amino acid sequence from position 65 to amino acid 355 of SEQ ID NO:40, SEQ ID NO:43, or SEQ ID NO:45, in which the variant includes a M1741 mutation and has enhanced activity with respect to the plant acyl-ACP thioesterase lacking the mutation at consensus position 174. In some embodiments of the invention, an isolated nucleic acid encoding a variant acyl-ACP thioesterase having an M1741 mutation comprises a sequence encoding the amino acid sequence from position 65 to 355 of SEQ ID NO:40, SEQ ID NO:43, or SEQ ID NO:45.
Also included in the invention is an isolated nucleic acid molecule that encodes a variant plant Class II acyl-ACP thioesterase having at least 80%, at least 85%, at least 90%, or at least 95% identity to the amino acid sequence from position 34 to amino acid 355 of SEQ ID NO:40, SEQ ID NO:43, or SEQ ID NO:45, in which the variant has enhanced activity with respect to the plant acyl-ACP thioesterase lacking the mutation at consensus position 174. In some embodiments of the invention, an isolated nucleic acid encoding a variant acyl-ACP thioesterase having an M1741 mutation comprises a sequence encoding the amino acid sequence from position 34 to 355 of SEQ ID NO:40, SEQ ID NO:43, or SEQ ID NO:45. The isolated nucleic acid molecule in some embodiments comprises a sequence encoding the amino acid sequence of SEQ ID NO:40, SEQ ID NO:43, or SEQ ID NO:45. In some embodiments, the nucleic acid molecule comprises SEQ ID NO:39, SEQ ID NO:42, or SEQ ID NO:44.
A further aspect of the invention is a transgenic organism that includes an exogenous nucleic acid molecule that encodes a variant plant acyl-ACP thioesterase, in which the variant thioesterase has a mutation at the amino acid position corresponding to amino acid position 174 of SEQ ID NO:29 and exhibits increased thioesterase activity. Specifically included are transgenic organisms that include genes encoding any of the aforementioned variants having a mutation at amino acid position 174, including, for example, variants having an isoleucine, methionine, valine, leucine, cysteine, or phenylalanine at positions 174. In some embodiments, the transgenic organism has an exogenous nucleic acid molecule encoding a thioesterase having an isoleucine, valine, leucine, cysteine, or phenylalanine at position 174 and an isoleucine at position 103. In an exemplary embodiment, a transgenic organism has an exogenous gene encoding a thioesterase having an isoleucine at position 174 and an isoleucine at position 103. A transgenic organism is in various embodiments a plant, an alga, or a prokaryote.
For example, in some embodiments, the transgenic organism is a bacterium, such as, but not limited to, an Acetobacter, Acinetobacter, Arthrobacter, Bacillus, Brevibacterium, Chromatium, Chlorobium, Clostridium, Corynebacterium, Deinococcus, Delftia, Desulfovibrio, Enterococcus, Escherichia, Kineococcus, Klebsiella, Lactobacillus, Lactococcus, Micrococcus, Mycobacterium, Jeotgalicoccus, Paenibacillus, Propionibacter, Pseudomonas, Rhodopseudomonas, Rhodobacter, Rhodococcus, Rhodospirillium, Rhodomicrobium, Salmonella, Serratia, Stenotrophomonas, Streptococcus, Vibrio, or Zymomonas species.
In other embodiments, a transgenic organism harboring an acyl-ACP variant having a mutation at amino acid residue 174 is an alga, for example, a microalga such as an Achnanthes, Amphiprora, Amphora, Ankistrodesmus, Asteromonas, Boekelovia, Borodinella, Botryococcus, Bracteococcus, Chaetoceros, Carteria, Chlamydomonas, Chlorococcum, Chlorogonium, Chlorella, Chroomonas, Chrysosphaera, Cricosphaera, Crypthecodinium, Cryptomonas, Cyclotella, Dunaliella, Ellipsoidon, Emiliania, Eremosphaera, Ernodesmius, Euglena, Franceia, Fragilaria, Gloeothamnion, Haematococcus, Halocafeteria, Hymenomonas, Isochrysis, Lepocinclis, Micractinium, Monoraphidium, Nannochloris, Nannochloropsis, Navicula, Neochloris, Nephrochloris, Nephroselmis, Nitzschia, Ochromonas, Oedogonium, Oocystis, Ostreococcus, Pavlova, Parachlorella, Pascheria, Phaeodactylum, Phagus, Platymonas, Pleurochrysis, Pleurococcus, Prototheca, Pseudochlorella, Pyramimonas, Pyrobotrys, Scenedesmus, Schizochytrium, Skeletonema, Spyrogyra, Stichococcus, Tetraselmis, Thalassiosira, Viridiella, or Volvox species. In some embodiments, a transgenic organism is a cyanobacterium, such as an Agmenellum, Anabaena, Anabaenopsis, Anacystis, Aphanizomenon, Arthrospira, Asterocapsa, Borzia, Calothrix, Chamaesiphon, Chlorogloeopsis, Chroococcidiopsis, Chroococcus, Crinalium, Cyanobacterium, Cyanobium, Cyanocystis, Cyanospira, Cyanothece, Cylindrospermopsis, Cylindrospermum, Dactylococcopsis, Dermocarpella, Fischerella, Fremyella, Geitleria, Geitlerinema, Gloeobacter, Gloeocapsa, Gloeothece, Halospirulina, Iyengariella, Leptolyngbya, Limnothrix, Lyngbya, Microcoleus, Microcystis, Myxosarcina, Nodularia, Nostoc, Nostochopsis, Oscillatoria, Phormidium, Planktothrix, Pleurocapsa, Prochlorococcus, Prochloron, Prochlorothrix, Pseudanabaena, Rivularia, Schizothrix, Scytonema, Spirulina, Stanieria, Starria, Stigonema, Symploca, Synechococcus, Synechocystis, Tolypothrix, Trichodesmium, Tychonema, or Xenococcus species.
A transgenic organism transformed with a nucleic acid molecule encoding a variant acyl-ACP thioesterase having a mutation at position 174 is in some embodiments a higher plant, such as, for example, Arabidopsis thatliana, Arachis hypogaea, Avena sativa, Brassica species (e.g., Brassica napus, Brassica campestris, Brassica juncea ), Camelina sativa, Carthamus tinctorius, Cocos nucifera, Crambe abyssinica, Cuphea species, an Elaeis species (e.g., Elaeis guineensis, Elaeis oleifera ), Gossypium hirsutum, Glycine max, Helianthus annulus, a Jatropha species, Cucurbita pepo, Oryza satvia, Sesamum indicum, Simmondsia chinensis, Theobroma cacao, Ricinus communis, or Zea mays.
In yet another aspect, the invention provides a method of producing a fatty acid or a fatty acid product, in which the method includes cultivating an organism having an exogenous nucleic acid molecule that includes a sequence encoding a variant acyl-ACP thioesterase having a mutation at the amino acid position corresponding to position 174 of SEQ ID NO:29, and isolating a fatty acid or a fatty acid product from the organism or culture medium. The variant acyl-ACP thioesterase in some embodiments has an isoleucine at position 103 and an isoleucine at position 174. The transgenic host organism can be a bacterium, alga, cyanobacterium, or plant as provided herein, and the sequence encoding the plant acyl-ACP thioesterase in some embodiments is codon-optimized for expression in the host organism. In some preferred embodiments, the nucleic acid molecule encodes a variant of a naturally-occurring medium chain length acyl-ACP thioesterase having a mutation at the amino acid position corresponding to amino acid position 174 in SEQ ID NO:29, in which the variant has enhanced activity towards a C8 acyl substrate with respect to the wild type thioesterase.
The methods can be used for the production and isolation of a fatty acid product such as a triglyceride, a fatty aldehyde, a fatty alcohol, a fatty ester, or a hydrocarbon such as an alkene or alkane. In some embodiments, the fatty acid product is a fatty acid. In exemplary embodiments, the fatty acid product is a C8 fatty acid.
In some preferred embodiments expression of a variant acyl-ACP thioesterase gene as provided herein in a transgenic organism results in an increased percentage of a specific chain length fatty acid product being recovered from the organism and/or culture medium. In some embodiments, at least 5%, at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, or at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the isolated fatty acid products from an organism and/or medium from culturing of an organism having an exogenous nucleic acid molecule encoding a variant acyl-ACP thioesterase of the invention are fatty acid products of a specific chain length. For example, in some embodiments, at least 5%, at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, or at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the isolated fatty acid products from an organism expressing an exogenous variant acyl-ACP thioesterase of the invention are C8 fatty acid products. In some preferred embodiments, the fatty acid product is a C8 fatty acid, and at least 5%, at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, or at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the fatty acids isolated from the organism and/or the growth medium is a C8 fatty acid, such as octanoic acid.
In some illustrative embodiments, the transgenic organism is a prokaryote, such as a bacterium or a cyanobacterium, and the method includes isolating fatty acid products from the culture medium, in which at least 5%, at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, or at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the fatty acid products isolated from the organism or the growth medium are fatty acid products of a specific chain length. For example, in some embodiments, at least 5%, at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, or at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the fatty acid products isolated from the culture medium of a prokaryotic organism transformed with a variant acyl-ACP thioesterase of the invention are C8 fatty acid products. In an illustrative embodiment, at least 5%, at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, or at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the fatty acid products isolated from the culture medium of a prokaryotic organism transformed with a variant acyl-ACP thioesterase of the invention are C8 fatty acid products, such as octanoic acid.
Nucleic acid molecules encoding variant acyl-ACP thioesterases mutated at position 174 that can be expressed in a transgenic host organism can be any disclosed herein. For example, in some embodiments, the variant has a mutation that changes the amino acid at position 174 to an uncharged amino acid. In some embodiments, the amino acid position corresponding to amino acid position 174 of SEQ ID NO:29 is mutated from methionine to any of phenylalanine, cysteine, leucine, valine, or isoleucine. In some embodiments, the variant thioesterase has an isoleucine at position 103, and the amino acid at position 174 is phenylalanine, cysteine, valine, leucine, or isoleucine. In some embodiments, the amino acid position corresponding to amino acid position 103 of SEQ ID NO:29 is isoleucine and the amino acid corresponding to amino acid position 174 of SEQ ID NO:29 is isoleucine. The thioesterase from which the variant sequence is derived can be any plant acyl-ACP thioesterase, such as a plant Class II acyl-ACP thioesterase. In some embodiments, the thioesterase encoded by the exogenous nucleic acid molecule comprises an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 97%, at least 98%, or at least 99% identity to amino acids 65 to 355 of SEQ ID NO:40, SEQ ID NO:43, or SEQ ID NO:45. In some embodiments, the thioesterase encoded by the exogenous nucleic acid molecule comprises amino acids 65 to 355 of SEQ ID NO:40, SEQ ID NO:43, or SEQ ID NO:45. In some embodiments, the thioesterase encoded by the exogenous nucleic acid molecule comprises amino acids 34 to 355 of SEQ ID NO:40, SEQ ID NO:43, or SEQ ID NO:45.
Additional Genes Encoding Enzymes for Synthesizing Fatty Acid Products
Also included in the invention are transgenic host organisms and methods of using transgenic host organisms that include an exogenous acyl-ACP thioesterase as disclosed herein, and further include one or more exogenous genes encoding enzymes that participate in the synthesis of fatty aldehydes, fatty alcohols, fatty esters, or hydrocarbons (e.g., alkanes, alkenes) such as, for example, an acetyl CoA carboxylase, an acyl-CoA synthetase, a ketoacyl-CoA synthase, a fatty acyl-CoA/aldehyde reductase, a fatty acid elongase, a fatty acyl-CoA reductase, a fatty aldehyde reductase, an alcohol acetyl transferase, an acyl-CoA alcohol transacylase, an acyltransferase, a wax synthase, a fatty aldehyde decarbonylase, or a fatty acid decarboxylase.
In some embodiments, genes encoding a fatty acyl-ACP thioesterase and one or more genes encoding other hydrocarbon modification enzymes are transformed into a host organism, and the organism is used for the production of a fatty aldehyde, a fatty alcohol, a fatty ester (including a wax-ester), or a hydrocarbon.
Genes encoding fatty acyl-CoA/aldehyde reductases that can be used include, without limitation, those having Genbank accession numbers AAC45217, YP — 047869, BAB85476, YP — 001086217, YP — 580344, YP — 001280274, YP — 264583, YP — 436109, YP — 959769, ZP — 01736962, ZP — 01900335, ZP — 01892096, ZP — 01103974, ZP — 01915077, YP — 924106, YP — 130411, ZP — 01222731, YP — 550815, YP — 983712, YP — 001019688, YP — 524762, YP — 856798, ZP — 01115500, YP — 001141848, NP — 336047, NP — 216059, YP — 882409, YP — 706156, YP — 001136150, YP — 952365, ZP — 01221833, YP — 130076, NP — 567936, AAR88762, ABK28586, NP — 197634, CAD30694, NP — 001063962, BAD46254, NP — 001030809, EAZ10132, EAZ43639, EAZ07989, NP — 001062488, CAB88537, NP — 001052541, CAH66597, CAE02214, CAH66590, CAB88538, EAZ39844, AAZ06658, CAA68190, CAA52019, and BAC84377. Also included are genes encoding variants of these and other naturally-occurring fatty acyl-CoA/aldehyde reductases having at least 65% identity to the referenced or naturally occurring proteins, in which the activity of the enzyme is not substantially reduced with respect to the wild-type or above referenced enzyme.
Genes encoding fatty acyl-CoA reductases can include genes that encode, without limitation, the fatty acyl-CoA reductases having GenBank accession numbers NP — 187805, ABO14927, NP — 001049083, CAN83375, NP — 191229, EAZ42242, EAZ06453, CAD30696, BAD31814, NP — 190040, AAD38039, CAD30692, CAN81280, NP — 197642, NP — 190041, AAL15288, and NP — 190042. Also included are genes encoding variants of these and other naturally-occurring fatty acyl-CoA reductases having at least 65% identity to the referenced or naturally occurring proteins, in which the activity of the enzyme is not substantially reduced with respect to the wild-type or above referenced enzyme.
Genes encoding fatty aldehyde decarbonylases that can be transformed into an organism harboring an exogenous gene that encodes a plant acyl-ACP thioesterase as disclosed herein include genes that encode the fatty aldehyde decarbonylases listed by GenBank accession numbers. NP — 850932, ABN07985, CAN60676, AAC23640, CAA65199, AAC24373, CAE03390, ABD28319, NP — 181306, EAZ31322, CAN63491, EAY94825, EAY86731, CAL55686, XP — 001420263, EAZ23849, NP — 200588, NP — 001063227, CAN83072, AAR90847, and AAR97643. Also included are genes encoding variants of these and other naturally-occurring fatty aldehyde decarbonylases having at least 65% identity to the referenced or naturally occurring proteins, in which the activity of the enzyme is not substantially reduced with respect to the wild-type or above referenced enzyme.
In particular embodiments, organisms of the present invention are genetically engineered to express a fatty acyl-ACP thioesterase as provided herein, and one or more of an acyl-CoA synthetase, a fatty acyl-CoA/aldehyde reductase, a fatty acyl-CoA reductase, a fatty aldehyde reductase, a fatty aldehyde decarbonylase, or a fatty acid decarboxylase. Suitable expression methods are described below with respect to the thioesterase gene, including, among other methods, inducible expression and tissue-specific expression.
The enzymes described directly above may have a specificity for acting on a substrate having an acyl chain of a specific length. In some embodiments the transgenic host used for producing a fatty acid product contains an acyl-ACP thioesterase as described herein, and one or more exogenous genes that encode enzymes with specificity for substrates of the same acyl chain length. The enzymatic specificity can, in various embodiments, be for a substrate having from 8 to 34 carbon atoms, preferably from 8 to 18 carbon atoms. For example, the nucleic acid molecules introduced into a transgenic host can encode enzymes that have specificity for substrates having 8, 10, 12, 14, 16, or 18 carbon atoms in the acyl chain.
Also included in the invention are embodiments in which a transgenic organism expresses, in addition to a heterologous acyl-ACP thioesterase, a ketoacyl synthase (KAS). In some embodiments, the gene that encodes a β-ketoacyl synthase (KAS) that preferentially produces acyl-ACPs having medium chain lengths. Such KAS enzymes have been described from several plants, including various species of Cuphea (Dehesh et al., 1998; Slabaugh et al., 1998), and would serve to increase the availability of acyl-ACP molecules of the proper length for recognition and cleavage by the heterologous acyl-ACP thioesterase.
Additional embodiments of this invention include transgenic hosts expressing an exogenous plant acyl-ACP thioesterase as provided herein, and optionally one or more additional genes encoding enzymes that function in the synthesis of fatty acid products, in which one or more host genes that encode beta-oxidation pathway enzymes have been inactivated or downregulated. Inactivation of a beta-oxidation enzyme can prevent the degradation of fatty acids released from acyl-ACPs, thus enhancing the yield of accumulated or secreted fatty acids. For example, in cases where the desired products are medium chain fatty acids, the inactivation or downregulation of genes that encode medium chain-specific acyl-CoA synthetase and/or medium chain-specific acyl-CoA oxidase enzymes would be beneficial. Mutations in the genes encoding medium chain-specific acyl-CoA synthetase and/or medium chain-specific acyl-CoA oxidase enzymes such that the activity of the enzymes is diminished would also be effective in increasing the yield of accumulated or secreted fatty acids. Mutations in the genes can be introduced either by recombinant or non-recombinant methods.
Transformation of Host Organisms
Plants for use in the methods of the invention can be transformed by any feasible means, including, without limitation, the use of Agrobacterium, particle gun-mediated transformation, laser-mediated transformation, or electroporation. Algae and photosynthetic bacteria can be transformed by any suitable methods, including, as nonlimiting examples, natural DNA uptake (Chung et al. (1998) FEMS Microbiol. Lett. 164: 353-361; Frigaard et al. (2004) Methods Mol. Biol. 274: 325-40; Zang et al. (2007) J. Microbiol. 45: 241-245), conjugation, transduction, glass bead transformation (Kindle et al. (1989) J. Cell Biol. 109: 2589-601; Feng et al. (2009) Mol. Biol. Rep. 36: 1433-9; U.S. Pat. No. 5,661,017), silicon carbide whisker transformation (Dunahay et al. (1997) Methods Mol. Biol. (1997) 62: 503-9), biolistics (Dawson et al. (1997) Curr. Microbiol. 35: 356-62; Hallmann et al. (1997) Proc. Natl. Acad. USA 94: 7469-7474; Jakobiak et al. (2004) Protist 155:381-93; Tan et al. (2005) J. Microbiol. 43: 361-365; Steinbrenner et al. (2006) Appl Environ. Microbiol. 72: 7477-7484; Kroth (2007) Methods Mol. Biol. 390: 257-267; U.S. Pat. No. 5,661,017) electroporation (Kjaerulff et al. (1994) Photosynth. Res. 41: 277-283; Iwai et al. (2004) Plant Cell Physiol. 45: 171-5; Ravindran et al. (2006) J. Microbiol. Methods 66: 174-6; Sun et al. (2006) Gene 377: 140-149; Wang et al. (2007) Appl. Microbiol. Biotechnol. 76: 651-657; Chaurasia et al. (2008) J. Microbiol. Methods 73: 133-141; Ludwig et al. (2008) Appl. Microbiol. Biotechnol. 78: 729-35), laser-mediated transformation, or incubation with DNA in the presence of or after pre-treatment with any of poly(amidoamine) dendrimers (Pasupathy et al. (2008) Biotechnol. J. 3: 1078-82), polyethylene glycol (Ohnuma et al. (2008) Plant Cell Physiol. 49: 117-120), cationic lipids (Muradawa et al. (2008) J. Biosci. Bioeng. 105: 77-80), dextran, calcium phosphate, or calcium chloride (Mendez-Alvarez et al. (1994) J. Bacteriol. 176: 7395-7397), optionally after treatment of the cells with cell wall-degrading enzymes (Perrone et al. (1998) Mol. Biol. Cell 9: 3351-3365). Agrobacterium -mediated transformation can also be performed on algal cells, for example after removing or wounding the algal cell wall (e.g., WO 2000/62601; Kumar et al. (2004) Plant Sci. 166: 731-738). Biolistic methods are particularly successful for transformation of the chloroplasts of plant and eukaryotic algal species (see, for example, Ramesh et al. (2004) Methods Mol. Biol. 274: 355-307; Doestch et al. (2001) Curr. Genet. 39: 49-60; U.S. Pat. No. 7,294,506; WO 2003/091413; WO 2005/005643; and WO 2007/133558, all incorporated herein by reference in their entireties).
In some preferred embodiments of the invention, an acyl-ACP thioesterase gene (such as a gene as disclosed herein), is cloned into an expression vector for transformation into a plant, alga, or photosynthetic or nonphotosynthetic bacterium. The vector includes sequences that promote expression of the transgene of interest, e.g., an exogenous acyl-ACP thioesterase gene, such as a promoter, and may optionally include a transit peptide-encoding sequence for directing the expressed thioesterase to the chloroplast of transformed eukaryotic cells, an intron sequence, a sequence having a polyadenylation signal, etc. Alternatively, if the vector does not contain a promoter in operable linkage with the gene of interest, the gene can be transformed into the cells such that it becomes operably linked to an endogenous promoter by homologous recombination or vector integration.
In some embodiments, a vector is designed for integration of the acyl-ACP thioesterase gene into the host genome. For example, vectors used for higher plant transformation include but are not limited to Agrobacterium -based vectors that are designed for integrating transgenes (exogenous genes transformed into the host plant) into the genome of the plant. In other embodiments, vectors can be: 1) targeted for integration into a plant or algal chromosome by including flanking sequences that enable homologous recombination into the chromosome, 2) targeted for integration into endogenous host plasmids by including flanking sequences that enable homologous recombination into the endogenous plasmids, or 3) designed such that the expression vectors replicate within the chosen host.
Artificial chromosome vectors can also be used for the transformation of higher plants, for example, vector constructs that include a centromere sequence and an origin of replication so that the vector and its integrated sequences can be maintained in the plant (see, for example, U.S. Pat. No. 7,456,013 incorporated by reference herein in its entirety). Artificial chromosomes can accommodate more transgenes than can other types of vectors such as, for example, Agrobacterium -based vectors, and therefore can be used in higher plant or algal systems when more than one gene that encodes an enzyme that participates in the synthesis of a fatty acid product is transformed into an organism.
In some cases in which it may be advantageous to transform the chloroplast of a higher plant or alga, vectors can be designed to have regions of sequences flanking the transgene (e.g., the acyl-ACP thioesterase gene or another gene for synthesis of a fatty acid product) that are homologous to chloroplast sequences to promote homologous recombination and integration of the sequence of interest. In these embodiments, the vector preferably includes a promoter for expressing the transgene, in which the promoter functions in the chloroplast.
Vectors that include gene regulatory sequences for transformation of higher plants are well known in the art. Seed specific or inducible promoters can optionally be used in the vectors and constructs transformed into higher plants engineered for synthesis of fatty acid products (for example, U.S. Pat. No. 5,421,034; U.S. Pat. No. 5,608,152; U.S. Pat. No. 6,642,437).
Vectors designed for expression of a gene in microalgae can in some embodiments include a promoter active in microalgae operably linked to the exogenous gene being introduced. A variety of gene promoters and terminators that function in green algae can be utilized in expression vectors, including, but not limited to promoters and terminators from Chlamydomonas and other algae (see, for example, Plant Cell Physiol 49: 625-632 (2008)), promoters and terminators from viruses, and synthetic promoters and terminators.
For transformation of diatoms, a variety of gene promoters that function in diatoms can be utilized in these expression vectors, including, but not limited to: 1) promoters from Thalassiosira and other heterokont algae, promoters from viruses, and synthetic promoters. Promoters from Thalassiosira pseudonana that would be suitable for use in expression vectors include an alpha-tubulin promoter, a beta-tubulin promoter, and an actin promoter. Promoters from Phaeodactylum tricornutum that would be suitable for use in expression vectors include an alpha-tubulin promoter, a beta-tubulin promoter, and an actin promoter. The terminators associated with these genes, other diatom genes, or particular heterologous genes can be used to stop transcription and provide the appropriate signal for polyadenylation.
In some instances it can be advantageous to express a heterologous enzyme, such as but not limited to a thioesterase, at a certain point during the growth of the transgenic host to minimize any deleterious effects on the growth of the transgenic organism and/or to maximize production of the fatty acid product of interest. In these instances one or more exogenous genes introduced into the transgenic organism can be operably linked to an inducible promoter. The promoter can be a lac promoter, a tet promoter (e.g., U.S. Pat. No. 5,851,796), a hybrid promoter that includes either or both of portions of a tet or lac promoter, a hormone-responsive promoter (e.g., an ecdysone-responsive promoter, e.g., U.S. Pat. No. 6,379,945) a metallothionien promoter (U.S. Pat. No. 6,410,828), or a pathogenesis-related (PR) promoter that can be responsive to a chemical such as, for example, salicylic acid, ethylene, thiamine, or BTH (U.S. Pat. No. 5,689,044). An inducible promoter can also be responsive to light or dark (U.S. Pat. No. 5,750,385, U.S. Pat. No. 5,639,952) or temperature (U.S. Pat. No. 5,447,858; Abe et al., Plant Cell Physiol. 49: 625-632 (2008); Shroda et al. Plant J. 21: 121-131 (2000)). The foregoing list is exemplary and not limiting. The promoter sequences can be from any organism, provided that they are functional in the host organism. Inducible promoters as used in the constructs of the present invention can use one or more portions or one or more domains of the aforementioned promoters or other inducible promoters fused to at least a portion of a different promoter that operates in the host organism to confer inducibility on a promoter that operates in the host species.
A variety of gene promoters that function in cyanobacteria can be utilized in expression vectors, including, but not limited to: 1) the lac, tac, and trc promoters that are inducible by the addition of isopropyl β-D-1-thiogalactopyranoside (IPTG), 2) promoters that are naturally associated with transposon- or bacterial chromosome-borne antibiotic resistance genes (neomycin phosphotransferase, chloramphenicol acetyltrasferase, spectinomycin adenyltransferase, etc.), 3) promoters of various heterologous bacterial and native cyanobacterial genes, 4) promoters from viruses and phages, and 5) synthetic promoters. Promoters isolated from cyanobacteria that have been used successfully include the following:
secA (secretion; controlled by the redox state of the cell) rbc (Rubisco operon) psaAB—(PS I reaction center proteins; light regulated) psbA—(D1 protein of PSII; light-inducible)
Likewise, a wide variety of transcriptional terminators can be used for expression vector construction. Examples of possible terminators include, but are not limited to, psbA, psaAB, rbc, secA, and T7 coat protein.
Transformation vectors preferably also include a selectable marker, such as but not limited to a drug resistance gene, an herbicide resistance gene, a metabolic enzyme or factor required for survival of the host (for example, an auxotrophic marker), etc. Transformed cells can be optionally selected based upon the ability to grow in the presence of the antibiotic or other selectable marker under conditions in which cells lacking the resistance cassette or auxotrophic marker would not grow. In some embodiments a non-selectable marker may be present on a vector, such as a gene encoding a fluorescent protein or enzyme that generates a detectable reaction product. In an alternative transformation strategy, selectable or non-selectable markers can be provided on a separate construct, where both the gene-of-interest construct and the selectable marker construct are used together in transformation protocols, and selected transformants are analyzed for co-transformation of the construct that includes the gene-of-interest (see, for example, Kindle (1990) Proc. Natl. Acad. Sci. USA 87: 1228-32; Jakobiak et al. (2004) Protist 155:381-93).
Growth of Transformed Organisms
Plants can be grown on or in culture media or in soil, and can be grown in a greenhouse or growth chamber, or outdoors. Algae and photosynthetic bacteria can be cultured phototrophically, in the absence of a fixed carbon source, or mixotrophically, where the cultures are supplied with light for at least part of the day, and also supplied with a reduced carbon source, such as a (e.g., glucose, fructose, galactose, mannose, rhamnose, arabinose, xylose, lactose, sucrose, maltose), an organic acid (e.g., actetate, citrate, succinate), or glycerol. The photosynthetic organism in some embodiments is cultured mixotrophically, in which the organism is grown in the presence of light for at least a part of the day, and also provided with one or more sources of reduced carbon. A photosynthetic organism can be grown mixotrophically for a period of time, followed by a period of phototrophic growth, or vice versa.
Media for phototrophic or mixotrophic growth of algae are well known, and media can be optimized to enhance growth or production of fatty acid products for a particular species. Artificial light sources can be used as the sole light source or to enhance or extend natural light.
In some embodiments, a transgenic organism contains an exogenous gene for an acyl-ACP thioesterase as described herein (and, optionally one or more additional exogenous genes) that is under the control of an inducible promoter, as described above, and the transgenic organism is grown or cultured for a period of time while the transgene(s) is/are not induced. At a point during the growth period, which can be empirically determined based on production levels of the fatty acid product, the gene can be induced, for example, by a period of dark or light, raising or lowering of the temperature, or addition of one or more nutrients or chemicals to the culture medium. The transgenic organism can be maintained under inducing conditions for any feasible amount of time for production of protein(s) encoded by the transgene(s).
Growth of algae can be in open areas, such as, for example, ponds, canals, channels, raceways, or tanks, or can be in bioreactors. Bioreactors are preferred for mixotrophic growth, and can also be used for phototrophic growth. The bioreactors can be of any sizes and form, and can include inlets for providing nutrients, additives, or gases, such as but not limited to air or CO 2 . A bioreactor preferably also has an outlet for sampling of the culture. A bioreactor can be configured such that the algal culture is mixed during the growth period, for example, by stirring, rocking, shaking, inverting, bubbling of gases through the culture, etc. Outdoor ponds, raceways, tanks, canals, etc. can also be designed for mixing of cultures through, for example, paddles, pumps, hoses or jets for circulation of the culture media, or tubes, hoses or inlets for supplying air or CO 2 to the culture.
Production of Fatty Acid Products
Where cultures of algae or photosynthetic bacteria are employed in the methods, the fatty acid products can be isolated from the culture medium, from the cells, or from whole culture (culture medium plus cells). In some embodiments the fatty acid products include a C8 fatty acid product, such as octanoic acid, triglycerides that include octanoic acid, or a fatty aldehyde, fatty alcohol, fatty ester, or hydrocarbon derived from octanoic acid. In some embodiments the fatty acid products include a C10 fatty acid product, such as decanoic acid, triglycerides that include decanoic acid, or a fatty aldehyde, fatty alcohol, fatty ester, or hydrocarbon derived from decanoic acid.
In embodiments in which a fatty acid product such as a triglyceride, a fatty aldehyde, a fatty alcohol, a fatty ester, or a hydrocarbon are produced by the transgenic organism, the transgenic organism optionally includes an additional exogenous gene, in which the additional transgene encodes another enzyme that functions in the synthesis of a fatty acid product. In embodiments in which the fatty acid product is a fatty aldehyde, for example, a C8 fatty aldehyde or a C10 fatty aldehyde, the transgenic host organism can further comprise an exogenous nucleic acid molecule that encodes an acyl-CoA reductase. Where the isolated fatty acid product is a fatty alcohol, the transgenic photosynthetic organism in some embodiments comprises, in addition to the transgene that encodes a C8-preferring or a C10-preferring acyl-ACP thioesterase, an exogenous nucleic acid molecule encoding an acyl-CoA reductase. In embodiments in which the fatty acid product is a fatty ester, such as a wax ester, the transgenic organism used for production of the wax ester can include a fatty acyl-CoA reductase and an exogenous nucleic acid molecule encoding a wax ester synthase (which may or may not also have diacylglycerol acyltransferase activity). Nucleic acid molecules encoding additional enzymes for the synthesis of fatty acid products can be provided in expression constructs. The genes can be codon-optimized for expression in the host.
In embodiments in which a fatty acid is isolated or separated from the cells and/or culture medium, the isolated or separated fatty acid can be converted to one or more of a fatty aldehyde, fatty alcohol, fatty ester, or hydrocarbon through chemical or enzymatic methods.
In some preferred embodiments, the method includes culturing a photosynthetic organism transformed with a nucleic acid molecule encoding a Class II acyl-ACP thioesterase, and isolating one or more fatty acid products of specific chain length(s) from the culture. In preferred embodiments, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, at least 45%, or at least 50% of the fatty acid product isolated from the culture is a fatty acid product of a specific chain length. In some preferred embodiments, between 50% and 55%, between 55% and 60%, between 60% and 65%, between 65% and 70%, between 70% and 75%, between 75% and 80%, between 80 and 85%, between 85% and 90%, between 90% and 95%, between 95% and 97%, between 97% and 99%, or between 99% and 100% of the fatty acid product isolated from the culture is one or more fatty acids of specific chain length(s). In some embodiments of these methods, a prokaryotic photosynthetic organism transformed with a nucleic acid molecule encoding an acyl-ACP thioesterase is grown in culture, and one or more fatty acids is isolated from the culture media, where at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, between 80% and 85%, between 85% and 90%, between 90% and 95%, between 95% and 97%, between 97% and 99%, or between 99% and 100% of the fatty acids isolated from the culture are fatty acids of specific chain lengths.
Isolation of Fatty Acid Products
Fatty acids and fatty acid products can be extracted from the seeds, fruit, or nuts of higher plants by grinding, crushing, or pressing the seeds, fruit or nuts. In some preferred embodiments, the seeds, nuts, or fruit are heated prior to or during the extraction process to soften plant tissues and improve solubility of the fatty acid product. Algae that produce fatty acid products can also be subject to extraction procedures in which the cells are ground, sonicated, or otherwise disrupted and pressed to separate the oil and other liquids from solid cell or tissue components. Fatty acids can be extracted with an organic solvent, for example, triglycerides and fatty acids can be extracted with hexane.
Extracellular hydrocarbons can also be extracted from living microalgae cells which are then returned to a bioreactor by exposure of the cells, in an otherwise sterile environment, to a non-toxic extraction solvent, followed by separation of the living cells and the hydrophobic fraction of extraction solvent and hydrocarbons, in which the separated living cells are then returned to a culture container such as a stainless steel fermentor or photobioreactor (see Biotechnol Bioeng. 2004 Dec. 5; 88(5):593-600 and Biotechnol Bioeng. 2004 Mar. 5; 85(5):475-81).
Fatty acid products (e.g., lipids, fatty acids, aldehydes, alcohols, alkenes, and alkanes) produced by cells of the invention can be harvested, or otherwise collected, by any convenient means. For example, hydrocarbons secreted from cells can be centrifuged to separate the hydrocarbons in a hydrophobic layer from contaminants in an aqueous layer and optionally from any solid materials as a precipitate in after centrifugation. Material containing cell or cell fractions can be treated with proteases to degrade contaminating proteins before or after centrifugation. In some instances the contaminating proteins are associated, possibly covalently, to hydrocarbons or hydrocarbon precursors which form hydrocarbons upon removal of the protein. In other instances the hydrocarbon molecules are in a preparation that also contains proteins. Proteases can be added to hydrocarbon preparations containing proteins to degrade proteins (for example, the protease from Streptomyces griseus can be used (SigmaAldrich catalog number P5147). After digestion, the hydrocarbons are preferably purified from residual proteins, peptide fragments, and amino acids. This purification can be accomplished, for example, by methods listed above such as centrifugation and filtration.
In some embodiments, fatty acid products are isolated from algal cells or whole culture that includes cells by generating a cell lysate. The cells are first disrupted, for example, by heat, treatment with an acid or base, treatment with enzymes, osmotic shock, mechanical disruption, sonication, freeze-thaw, etc., and then intracellular and cell membrane/cell wall-associated fatty acids can be collected from the lysed cells.
The fatty acid products can be extracted with a hydrophobic solvent such as hexane (see Frenz et al. 1989, Enzyme Microb. Technol., 11:717) or by liquefaction (see for example Sawayama et al. 1999, Biomass and Bioenergy 17:33-39 and Inoue et al. 1993, Biomass Bioenergy 6(4):269-274); oil liquefaction (see for example Minowa et al. 1995, Fuel 74(12):1735-1738); or supercritical CO 2 extraction (see for example Mendes et al. 2003, Inorganica Chimica Acta 356:328-334). Cells can also be freeze dried and pulverized followed by extraction with n-hexane (Miao and Wu, Biosource Technology (2006) 97:841-846).
In embodiments in which algae or microorganisms secrete fatty acid products, the cells can be removed from the culture medium, for example, by centrifugation, sedimentation, flocculation, or filtering, and the culture medium can be extracted with a solvent such as hexane.
Capture and recovery of fatty acids or fatty acid products that are secreted into the culture medium by recombinant bacteria and algae, such as cyanobacteria, as described above, can also be performed by adsorbing the fatty acids secreted into the culture medium to small, easily harvested objects. In this method, small objects that are able to bind free fatty acids and other lipids, referred to for purposes of this specification as “fat adsorbing objects,” are circulated in the culture medium for an appropriate amount of time and then collected by physical separation. The fatty acids are then eluted from the fat adsorbing objects by the use of an appropriate non-polar solvent. Evaporation of the solvent, followed by further processing of the isolated fatty acids and lipids can then be carried out to yield chemicals and fuels that can be used for a variety of commercial purposes.
The fat adsorbing objects (for example, spheres ranging from 1 mm to 30 mm) can be manufactured from various materials including, but not limited to, polymers including, for example, polyethylene and derivatives, polystyrene and derivatives, polyamide and derivatives, polyester and derivatives, polyurethane and derivatives, polyacrylates and derivatives, silicone and derivatives, and polysaccharide and derivatives. Certain glass and ceramic materials can also be used as the solid support component of the fat adsorbing objects. The surfaces of the fat adsorbing objects are modified so that they are able to bind fatty acids and lipids. An example of such modification is the introduction of ether-linked alkyl groups having various chain lengths, preferably 10-30 carbons. In another example, acyl chains of various lengths can be attached to the surface of the fat adsorbing objects via ester, thioester, or amide linkages.
In another embodiment of this invention, the fat adsorbing objects are coated with inorganic compounds known to bind fatty acids and lipids. Examples of such compounds include but are not limited to aluminum hydroxide, graphite, anthracite, and silica.
To capture secreted fatty acids from the culture medium used to cultivate the photosynthetic microorganisms, the fat adsorbing objects are circulated in the culture medium for an appropriate period of time, and then removed from the culture by the use of filters or screens or other physical separation devices. Alternatively, the fat absorbing objects can be provided in a column or tube through which the algal culture can be passed.
The fatty acids bound to the fat adsorbing objects are then eluted by the use of an appropriate non-polar solvent such as hexane, after which the fat adsorbing objects can be dried and returned to the culture medium so that more fatty acids can be bound and removed. The hexane containing the dissolved fatty acids is then evaporated, leaving the fatty acids in a purified state for further conversion to chemicals and fuels. The fat adsorbing objects can be designed to be neutrally buoyant or positively buoyant to enhance circulation in the culture medium. It is anticipated that a continuous cycle of fatty acid removal and recovery using the fat adsorbing objects can be implemented by utilizing the steps outlined above.
The following examples are offered to illustrate but not to limit the invention.
EXAMPLE 1
Isolation of a Gene that Encodes a Novel Acyl-ACP Thioesterase (Ca1FatB2) from Cuphea Aequipetala
To isolate a gene encoding a medium chain acyl-ACP thioesterase, seeds of Cuphea aequipetala (Accession No. PI561477) were obtained from the USDA National Plant Germplasm System through the North Central Regional Plant Introduction Station in Ames, Iowa. Genomic DNA was isolated from the seeds as follows: 50 seeds were transferred to a microfuge tube and incubated for one hour at 50-55° C. in 0.35 mL of Extraction Buffer (200 mM Tris-HCl pH 8.0, 200 mM NaCl, 25 mM EDTA, 0.5% SDS, and 20 mg/mL proteinase K). The hydrated and lysed seeds were then ground using a plastic pestle. 0.35 mL of CTAB solution (2% w/v CTAB, 100 mM Tris-HCl, pH 8.0, 20 mM EDTA, 1.4 M NaCl, 1% PVP) was added and incubated at room temperature for one hour. The mixture was then centrifuged at 14000×g for 5 minutes and the supernatant solution was transferred to a Phase Lock Gel tube (5 Prime, Inc.). DNA was extracted with one volume of phenol:chloroform (1:1) and the aqueous phase was transferred to a new tube; this step was repeated twice. DNA was precipitated in 1/10 volume of 3 M sodium acetate, pH 5.5, and 0.8 volumes of isopropanol. The pellet was rinsed with 70% ethanol and the genomic DNA was resuspended in water.
A nested polymerase chain reaction (PCR) approach was used to amplify a large portion of the Ca1FatB2 gene using degenerate oligonucleotide primers. The primary PCR was performed with primers ‘fatB degen1 2F’ (SEQ ID NO:1) and ‘fatB degen6 1R’ (SEQ ID NO:2). The secondary PCR was performed with primers ‘fatB degen7 1F’ (SEQ ID NO:3) and ‘fatB degen8 1R’ (SEQ ID NO:4) that were nested inside the ‘fatB degen1 2F’ and ‘fatB degen6 1R’ primer sequences. A mixture of Phusion DNA polymerase (New England Biolabs, Ipswich, Mass.) plus RedTaq DNA polymerase (Sigma, St. Louis, Mo.) was used for both PCR reactions under the following thermocycler conditions: 94° C. for 5 min; 40 cycles of (94° C. for 30 s; 55° C. for 30 s; 72° C. for 4 min); 72° C. for 5 min. After electrophoresis through 1% agarose gels, 1.7- to 3-kbp amplicons from the secondary PCR were excised and purified using the ZYMOCLEAN™ Gel DNA Recovery Kit (Zymo Research, Orange, Calif.). The isolated DNA was subsequently incubated for 15 min at 72° C. with Taq DNA polymerase and dNTPs, followed by insertion into the pCR4-TOPO vector (Invitrogen, Carlsbad, Calif.), which was used to transform chemically competent E. coli TOP10 cells (Invitrogen). Transformants were colony-screened using the primers ‘fatB degen7 1F’ (SEQ ID NO:3) and ‘fatB seq2 R’ (SEQ ID NO:5) to confirm the presence of the Ca1FatB2 gene. Positive clones were then sequenced.
The sequence of the isolated Cuphea aequipetala FatB2 genomic fragment is provided as SEQ ID NO:6. The first 22 and last 21 nucleotides of SEQ ID NO:6 correspond to the amplification primer sequences that were based on homology to other acyl-ACP thioesterases. Intron locations were predicted by comparison of the translated sequences from all three reading frames with known FatB protein sequences along with examination for consensus intron/exon boundaries, allowing the coding regions of the gene and deduced amino acid sequence of the encoded protein to be determined. The sequence was found to be highly homologous at the amino acid level to FatB genes of other Cuphea species, and the corresponding gene was designated “Ca1FatB2”. The cloned region lacked sequences encoding the complete chloroplast transit peptide and the carboxy terminus since the primers used to isolate the sequence annealed to sequences within the coding region.
EXAMPLE 2
Expression of a Synthetic Ca1FatB2 Gene in E. Coli
A synthetic acyl-ACP thioesterase gene based on the coding sequences of the isolated Ca1FatB2 genomic clone was constructed for expression studies. The nucleotide sequence of this synthetic version of the Ca1FatB2 gene is indicated as SEQ ID NO:7, and the amino acid sequence derived from this synthetic gene is indicated as SEQ ID NO:8. The plasmid containing the synthetic gene is referred to as pJ201:24592.
The synthetic gene was truncated at the 5′ end to eliminate sequences encoding the putative chloroplast transit peptide. Although the site of processing of plant acyl-ACP thioestease precursors is not known with certainty, it is believed that the truncation of the synthetic gene excludes all or most of the plastid transit peptide-encoding region at the amino-terminus of the Ca1FatB2 thioesterase. Furthermore, as the gene sequence obtained by PCR lacked a carboxy-terminus-encoding region, a consensus carboxy-terminus sequence was designed based on published acyl-ACP thioesterase sequences in order to complete the 3′ region of the gene (amino acid positions 356-362 of SEQ ID NO:8). The gene was synthesized using the codon usage preference of Synechocystis for functional testing of the gene product via expression in E. coli and Synechocystis 6803 (kazusa.or.jp/codon/cgi-bin/showcodon.cgi?species=1148).
In order to produce an expression vector, the synthetic Ca1FatB2 gene was amplified from pJ201:24592 using primers ‘fatB GLA162 SYopt NT F’ (SEQ ID NO:9) and ‘fatB GLA162 SYopt R’ (SEQ ID NO:10), and the IN-FUSION™ Dry-Down PCR Cloning Kit (Clontech, Mountain View, Calif.) was used to insert the gene into pTrcHisB (Invitrogen, Carlsbad, Calif.) having the TrcE promoter, which was then introduced into TOP10 E. coli cells to create plasmid GLA256 in strain PE-0284. Plasmid GLA256 was then transformed into the E. coli strain K27, which has a mutation in the fadD (acyl-CoA synthetase) gene (Overath et al., Eur. J. Biochem. 7:559-574), to create strain PE-0285. During the cloning process, an inadvertent elongation of the 3′ consensus sequence by 15 nucleotides occurred, such that the last 2 amino acids (IS, i.e., isoleucine and serine) were replaced by KLGCFGG (SEQ ID NO: 11). The substrate preference and protein function of this thioesterase having a variant C-terminus (SEQ ID NO:12) were not significantly altered by this change in the carboxy-terminus when compared to the native sequence (the activity of the native sequence is shown as “Variant I” in Table 2 of Example 4). The Synechocystis codon-optimized nucleic acid sequence encoding this carboxy terminus variant is provided as SEQ ID NO:13.
Transformed E. coli K27 cells were inoculated into 4 mL of LB medium at OD 600 =0.2 and induced with 0.5 mM IPTG during log phase; E. coli Top10 strains did not require induction. The cells were cultured in 15 mL Falcon round-bottom tubes for 24 hours and assayed for free fatty acid (FFA) production and secretion into the medium by the use of gas chromatography as follows: Cultures were centrifuged at 3,000×g and the supernatant solutions were filtered through 0.7 μm WHATMAN™ glass microfiber filters using a Millipore vacuum filter manifold. Two mL of the filtrate were transferred to glass tubes with Teflon-lined caps. Each 2-mL sample was extracted with a mixture of 40 μL internal standard solution (C11:0, 2 mg/mL), 50 μL phosphoric acid (1 M), 100 μL NaCl (5 M) and 2 mL hexane. After incubation for one hour with gentle rocking at room temperature, the organic phase was transferred to a GC vial. A 1 μL sample was injected into an Agilent Model 7890A gas chromatograph using a 40:1 split ratio onto a DB-FFAP column (J&W Scientific, 15 m×250 μm×0.25 μm), with a temperature profile starting at 150° C. for 0.5 min, then heating at 15° C./min to 230° C. and holding for 7.1 min (1.1 mL/min He). As shown in Table 1, octanoic acid was the predominant fatty acid secreted into the medium by the E. coli cells containing the Ca1FatB2 gene. No fatty acids were detected in the media of control cells lacking the Ca1FatB2 gene (but containing plasmid pTrcHisB).
TABLE 1
Production and Secretion of FFAs in E. coli
Cells Expressing a Synthetic Ca1FatB2 Gene
FFA levels (mg/L)
Strain ID
Plasmid
8:0
10:0
12:0
14:0
16:0
16:1
18:0
18:1
Ca1FatB2 in E.
GLA256
9.3
0.2
0.0
0.0
0.0
0.0
0.0
0.0
coli Top 10 cells
(Strain PE-0284)
Ca1FatB2 in E.
GLA256
39.8
1.8
1.2
0.0
0.0
0.0
0.0
0.0
coli K27 cells
(Strain PE-0285)
Empty vector
pTrcHisB
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
control
(Strain PE-0286)
Example 3
Completion of the 3′ End of the Native Ca1FatB2 Gene
Genome walking was performed to determine the complete actual sequence at the 3′ end of the Ca1FatB2 coding region. An adaptor ‘GW ad’ was constructed by annealing oligos ‘GW adL’ (SEQ ID NO:14) and ‘GW adS’ (SEQ ID NO:15) at a final concentration of 100 mM each in 1× DNA ligase buffer (Invitrogen Corp., Carlsbad, Calif.). The GW adS oligomer was phosphorylated at the 5′ end and included a 3′ amino modifier. The following incubation conditions were used: 95° C. for 3 min; followed by 55° C. for 3 min; 45° C. for 3 min; 35° C. for 3 min; 25° C. for 3 min; 15° C. for 3 min; and then 4° C. hold. Single endonuclease digests were performed on C. aequipetala genomic DNA (gDNA) with PmlI, SnaBI, MscI, and StuI (New England Biolabs, Ipswich, Mass.) with overnight incubation at 37° C. The reactions were heat inactivated at 80° C. and the DNA was purified by standard phenol/chloroform procedures. Adaptor ‘GW ad’ was then ligated to the digested gDNA at 16° C. overnight with T4 DNA ligase (Invitrogen Corp., Carlsbad, Calif.). A nested PCR approach was used to amplify the 3′ end of Ca1FatB2 gene. The primary PCR was performed with primers ‘adP1’ (SEQ ID NO:16) and ‘GLA162-1F’ (SEQ ID NO:17). The secondary PCR was performed with ‘adP2’ (SEQ ID NO:18) and ‘GLA162-2BF’ (SEQ ID NO:19). Phusion DNA polymerase (New England Biolabs, Ipswich, Mass.) was used for both PCRs using the following thermocycler conditions: 98° C. for 3 min; 10 cycles (98° C. for 10 sec; 67° C. for 30 sec; 72° C. for 4 min); 30 cycles (98° C. for 10 sec; 70° C. for 30 sec; 72° C. for 4 min); 72° C. for 5 min; 4° C. hold. dNTPs were added to the secondary amplicons and incubated with Taq polymerase at 72° C. for 5 min. The PCR products were cloned into the pCR4-TOPO vector by use of the TOPO TA Cloning kit (Invitrogen Corp., Carlsbad, Calif.) and sequenced. Sequence alignments were performed with Sequencher (Gene Codes Corp., Ann Arbor, Mich.).
The sequence of the resulting isolated Cuphea aequipetala FatB2 genomic DNA fragment is provided as SEQ ID NO:20. The predicted native Ca1FatB2 coding nucleotide sequence is indicated as SEQ ID NO:21. A small portion of the region of the gene that encodes the plastid transit peptide is not included in this sequence, although the entire sequence could be obtained by additional 5′ genome walking The deduced protein sequence that is encoded by this Ca1FatB2 gene, assembled by PCR of genomic DNA with primers designed to hybridize within the coding region of a Class II acyl-ACP thioesterase followed by removal of intron sequences and gene walking to obtain sequences C-terminal sequences downstream of the amplified region of the gene is indicated as SEQ ID NO:22 ( FIG. 1 ).
In order to confirm the absence of a chimeric assembly in the gene sequence extended by genome walking, a one-piece amplicon was obtained using primers ‘GLA162 seq1F’ (SEQ ID NO:23) and ‘GLA162-290R’ (SEQ ID NO:24). The 2.1 kb amplicon was gel purified and TOPO cloned into the pCRII-Blunt vector (Invitrogen Corp., Carlsbad, Calif.). The one-piece amplicon differed slightly within the coding regions of the version originally amplified from the seed DNA at two residues: M67I (methionine at residue 67 replaced by isoleucine) and L103I (leucine at residue 103 replaced by isoleucine). These amino acid substitutions were incorporated as a variant of the gene. These amino acid changes are present in “Variant III”; the nucleotide sequence of this variant is provided as SEQ ID NO:25 and the protein translation is provided as SEQ ID NO:26. The protein functionality of Variant III was not found to be affected to a significant extent (see Example 4).
EXAMPLE 4
Production of Ca1FatB2 Gene Variants and Expression in E. Coli
As described above, genome walking was performed to determine the 3′ DNA sequence of the native Ca1FatB2 gene. The region encoding the hybrid carboxy-terminus consensus sequence present in plasmid GLA256 was replaced by a codon-optimized version of the native 3′ end of the Ca1FatB2 gene using primers ‘fatB GLA162 SYopt NT F’ (SEQ ID NO:9) and ‘fatB GLA162 SYopt 2R’ (SEQ ID NO:27). The resulting amplicon (SEQ ID NO:28) encoded the protein indicated as SEQ ID NO:29 (“Variant I”) and was inserted into the Synechocystis expression vector pSGI-YC28 using the InFusion system to create plasmid PR2B. pSGI-YC28 contains the TrcE promoter from pTrcHisA (Invitrogen Corp) the lacI q gene, and the homology arms that enable integration of the expression cassette into the “RS1” site of the Synechocystis PCC 6803 genome (Williams, Methods Enzymol. 167:766-778). This vector replicates autonomously in E. coli and allows gene expression in both E. coli and Synechocystis sp. PR2B was transformed into E. coli K27 to create strain PE-0238.
As described below, additional variants of the Ca1FatB2 gene were produced in order to assess potential structure-function relationships. Results of expression analyses normalized to optical density at 600 nm (OD600) are provided in Table 2.
Variant II: The encoded gene product has an isoleucine at amino acid position 103 rather than a leucine. The gene was produced from the Variant I gene via overlap PCR using the primers ‘fatB GLA162 SYopt NT F’ (SEQ ID NO:9), ‘GLA162 SYopt mut2 R’ (SEQ ID NO:68), ‘GLA162SYopt mut2 F’ (SEQ ID NO:69), and ‘fatB GLA162 SYopt 2R’ (SEQ ID NO:65). The nucleotide sequence of the Variant II gene product is given as SEQ ID NO:70, and the amino acid sequence of the Variant II gene product is given as SEQ ID NO:71.
Variant III: The encoded gene product has an isoleucine at amino acid position 103 rather than a leucine and an isoleucine at amino acid position 67 rather than a methionine. The gene was produced from the Variant II gene via overlap PCR using the primers ‘fatB GLA162 SYopt NT F’ (SEQ ID NO:9), ‘GLA162SYopt mut3 R’ (SEQ ID NO:30), ‘GLA162SYopt mut3 F’ (SEQ ID NO:31), and ‘fatB GLA162 SYopt 2R’ (SEQ ID NO:27). The nucleotide sequence of the Variant III gene is given as SEQ ID NO:25, and the amino acid sequence of the Variant III gene product is given as SEQ ID NO:26.
Variant IV: The encoded gene product has an isoleucine at amino acid position 103 rather than a leucine. In addition, the amino-terminus of the gene product was truncated by an additional 33 amino acids. The gene was produced from Variant II via PCR using the primers ‘fatB GLA162 SYopt NT2 F’ (SEQ ID NO:36) and ‘fatB GLA162 SYopt 2R’ (SEQ ID NO:27). The nucleotide sequence of Variant IV is provided as SEQ ID NO:37, and the amino acid sequence of the Variant IV gene product is given as SEQ ID NO:38.
Variant V: The encoded gene product has an isoleucine at amino acid position 103 rather than a leucine, an asparagine at amino acid position 184 rather than a serine, and an isoleucine at amino acid position 174 rather than a methionine. The gene was produced from Variant II via PCR. The nucleotide sequence of Variant V is provided as SEQ ID NO:39, and the amino acid sequence of the Variant V gene product is given as SEQ ID NO:40. This variant unexpectedly led to a much higher rate of octanoic acid secretion compared to the other variants and produced a higher proportion of octanoic acid. This result was surprising not only because mutants demonstrating increased activity toward the enzyme's preferred substrate have been unattainable until now, but also because other researchers have identified the active site of the enzyme as encompassing amino acids at least 100 residues away from the region of the protein exhibiting these mutations (see for example, U.S. Pat. No. 6,150,512, identifying amino acids YRREC (SEQ ID NO:41) as being at the active site (corresponding to amino acids 293-297 of SEQ ID NO:29 ( FIG. 1 )).
TABLE 2
Production and Secretion of FFAs in E. coli K27-Derived
Cells Expressing Variants of a Synthetic Ca1FatB2 Gene
Production
% total FFA
mg
Variant
Encoded protein
Vector
Strain ID
C8:0
C10:0
C12:0
C8:0/L/OD600
I (native)
Original sequence
PR2B
PE-0238
87
6
3
15
SEQ ID NO: 28
of CaFatB1 mature
protein
SEQ ID NO: 29
II
L103I
GLA518
PE-0288
87
6
3
19
SEQ ID NO: 32
SEQ ID NO: 33
III
M67I, L103I
GLA700
PE-0295
92
6
2
19
SEQ ID NO: 25
SEQ ID NO: 26
IV
L103I
GLA513
PE-0292
89
5
2
19
SEQ ID NO: 37
96-bp 5′ deletion
SEQ ID NO: 38
V
S184N, L103I,
GLA648
PE-0049
95
4
1
65
SEQ ID NO: 39
M174I
SEQ ID NO: 40
EXAMPLE 5
Synthesis and Assay of Additional Thioesterase Variants
Based on the above results, additional variants of the FatB acyl-ACP thioesterase were constructed by overlap PCR amplification in which the mutations were incorporated into primer sequences. A first set of mutants is based on the wild-type C. aequipetala sequence, in which the mutants have various substitutions at amino acid position 174. A second set of mutants was constructed in which the mutants had substitutions at position 174, in addition to the mutations L103I and S184N. Two isolates of each variant were selected for determining the level of production and secretion of various chain length fatty acids in E. coli K27 according to the methods provided in Example 2. The results are provided in the tables of FIGS. 2A-2D and FIGS. 3A-3D , and depicted graphically in FIGS. 4A-4B ).
Results of the fatty acid determination of samples from single amino acid position mutants indicate that isoleucine at position 174 results in the highest levels of production of C8 fatty acid. The M174I mutant (isolates 37 and 38 in FIGS. 2A-2D and FIGS. 3A-3D , having the nucleotide sequence provided as SEQ ID NO:42 and the amino acid sequence provided as SEQ ID NO:43) produces more than twice the octanoic acid produced by the isolates having the wild type gene (isolates 33 and 34 in FIGS. 2A-2D and FIG. 3A-3D ). A mutant having valine at position 174 (isolates 23 and 24) also produced higher than wild-type levels of C8 fatty acid, and mutants having phenylalanine (isolates 15 and 16), cysteine (isolates 27 and 28), or leucine (isolates 11 and 12) at position 174 produced high levels and high percentages of octanoic acid as well. This was true for the cultures as a whole ( FIG. 4A ) and when the values were normalized for cell density ( FIG. 4B ).
The production of octanoic acid was enhanced even further when additional mutations were combined with the mutations at position 174. The highest producing isolates, isolates 71 and 72, which included the S184N and L103I mutations in addition to the M174I mutation, yielded almost three-fold the amount of octanoic acid as did the wild-type strain (isolates 33 and 34), confirming the results shown in Table 2, in which the S184N, L103I, M174I mutant (“Variant V” having the nucleotide sequence SEQ ID NO:39, encoding amino acid sequence of SEQ ID NO:40) produced about four-fold the amount of octanoic acid as did the native C. aequipetala sequence (“Variant I”). Mutations of M174 to valine, phenylalanine, or leucine in combination with the L103I and S184N mutations (variants 49 and 50, 63 and 64, and 59 and 60, respectively) also showed enhancement of C8 fatty acid production with respect to transformants expressing the M174V, M174F, and M174L mutations on their own (isolates 23 and 24, 15 and 16, and 11 and 12, respectively).
EXAMPLE 6
Synthesis and Assay of Additional Thioesterase Variants
To complete the set of single site mutants having different substitutions at position 174 that was provided in Example 5, the single site mutant M174R was constructed. The triple site mutants L103I, M174C, S184N and L103, M174P, S184N were also constructed to determine the effect of the L103I and S184N substitutions on a moderately high-producing mutant (M174C, having activity comparable to wild-type) and a low-producing mutant (M174P). Finally, to elucidate the relative contribution of the mutations at positions 103 and 184 to the increased activity of the L103I, M174I, S184N triple site mutant over the M174I single site mutant, the double mutant L103I, M174I was also constructed by PCR amplification.
E. coli K27 cells were transformed with each of the constructs, and as a control, cells were transformed with empty vector. Additional isolates of cells transformed with constructs containing the M174I thioesterase mutant gene and triple L103I, M174I, S184N thioesterase mutant gene used in the experiments of Example 5 were also obtained for comparison of the results to previous experiments. Two isolates were obtained for each of the mutants and the empty vector control. The sequences of the thioesterase constructs in isolated TOP10 E. coli transformants were confirmed by sequencing prior to transforming the constructs into the K27 expression strain.
The thioesterase mutant-containing cells and empty vector-containing cells were cultured and induced for thioesterase expression, and fatty acids were isolated from the media after culturing the isolates overnight and assayed as provided in Example 5. Due to co-eluting contaminating peaks, C12 fatty acid amounts could not be determined; however, based on Example 2, the amount of C12 fatty acid in the samples was likely to be less than 3% of the total fatty acids in the samples.
The data presented in the table of FIG. 5A shows that the amounts of C8 and total fatty acids produced by the wild-type, M174I mutant, and L103I, M174I, S184N mutant were comparable to the levels seen in FIGS. 2A-2D (compare isolates 37, 38, 71, and 72 of FIGS. 2A-2D with isolates of 81, 82, 79, and 80 of FIGS. 5A-5B ), demonstrating the reproducibility of the results. Isolates 83 and 84 of FIG. 5 (nucleotide and amino acid sequences provided as SEQ ID NO:44 and SEQ ID NO:45, respectively), which include the L103I and M174I mutations (but lack the S184N mutation), produce levels of C8 fatty acid and total fatty acid that are essentially the same as that of the triple mutant L103I, M174I, S184N, indicating that a mutant thioesterase that includes the L103I mutation in addition to the M174I mutation has enhanced fatty acid production with respect to a mutant thioesterase that includes only the M174I mutation, while the S184N mutation has no discernible affect on fatty acid production. Normalized fatty acid production is provided in the table of FIG. 5B and presented graphically in FIG. 6 .
This result also indicates that the mutation of position M174, alone or in combination with a mutation at position 103, is tolerant of at least some mutations at other amino acid positions in the protein, as the S184N mutation did not affect the yield.
The data also demonstrate that modifying the gene such that an isoleucine is encoded at position 103 (here, in combination with S184N) increases the activity of a thioesterase mutant having a C or P at position 174 (comparing the higher production levels of isolates 87-90 of FIGS. 5A-5B with those of isolates 27, 28, 35, and 36 of FIGS. 2A-2D ). A variant having isoleucine at position 103 and cysteine at position 174 also showed enhancement of C8 fatty acid production with respect to wild-type bearing isolates.
EXAMPLE 7
Expression of the Ca1FatB2 Gene in the Cyanobacterium Synechocystis Sp.
Plasmid PR2B of Example 4 was also transformed into Synechocystis sp. PCC 6803 to create strain PH-0094. The transformation protocol used was essentially as described by Zang et al. ( Microbiology 45:241-245). To test for the production of free fatty acids in phototrophically grown Synechocystis, the Ca1FatB2-containing cells were pre-cultivated in 100 mL of BG-11 medium supplied with kanamycin (20 mg/L) to late-log phase (OD 730 nm =1.0) on a rotary shaker (150 rpm) at 30° C. with constant illumination (60 μE·m −2 ·sec −1 ). Cultures were then subcultured at initial OD 730 nm =0.4-0.5 in BG-11 and cultivated overnight to OD 730 nm =0.7-0.9. For time-course studies, 50-mL aliquots of the culture were transferred into 250-mL flasks and induced by adding IPTG (final conc.=1 mM). Cultures were sampled at various time points after IPTG induction and then filtered through WHATMAN™ GF/B glass microfiber filters using a MILLIPORE® vacuum filter manifold (Millipore, Billerica, Mass.). Filtrates were collected in screw top culture tubes for gas chromatographic (GC) analysis. Free fatty acids (FFA) were separated from the filtered culture supernatant solutions by liquid-liquid extraction. For each sample, 2 mL filtered culture was extracted with a mixture of 40 μL internal standard solution (C11:0, 2 mg/mL), 50 μl phosphoric acid (1 M), 100 μl NaCl (5 M) and 2 mL hexane. A 1 μl sample was injected using a 40:1 split ratio on to a DB-FFAP column (J&W Scientific, 15 m×250 μm×0.25 μm), with a temperature profile starting at 150° C. for 0.5 min, then heating at 15° C./min to 230° C. and holding for 7.1 min (1.1 mL/min He). The level of secreted FFAs in the medium 10 days after IPTG induction is provided in Table 3. The results demonstrate that the high activity thioesterase variants also result in higher fatty acid production by a photosynthetic organism.
TABLE 3
Production and Secretion of FFAs in Synechocytis Cells Expressing a Synthetic Ca1FatB2 Gene
Total
Strain ID
Plasmid
C8:0
C10:0
C12:0
C14:0
C16:0
C16:1
C18:0
C18:1
FFA (mg/L)
Vector control
YC27
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
(Strain PH-0019)
Ca1FatB2
PR2B
54.8
6.4
0.0
0.0
0.0
0.0
0.0
0.0
61.2
native gene
(Strain PH-0094)
Ca1FatB2
GLA648
156.4
11.4
0.2
0.0
0.0
0.0
0.0
0.0
167.8
S184N, L103I,
M174I gene
(Strain PH-0095)
EXAMPLE 8
Isolation of Additional Novel Acyl-ACP Thioesterase (FatB) Genes from Various Cuphea Species
An additional seventeen novel FatB genes, listed in Table 4, were also isolated from Cuphea samples by extracting genomic DNA from Cuphea seeds or vegetative tissues. Nested degenerate primers were used to clone individual FatB genes from the DNA samples. This approach results in gene sequences lacking complete 5′ and 3′ ends of the genes. The genes obtained by amplification of genomic DNA provided sequences that started from within the plastid transit peptide, therefore it was unnecessary to complete the terminal 5′ nucleotide sequence in order to obtain a functional gene. (The activity of the thioesterase is unaffected by the presence or the absence of this transit peptide (Jones et al. (1995) The Plant Cell 7: 359-371; Voelker et al. (1992) Science 257:72-74).) The 3′ ends of many of the novel thioesterase genes were completed via genome walking For those genes whose 3′ ends were not determined, a consensus hybrid sequence was appended based on known Cuphea FatB protein sequences prior to expressing the genes in vivo. We have found that altering the 3′ sequence does not significantly modify substrate preference or function of FatB genes.
Genomic DNA Isolation from Cuphea Samples
Genomic DNA was isolated from Cuphea avigera, Cuphea carthagenesis, Cuphea decandra, Cuphea inflate, Cuphea paucipetala, and Cuphea leptopoda tissues as follows: 2 cm stem and leaf cuttings ( Cuphea avigera ) or 40-50 seeds (other species) from each Cuphea sample were transferred to separate microfuge tubes and incubated for one hour at 55° C. in 350 μl of Extraction Buffer (200 mM Tris-HCl pH 8.0, 200 mM NaCl, 25 mM EDTA, 0.5% SDS, and 20 mg/ml proteinase K). The hydrated and lysed tissues were then ground using a plastic pestle. 350 μl of CTAB solution (2% w/v CTAB, 100 mM Tris-Cl, pH 8.0, 20 mM EDTA, 1.4 M NaCl, 1% PVP) were added and incubated at room temperature for one hour. The mixture was then centrifuged at 14000×g for 5 minutes and the supernatant solution was transferred to a Phase Lock Gel tube (5 Prime, Inc., Gaithersburg, Md.). DNA was extracted with one volume of phenol:chloroform (1:1) and the aqueous phase was transferred to a new tube; this step was repeated 2-3 times. DNA was precipitated in 1/10 volume of 3 M sodium acetate, pH 5.5, and 0.8 volumes of isopropanol. The pellet was rinsed with 70% ethanol and the genomic DNA was resuspended in water.
Gene Isolation and Cloning
A nested PCR approach was employed to amplify FatB genes using degenerate primers as described below. The primary PCR was performed with primers fatB degen1 2F (5′-ATGGTGGCTRCYGMWGCAAG; SEQ ID NO:1) and fatB degen6 1R (5′-CTAAGAKAYMGAGTYTCCAKKTSARGTC; SEQ ID NO:2). The secondary PCR was performed with primers fatB degen7 1F (5′-GCAGCAAGTTCHGCATKCTTCC; SEQ ID NO:3) and fatB degen8 1R (5′-CAKTCTTSGGYCKCCACTCAG; SEQ ID NO:4). A mixture of Phusion DNA polymerase (New England Biolabs, Ipswich, Mass.) plus RedTaq (Sigma, St. Louis, Mo.) was used for both PCRs under the following thermocycler conditions: 94° C. for 5 min; 40 cycles (94° C. for 30 s; 55° C. for 30 s; 72° C. for 4 min); 72° C. for 5 min. 1.7- to 3-kbp amplicons from the secondary PCR were excised and purified after electrophoresis through 1% agarose gels (Bio-Rad, Hercules, Calif.). The isolated DNA was subsequently incubated for 15 min at 72° C. with Taq DNA polymerase and dNTPs, followed by cloning into the pCR4-TOPO vector (Invitrogen, Carlsbad, Calif.) and transformed into chemically competent E. coli TOP10 cells (Invitrogen). Selected E. coli clones that were positive for gene insertions were then sequenced. Intron locations were predicted by comparison of the translated sequences from all three reading frames with known FatB protein sequences, allowing the coding regions of the genes and deduced amino acid sequences of the encoded proteins to be determined.
Genome Walking to Determine 3′ Carboxy Terminus Coding Sequence
Genome walking was performed on the Cc1FatB1, Ci1FatB1, Cl1FatB1, Cl3FatB1, Cd1FatB1, Cl4FatB1 and Ca2FatB2 genes to complete the sequences at the 3′ ends of the coding regions. An adaptor ‘GW ad’ was constructed by annealing oligos ‘GW adL’ (GTAATACGACTCACTATAGGGCACGCGTGGTCGACGGCCCGGGCT GGTT; SEQ ID NO:14) and ‘GW adS’ (AACCAGCCCG; SEQ ID NO:15) at a final concentration of 100 μM each in 1× ligase buffer (Invitrogen Corp.). The following thermocycler conditions were used: 95° C. for 3 min; 55° C. for 3 min; 45° C. for 3 min; 35° C. for 3 min; 25° C. for 3 min; 15° C. for 3 min; 4° C. hold. Single endonuclease digests were performed on the Cuphea genomic DNAs with PmlI, SnaBI, MscI, EcoRV, and/or StuI (Fermentas, Glen Burnies, Md.; New England Biolabs, Ipswich, Mass.) with overnight incubation at 37° C. The reactions were heat inactivated at 80° C. and were followed by standard phenol/chloroform cleanup. Adaptor ‘GW ad’ was then ligated to the digested genomic DNA at 16° C. overnight with T4 DNA ligase (Invitrogen). A nested PCR approach was used to amplify the genomic 3′ ends of the FatB genes. Phusion DNA polymerase (New England Biolabs) was used for both PCRs using the following thermocycler conditions: 98° C. for 3 min; 10 cycles (98° C. for 10 sec; 67° C. for 30 sec; 72° C. for 4 min); 30 cycles (98° C. for 10 sec; 70° C. for 30 sec; 72° C. for 4 min); 72° C. for 5 min; 4° C. hold. dNTPs were added to the secondary amplicons and incubated with Taq at 72° C. for 5 min. The PCR products were cloned into the pCR4 vector (Invitrogen Corp.) and sequenced (Bio Applied Technologies Joint, Inc., San Diego, Calif.). Alignments were performed with the Sequencher program (Gene Codes Corp., Ann Arbor, Mich.).
Cloning of Codon-Optimized Synthetic FatB Genes
The Synechocystis sp. PCC 6803 codon usage table was utilized to codon optimize the coding regions for most of the novel thioesterase genes. Gene constructs encoding the sequences of SEQ ID NO:55 was synthesized to include the carboxy-terminus consensus sequence ANGAISTGKTSNGNSIS (SEQ ID NO:46), gene constructs encoding the sequences of SEQ ID NO:30 and SEQ ID NO:36 were synthesized to include the carboxy-terminus consensus sequence TNGAISTTKTSPGNSVS (SEQ ID NO:47), and genes encoding the sequences of SEQ ID NO:51, SEQ ID NO:59, SEQ ID NO:63, SEQ ID NO:79, SEQ ID NO:85, SEQ ID NO:89, and SEQ ID NO:99 were cloned with the native 3′ sequences that were determined by genome walking Both consensus sequences were based on published acyl-ACP thioesterase 3′ DNA sequences. The synthetic gene constructs for expression were made with a truncation of the 5′ end to exclude the predicted plastid transit peptide-encoding region at the amino-terminus.
References to the disclosed sequences (SEQ ID NOs) of these synthetic genes are indicated in Table 4. The CiFatB1 gene was synthesized by Integrated DNA Technologies (Coralville, Iowa); all other genes were synthesized by DNA 2.0 (Menlo Park, Calif.). All genes were cloned into a Synechocystis sp. PCC 6803 integration vector pSGI-YC28 with the exception of Ca1FatB1, which was cloned into the pTrcHisB vector (Invitrogen), and Cl3FatB1 and Ca2FatB2, which were cloned into the pJexpress plasmid at the time of synthesis. pSGI-YC28 contains the “TrcE” trc promoter from pTrcHisA, the lacI q gene, and the homology arms that enable integration of the expression cassette into the “RS1” site of the Synechocystis PCC 6803 genome (Williams, Methods Enzymol. 167:766-778). This vector replicates autonomously in E. coli and allows gene expression in both E. coli and Synechocystis sp. 6803. pJexpress is an E. coli expression system developed at DNA2.0 in which a modified inducible T5 promoter drives gene expression. Gene inserts were either cloned using the InFusion system (Clontech, Mountainview, Calif.) or double-digested with BamHI and NcoI (New England Biolabs) and ligated with T4 DNA ligase (New England Biolabs). An alignment of the amino terminal regions of the proteins encoded by the expression constructs is provided as FIG. 7 .
TABLE 4
Novel FatB Genes Isolated from Various Cuphea Species
NGPR
Isolated
Isolated gene,
Codon-optimized
Amino acid
Acc.
genomic DNA
amino acid
gene sequence,
Sequence,
Number
Cuphea Species
Gene
sequence
sequence
expression constructs
Expression constructs
PI 534673
C. carthagenensis
Cc1FatB1
SEQ ID NO: 48
SEQ ID NO: 49
SEQ ID NO: 50
SEQ ID NO: 51
PI 561477
C. aequipetala
Ca1FatB1
SEQ ID NO: 52
SEQ ID NO: 53
SEQ ID NO: 54
SEQ ID NO: 55
PI 534687
C. inflata
Ci1FatB1
SEQ ID NO: 56
SEQ ID NO: 57
SEQ ID NO: 58
SEQ ID NO: 59
PI 534694
C. leptopoda
Cl1FatB1
SEQ ID NO: 60
SEQ ID NO: 61
SEQ ID NO: 62
SEQ ID NO: 63
PI 534694
C. leptopoda
Cl1FatB2
SEQ ID NO: 64
SEQ ID NO: 65
PI 561495
C. paucipetala
Cp1FatB1
SEQ ID NO: 66
SEQ ID NO: 67
SEQ ID NO: 68
SEQ ID NO: 69
PI 561487
C. leptopoda
Cl2FatB1
SEQ ID NO: 70
SEQ ID NO: 71
PI 561487
C. leptopoda
Cl2FatB2
SEQ ID NO: 72
SEQ ID NO: 73
SEQ ID NO: 74
SEQ ID NO: 75
PI 578175
C. leptopoda
Cl3FatB1
SEQ ID NO: 76
SEQ ID NO: 77
SEQ ID NO: 78
SEQ ID NO: 79
PI 578175
C. leptopoda
Cl3FatB2
SEQ ID NO: 80
SEQ ID NO: 81
PI 594928
C. decandra
Cd1FatB1
SEQ ID NO: 82
SEQ ID NO: 83
SEQ ID NO: 84
SEQ ID NO: 85
PI 650910
C. leptopoda
Cl4FatB1
SEQ ID NO: 86
SEQ ID NO: 87
SEQ ID NO: 88
SEQ ID NO: 89
PI 650910
C. leptopoda
Cl4FatB2
SEQ ID NO: 90
SEQ ID NO: 91
PI 650910
C. leptopoda
Cl4FatB3
SEQ ID NO: 92
SEQ ID NO: 93
Ames 17868
C. avigera
Ca2FatB1
SEQ ID NO: 94
SEQ ID NO: 95
Ames 17868
C. avigera
Ca2FatB2
SEQ ID NO: 96
SEQ ID NO: 97
SEQ ID NO: 98
SEQ ID NO: 99
Ames 17868
C. avigera
Ca2FatB3
SEQ ID NO: 100
SEQ ID NO: 101
EXAMPLE 9
Expression of FatB Thioesterases in E. Coli and Analysis Of FFA Products
Constructs of Example 8 were transformed into E. coli strain K27, which has a mutation in the fadD (acyl-CoA synthetase) gene (Overath et al., Eur. J. Biochem. 7:559-574), to create the indicated strains. Ca2FatB2 and Cl3FatB1 were under the control of the inducible T5 promoter; all other thioesterase genes were driven by the inducible pTrcE promoter. These strains were inoculated into 10 mL of LB medium supplemented with 50 mg/L kanamycin at OD 600 =0.2 and induced with 0.5 mM IPTG during log phase.
The cultures were grown in 25 mL glass vials for 24 hours and assayed for free fatty acid (FFA) production and secretion into the medium by the use of gas chromatography as follows: Extractions were performed on 7.2 mL whole culture with a mixture of 40 μl internal standard solution (C9:0, C13:0, and C17:0, final concentration of 50 μg/mL), 0.6 mL of 50% sulfuric acid, 1.2 mL NaCl (5 M), and 10.8 mL hexane. Samples were vortexed vigorously to emulsify, incubated at room temperature for one hour, and vortexed again. The mixture was spun at 1800 rpm for 5 minutes, and the organic phase was transferred to a GC vial. A 1 μL sample was injected into an Agilent Model 7890A gas chromatograph using a 40:1 split ratio onto a DB-FFAP column (J&W Scientific, 15 m×250 μm×0.25 μm), with a temperature profile starting at 180° C. for 0.5 minute, then heated at a rate of 30° C. per minute to 230° C., and holding for 3.9. minutes (1.8 mL/min He). Free fatty acid peaks were detected on an FID instrument.
Table 5 shows the predominant fatty acids produced by the various strains.
The E. coli strain transformed with the Ca2FatB2 thioesterase predominantly synthesized C8 free fatty acids, which made up 40% of the C8-C18 free fatty acids produced by the strain.
The E. coli strains transformed with the Cl2FatB2 and Cl4FatB1 thioesterases predominantly synthesized C10 free fatty acids, which made up 42.6% and 37.7% of the total C8-C18 free fatty acids produced by Cl2FatB2 and Cl4FatB1 strains, respectively, but the transformed strains also made a significant amount of C16 fatty acids, which made up 25.4% and 27.7% of the total C8-C16 free fatty acids produced by Cl2FatB2 and Cl4FatB1 strains, respectively.
The Cc1FatB1-containing E. coli strain produced mainly C12, C14, and C16 free fatty acids, with a greater percentage of C14 and C16 free fatty acids that C12 free fatty acids being produced by the E. coli host. Cp1FatB1, Cl1FatB1, Cd1FatB1, and Cl3FatB1-containing strains produced predominantly C14 and C16 free fatty acids, with 80% to greater than 90% of the free fatty acids being produced being C14 or C16 fatty acids. Although more than 50% of the free fatty acids produced by the Ci1FatB1-carrying strain were C16 fatty acids, this strain also produces some C18 fatty acids (>20% of the fatty acids produced). The results are depicted graphically in FIG. 8 , FIG. 9 , and FIG. 10 .
TABLE 5
Production and Secretion of Free Fatty Acids by E. coli Expressing FatB Genes
Total
OD
FFAs
Genotype
600
C8:0
C10:0
C10:1
C12:0
C12:1
C14:0
C14:1
C16:0
C16:1
C18:0
C18:1
mg/L/OD
Experiment #1
empty vector
4.8
0.2
0.1
0.0
0.1
0.0
0.4
0.1
1.3
0.3
0.4
0.3
3.2
Cc1FatB1
1.3
3.5
1.2
0.4
46.8
8.6
29.3
56.4
5.9
73.4
1.6
6.8
234.1
Cp1FatB1
2.3
0.0
0.2
0.0
1.4
0.0
84.2
3.0
10.5
74.9
0.4
11.3
185.9
Cl2FatB2
3.2
3.2
30.4
17.0
5.1
7.9
11.3
2.1
9.1
19.2
0.2
6.0
111.4
Cl4FatB1
3.9
1.8
16.3
7.8
3.0
4.8
7.2
1.3
5.9
11.8
0.1
4.0
63.9
Cl1FatB1
3.6
0.2
0.2
0.0
0.3
0.0
22.4
0.4
9.4
12.4
0.2
5.3
50.6
Ci1FatB1
4.5
0.0
0.1
0.0
0.0
0.0
0.4
0.0
1.0
0.4
0.0
0.6
2.6
Cd1FatB1
1.1
0.7
0.5
0.0
0.8
0.0
78.4
2.1
24.8
131.5
0.3
13.6
252.6
Experiment #2
empty vector
4.3
0.0
0.1
0.0
0.1
0.0
0.5
0.2
1.8
0.7
0.0
0.2
3.6
Cl3FatB1
2.1
0.5
0.3
0.0
0.3
0.0
36.7
0.7
13.3
44.3
0.0
6.1
102.3
Ca2FatB2
4.1
4.4
0.6
0.0
0.2
0.0
1.3
0.2
2.0
1.2
0.3
0.8
11.0
Experiment #3
empty vector
3.3
0.2
0.3
0.0
0.3
0.0
0.7
0.0
4.2
1.8
0.0
0.0
7.4
Ca1FatB1
0.9
0.0
0.0
0.0
8.6
0.0
80.2
9.3
7.8
49.9
0.0
0.0
155.8
EXAMPLE 10
Expression of FatB Thioesterases in the Cyanobacterium Synechocystis Sp.
The plasmid constructs were also transformed into Synechocystis sp. PCC 6803. The transformation protocol used was essentially as described by Zang et al. ( Microbiology 45:241-245). To test for the production of free fatty acids in the various cyanobacterial isolates, the strains were pre-cultivated in 30 mL of BG-11 medium supplemented with kanamycin (20 mg/L) to late-log phase (OD 730 nm =1.0) on a rotary shaker (150 rpm) at 30° C. with constant illumination (60 μE·m −2 ·sec −1 ). Cultures were then subcultured into 125 mL glass flasks with silicone stoppers at initial OD 730 nm =0.4-0.5 in BG-11 and cultivated overnight to OD 730 nm =0.7-0.9, and induced by addition of IPTG (final concentration, 1 mM).
Free fatty acid (FFA) analyses were performed on extractions of 20 mL whole cell culture with a mixture of internal standard solution (C9:0, C13:0, and C17:0, final concentration of 50 μg/mL), 1.7 mL 50% sulfuric acid, 3.4 mL NaCl (5M), and 30 mL hexane. Samples were vortexed vigorously to emulsify, incubated at room temperature for one hour, and vortexed again. The mixture was transferred to 50 mL glass centrifuge tubes and spun at 1800 rpm for 5 minutes, and the organic phase was transferred to a GC vial. A 1 ul sample was injected into an Agilent model 7890A gas chromatograph using a 40:1 split ration onto a DB-FFAP column (J&W Scientific, 15 m×250 μm×0.25 μm), with a temperature profile starting at 180° C. for 0.5 minute, then heating at 30° C./minute to 230° C. and holding for 3.9 minutes (1.8 mL/min He). Free fatty acid peaks were detected on an FID instrument.
The levels of secreted FFAs produced six days after IPTG induction are provided in Table 6 and Table 7, and depicted graphically in FIG. 11 , FIG. 12 , and FIGS. 13A-13B ). The Synechocystis isolate transformed with Cd1FatB1, depicted in FIG. 11 , produced essentially no free fatty acids and was later found by DNA sequencing to have incurred a premature stop codon within the reading frame. An alternate Cd1FatB1-carrying Synechocystis isolate, was found to be one of the highest free fatty acid producers tested, as shown in Table 7 and depicted in FIGS. 13A-13B .
TABLE 6
Production and Secretion of Free Fatty Acids by Synechocystis Expressing FatB Genes
Total
OD
FFAs
Genotype
730
C8:0
C10:0
C12:0
C14:0
C16:0
C16:1
C18:0
C18:1
mg/L/OD
Experiment #1
empty vector
6.2
0.0
0.0
0.0
0.0
0.3
0.2
0.4
0.3
1.3
Cc1FatB1
4.5
0.2
0.2
6.8
23.2
32.9
1.0
3.2
1.7
69.4
Cp1FatB1
6.8
0.0
0.0
0.1
2.0
8.7
0.1
0.6
0.2
11.7
Cl2FatB2
6.8
0.2
8.1
0.3
0.7
7.3
0.1
0.5
0.1
17.3
Cl4FatB1
6.4
0.4
14.9
0.6
1.5
13.5
0.3
0.9
0.2
32.3
Cl1FatB1
6.5
0.0
0.2
0.0
0.0
0.8
0.0
0.1
0.0
1.1
Cd1FatB1
8.0
0.0
0.0
0.1
0.1
0.5
0.0
0.2
0.0
0.9
Experiment #2
empty vector
5.2
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
Ca2FatB2
4.1
27.2
6.8
0.0
0.0
0.5
0.0
0.0
0.0
34.5
TABLE 7
Production and Secretion of Free Fatty Acids by Synechocystis Expressing FatB Genes
Total
OD
C18:1
C18:1
C18:2
FFAs
Genotype
730
C8:0
C10:0
C12:0
C14:0
C16:0
C16:1
C18:0
cis9
cis11
cis9, 12
mg/L
empty vector
7.3
0.7
0.0
0.0
0.0
1.3
0.0
0.0
0.0
0.0
0.0
1.9
ChFatB2
8.6
67.0
60.6
0.7
0.0
2.7
0.0
1.5
0.0
0.0
1.3
133.7
Cc1FatB1
6.5
1.3
1.6
30.4
107.1
139.9
1.9
9.5
2.0
0.0
4.7
298.3
Cd1FatB1
4.4
0.0
0.9
0.6
15.0
247.6
1.1
11.3
1.4
0.0
3.3
281.2
Total
OD
C18:1
C18:1
C18:2
FFAs
Genotype
730
C8:0
C10:0
C12:0
C14:0
C16:0
C16:1
C18:0
cis9
cis11
cis9, 12
mg/L/OD
empty vector
7.3
0.1
0.0
0.0
0.0
0.2
0.0
0.0
0.0
0.0
0.0
0.3
ChFatB2
8.6
7.8
7.0
0.1
0.0
0.3
0.0
0.2
0.0
0.0
0.1
15.6
Cc1FatB1
6.5
0.2
0.2
4.7
16.5
21.5
0.3
1.5
0.3
0.0
0.7
45.9
Cd1FatB1
4.4
0.0
0.2
0.1
3.4
56.3
0.2
2.6
0.3
0.0
0.8
63.9
As seen in Table 6 and Table 7, Synechocystis transformed with the Ca2FatB2 thioesterase gene makes predominantly C8 free fatty acids, and also produces some C10 free fatty acids: 78.84% of the free fatty acids secreted into the media are C8 free fatty acids, and 19.71% are C10 free fatty acids. Synechocystis transformed with the Cl2FatB2 thioesterase gene and Synechocystis transformed with the Cl4FatB1 thioesterase gene synthesize predominantly C10 and C16 fatty acids, with slightly more C10 than C16 being produced: The Cl2FatB2 strain produced 46.8% C10 FFAs and 42.7% C16 FFAs, and the Cl4FatB1 strain produced 46.8% C10 FFAs and 42.1% C16 FFAs. Synechocystis cyanobacterial cells transformed with the Cp1FatB1 gene, the Cl1FatB1 gene, the Ci1FatB1 gene, the Cd1FatB1 gene, the Cl3FatB1 gene, and the Ca1FatB1 gene produced predominantly C14 and C16 free fatty acids, while Synechocystis transformed with Cc1FatB1 produced a majority of C14 and C16 fatty acids along with some C12 fatty acids.
EXAMPLE 11
Production of Wax Ester by E. Coli Expressing Cuphea Acyl-ACP Thioesterases
To demonstrate that a microorganism transformed with one of the Cuphea thioesterases disclosed herein could produce a fatty acid product derived from one or more fatty acids, E. coli cells were transformed with a construct containing three exogenous genes: a Cuphea thioesterase (either the C8 and C10-preferring Cuphea hookeriana Ch1FatB2 gene (Dehesh, K. et al., The Plant Journal 9:167-172 (1996)) or the Cc1FatB1 gene (SEQ ID NO:51) disclosed herein), a Mus musculus wax synthase gene (NCBI Genbank GI:49854217) and an Arabidopsis thaliana fatty acyl-CoA reductase gene, FAR6 (NCBI Genbank GI:67633703). All three genes were cloned on the same expression plasmid, in which all three genes were driven by separate trc promoters.
The FAR6 gene did not appear to be active in E. coli, probably due to the presence of the chloroplast transit peptide in the expressed protein, which likely interfered with enzyme activity. However, the cells did produce esters when provided with 5 mM decanol in the culture medium.
To test for wax ester formation, E. coli cells were grown at 30° C. with shaking until they reached an OD 600 of 0.7 to 0.9, at which time the transgenes were induced by the addition of 0.5 mM IPTG. At the same time IPTG was added, decanol was added to a final concentration of 5 mM, and the cultures were incubated overnight. The cells were then harvested, washed once with PBS and then resuspended in water and transferred to a glass vial. An equal volume of 2:1 chloroform:methanol was added to each sample, and the suspension was vortexed vigorously and then centrifuged to separate the phases. The organic layer was transferred to a 2 mL glass GC vial and the contents were evaporated under nitrogen. The residue was resuspended in chloroform: methanol for GC analysis.
The results are depicted in FIGS. 14A-14B . FIG. 14B shows the analysis of products isolated from E. coli cells transformed with the C. hookeriana ChFatB2 thioesterase. The wax esters produced by the cells were predominantly decyl octanoate and decyl decanoate (expected from the C10-preference of the ChFatB2 thioesterase) and decyl hexadecanoate (reflecting the preference of the E. coli host for generating C16 fatty acids). FIG. 14A shows the analysis of products isolated from the media of E. coli cells transformed with the Cc1FatB1 thioesterase, demonstrated in Example 9 to generate free C14 and C16 fatty acids in E. coli. Consistent with the substrate preference of this thioesterase, co-expression of the Cc1FatB1 thioesterase with the Mus musculus wax synthase resulted in the most prevalent wax ester isolated from the cells being decyl tetradecanoate, followed by decyl hexadecenoate.
1.PublishNumber: US-2015147790-A1
2.Date Publish: 20150528
3.Inventor: ROESSLER PAUL GORDON
ROY GENA
4.Inventor Harmonized: ROESSLER PAUL GORDON(US)
ROY GENA(US)
5.Country: US
6.Claims:
(en)The present invention provides novel genes encoding Class II acyl-ACP thioesterases and variants thereof that are active on C8, C10, C12, C14, C16, and C18 acyl-ACP substrates. The thioesterases can be introduced into transgenic organisms, including microorganisms and photosynthetic organisms, for producing fatty acids and fatty acid products.
7.Description:
(en)CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation application of U.S. application Ser. No. 12/826,592 filed Jun. 29, 2010, now pending; which claims the benefit under 35 USC §119(e) to U.S. Application Ser. No. 61/223,328 filed Jul. 6, 2009 and to U.S. Application Ser. No. 61/221,500 filed Jun. 29, 2009, both now expired. The disclosure of each of the prior applications is considered part of and is incorporated by reference in the disclosure of this application.
REFERENCE TO SEQUENCE LISTING
The instant application contains a Sequence Listing which has been submitted via EFS-Web and is hereby incorporated by reference in its entirety. Said ASCII copy, created on Jan. 26, 2015, is named SGI1230-3_ST25.txt and is 218 KB in size. The aforementioned sequence listing is hereby incorporated by reference in its entirety pursuant to 37 C.F.R. §1.52(e)(5).
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to the production of fatty acids and fatty acid products in transgenic or genetically modified organisms, such as microorganisms and photosynthetic organisms. The invention also relates to genes encoding enzymes that function in the biosynthesis of fatty acids and related products, and in particular to acyl-ACP thioesterases.
2. Background Information
Plants supply most of the oils used in food products, and plant-derived lipids are also used in the manufacture of many non-dietary products, such as lubricants, soaps, detergents, cosmetics, and thickeners. In higher plants, fatty acids are synthesized in plastids and incorporated into triacylglycerols (triglycerides) in the endoplasmic reticulum (ER). In cells that store fats, such as the cells of seeds or nuts, fat droplets bud off of the ER to form lipid bodies within the cytoplasm. These reservoirs of lipids in the form of triglycerides provide an energy resource for germinating seeds.
The diversity of fatty acids produced by plant cells and incorporated into triglycerides can add to the time and cost of purification of fatty acids of particular chain lengths used for particular purposes. Medium chain fatty acids, for example, are used in the manufacture of surface disinfectants, anti-foaming agents, surfactants, lubricants, perfumes, dyes, and flavoring agents, and can be used to produce polymers and fuels. Long chain fatty acids are used in food products as well as detergents, soaps, surfactants, cosmetics, plastics, and lubricants, and can also be used in the production of fuels.
Acyl-acyl carrier protein (ACP) thioesterases are key enzymes in determining the chain lengths of fatty acids produced by a plant. Two families of acyl-ACP thioesterases are present in higher plants, the “Class I” acyl-ACP thioesterases encoded by FatA genes, and responsible for cleaving long chain (for example, C16 and C18) unsaturated fatty acids from acyl-ACP and the “Class II” acyl-ACP thioesterases encoded by FatB genes, that are active on saturated fatty acyl chains and can be specific for medium chain (C8-C14) acyl-ACPs or can be active on both medium and long chain fatty acyl-ACPs. Different acyl-ACP thioesterases have different degrees of chain length specificity, sometimes referred to as the enzyme's “preference” for cleaving a particular length of fatty acid from ACP, and thioesterases are typically most active in cleaving a particular chain length fatty acid while having lesser activity in cleaving one or more other chain length fatty acids. Some Class II (FatB) acyl-ACP thioesterases have binary activity, having a first peak of activity against a specific medium chain length acyl substrate and a second peak of activity against one or more specific long chain length acyl substrates.
The isolation of Class II acyl-ACP thioesterase genes from higher plants with medium chain specificity or having activity on both medium and long chain fatty acids has been described previously. Examples include U.S. Pat. No. 5,298,421, entitled “Plant medium-chain-preferring acyl-ACP thioesterases and related methods”, which describes the isolation of an acyl-ACP thioesterase and the gene that encodes it from the immature seeds of Umbellularia californica. Other patents of interest include U.S. Pat. No. 5,304,481, entitled “Plant thioesterase having preferential hydrolase activity toward C12 acyl-ACP substrate”, U.S. Pat. No. 5,344,771, entitled “Plant thioesterases”, U.S. Pat. No. 5,455,167, entitled “Medium-chain thioesterases in plants”, U.S. Pat. No. 5,512,482, entitled “Plant thioesterases”, U.S. Pat. No. 5,639,790, entitled “Plant medium-chain thioesterases”, U.S. Pat. No. 5,667,997, entitled “C8 and C10 medium-chain thioesterases in plants”, U.S. Pat. No. 5,807,893, entitled “Plant thioesterases and use for modification of fatty acid composition in plant seed oils”, U.S. Pat. No. 5,850,022, entitled “Production of myristate in plant cells”, and U.S. Pat. No. 5,910,631, entitled “Middle chain-specific thioesterase genes from Cuphea lanceolata” , U.S. Pat. No. 5,955,329, entitled “Engineering plant thioesterases for altered substrate specificity”, and U.S. Pat. No. 6,150,512, entitled “Engineering plant thioesterases and disclosure of plant thioesterases having novel substrate specificity”, disclose variants of plant thioesterase genes having altered chain length specificities for the encoded thioesterase enzymes.
Journal articles disclosing Class II chain acyl-ACP thioesterases include Dehesh, K. et al., “Production of high levels of 8:0 and 10:0 fatty acids in transgenic canola by overexpression of Ch FatB2, a thioesterase cDNA from Cuphea hookeriana”, The Plant Journal 9:167-172 (1996), Dehesh, K. et al., “Two novel thioesterases are key determinants of the bimodal distribution of acyl chain length of Cuphea palustris seed oil”, Plant Physiology 110:203-210 (1996), Dehesh, K., et al., “KAS IV: a 3-ketoacyl-ACP synthase from Cuphea sp. is a medium chain specific condensing enzyme”, The Plant Journal 15:383-390 (1998), Dormann, P. et al., “Characterization of two acyl-acyl carrier protein thioesterases from developing Cuphea seeds specific for medium-chain and oleoyl-acyl carrier protein”, Planta 189:425-432 (1993), Filichkin, S., et al., “New FATB thioesterases from a high-laurate Cuphea species: Functional and complementation analyses”, European Journal of Lipid Science and Technology 108:979-990 (2006), Slabaugh, M., et al., “Condensing enzymes from Cuphea wrightii associated with medium chain fatty acid biosynthesis”, The Plant Journal 13:611-620 (1998), Voelker, T., et al., “Fatty acid biosynthesis redirected to medium chains in transgenic oilseed plants”, Science 257:72-74 (1992), Voelker, T., and Davies, M., “Alteration of the specificity and regulation of fatty acid synthesis of Escherichia coli by expression of a plant medium-chain acyl-acyl carrier protein thioesterase”, Journal of Bacteriology 176:7320-7327 (1994).
In addition to synthesizing fatty acids for nonfuel products, microorganisms or photosynthetic organisms can be used to produce fatty acids or fatty acid products for the production of fuels and chemicals such as alcohols or hydrocarbons. In synthesizing fatty acids, these organisms can use atmospheric CO 2 or plant products such as starch, sugars, or cellulose that are themselves based on fixed atmospheric CO 2 as a source of carbon, thereby reducing the net amount of CO 2 generated in the production and use of the fuel or chemical. Increasing the yield and recovery of fatty acids and fatty acid products of a particular chain length from cultured microorganisms and photosynthetic organisms can improve the cost effectiveness of providing a renewable source of a variety of products, including fuel products.
SUMMARY OF THE INVENTION
The invention provides compositions and methods for producing fatty acids and fatty acid products of specific chain lengths for synthesis of a variety of intermediary or final products for various uses, for example, in foods and nutritional products, lubricants, surfactants, chemicals, plastics, soaps, and fuels. Nucleic acid molecules are provided that encode acyl-ACP thioesterases exhibiting a preference for specific acyl chain lengths, such that fatty acid preparations in which a preponderance of the isolated fatty acids are of one or more specific chain lengths can be recovered from cultures of transgenic organisms expressing the exogenous acyl-ACP thioesterase.
A first aspect of the invention provides recombinant or isolated nucleic acid molecules encoding acyl-ACP thioesterases in which the encoded thioesterases include an amino acid sequence having at least 85%, at least 90%, at least 92%, at least 95%, or at least 99% identity with the amino acid sequence from amino acid position 64 to amino acid position 361 of SEQ ID NO:51; at least 98% identity with the amino acid sequence from amino acid position 66 to amino acid position 362 of SEQ ID NO:55; at least 97% identity with the amino acid sequence from amino acid position 65 to amino acid position 360 of SEQ ID NO:59; at least 90% identity with the amino acid sequence from amino acid position 65 to amino acid position 359 of SEQ ID NO:63; at least 98% identity with the amino acid sequence from amino acid position 115 to amino acid position 410 of SEQ ID NO:65; at least 96% identity with the amino acid sequence from amino acid position 65 to amino acid position 356 of SEQ ID NO:69; at least 98% identity with the amino acid sequence from amino acid position 115 to amino acid position 410 of SEQ ID NO:71; at least 96% identity with the amino acid sequence from amino acid position 64 to amino acid position 361 of SEQ ID NO:75; at least 97% identity with the amino acid sequence from amino acid position 65 to amino acid position 360 of SEQ ID NO:79; at least 96% identity with the amino acid sequence from amino acid position 116 to amino acid position 413 of SEQ ID NO:81; at least 96% identity with the amino acid sequence from amino acid position 65 to amino acid position 362 of SEQ ID NO:85; at least 96% identity with the amino acid sequence from amino acid position 64 to amino acid position 361 of SEQ ID NO:89; at least 97% identity with the amino acid sequence from amino acid position 115 to amino acid position 394 of SEQ ID NO:91; at least 97% identity with the amino acid sequence from amino acid position 115 to amino acid position 394 of SEQ ID NO:93; at least 99% identity with the amino acid sequence from amino acid position 115 to amino acid position 394 of SEQ ID NO:95; at least 92% identity with the amino acid sequence from amino acid position 63 to amino acid position 360 of SEQ ID NO:99; or at least 98% identity with the amino acid sequence from amino acid position 115 to amino acid position 393 of SEQ ID NO:101, in which the thioesterase encoded by the isolated nucleic acid molecule has at least the level of activity as the thioesterase encoded by the reference sequence from which it is derived.
In some embodiments, the recombinant or isolated nucleic acid molecule encoding an acyl-ACP thioesterase includes an amino acid sequence having at least 85% identity with the amino acid sequence from amino acid position 33 to amino acid position 361 of SEQ ID NO:51; having at least 98% identity with the amino acid sequence from amino acid position 35 to amino acid position 362 of SEQ ID NO:55; having at least 97% identity with the amino acid sequence from amino acid position 34 to amino acid position 360 of SEQ ID NO:59; having at least 90% identity with the amino acid sequence from amino acid position 34 to amino acid position 359 of SEQ ID NO:63; having at least 98% identity with the amino acid sequence from amino acid position 84 to amino acid position 410 of SEQ ID NO:65; having at least 96% identity with the amino acid sequence from amino acid position 34 to amino acid position 356 of SEQ ID NO:69; having at least 98% identity with the amino acid sequence from amino acid position 84 to amino acid position 410 of SEQ ID NO:71; having at least 96% identity with the amino acid sequence from amino acid position 33 to amino acid position 361 of SEQ ID NO:75; having at least 97% identity with the amino acid sequence from amino acid position 34 to amino acid position 360 of SEQ ID NO:79; having at least 96% identity with the amino acid sequence from amino acid position 85 to amino acid position 413 of SEQ ID NO:81; having at least 96% identity with the amino acid sequence from amino acid position 34 to amino acid position 362 of SEQ ID NO:85; having at least 96% identity with the amino acid sequence from amino acid position 33 to amino acid position 361 of SEQ ID NO:89; having at least 97% identity with the amino acid sequence from amino acid position 84 to amino acid position 394 of SEQ ID NO:91; having at least 97% identity with the amino acid sequence from amino acid position 84 to amino acid position 394 of SEQ ID NO:93; having at least 99% identity with the amino acid sequence from amino acid position 84 to amino acid position 394 of SEQ ID NO:95; having at least 92% identity with the amino acid sequence from amino acid position 33 to amino acid position 360 of SEQ ID NO:99; or having at least 98% identity with the amino acid sequence from amino acid position 84 to amino acid position 393 of SEQ ID NO:101, and has at least the level of activity of the reference thioesterase from which the encoded thioesterase sequence is derived. In some embodiments, the encoded thioesterase shares at least 85%, at least 90%, at least 92%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or at least 99.5% identity with the above provided amino acid sequences, and the thioesterase encoded by the isolated nucleic acid molecule has at least the level of activity of the reference thioesterase from which the sequence is derived.
In some embodiments, the recombinant or isolated nucleic acid molecule encoding an acyl-ACP thioesterase includes an amino acid sequence having at least 85% identity with the amino acid sequence from amino acid position 1 to amino acid position 361 of SEQ ID NO:51; an amino acid sequence having at least 98% identity with the amino acid sequence from amino acid position 1 to amino acid position 362 of SEQ ID NO:55; an amino acid sequence having at least 97% identity with the amino acid sequence from amino acid position 1 to amino acid position 360 of SEQ ID NO:59; an amino acid sequence having at least 90% identity with the amino acid sequence from amino acid position 1 to amino acid position 359 of SEQ ID NO:63; an amino acid sequence having at least 98% identity with the amino acid sequence from amino acid position 53 to amino acid position 410 of SEQ ID NO:65; an amino acid sequence having at least 96% identity with the amino acid sequence from amino acid position 1 to amino acid position 356 of SEQ ID NO:69; an amino acid sequence having at least 98% identity with the amino acid sequence from amino acid position 53 to amino acid position 410 of SEQ ID NO:71; an amino acid sequence having at least 96% identity with the amino acid sequence from amino acid position 1 to amino acid position 361 of SEQ ID NO:75; an amino acid sequence having at least 97% identity with the amino acid sequence from amino acid position 1 to amino acid position 360 of SEQ ID NO:79; an amino acid sequence having at least 96% identity with the amino acid sequence from amino acid position 54 to amino acid position 413 of SEQ ID NO:81; an amino acid sequence having at least 96% identity with the amino acid sequence from amino acid position 1 to amino acid position 362 of SEQ ID NO:85; an amino acid sequence having at least 96% identity with the amino acid sequence from amino acid position 1 to amino acid position 361 of SEQ ID NO:89; an amino acid sequence having at least 97% identity with the amino acid sequence from amino acid position 53 to amino acid position 394 of SEQ ID NO:91; an amino acid sequence having at least 97% identity with the amino acid sequence from amino acid position 53 to amino acid position 394 of SEQ ID NO:93; an amino acid sequence having at least 99% identity with the amino acid sequence from amino acid position 53 to amino acid position 394 of SEQ ID NO:95; an amino acid sequence having at least 92% identity with the amino acid sequence from amino acid position 1 to amino acid position 360 of SEQ ID NO:99; or an amino acid sequence having at least 98% identity with the amino acid sequence from amino acid position 53 to amino acid position 393 of SEQ ID NO:101, and has at least the level of activity of the reference thioesterase from which the encoded thioesterase sequence is derived.
In additional aspects, the invention includes a transgenic organism that carries a recombinant nucleic acid molecule encoding any of the thioesterases provided herein, such as those having at least 85%, at least 87%, at least 90%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identity with amino acid sequences of SEQ ID NO:49, SEQ ID NO:51, SEQ ID NO:53, SEQ ID NO:55, SEQ ID NO:59, SEQ ID NO:61, SEQ ID NO:63, SEQ ID NO:65, SEQ ID NO:67, SEQ ID NO:69, SEQ ID NO:71, SEQ ID NO:73, SEQ ID NO:75, SEQ ID NO:77, SEQ ID NO:79, SEQ ID NO:81, SEQ ID NO:83, SEQ ID NO:85, SEQ ID NO:87, SEQ ID NO:89, SEQ ID NO:91, SEQ ID NO:93, SEQ ID NO:95, SEQ ID NO:97, SEQ ID NO:99, or SEQ ID NO:101. The transgenic organism can be, for example, a plant, a bacterium, a fungus, a chromist, an alga, or a cyanobacterium.
Also included in the invention is a recombinant nucleic acid molecule encoding an acyl-ACP thioesterase that includes an amino acid sequence that has at least 99% identity to the amino acid sequence from amino acid position 65 to 355 of SEQ ID NO:29, in which expression of the thioesterase in a microorganism results in at least 60%, at least 70%, at least 80%, at least 85%, at least 90%, or at least 95% of the free fatty acid isolated from the cells or culture media have a single chain length, such as a C8 chain length. In some embodiments, the thioesterase includes an amino acid sequence that has at least 99% identity to the amino acid sequence from amino acid position 65 to 355 or from amino acid position 34 to 355 of SEQ ID NO:29, SEQ ID NO:8, SEQ ID NO:12, SEQ ID NO:26, SEQ ID NO:33, SEQ ID NO:40, SEQ ID NO:43, or SEQ ID NO:45, or from amino acid position 1 to 323 of SEQ ID NO:38. In some embodiments, the thioesterase includes an amino acid sequence that has at least 99% identity to the amino acid sequence from amino acid position 1 to 355 of SEQ ID NO:29, SEQ ID NO:8, SEQ ID NO:12, SEQ ID NO:22, SEQ ID NO:26, SEQ ID NO:33, SEQ ID NO:40, SEQ ID NO:43, or SEQ ID NO:45. In some embodiments, the thioesterase includes the amino acid sequence from amino acid position 1 to position 355 of SEQ ID NO:29.
In a further aspect, the invention includes an isolated nucleic acid molecule encoding a variant of a plant acyl-ACP thioesterase having increased activity with respect to the native thioesterase it is derived from, in which the variant comprises a mutation of the amino acid corresponding to the amino acid at position 174 of SEQ ID NO:29. In preferred embodiments, expression of the variant acyl-ACP thioesterase encoded by the isolated nucleic acid molecule in a transgenic organism increases the amount of fatty acid product produced by the organism with respect to the amount produced by the organism transformed with the gene encoding the acyl-ACP thioesterase that does not include the mutation at position 174.
In some embodiments, the acyl-ACP thioesterase gene having a mutation at position 174 encodes a variant that has increased activity toward a preferred fatty acyl substrate. In some embodiments, the acyl-ACP thioesterase gene having a mutation at position 174 encodes a variant that has increased activity toward a C8 fatty acyl substrate. In preferred embodiments, the percentage of a C8 fatty acid product to the total fatty acid product produced by a transgenic organism expressing the variant thioesterase is at least 5%, at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, at least 45%, at least 50%, at least 55%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the total fatty acid product produced by the organism.
In some preferred embodiments, the plant acyl-ACP thioesterase is a Class II, or “FatB” acyl-ACP thioesterase. The Class II acyl-ACP thioesterase in some embodiments comprises an amino acid sequence that is at least 65% identical, at least 70% identical, at least 75% identical, at least 80% identical, at least 85% identical, at least 90% identical, or at least 95% identical to amino acids 65 to 355 of SEQ ID NO:29. In some embodiments, a mutation in a variant of a plant acyl-ACP thioesterase changes the amino acid corresponding to position 174 of SEQ ID NO:29 to an uncharged amino acid, which in some embodiments is a branched chain aliphatic amino acid. In some embodiments, the mutation changes the amino acid at position 174 to cysteine, methionine, phenylalanine, valine, leucine, or isoleucine. In some embodiments, the mutation changes a methionine at position 174 to cysteine, phenylalanine, valine, leucine, or isoleucine. In some embodiments, the variant acyl-ACP thioesterase has one, two, three, or more mutations in addition to the mutation at position 174. In an exemplary embodiment, the isolated nucleic acid molecule encodes a variant of a plant acyl-ACP thioesterase that has an isoleucine at position 103 and comprises the mutation M1741. In some embodiments, the variant acyl-ACP thioesterase has one, two, three, or more mutations in addition to the mutation at position 174.
In some embodiments, the isolated nucleic acid molecule encodes a variant of a plant acyl-ACP thioesterase, in which the variant has at least 90% identity or at least 95% identity to the amino acid sequence from amino acid position 65 to 355 of SEQ ID NO:40, SEQ ID NO:43, or SEQ ID NO:45. In exemplary embodiments the isolated nucleic acid molecule comprises a sequence encoding the amino acid sequence from position 65 to 355 of SEQ ID NO:40, SEQ ID NO:43, or SEQ ID NO:45, or from position 34 to 355 of SEQ ID NO:40, SEQ ID NO:43, or SEQ ID NO:45. The isolated nucleic acid molecule in some embodiments comprises SEQ ID NO:39, SEQ ID NO:42, or SEQ ID NO:44.
In additional aspects, the invention includes transgenic organisms that harbor recombinant nucleic acid molecules encoding acyl-ACP thioesterase variants having increased activity as described herein, in which the variants include a mutation at the amino acid position corresponding to amino acid 174 of SEQ ID NO:29. The organisms can be transformed with or carry an exogenous gene encoding a variant acyl-ACP thioesterase that has one, two, three, or more mutations in addition to the mutation at position 174. In some preferred embodiments, a transgenic organism includes an exogenous gene encoding a variant acyl-ACP thioesterase having a mutation at position 174 and an isoleucine at position 103, for example, the transgenic organism may have an isoleucine, methionine, phenylalanine, cysteine, leucine, or valine at position 174 and an isoleucine at position 103. In an exemplary embodiment, the variant thioesterase has an isoleucine at amino acid position 103 and an isoleucine at amino acid position 174. The transgenic organism can be, for example, a plant, a bacterium, a fungus, a chromist, an alga, or a cyanobacterium.
Also included in the invention is a method of producing a fatty acid product (including a fatty acid), in which the method includes culturing cells of an organism having an exogenous nucleic acid molecule encoding any of the Class II acyl-ACP thioesterases disclosed herein, and isolating a fatty acid product from the organism or culture medium. In some embodiments, the organism is a photosynthetic organisms, a prokaryotic organism, a fungal species, or a chromist species (e.g, a member of the Sagenista, Oomycota, Bacillariophyta, Silicoflagellata, Chrysophyta, or Xanthophyta). In some embodiments of the methods, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, at least 45%, or at least 50% of the isolated fatty acid or fatty acid product is a fatty acid or fatty acid product of a specific chain length. In some embodiments of the methods, at least 5%, at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, at least 45%, or at least 50% of the isolated fatty acids or fatty acid products are fatty acids or fatty acid products of two specific chain lengths or three specific chain lengths.
The organism carrying the exogenous acyl-ACP thioesterase gene in some embodiments is a photosynthetic organism, and in some embodiments is an alga, such as a microalga, and can be a eukaryotic alga or a cyanobacterium, for example. The sequence encoding the thioesterase is in some embodiments codon-optimized for expression in the host organism.
The photosynthetic organism can be cultured or grown phototrophically or mixotrophically. The fatty acid or fatty acid product can be isolated from the culture medium, from cells or tissue, or from whole culture, including both the culture medium and cells of the transgenic organism. In some embodiments, the fatty acid or fatty acid product is a triglyceride. The fatty acid or fatty acid product in alternative embodiments is a free fatty acid, a fatty aldehyde, a fatty alcohol, a fatty ester (including a wax ester) or a hydrocarbon, such as an alkane or alkene. In some embodiments, the host organism also includes one or more additional transgenes that encode enzymes used in the biosynthesis of the fatty acid product, such as, for example, an acetyl-CoA carboxylase, a ketoacyl-CoA synthase, a fatty acid elongase, an acyl-CoA synthetase, a fatty acyl-CoA reductase, a fatty aldehyde reductase, an alcohol acetyl transferase, an acyl-CoA alcohol transacylase, an acyltransferase, a wax synthase, an aldehyde decarbonylase, or a fatty acid decarboxylase.
The method can be used to produce fatty acids or fatty acid products such as triglycerides, fatty aldehydes, fatty alcohols, fatty esters, hydrocarbons, or fatty acids. In some embodiments, at least 5%, at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, or at least 40%, at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, or at least 90% of the isolated fatty acids or fatty acid products are one or more of a C8, a C10, a C12, a C14, a C16, or a C18 fatty acid or fatty acid product, such as a free fatty acid or derivative thereof.
A further aspect of the invention is a method of producing a fatty acid product, in which the method includes cultivating an organism containing an exogenous nucleic acid molecule encoding a variant plant acyl-ACP thioesterase having a mutation at the amino acid position corresponding to amino acid 174 of SEQ ID NO:29, and isolating a fatty acid product from the organism or culture medium. The transgenic organism can be, for example, a bacterium or a photosynthetic organism, such as a plant, microalga, or cyanobacterium. In some embodiments, for example, the transgenic organism is a prokaryote, and the method comprises isolating fatty acids from the culture medium. The sequence encoding the plant acyl-ACP thioesterase is codon-optimized for expression in the organism in some preferred embodiments.
In some preferred embodiments, the organism is a microorganism, and a fatty acid or fatty acid product is isolated from the culture medium. In some preferred embodiments, at least 10% of the fatty acid product isolated from the cells or medium is a C8 fatty acid or fatty acid product, and in some preferred embodiments, at least 30%, at least 35%, least 40%, at least 45%, at least 50%, at least 55%, at least 60%, or at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, least 90%, or at least 95%, of the fatty acid or fatty acid product isolated from the cells or culture medium is a C8 fatty acid or fatty acid product. In some embodiments, the fatty acid product isolated from the cells or medium of a culture of a transgenic microorganism is octanoic acid.
Included in the method are embodiments in which the host organism carries an exogenous nucleic acid molecule that encodes a variant of a naturally-occurring medium chain length acyl-ACP thioesterase having a mutation at position 174, in which the variant has enhanced activity towards a C8 acyl substrate with respect to the naturally-occurring thioesterase. In some preferred embodiments, the variant thioesterase having enhanced activity toward a C8 acyl substrate has an isoleucine residue at the amino acid position corresponding to amino acid position 174 of SEQ ID NO:29. In an exemplary embodiment, the variant thioesterase has an isoleucine at amino acid position 103 and an isoleucine at amino acid position 174. In illustrative embodiments, the variant comprises the amino acid sequence from position 65 to amino acid 355 of SEQ ID NO:40, SEQ ID NO:43, or SEQ ID NO:45.
The method can be used to produce fatty acids or fatty acid products such as triglycerides, fatty aldehydes, fatty alcohols, fatty esters, hydrocarbons, or fatty acids. In some embodiments, fatty acids are isolated, and at least 5%, at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, or at least 40%, at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, or at least 90% of the isolated fatty acid products are a C8 fatty acid or fatty acid product, such as a C8 fatty acid or derivative thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 provides an alignment of the deduced amino acid sequence of the wild-type C. aequipetala FatB2 acyl-ACP thioesterase (Ca1FatB2) from a gene assembled by PCR of genomic DNA with the removal of intron sequences (SEQ ID NO:29) and the wild-type gene in which the N-terminal sequence was extended (SEQ ID NO:22). The methionine at position 174 is underlined.
FIGS. 2A-2D are tables showing the amount of C8, C10, C12, C14, C16, and C18 fatty acids produced by bacterial isolates which had been transformed with genes encoding variants of the Ca1FatB2 gene.
FIGS. 3A-3D are tables showing the amount of C8, C10, C12, C14, C16, and C18 fatty acids produced by strains, of bacterial isolates which had been transformed with genes encoding variants of the Ca1FatB2 gene, normalized for cell density.
FIG. 4A depicts graphically the C8 fatty acid production of the isolates of FIGS. 2A-2D that harbor the acyl-ACP thioesterase gene mutated at position 174 (isolates 1-38) or positions 103, 184, and 174 (isolates 39-72).
FIG. 4B depicts graphically the data from FIGS. 3A-3D of C8 fatty acid production normalized to cell density of the same isolates overnight growth.
FIG. 5A is a table showing the amount of C8, C10, C12, C14, C16, and C18 fatty acids produced by bacterial isolates encoding variants of the Ca1FatB2 gene mutated at position 174 (isolates 81, 82, 85, and 86); at positions 174 and 103 (isolates 83 and 84), or at positions 103, 184, and 174 (isolates 79, 80, 87, 88, 89, and 90).
FIG. 5B is a table of the bacterial isolates of FIG. 5A in which the amount of C8, C10, C12, C14, C16, and C18 fatty acids produced by the strains has been normalized for cell density.
FIG. 6 depicts graphically the C8 fatty acid production, normalized for cell density, of the isolates of FIGS. 5A-5B .
FIG. 7 is an alignment of the translated sequence of the 5′ portion of the Ca1FatB2 thioesterase genes cloned in expression constructs. Amino acid positions in the aligned thioesterases corresponding to position 33/34 and position 63/64 are shown in bold.
FIG. 8 provides a graph showing the amount of C8:0, C10:0, C10:1, C12:0, C12:1, C14:0, C14:1, C16:0, C16:1, C18:0, and C18:1 free fatty acids, normalized to cell density, isolated from cultures of E. coli transformed with various Cuphea FatB thioesterase genes.
FIG. 9 provides a graph showing the amount of C8:0, C10:0, C10:1, C12:0, C12:1, C14:0, C14:1, C16:0, C16:1, C18:0, and C18:1 free fatty acids, normalized to cell density, isolated from cultures of E. coli transformed with various Cuphea FatB thioesterase genes.
FIG. 10 provides a graph showing the amount of C8:0, C10:0, C12:0, C14:0, C16:0, C16:1, C18:0, and C18:1 free fatty acids, normalized to cell density, isolated from cultures of E. coli transformed with the Ca1FatB1 thioesterase gene.
FIG. 11 provides a graph showing the amount of C8:0, C10:0, C12:0, C14:0, C16:0, C16:1, C18:0, and C18:1 free fatty acids, normalized to cell density, isolated from cultures of Synechocystis transformed with various Cuphea FatB thioesterase genes.
FIG. 11 provides a graph showing the amount of C8:0, C10:0, C12:0, C14:0, C16:0, C16:1, C18:0, and C18:1 free fatty acids, normalized to cell density, isolated from cultures of Synechocystis transformed with various Cuphea FatB thioesterase genes.
FIG. 12 provides a graph showing the amount of C8:0, C10:0, C12:0, C14:0, C16:0, C16:1, C18:0, and C18:1 free fatty acids, normalized to cell density, isolated from a culture of Synechocystis transformed with the Ca2FatB2 thioesterase gene.
FIG. 13A provides a graph showing the amount of C8:0, C10:0, C12:0, C14:0, C16:0, C16:1, C18:0, and C18:1 free fatty acids isolated from cultures of Synechocystis transformed with various Cuphea FatB thioesterase genes.
FIG. 13B provides a graph of the same data, in which the production values were normalized for cell density.
FIG. 14A depicts the results of gas chromatography analysis of wax ester products extracted from E. coli cells transformed with the Mus musculus wax synthase gene and the Cc1FatB1 thioesterase gene and supplied with decanol.
FIG. 14B depicts the results of gas chromatography analysis of wax ester products extracted from E. coli cells transformed with the Mus musculus wax synthase gene and C. hookeriana thioesterase ChFatB2.
DETAILED DESCRIPTION OF THE INVENTION
Disclosed in the present application are nucleic acid molecules encoding novel plant acyl-ACP thioesterases. Such nucleic acid molecules can be used to transform organisms, such as photosynthetic organisms and prokaryotic organisms, for synthesizing fatty acids and fatty acid products such as fatty aldehydes, fatty alcohols, fatty esters, including wax esters, and hydrocarbons. Also included in the invention are organisms transformed with the nucleic acid molecules provided herein, and methods of making fatty acid products using the organisms transformed with nucleic acid molecules encoding novel acyl-ACP thioesterases.
Elements of the embodiments described herein can be combined to make additional embodiments not specifically described that are also within the scope of the invention. Headings within the application are solely for the convenience of the reader, and do not limit in any way the scope of the invention or its embodiments.
All publications and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention is related. The following terms are defined for purposes of the invention as described herein.
Accession numbers are unique identifiers for a sequence record publicly available at the National Center for Biotechnology Information internet site maintained by the United States National Institutes of Health which can be accessed at ncbi.nlm.nih.gov. The “GenInfo Identifier” (GI) sequence identification number is specific to a nucleotide or amino acid sequence. If a sequence changes in any way, a new GI number is assigned. A Sequence Revision History tool is available to track the various GI numbers, version numbers, and update dates for sequences that appeared in a specific GenBank record. Searching and obtaining nucleic acid or gene sequences or protein sequences based on Accession numbers and GI numbers is well known in the arts of cell biology, biochemistry, molecular biology, and molecular genetics.
The singular form “a”, “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a cell” includes a plurality of cells and reference to “an antibody” includes a plurality of antibodies, etc.
As used herein, the terms “about” or “approximately” when referring to any numerical value are intended to mean a value of plus or minus 10% of the stated value. For example, “about 50 degrees C.” (or “approximately 50 degrees C.”) encompasses a range of temperatures from 45 degrees C. to 55 degrees C., inclusive. Similarly, “about 100 mM” (or “approximately 100 mM”) encompasses a range of concentrations from 90 mM to 110 mM, inclusive. All ranges provided within the application are inclusive of the values of the upper and lower ends of the range.
An “isolated” biomolecule such as an isolated protein or nucleic acid, is a biomolecule removed from the context in which the biomolecule exist in nature. For example, an isolated protein or nucleic acid molecule is removed from the cell or organism with which it is associated in its natural state. An isolated biomolecule can be, in some instances, partially or substantially purified, for example, an isolated nucleic acid molecule can be a nucleic acid sequence that has been excised from the chromosome, genome, or episome that it is integrated into in nature.
A recombinant or “engineered” nucleic acid molecule is a nucleic acid molecule that has been altered through human manipulation. As nonlimiting examples, a recombinant nucleic acid molecule: 1) includes conjoined nucleotide sequences that are not conjoined in nature, 2) has been engineered using molecular cloning techniques such that it lacks one or more nucleotides with respect to the naturally occurring nucleic acid molecule sequence, or 3) has been manipulated using molecular cloning techniques such that it has one or more sequence changes or rearrangements with respect to the naturally occurring nucleic acid sequence. As nonlimiting examples, a cDNA is a recombinant DNA molecule, as is any nucleic acid molecule that has been generated by in vitro polymerase reaction(s), or to which linkers have been attached, or that has been integrated into a vector, such as a cloning vector or expression vector.
A “homolog” of a gene or protein refers to its functional equivalent in another species.
A “variant” of a gene or nucleic acid sequence is a sequence having at least 65% identity with the referenced gene or nucleic acid sequence, and can include one or more base deletions, additions, or substitutions with respect to the referenced sequence. Variants also include chimeric genes that include sequences from two or more sources. A variant can be a naturally-occurring variant or the result of a spontaneous or induced mutation. Induced mutations can be created using methods known in the art for mutagenesis of organisms or cells (for example, using gamma or UV irradiation or chemical mutagens such as 5-bromo deoxyuridine, ethyl methane sulfonate (EMS), methyl methane sulfonate (MMS), diethylsulfate (DES), nitrosoguanidine (NTG), ICR compounds, etc., or can be introduced using genetic engineering techniques, such as gene synthesis, in vivo single strand repair techniques, polymerase-based amplification at error-permissive temperature and/or polymerase-based amplification using primers that incorporate base changes.
A “variant” of a peptide or protein is a peptide or protein sequence that varies at one or more amino acid positions with respect to the reference peptide or protein. A variant can be a naturally-occurring variant or can be the result of spontaneous, induced, or genetically engineered mutation(s) to the nucleic acid molecule encoding the variant peptide or protein. A variant peptide can also be a chemically synthesized variant.
As used herein “thioesterase” includes wild-type thioesterase proteins as well as variants thereof, and “thioesterase gene” refers to any nucleotide sequence encoding a thioesterase, which can be a wild-type thioesterase or a variant thioesterase.
“Exogenous” in the context of a gene or protein is a gene or protein that is not derived from the host organism species.
A “heterologous” gene or nucleic acid sequence is a gene or sequence from a different source than the host organism it is introduced into, or from a different source than another nucleic acid sequence with which is juxtaposed in a nucleic acid construct. For example, a gene of one species introduced into another species may be referred to as a heterologous gene. A promoter linked to a gene not operably linked to the promoter in its natural state in the organism may be referred to as a heterologous promoter.
A gene that is “codon-optimized” for expression in an organism is a gene whose nucleotide sequence has been altered with respect to the original nucleotide sequence, such that one or more codons of the nucleotide sequence has been changed to a different codon that encodes the same amino acid, in which the new codon is used more frequently in genes of the organism of interest than the original codon. The degeneracy of the genetic code provides that all amino acids except for methionine and tryptophan are encoded by more than one codon. For example, arginine, leucine, and serine are encoded by different six different codons; glycine, alanine, valine, threonine, and proline are encoded by four different codons. Many organisms use certain codons to encode a particular amino acid more frequently than others. Without limiting any aspects of the invention to any particular mechanism, it is believed that some tRNAs for a given amino acid are more prevalent than others within a particular organism, and genes requiring a rare tRNA for translation of the encoded protein may be expressed at a low level due in part to a limiting amount of the rare tRNA. Thus, for adequate or optimal levels of expression of an encoded protein, a gene may be “codon-optimized” to change one or more codons to new codons (“preferred codons”) that are among those used more frequently in the genes of the host organism (referred to as the “codon preference” of the organism). As used in the context of the invention, a “codon-optimized” gene or nucleic acid molecule of the invention need not have every codon altered to conform to the codon preference of the intended host organism, nor is it required that altered codons of a “codon-optimized” gene or nucleic acid molecule be changed to the most prevalent codon used by the organism of interest. For example, a codon-optimized gene may have one or more codons changed to codons that are used more frequently that the original codon(s), whether or not they are used most frequently in the organism to encode a particular amino acid.
“Photosynthetic organisms” are any prokaryotic or eukaryotic organisms that can perform photosynthesis. Photosynthetic organisms include higher plants (i.e., vascular plants), bryophytes, algae, and photosynthetic bacteria. The term “algae” includes cyanobacteria (Cyanophyceae), green algae (Chlorophyceae), yellow-green algae (Xanthophyceae), golden algae (Chrysophyceae), brown algae (Phaeophyceae), red algae (Rhodophyceae), diatoms (Bacillariophyceae), and “pico-plankton” (Prasinophyceae and Eustigmatophyceae). Also included in the term algae are members of the taxonomic classes Dinophyceae, Cryptophyceae, Euglenophyceae, Glaucophyceae, and Prymnesiophyceae. Microalgae are unicellular or colonial algae that can be seen as single organisms only with the aid of a microscope. Microalgae include both eukaryotic and prokaryotic algae (e.g., cyanobacteria). Photosynthetic bacteria include cyanobacteria, green sulfur bacteria, purple sulfur bacteria, purple nonsulfur bacteria, and green nonsulfur bacteria.
A “plant acyl-ACP thioesterase” is an acyl-ACP thioesterase derived from a plant species, which includes species of higher plants, ferns, and mosses, for example, bryophyte, pteridophyte, cycadophyte, ginkgophyte, pinophyte, gnetophyte, and magnoliophyte species.
A “fatty acid product” includes a fatty acid, a fatty aldehyde, a fatty alcohol, a fatty ester (including a wax ester), a triglyceride, a hydrocarbon, or any other fatty acid derivatives.
A “C8 fatty acid” or a “C8 fatty acid product” is a fatty acid or a fatty acid product having an acyl chain of 8 carbons. An example of a saturated C8 fatty acid is octanoic acid, also called caprylic acid.
A “C10 fatty acid” or a “C10 fatty acid product” is a fatty acid or a fatty acid product having an acyl chain of 10 carbons. An example of a C10 fatty acid is decanoic acid, also known as capric acid.
A “C12 fatty acid” or a “C12 fatty acid product” is a fatty acid or a fatty acid product having an acyl chain of 12 carbons. An example of a C12 fatty acid is dodecanoic acid, also known as lauric acid.
A “C14 fatty acid” or a “C14 fatty acid product” is a fatty acid or a fatty acid product having an acyl chain of 14 carbons. An example of a C14 fatty acid is tetradecanoic acid, also known as myristic acid.
A “C16 fatty acid” or a “C16 fatty acid product” is a fatty acid or a fatty acid product having an acyl chain of 16 carbons. An example of a C14 fatty acid is hexadecanoic acid, also known as palmitic acid.
A “C18 fatty acid” or a “C18 fatty acid product” is a fatty acid or a fatty acid product having an acyl chain of 18 carbons. An example of a C18 fatty acid is octadecanoic acid, also known as stearic acid.
A “C8 preferring” acyl-ACP thioesterase is an acyl-ACP thioesterase having higher activity on a C8 acyl-ACP substrate (e.g., octanoyl-ACP) than on any other chain length substrate. Analogously, a “C10 preferring” acyl-ACP thioesterase is an acyl-ACP thioesterase having higher activity on a C10 acyl-ACP substrate (e.g., decanoyl-ACP) than on any other chain length substrate, a “C12 preferring” acyl-ACP thioesterase is an acyl-ACP thioesterase having higher activity on a C12 acyl-ACP substrate (e.g., dodecanoyl-ACP) than on any other chain length substrate, a “C14 preferring” acyl-ACP thioesterase is an acyl-ACP thioesterase having higher activity on a C14 acyl-ACP substrate (e.g., tetradecanoyl-ACP) than on any other chain length substrate, a “C16 preferring” acyl-ACP thioesterase is an acyl-ACP thioesterase having higher activity on a C16 acyl-ACP substrate (e.g., hexadecanoyl-ACP) than on any other chain length substrate, and a “C18 preferring” acyl-ACP thioesterase is an acyl-ACP thioesterase having higher activity on a C18 acyl-ACP substrate (e.g., octadecanoyl-ACP) than on any other chain length substrate.
An acyl-ACP thioesterase with “binary activity” is a thioesterase that has a preference for one or more medium chain length acyl-ACP substrates as well as a preference for one or more long chain length acyl-ACP substrates.
A “medium chain length” fatty acid or fatty acid product is a fatty acid or fatty acid product having an acyl chain length of from 8-14 carbons.
A “long chain length” fatty acid or fatty acid product is a fatty acid or fatty acid product having an acyl chain length of greater than 14 carbons.
The degree of amino acid or nucleic acid sequence identity can be determined by various computer programs for aligning the sequences to be compared based on designated program parameters. For example, sequences can be aligned and compared using the local homology algorithm of Smith & Waterman, Adv. Appl. Math. 2:482 (1981), the homology alignment algorithm of Needleman & Wunsch, J. Mol. Biol. 48:443 (1970), or the search for similarity method of Pearson & Lipman, Proc. Nat'l. Acad. Sci. USA 85:2444 (1988), and can be aligned and compared based on visual inspection or can use computer programs for the analysis (for example, GAP, BESTFIT, FASTA, and TFASTA in the Wisconsin Genetics Software Package, Genetics Computer Group, 575 Science Dr., Madison, Wis.).
The BLAST algorithm, described in Altschul et al., J. Mol. Biol. 215:403-410 (1990), is publicly available through software provided by the National Center for Biotechnology Information (at the web address www.ncbi.nlm.nih.gov). This algorithm identifies high scoring sequence pairs (HSPs) by identifying short words of length W in the query sequence, which either match or satisfy some positive-valued threshold score T when aligned with a word of the same length in a database sequence. T is referred to as the neighborhood word score threshold (Altschul et al., supra.). Initial neighborhood word hits act as seeds for initiating searches to find longer HSPs containing them. The word hits are then extended in both directions along each sequence for as far as the cumulative alignment score can be increased. Cumulative scores are calculated using, for nucleotide sequences, the parameters M (reward score for a pair of matching residues; always >0) and N (penalty score for mismatching residues; always <0). For amino acid sequences, a scoring matrix is used to calculate the cumulative score. Extension of the word hits in each direction are halted when: the cumulative alignment score falls off by the quantity X from its maximum achieved value; the cumulative score goes to zero or below due to the accumulation of one or more negative-scoring residue alignments; or the end of either sequence is reached. For determining the percent identity of an amino acid sequence or nucleic acid sequence, the default parameters of the BLAST programs can be used. For analysis of amino acid sequences, the BLASTP defaults are: word length (W), 3; expectation (E), 10; and the BLOSUM62 scoring matrix. For analysis of nucleic acid sequences, the BLASTN program defaults are word length (W), 11; expectation (E), 10; M=5; N=−4; and a comparison of both strands. The TBLASTN program (using a protein sequence to query nucleotide sequence databases) uses as defaults a word length (W) of 3, an expectation (E) of 10, and a BLOSUM 62 scoring matrix. (see Henikoff & Henikoff, Proc. Natl. Acad. Sci. USA 89:10915 (1989)).
In addition to calculating percent sequence identity, the BLAST algorithm also performs a statistical analysis of the similarity between two sequences (see, e.g., Karlin & Altschul, Proc. Nat'l. Acad. Sci. USA 90:5873-5787 (1993)). The smallest sum probability (P(N)), provides an indication of the probability by which a match between two nucleotide or amino acid sequences would occur by chance. For example, a nucleic acid is considered similar to a reference sequence if the smallest sum probability in a comparison of the test nucleic acid to the reference nucleic acid is less than about 0.1, preferably less than about 0.01, and more preferably less than about 0.001.
Nucleic Acid Molecules Encoding Class II Thioesterases
Provided herein are new thioesterase FatB genes from various Cuphea species. As detailed in the examples, the native or wild-type FatB genes Ca1FatB2 (SEQ ID NO:21), Cc1FatB1 (SEQ ID NO:48), Ca1FatB1 (SEQ ID NO:52), Ci1FatB1 (SEQ ID NO:56), Cl1FatB1 (SEQ ID NO:60), Cl1FatB2 (SEQ ID NO:64), Cp1FatB1 (SEQ ID NO:66), Cl2FatB1 (SEQ ID NO:70), Cl2FatB2 (SEQ ID NO:72), Cl3FatB1 (SEQ ID NO:76), Cl3FatB2 (SEQ ID NO:80), Cd1FatB l (SEQ ID NO:82), Cl4FatB1 (SEQ ID NO:86), Cl4FatB2 (SEQ ID NO:90), Cl4FatB3 (SEQ ID NO:92), Ca2FatB1 (SEQ ID NO:94), Ca2FatB2 (SEQ ID NO:96), and Ca2FatB3 (SEQ ID NO:100), have been reconstructed using primer-based amplification (i.e., polymerase chain reaction, or PCR) and gene walking such that, based on homology with other plant thioesterases, it is estimated that all of the protein-encoding sequence except for sequences encoding approximately ten to fifteen amino acids of the N-terminuses have been determined. The deduced amino acid sequences of the encoded proteins are provided as SEQ ID NO:22 (Ca1FatB2), SEQ ID NO:49 (Cc1FatB1), SEQ ID NO:53 (Ca1FatB1), SEQ ID NO:57 (Ci1FatB1), SEQ ID NO:61 (Cl1FatB1), SEQ ID NO:65 (Cl1FatB2), SEQ ID NO:67 (Cp1FatB), SEQ ID NO:71 (Cl2FatB1), SEQ ID NO:73 (Cl2FatB2), SEQ ID NO:77 (Cl3FatB1), SEQ ID NO:81 (Cl3FatB2), SEQ ID NO:83 (Cd1FatB1), SEQ ID NO:87 (Cl4FatB1), SEQ ID NO:91 (Cl4FatB2), SEQ ID NO:93 (Cl4FatB3), SEQ ID NO:95 (Ca2FatB1), SEQ ID NO:97 (Ca2FatB2), and SEQ ID NO:101 (Ca2FatB3). Protein-encoding sequences of gene constructs for the expression of thioesterases based on some of these genes and the deduced amino acid sequences are provided in Table 4. The nucleotide and amino acid sequences disclosed herein are reference sequences when referring to variants based on those sequences. A reference thioesterase is a thioesterase having the sequence of the reference sequence.
The invention includes isolated or recombinant nucleic acid molecules encoding Class II thioesterases having at least at least 85%, at least 90%, at least 95%, or at least 99% identity with the amino acid sequence from amino acid position 1 to amino acid position 361 of SEQ ID NO:51; an amino acid sequence having at least 98% identity with the amino acid sequence from amino acid position 1 to amino acid position 362 of SEQ ID NO:55; an amino acid sequence having at least 97% identity with the amino acid sequence from amino acid position 1 to amino acid position 360 of SEQ ID NO:59; an amino acid sequence having at least 90% identity with the amino acid sequence from amino acid position 1 to amino acid position 359 of SEQ ID NO:63; an amino acid sequence having at least 98% identity with the amino acid sequence from amino acid position 53 to amino acid position 410 of SEQ ID NO:65; an amino acid sequence having at least 96% identity with the amino acid sequence from amino acid position 1 to amino acid position 356 of SEQ ID NO:69; an amino acid sequence having at least 98% identity with the amino acid sequence from amino acid position 53 to amino acid position 410 of SEQ ID NO:71; an amino acid sequence having at least 96% identity with the amino acid sequence from amino acid position 1 to amino acid position 361 of SEQ ID NO:75; an amino acid sequence having at least 97% identity with the amino acid sequence from amino acid position 1 to amino acid position 360 of SEQ ID NO:79; an amino acid sequence having at least 96% identity with the amino acid sequence from amino acid position 54 to amino acid position 413 of SEQ ID NO:81; an amino acid sequence having at least 96% identity with the amino acid sequence from amino acid position 1 to amino acid position 362 of SEQ ID NO:85; an amino acid sequence having at least 96% identity with the amino acid sequence from amino acid position 1 to amino acid position 361 of SEQ ID NO:89; an amino acid sequence having at least 97% identity with the amino acid sequence from amino acid position 53 to amino acid position 394 of SEQ ID NO:91; an amino acid sequence having at least 97% identity with the amino acid sequence from amino acid position 53 to amino acid position 394 of SEQ ID NO:93; an amino acid sequence having at least 99% identity with the amino acid sequence from amino acid position 53 to amino acid position 394 of SEQ ID NO:95; an amino acid sequence having at least 92% identity with the amino acid sequence from amino acid position 1 to amino acid position 360 of SEQ ID NO:99; or an amino acid sequence having at least 98% identity with the amino acid sequence from amino acid position 53 to amino acid position 393 of SEQ ID NO:101, in which the expressed protein encoded by the nucleic acid molecule has thioesterase activity. In some embodiments, the expressed thioesterase has at least the level of activity against an acyl-ACP substrate as the reference thioesterase from which the encoded thioesterase sequence is derived.
Also contemplated are nucleic acid molecules encoding acyl-ACP thioesterases with mature polypeptide sequences having at least 85%, 87%, 90%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity to the sequences of a mature thioesterase as disclosed herein, in which the thioesterases have N-terminal sequences that differ from the wild-type thioesterases from which they are derived. Thioesterase genes from plants such as Cuphea encode transit peptides. The cleavage site for removal of the transit peptide upon import of thioesterases into chloroplasts is hypothesized to be between positions 33 and 34 of SEQ ID NO:29 (Mayer and Shanklin BMC Plant Biology 7:1 (2007); see FIG. 1 and FIG. 7 ). As the transit peptide of plant thioesterases for import of the enzymes into plastids is not necessary for the activity of a thioesterase expressed in a prokaryotic organism, in many embodiments thioesterase genes designed for expression in prokaryotes, as exemplified in the Examples herein, do not encode all or a portion of a transit peptide.
In some embodiments, the recombinant or isolated nucleic acid molecule encoding an acyl-ACP thioesterase includes an amino acid sequence having at least 85%, at least 90%, at least 95%, or at least 99% identity with the amino acid sequence from amino acid position 33 to amino acid position 361 of SEQ ID NO:51; having at least 98% identity with the amino acid sequence from amino acid position 35 to amino acid position 362 of SEQ ID NO:55; having at least 97% identity with the amino acid sequence from amino acid position 34 to amino acid position 360 of SEQ ID NO:59; having at least 90% identity with the amino acid sequence from amino acid position 34 to amino acid position 359 of SEQ ID NO:63; having at least 98% identity with the amino acid sequence from amino acid position 84 to amino acid position 410 of SEQ ID NO:65; having at least 96% identity with the amino acid sequence from amino acid position 34 to amino acid position 356 of SEQ ID NO:69; having at least 98% identity with the amino acid sequence from amino acid position 84 to amino acid position 410 of SEQ ID NO:71; having at least 96% identity with the amino acid sequence from amino acid position 33 to amino acid position 361 of SEQ ID NO:75; having at least 97% identity with the amino acid sequence from amino acid position 34 to amino acid position 360 of SEQ ID NO:79; having at least 96% identity with the amino acid sequence from amino acid position 85 to amino acid position 413 of SEQ ID NO:81; having at least 96% identity with the amino acid sequence from amino acid position 34 to amino acid position 362 of SEQ ID NO:85; having at least 96% identity with the amino acid sequence from amino acid position 33 to amino acid position 361 of SEQ ID NO:89; having at least 97% identity with the amino acid sequence from amino acid position 84 to amino acid position 394 of SEQ ID NO:91; having at least 97% identity with the amino acid sequence from amino acid position 84 to amino acid position 394 of SEQ ID NO:93; having at least 99% identity with the amino acid sequence from amino acid position 84 to amino acid position 394 of SEQ ID NO:95; having at least 92% identity with the amino acid sequence from amino acid position 33 to amino acid position 360 of SEQ ID NO:99; or having at least 98% identity with the amino acid sequence from amino acid position 84 to amino acid position 393 of SEQ ID NO:101, and has at least the level of activity of the reference thioesterase from which the encoded thioesterase sequence is derived. In some embodiments, the encoded thioesterase shares at least 85%, at least 90%, at least 92%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or at least 99.5% identity with the above provided amino acid sequences, and the thioesterase encoded by the isolated nucleic acid molecule has at least the level of activity of the reference thioesterase from which the sequence is derived.
In some embodiments of the invention, a nucleic acid molecule may encode acyl-ACP thioesterases having a transit peptide sequence derived from one or more different acyl-ACP thioesterases, or from one or more proteins other than thioesterases that are imported into plastids. For example, in some embodiments in which a thioesterase gene is transformed into a eukaryotic photosynthetic organism for the production of a fatty acid product, the acyl-ACP thioesterase gene can encode a thioesterase that is at least 85%, at least 90%, at least 92%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or at least 99.5% identical to a thioesterase disclosed herein, while optionally including a sequence encoding any functional plastid transit peptide, such as a chloroplast transit peptide having an amino acid sequence that is less than 95% identical, less than 90% identical, less than 80% identical, less than 70% identical, less than 60% identical, less than 50% identical, less than 40% identical, less than 30% identical or less than 20% identical to sequences of the reference thioesterase precursor transit peptide. The transit peptide operably linked to the mature acyl-ACP thioesterase protein is in some embodiments from a chloroplast-directed protein from the species to be used as a transgenic host in the methods of the invention.
Furthermore, plant Class II thioesterases having deletions of the N-terminal amino acids extending to and including the amino acid corresponding to amino acid 65 of SEQ ID NO:29 (see FIG. 7 ), in which the thioesterase encoded by the isolated nucleic acid molecule has thioesterase activity. In preferred embodiments the encoded thioesterase has at least the level of activity as the reference thioesterase.
The invention includes, in exemplary embodiments, nucleic acid molecules encoding a thioesterase comprising an amino acid sequences having at least 96% identity to the amino acid sequence of SEQ ID NO:75, or from amino acid 64 to amino acid 361 of SEQ ID NO:75; or at least 92% identity to the amino acid sequence of SEQ ID NO:99 or from amino acid 64 to amino acid 361 of SEQ ID NO:99, in which the encoded thioesterase has a C10 acyl substrate preference, a C16 acyl substrate preference, or a binary preference for C10 and C16 acyl substrates. In illustrative examples expression of nucleic acid molecules encoding a thioesterase in a transgenic prokaryotic organism results in at least 20%, at least 30%, at least 35%, at least 40%, at least 45%, at least 50%, or at least 60% of the free fatty acids produced by or isolated from the prokaryotic organism being C10 and/or C16 fatty acids. In some embodiments, a nucleic acid molecule has at least 96% identity to the amino acid sequence of SEQ ID NO:75, or from amino acid 64 to amino acid 361 of SEQ ID NO:75; or at least 92% identity to the amino acid sequence of SEQ ID NO:99 or from amino acid 64 to amino acid 361 of SEQ ID NO:99, and expression of the thioesterase in a transgenic photosynthetic organism results in at least 20%, at least 30%, or at least 40%, of the free fatty acids produced by or isolated from the prokaryotic organism being C10 fatty acids.
In some embodiments, a nucleic acid molecule encodes a thioesterase having binary substrate preference, for example, the encoded thioesterase having at least 96% identity to SEQ ID NO:75 or at least 92% identity to SEQ ID NO:99, or a portion thereof, in some embodiments has a preference for one or more C10 substrates and one or more C16 substrates.
In another example, the invention includes nucleic acid molecules encoding a thioesterase comprising an amino acid sequences having at least 92% identity to from amino acid 63 to amino acid 360 of SEQ ID NO:99 or at least 99% identity to from amino acid 65 to amino acid 360 of SEQ ID NO:29, and the encoded thioesterase has a C8 acyl substrate preference. In some embodiments, a nucleic acid molecule encodes a thioesterase comprising an amino acid sequences having at least 92% identity to from amino acid 63 to amino acid 360 of SEQ ID NO:95 and expression of the thioesterase in a transgenic prokaryotic organism results in at least 20%, at least 30%, at least 35%, at least 40%, at least 45%, or at least 50% of the free fatty acids produced by or isolated from the prokaryotic organism being C8 and/or C10 fatty acids. In some embodiments, a nucleic acid molecule has at least 92% identity to from amino acid 63 to amino acid 360 of SEQ ID NO:99 or at least 99% identity to from amino acid 65 to amino acid 360 of SEQ ID NO:29, and expression of the thioesterase in a transgenic photosynthetic organism results in at least 20%, at least 30%, at least 35%, at least 40%, at least 45%, or at least 50% of the free fatty acids produced by or isolated from the prokaryotic organism being C8 fatty acids.
In other examples, the invention includes nucleic acid molecules encoding a thioesterase comprising an amino acid sequences having at least 85%, at least 90%, at least 92%, at least 95%, or at least 99% identity with the amino acid sequence from amino acid position 64 to amino acid position 361 of SEQ ID NO:51; at least 98% identity with the amino acid sequence from amino acid position 66 to amino acid position 362 of SEQ ID NO:55; at least 97% identity with the amino acid sequence from amino acid position 65 to amino acid position 360 of SEQ ID NO:59; at least 90% identity with the amino acid sequence from amino acid position 65 to amino acid position 359 of SEQ ID NO:63; at least 98% identity with the amino acid sequence from amino acid position 115 to amino acid position 410 of SEQ ID NO:65; at least 96% identity with the amino acid sequence from amino acid position 65 to amino acid position 356 of SEQ ID NO:69; at least 98% identity with the amino acid sequence from amino acid position 115 to amino acid position 410 of SEQ ID NO:71; at least 96% identity with the amino acid sequence from amino acid position 64 to amino acid position 361 of SEQ ID NO:75; at least 97% identity with the amino acid sequence from amino acid position 65 to amino acid position 360 of SEQ ID NO:79; at least 96% identity with the amino acid sequence from amino acid position 116 to amino acid position 413 of SEQ ID NO:81; at least 96% identity with the amino acid sequence from amino acid position 65 to amino acid position 362 of SEQ ID NO:85; at least 96% identity with the amino acid sequence from amino acid position 64 to amino acid position 361 of SEQ ID NO:89; at least 97% identity with the amino acid sequence from amino acid position 115 to amino acid position 394 of SEQ ID NO:91; at least 97% identity with the amino acid sequence from amino acid position 115 to amino acid position 394 of SEQ ID NO:93; at least 99% identity with the amino acid sequence from amino acid position 115 to amino acid position 394 of SEQ ID NO:95; at least 92% identity with the amino acid sequence from amino acid position 63 to amino acid position 360 of SEQ ID NO:99; or at least 98% identity with the amino acid sequence from amino acid position 115 to amino acid position 393 of SEQ ID NO:101, in which the encoded thioesterase has a C12, C14, and/or C16 acyl substrate preference. In some examples, the encoded acyl-ACP thioesterase has a C14 and/or C16 substrate preference. In illustrative examples expression of nucleic acid molecules encoding a thioesterase in a transgenic prokaryotic organism results in at least 20%, at least 30%, at least 35%, at least 40%, at least 45%, at least 50%, or at least 60% of the free fatty acids produced by or isolated from the prokaryotic organism being C12, C14 and/or C16 fatty acids.
An acyl-ACP thioesterase, such any of those disclosed herein, can be tested for its ability to direct synthesis of fatty acids or fatty acid products that are produced by transgenic organisms transformed with the nucleic acid molecules. Provided in the examples are descriptions of transforming host organisms with recombinant nucleic acid molecules encoding acyl-ACP thioesterases and recovering fatty acid products to determine the amount of fatty acid products of different chain lengths produced by the transgenic host.
Assays of a thioesterase can also be performed using lysates of transgenic organisms such as E. coli that are transformed with expression constructs that include the acyl-ACP thioesterase gene. Such assays can use labeled acyl substrates (see, for example, U.S. Pat. No. 5,667,997, incorporated herein by reference). An acyl-ACP thioesterase can also be partially or substantially purified prior to performing an assay; for example, the thioesterase can be expressed with an affinity tag (for example, a His tag) for affinity purification prior to performing the assay (Dehesh et al. Plant Physiol 110: 203-210 (1996), incorporated herein by reference).
The nucleic acid molecules encoding acyl-ACP thioesterases can be used to transform prokaryotic organisms or photosynthetic organisms, such as plants or algae, for the production of fatty acid products in the organisms. In some preferred embodiments, the sequence encoding the Class II thioesterase is codon-optimized for expression in the host organism. Codons can be optimized by methods such as those provided in U.S. Pat. No. 7,135,290, incorporated herein by reference. A codon usage database is available at the world wide web site kazusa.or.jp/codon/. Preferred codon usage can also be determined by a practitioner based on gene sequences entered in databases such as Genbank (ncbi.nlm.nih.gov/GenBank/), or a subset of genes of the organism (for example, highly expressed genes).
In some embodiments, the transgenic organism that includes a thioesterase gene of the invention is a bacterium, such as, but not limited to, an Acetobacter, Acinetobacter, Arthrobacter, Bacillus, Brevibacterium, Chromatium, Chlorobium, Clostridium, Corynebacterium, Deinococcus, Delftia, Desulfovibrio, Enterococcus, Escherichia, Kineococcus, Klebsiella, Lactobacillus, Lactococcus, Micrococcus, Mycobacterium, Jeotgalicoccus, Paenibacillus, Propionibacter, Pseudomonas, Rhodopseudomonas, Rhodobacter, Rhodococcus, Rhodospirillium, Rhodomicrobium, Salmonella, Serratia, Shewanella, Stenotrophomonas, Streptomyces, Streptococcus, Vibrio, or Zymomonas species.
A photosynthetic organism transformed with the nucleic acid molecule that encodes a thioesterase gene can be a plant, such as but not limited to a higher plant, or can be an alga. Higher plants considered for use in the invention include, without limitation, Arabidopsis thaliana, Arachis hypogaea, Avena sativa, Brassica species (e.g., Brassica napus, Brassica campestris, Brassica juncea ), Camelina sativa, Carthamus tinctorius, Cocos nucifera, Crambe ahyssiraica, Cuphea species, Elaeis species (e.g., Elaeis guineensis, Elaeis oleifera ), Gossypium hirsutum, Glycine max, Helianthus annuulus, Jatropha species, Cucurbita pepo, Oryza satvia, Sesamum indicum, Simmondsia chinensis, Theobroma cacao, Ricinus communis, and Zea mays.
Algae that can be used in the methods of the invention can be any algae, and can include microalgae, such as but not limited to, Achnanthes, Amphiprora, Amphora, Ankistrodesmus, Asteromonas, Boekelovia, Borodinella, Botryococcus, Bracteococcus, Chaetoceros, Carteria, Chlamydomonas, Chlorococcum, Chlorogonium, Chlorella, Chroomonas, Chrysosphaera, Cricosphaera, Crypthecodinium, Cryptomonas, Cyclotella, Dunaliella, Ellipsoidon, Emiliania, Eremosphaera, Ernodesmius, Euglena, Franceia, Fragilaria, Gloeothamnion, Haematococcus, Halocafeteria, Hymenomonas, Isochrysis, Lepocinclis, Micractinium, Monoraphidium, Nannochloris, Nannochloropsis, Navicula, Neochloris, Nephrochloris, Nephroselmis, Nitzschia, Ochromonas, Oedogonium, Oocystis, Ostreococcus, Pavlova, Parachlorella, Pascheria, Phaeodactylum, Phagus, Platymonas, Pleurochrysis, Pleurococcus, Prototheca, Pseudochlorella, Pyramimonas, Pyrobotrys, Scenedesmus, Schizochytrium, Skeletonema, Spyrogyra, Stichococcus, Tetraselmis, Thraustochytrium, Viridiella, or Volvox species.
In some embodiments, photosynthetic bacteria, including for example, green sulfur bacteria, purple sulfur bacteria, green nonsulfur bacteria, purple nonsulfur bacteria, or cyanobacteria are used for producing a fatty acid product. Cyanobacterial species that can be used for production of fatty acid products include, without limitation, Agmenellum, Anabaena, Anabaenopsis, Anacystis, Aphanizomenon, Arthrospira, Asterocapsa, Borzia, Calothrix, Chamaesiphon, Chlorogloeopsis, Chroococcidiopsis, Chroococcus, Crinalium, Cyanobacterium, Cyanobium, Cyanocystis, Cyanospira, Cyanothece, Cylindrospermopsis, Cylindrospermum, Dactylococcopsis, Dermocarpella, Fischerella, Fremyella, Geitleria, Geitlerinema, Gloeobacter, Gloeocapsa, Gloeothece, Halospirulina, Iyengariella, Leptolyngbya, Limnothrix, Lyngbya, Microcoleus, Microcystis, Myxosarcina, Nodularia, Nostoc, Nostochopsis, Oscillatoria, Phormidium, Planktothrix, Pleurocapsa, Prochlorococcus, Prochloron, Prochlorothrix, Pseudanabaena, Rivularia, Schizothrix, Scytonema, Spirulina, Stanieria, Starria, Stigonema, Symploca, Synechococcus, Synechocystis, Tolypothrix, Trichodesmium, Tychonema, or Xenococcus species.
In addition to photosynthetic microorganisms, non-photosynthetic microorganisms such as fungi, and nonalgal stamenophiles can be transformed with one or more thioesterase genes as disclosed herein for producing fatty acid products. For example, oleaginous yeasts, including but not limited to Aspergillus niger, Yarrowia lypolytica, Cryptococcus curvatus, Cryptococcus terricolus, Candida species, Lipomyces starkeyi, Lipomyces lipofer, Endomycopsis vernalis, Rhodotorula glutinis, and Rhodotorula gracilis can also be hosts transformed with thioesterase genes as disclosed herein. Other fungi, including but not limited to species of Aspergillus, Trichoderma, Neurospora, Fusarium, Humicola, Rhizomucor, Kluyveromyces, Pichia, Mucor, Myceliophtora, Penicillium, Phanerochaete, Chrysosporium, Saccharomyces, and Schizosaccharomyces, are also considered as transgenic hosts expressing thioesterase genes as disclosed herein for use in making fatty acid products. Labyrinthulomycete species (e.g., Thraustichytrium, Ulkenia, and Schizochytrium species) can also be transformed with a thioesterase gene in the practice of the invention.
Production of Fatty Acid Products
In another aspect, the invention provides a method of producing a fatty acid or a fatty acid product, in which the method includes cultivating an organism having an exogenous nucleic acid molecule that includes a sequence encoding an acyl-ACP thioesterase as disclosed herein, and isolating a fatty acid or a fatty acid product from the organism or culture medium. The transgenic host organism can be a bacterium, alga, cyanobacterium, or plant as provided herein, and the sequence encoding the plant acyl-ACP thioesterase in some embodiments is codon-optimized for expression in the host organism.
The methods can be used for the production and isolation of a fatty acid product such as a triglyceride, a fatty aldehyde, a fatty alcohol, a fatty ester, or a hydrocarbon such as an alkene or alkane. In some embodiments, the methods include isolation of fatty acid products that include one or more of a C8, C10, C12, C14, C16, or C18 fatty acid product. In some embodiments, the methods include isolation of fatty acid products that include one or more of a C8 or C10 fatty acid product. In some exemplary embodiments, one or more fatty acids (free fatty acids) are isolated using the methods of the invention, such as, for example, one or more of a C8 fatty acid or a C10 fatty acid.
In some preferred embodiments expression of an acyl-ACP thioesterase gene as provided herein in a transgenic organism results in at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, or at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the isolated fatty acid products isolated from the organism and/or culture medium being a single chain length fatty acid product. For example, in some embodiments, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, or at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the isolated fatty acid products from an organism expressing an exogenous acyl-ACP thioesterase of the invention is a C8, a C10, a C12, a C14, a C16, or a C18 fatty acid product. In some preferred embodiments, the isolated fatty acid products are fatty acids, and at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, or at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the fatty acids isolated from the organism and/or the growth medium is a C8 or a C10 free fatty acid.
In some embodiments, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, or at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the isolated fatty acid products from an organism expressing an exogenous acyl-ACP thioesterase of the invention are fatty acid products or two or more chain lengths, such as two or more of a C8, a C10, a C12, a C14, a C16, or a C18 fatty acid product. In some preferred embodiments, the fatty acid products are fatty acids, and at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, or at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the fatty acids isolated from the organism and/or the growth medium are fatty acids of a specific chain length, such as two or more of C8, C10, C12, C14, C16, or C18 fatty acids.
In some embodiments, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, or at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the isolated fatty acid products from an organism expressing an exogenous acyl-ACP thioesterase of the invention are fatty acid products or two or more chain lengths, such as two or more of a C12, a C14, a C16, or a C18 fatty acid product. In some preferred embodiments, the fatty acid products are fatty acids, and at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, or at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the fatty acids isolated from the organism and/or the growth medium are fatty acids of a specific chain length, such as two or more of C12, C14, C16, or C18 fatty acids. In some preferred embodiments, the fatty acid products are fatty acids, and at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, or at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the fatty acids isolated from the organism and/or the growth medium are fatty acids of a specific chain length, such as C14 and C16 fatty acids.
Nucleic acid molecules used in the methods of the invention include those disclosed herein.
In some embodiments of the invention, the transgenic organism is transformed with a nucleic acid molecule that encodes a thioesterase having 96% or greater identity with amino acids 64 to 361 of SEQ ID NO:75 or 92% or greater identity with amino acids 64 to 361 of SEQ ID NO:99, and at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, or at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the fatty acid products isolated from the transgenic organism and/or medium from culturing of a transgenic organism are C10 fatty acid products, such as but not limited to a C10 fatty acid, C10 fatty aldehyde, or C10 fatty alcohol, or a wax ester, alkene, or alkane.
In some embodiments of the invention, the transgenic organism is transformed with a nucleic acid molecule that encodes a thioesterase having 96% or greater identity with amino acids 64 to 361 of SEQ ID NO:75, or to amino acids 64 to 361 of SEQ ID NO:99, and at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, or at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the fatty acid products isolated from the transgenic organism and/or medium from culturing of a transgenic organism are C16 fatty acid products, such as but not limited to a C16 fatty acid, C16 fatty aldehyde, or C16 fatty alcohol, or a wax ester, alkene, or alkane.
In some examples, a transgenic organism is transformed with a nucleic acid molecule that encodes a thioesterase having 92% or greater identity with amino acid 63 to amino acid 360 of SEQ ID NO:99, and at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, or at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the isolated fatty acid products are a C8 and/or a C10 fatty acid product. In some examples, a transgenic organism is transformed with a nucleic acid molecule that encodes a thioesterase having 92% or greater identity with amino acid 63 to amino acid 360 of SEQ ID NO:99, and at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, or at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the isolated fatty acid products are a C8 fatty acid product, such as but not limited to a C8 fatty acid, C8 fatty aldehyde, or C8 fatty alcohol, or a wax ester, alkene, or alkane.
In further examples, a transgenic organism is transformed with a nucleic acid molecule that encodes a thioesterase having at least 85%, at least 90%, at least 92%, at least 95%, or at least 99% identity with the amino acid sequence from amino acid position 64 to amino acid position 361 of SEQ ID NO:51; at least 98% identity with the amino acid sequence from amino acid position 66 to amino acid position 362 of SEQ ID NO:55; at least 97% identity with the amino acid sequence from amino acid position 65 to amino acid position 360 of SEQ ID NO:59; at least 90% identity with the amino acid sequence from amino acid position 65 to amino acid position 359 of SEQ ID NO:63; at least 98% identity with the amino acid sequence from amino acid position 115 to amino acid position 410 of SEQ ID NO:65; at least 96% identity with the amino acid sequence from amino acid position 65 to amino acid position 356 of SEQ ID NO:69; at least 98% identity with the amino acid sequence from amino acid position 115 to amino acid position 410 of SEQ ID NO:71; at least 96% identity with the amino acid sequence from amino acid position 64 to amino acid position 361 of SEQ ID NO:75; at least 97% identity with the amino acid sequence from amino acid position 65 to amino acid position 360 of SEQ ID NO:79; at least 96% identity with the amino acid sequence from amino acid position 116 to amino acid position 413 of SEQ ID NO:81; at least 96% identity with the amino acid sequence from amino acid position 65 to amino acid position 362 of SEQ ID NO:85; at least 96% identity with the amino acid sequence from amino acid position 64 to amino acid position 361 of SEQ ID NO:89; at least 97% identity with the amino acid sequence from amino acid position 115 to amino acid position 394 of SEQ ID NO:91; at least 97% identity with the amino acid sequence from amino acid position 115 to amino acid position 394 of SEQ ID NO:93; at least 99% identity with the amino acid sequence from amino acid position 115 to amino acid position 394 of SEQ ID NO:95; at least 92% identity with the amino acid sequence from amino acid position 63 to amino acid position 360 of SEQ ID NO:99; or at least 98% identity with the amino acid sequence from amino acid position 115 to amino acid position 393 of SEQ ID NO:101, and at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, or at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the isolated fatty acid products are a C12, C14, C16 and/or a C18 fatty acid product. In some examples, a transgenic organism is transformed with a nucleic acid molecule that encodes a thioesterase and at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, or at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the isolated fatty acid products are a C12, a C14, a C16, or a C18 fatty acid product, such as but not limited to a fatty acid, fatty aldehyde, or fatty alcohol, or a wax ester, alkene, or alkane. For example, the isolated fatty acid products from culturing a transgenic organism may be at least 50%, at least 60%, at least 70%, at least 80%, or at least 90% C14 and/or C16 fatty acid products.
The transgenic organism is in some embodiments a photosynthetic organism, such as, for example, a microalga. In some embodiments, the transgenic organism is a prokaryote.
In some illustrative embodiments, the method includes isolating fatty acid products from the culture medium, in which at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, or at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the fatty acid products isolated from the organism or the growth medium are fatty acid products of a specific chain length.
Production of Medium Chain Fatty Acid Products
As set forth in the Examples, a new Class II thioesterase gene from Cuphea aequipetala, denoted Ca1FatB2, has been isolated. The sequence of the putative mature form of the enzyme is provided in FIG. 1 as SEQ ID NO:29. The invention provides a method of producing a C8 fatty acid product in which the method includes culturing a photosynthetic organism that includes an exogenous nucleic acid molecule encoding a medium chain length acyl-ACP thioesterase that is at least 90% identical to amino acids 65 to 355 of SEQ ID NO:29 and isolating a fatty acid product from the organism or culture medium, in which at least 5% of the isolated fatty acid product is a C8 fatty acid product. The method includes the use of transgenic host organisms that include an exogenous nucleic acid molecule encoding a medium chain acyl-ACP thioesterase that is at least 90% identical to amino acids 34 to 355 of SEQ ID NO:29. A nucleic acid molecule used in these methods encodes a Class II medium chain plant acyl-ACP thioesterase or a variant thereof.
Nucleic acid molecules used in the methods of the invention encode acyl-ACP thioesterases having at least 90% identity to amino acids 65 to 355 of SEQ ID NO:29, in which expression of the thioesterase-encoding sequences in a photosynthetic transgenic organism results in production of a population of fatty acid products in the cells or growth media in which at least 5% of the fatty acid products isolated from the cells or growth media is a C8 fatty acid product. In some embodiments, a nucleic acid molecule used in the methods of the invention encodes an acyl-ACP thioesterase having at least 90% identity to amino acids 34 to 355 of SEQ ID NO:29. Using the methods of the invention, the percentage of a C8 fatty acid product, such as, for example, octanoic acid, in the recovered fatty acids is, for example, 5% or greater, 10% or greater, 15% or greater, 20% or greater, 25% or greater, 30% or greater, 35% or greater, 40% or greater, 45% or greater, 50% or greater, 55% or greater, 60% or greater, 65% or greater, 70% or greater, 75% or greater, or 80% or greater. In some preferred embodiments, the percentage of octanoic acid or another C8 fatty acid product in the fatty acids or fatty acid products recovered from the cultured cells and/or the culture medium is 85% or greater, such as 86%, 87%, between 87% and 90%, between 90% and 93%, between 93% and 95%, between 95% and 97%, between 97% and 98%, between 98% and 99%, or between 99% and 100%.
As detailed in Example 3, the Cuphea aequipetala FatB2 coding sequence has been reconstructed using PCR and gene walking such that, based on homology with other plant thioesterases, it is estimated that all but approximately ten to fifteen amino acids of the N-terminus have been determined. This sequence of the C. aequipetala FatB2 coding sequence (SEQ ID NO:22) is provided in FIG. 1 . As evident in the figure, SEQ ID NO:22 and SEQ ID NO:29 are identical from amino acid position 2 to amino acid position 355. (SEQ ID NO:22 includes additional amino acids −43 to −1, considered to be amino acids included in the chloroplast transit peptide, that are not present in SEQ ID NO:29.) Thus, reference to any amino acid sequences between amino acid position 2 and amino acid 355 of SEQ ID NO:22 are interchangeable with the same sequences of SEQ ID NO:29 and vice versa.
The acyl-ACP thioesterase variants encoded by the nucleic acid molecules carried by transgenic host organisms may have N-terminal or C-terminal regions that differ from the wild-type thioesterase from which they are derived. With regard to the N-terminus, it is noted that acyl-ACP thioesterases of higher plants, such as the acyl-ACP thioesterase of C. aequipetala, are synthesized as precursor proteins that are transported into plastids, where the enzymes function in fatty acid biosynthesis. The site within the precursor protein sequence at which cleavage of the N-terminal transit peptide occurs has not been empirically determined.
The examples provided herein confirm that the transit peptide (including amino acids -43 through -1 of SEQ ID NO:22 in FIG. 1 ) is not necessary for the activity of a thioesterase expressed in a prokaryotic organism. Example 4 further demonstrates that thioesterase activity is not reduced by additional deletion of amino acids 1 to 33 of the putative mature thioesterase (SEQ ID NO:29). Plant medium chain thioesterases having deletions of the N-terminal amino acids extending to the amino acid corresponding to amino acid 64 of SEQ ID NO:22 have been shown to be active (see, for example, U.S. Pat. 5,667,997). Thus, the invention recognizes that N-terminal deletions of up to amino acid 64 (referencing SEQ ID NO:22 and SEQ ID NO:29, FIG. 1 ) of a medium chain acyl-ACP thioesterase are useful in the methods of the invention. The invention therefore includes methods of producing a fatty acid product in which a transgenic organism used to synthesize the fatty acid product is transformed with a gene encoding an acyl-ACP thioesterase having a deletion in its N-terminal region, in which the acyl-ACP thioesterase is at least 90% identical to amino acids 65-355 of SEQ ID NO:29.
In some embodiments of the invention, a nucleic acid molecule may encode acyl-ACP thioesterases having a transit peptide sequence derived from a different acyl-ACP thioesterase, or from a protein other than a thioesterase that is imported into plastids. For example, in some embodiments in which a thioesterase gene is transformed into a eukaryotic photosynthetic organism for the production of a fatty acid product, the acyl-ACP thioesterase gene can encode a thioesterase that is at least 90% identical to amino acids 65 to 355 of SEQ ID NO:29, while including a sequence encoding a transit peptide having an amino acid sequence that is less than 90% identical, less than 80% identical, less than 70% identical, less than 60% identical, less than 50% identical, less than 40% identical or less than 30% identical to sequences of the thioesterase precursor of SEQ ID NO:22. The transit peptide operably linked to the mature acyl-ACP thioesterase protein is in some embodiments from a chloroplast-directed protein from the species to be used as a transgenic host in the methods of the invention.
Also demonstrated in examples herein is the ability to introduce variations into the sequence of the C-terminal portion of a medium chain acyl-ACP thioesterase without significant loss of activity (see Example 2). Thus the invention includes variants of acyl-ACP thioesterases that terminate at amino acid 355, that include a C-terminal sequence of a different acyl-ACP thioesterase, or that have one or more amino acids that differ from any known acyl-ACP thioesterase, so long as there is no substantial detrimental effect on the activity of the thioesterase with regard to its C8 specificity and activity level.
The examples further disclose genes encoding variant acyl-ACP thioesterases having one, two, or three mutations with respect to the wild-type sequence (SEQ ID NO:29), in which the mutants retain the C8 specificity of the wild-type molecule, and where expression of a variant results in recovery of as great or a greater amount of C8 fatty acid from the culture as results from expression of the wild-type thioesterase. In some embodiments, then, a nucleic acid molecule used in the methods of the invention encodes an acyl-ACP thioesterase having between 90% and 95% identity, between 95% and 97% identity, between 97% and 98% identity, between 98% and 99% identity, between 99% and 99.5% identity, or between 99.5% and 100% identity to amino acids 65 to 355 of SEQ ID NO:29, while retaining at least the level of activity toward a C8 acyl substrate of the thioesterase of SEQ ID NO:29. In some embodiments of the methods a nucleic acid molecule encodes an acyl-ACP thioesterase having between 90% and 95% identity, between 95% and 97% identity, between 97% and 98% identity, between 98% and 99% identity, between 99% and 99.5% identity, or between 99.5% and 100% identity to amino acids 34 to 355 of SEQ ID NO:29, while retaining at least the level of activity toward a C8 acyl substrate of the thioesterase of SEQ ID NO:29.
In some embodiments, a nucleic acid molecule used in the methods of the invention encodes an acyl-ACP thioesterase having between 90% and 95% identity, between 95% and 98% identity, between 98% and 99% identity, between 99% and 99.5% identity, or between 99.5% and 100% identity to amino acids 65 to 355 of SEQ ID NO:29, in which expression of the acyl-ACP thioesterase in a transgenic organism results in production of at least the level of a C8 fatty acid produced by the transgenic organism expressing the thioesterase of SEQ ID NO:29. In some embodiments of the methods a nucleic acid molecule encodes an acyl-ACP thioesterase having between 90% and 95% identity, between 95% and 97% identity, between 97% and 98% identity, between 98% and 99% identity, between 99% and 99.5% identity, or between 99.5% and 100% identity to amino acids 34 to 355 of SEQ ID NO:29, and expression of the acyl-ACP thioesterase in a transgenic organism results in production of at least the level of a C8 fatty acid produced by the transgenic organism expressing the thioesterase of SEQ ID NO:29.
For any variants of an acyl-ACP thioesterase, such as variants of the acyl-ACP thioesterase of SEQ ID NO:22 or SEQ ID NO:29, the nucleic acid molecule encoding a variant acyl-ACP thioesterase can be tested for its ability to direct synthesis of a high proportion of C8 fatty acids or C8 fatty acid products, that are produced by the organisms and can be isolated from higher plants or cultures of algae transformed with the nucleic acid molecules. Provided in the examples are descriptions of transforming host organisms with recombinant nucleic acid molecules encoding acyl-ACP thioesterases and recovering fatty acid products to determine the amount of fatty acid products of different chain lengths produced by the transgenic host.
Assays of a thioesterase can also be performed using lysates of transgenic organisms such as E. coli that are transformed with expression constructs that include the acyl-ACP thioesterase gene and its activity determined using labeled acyl substrates (see, for example, U.S. Pat. No. 5,667,997, incorporated herein by reference). An acyl-ACP thioesterase variant can also be partially or substantially purified prior to performing an assay; for example, the thioesterase or thioesterase variant can be expressed with an affinity tag (for example, a His tag) for affinity purification prior to performing the assay (Dehesh et al. Plant Physiol 110: 203-210 (1996), incorporated herein by reference).
In some preferred embodiments, a nucleic acid molecule used in the methods of the invention encodes a plant B-type acyl-ACP thioesterase or a variant thereof, in which the encoded B-type acyl-ACP thioesterase comprises an amino acid sequence that is at least 95%, at least 97%, at least 98%, at least 99%, or at least 99.5% identical to amino acids 65 to 355 of SEQ ID NO:29. In some embodiments, the nucleic acid molecule encodes SEQ ID NO:8, SEQ ID NO:12, SEQ ID NO:22, SEQ ID NO:26, SEQ ID NO:33, SEQ ID NO:40, SEQ ID NO:43, or SEQ ID NO:45, or a thioesterase having any combination of the mutations provided in Table 2, the table provided in FIGS. 3A-3D , or the table provided in FIGS. 5A-5B . In some embodiments, the nucleic acid molecule comprises a sequence that encodes at least amino acids 65-355 of SEQ ID NO:29. In some preferred embodiments, a nucleic acid molecule according to the invention encodes a plant B-type acyl-ACP thioesterase or a variant thereof, in which the encoded B-type acyl-ACP thioesterase comprises an amino acid sequence that is at least 95%, at least 97%, at least 98%, at least 99%, or at least 99.5% identical to amino acids 34 to 355 of SEQ ID NO:29. In some embodiments, the nucleic acid molecule encodes SEQ ID NO:8, SEQ ID NO:12, SEQ ID NO:22, SEQ ID NO:26, SEQ ID NO:33, SEQ ID NO:40, SEQ ID NO:43, or SEQ ID NO:45, or a thioesterase having any combination of the mutations provided in Table 2, the table provided in FIGS. 3A-3D , or the table provided in FIGS. 5A-5B . In some embodiments, the nucleic acid molecule comprises a sequence that encodes at least amino acids 34-355 SEQ ID NO:29. In some embodiments, the nucleic acid molecule comprises a sequence that encodes SEQ ID NO:29.
The nucleic acid molecules encoding acyl-ACP thioesterases can be used to transform photosynthetic organisms, such as plants or algae, for the production of C8-enriched fatty acid products in the organisms. In some preferred embodiments, the sequence encoding the medium chain length fatty acid is codon-optimized for expression in the host organism. Codons can be optimized by methods such as those provided in U.S. Pat. No. 7,135,290, incorporated herein by reference. A codon usage database is available at the world wide web site kazusa.or.jp/codon/. Preferred codon usage can also be determined by a practitioner based on gene sequences entered in databases such as Genbank (ncbi.nlm.nih.gov/GenBank/), or a subset of genes of the organism (for example, highly expressed genes).
A photosynthetic organism transformed with the nucleic acid molecule that encodes a thioesterase gene can be a plant, such as but not limited to a higher plant, or can be an alga. Higher plants considered for use in the invention include, without limitation, Arabidopsis thaliana, Arachis hypogaea, Avena sativa, Brassica species (e.g., Brassica napus, Brassica campestris, Brassica juncea ), Camelina sativa, Carthamus tinctorius, Cocos nucifera, Crambe abyssinica, Cuphea species, Elaeis species (e.g., Elaeis guineensis, Elaeis oleifera ), Gossypium hirsutum, Glycine max, Helianthus annuulus, Jatropha species, Cucurbita pepo, Oryza satvia, Sesamum indicum, Simmondsia chinensis, Theobroma cacao, Ricinus communis, and Zea mays.
Algae that can be used in the methods of the invention can be any algae, and can include microalgae, such as but not limited to, Achnanthes, Amphiprora, Amphora, Ankistrodesmus, Asteromonas, Boekelovia, Borodinella, Botryococcus, Bracteococcus, Chaetoceros, Carteria, Chlamydomonas, Chlorococcum, Chlorogonium, Chlorella, Chroomonas, Chrysosphaera, Cricosphaera, Crypthecodinium, Cryptomonas, Cyclotella, Dunaliella, Ellipsoidon, Emiliania, Eremosphaera, Ernodesmius, Euglena, Franceia, Fragilaria, Gloeothamnion, Haematococcus, Halocafeteria, Hymenomonas, Isochrysis, Lepocinclis, Micractinium, Monoraphidium, Nannochloris, Nannochloropsis, Navicula, Neochloris, Nephrochloris, Nephroselmis, Nitzschia, Ochromonas, Oedogonium, Oocystis, Ostreococcus, Pavlova, Parachlorella, Pascheria, Phaeodactylum, Phagus, Platymonas, Pleurochrysis, Pleurococcus, Prototheca, Pseudochlorella, Pyramimonas, Pyrobotrys, Scenedesmus, Schizochytrium, Skeletonema, Spyrogyra, Stichococcus, Tetraselmis, Thalassiosira, Viridiella, or Volvox species.
In some embodiments, photosynthetic bacteria, including for example, green sulfur bacteria, purple sulfur bacteria, green nonsulfur bacteria, purple nonsulfur bacteria, or cyanobacteria are used for producing a C8 fatty acid product. Cyanobacterial species that can be used for production of C8 fatty acid products include, without limitation, Agmenellum, Anabaena, Anabaenopsis, Anacystis, Aphanizomenon, Arthrospira, Asterocapsa, Borzia, Calothrix, Chamaesiphon, Chlorogloeopsis, Chroococcidiopsis, Chroococcus, Crinalium, Cyanobacterium, Cyanobium, Cyanocystis, Cyanospira, Cyanothece, Cylindrospermopsis, Cylindrospermum, Dactylococcopsis, Dermocarpella, Fischerella, Fremyella, Geitleria, Geitlerinema, Gloeobacter, Gloeocapsa, Gloeothece, Halospirulina, Iyengariella, Leptolyngbya, Limnothrix, Lyngbya, Microcoleus, Microcystis, Myxosarcina, Nodularia, Nostoc, Nostochopsis, Oscillatoria, Phormidium, Planktothrix, Pleurocapsa, Prochlorococcus, Prochloron, Prochlorothrix, Pseudanabaena, Rivularia, Schizothrix, Scytonema, Spirulina, Stanieria, Starria, Stigonema, Symploca, Synechococcus, Synechocystis, Tolypothrix, Trichodesmium, Tychonema, or Xenococcus species.
In another aspect the invention provides an isolated nucleic acid molecule that encodes a variant of a plant acyl-ACP thioesterase, in which the variant has a mutation at the amino acid corresponding to amino acid position 174 of SEQ ID NO:29 in which the variant has activity as high as or higher than the thioesterase from which the variant was derived. For example, in preferred embodiments, culturing of a transgenic organism that carries the variant gene in some embodiments allows isolation of as great or a greater amount of a fatty acid product of a specific chain length than does culturing of a transgenic organism that carries the native thioesterase gene. In preferred embodiments, expression of the variant in a transgenic host organism allows for isolation of fatty acid products of a specific chain length, in which the percentage of fatty acid products of a specific chain length to total fatty acid products isolated is at least as high as the percentage of fatty acid products of a specific chain length to total fatty acid products isolated from a host organism carrying the native gene.
In some preferred embodiments of the invention, the percentage of octanoic acid present in the population of fatty acids secreted by a prokaryotic organism transformed with a nucleic acid molecule encoding a variant of SEQ ID NO:29 having a mutation at position 174 is 55% or greater, 60% or greater, 65% or greater, 70% or greater, 75% or greater, or 80% or greater. In some preferred embodiments of the invention, the percentage of octanoic acid present in the population of fatty acids secreted by a prokaryotic organism transformed with a nucleic acid molecule encoding a variant of SEQ ID NO:29 having a mutation at position 174 is 85% or greater, such as 86%, 87%, between 87% and 90%, between 90% and 93%, between 93% and 95%, between 95% and 100%, between 95% and 97%, or between 97% and 100%. For example, in some embodiments expression of a variant of the acyl-ACP thioesterase of SEQ ID NO:29 in a bacterium or cyanobacterium results in secretion of a population of fatty acids enriched for octanoic acid.
The amino acid position corresponding to amino acid 174 of SEQ ID NO:29 refers to the amino acid position of an acyl-ACP thioesterase amino acid sequence that would align with amino acid 174 of SEQ ID NO:29 if the sequence of interest and SEQ ID NO:29 were aligned for maximum homology. Such alignments of Class II thioesterase sequences can be seen, for example, in U.S. Pat. No. 6,150,512 at FIG. 1 . The terms “amino acid position 174”, “position 174”, or “consensus position 174” or similar nomenclature all refer to the consensus position for an acyl-ACP thioesterase corresponding to amino acid position 174 of SEQ ID NO:29 (and of SEQ ID NO:22, see FIG. 1 ) when the sequence is aligned with SEQ ID NO:29 (and, optionally, the sequences of other plant acyl-ACP thioesterases) for maximal sequence matches. Analogously, references to other amino acid positions, such as but not limited to, position 34, 35, 64, 65, 67, 103, 184, 355, etc., refer to numbered positions of the thioesterase sequences provided herein, including SEQ ID NO:22 and SEQ ID NO:29 ( FIG. 1 ). These positions can be translated to numbered positions of other thioesterase genes as provided in patents, patent applications, publications, and gene and protein databases by aligning the sequence of SEQ ID NO:22 or SEQ ID NO:29 with the published, documented, or discovered thioesterase sequence for maximum homology.
In contrast to other acyl-ACP thioesterse mutants that have been isolated, the variants described in Examples 4-7 having an amino acid substitution at position 174 have increased activity while the chain length preference of the thioesterase has not been shifted from one acyl chain length to another acyl chain length. Isolation of a variant having a mutation at position 174 having increased activity was surprising not only because no previously identified acyl-ACP thioesterase mutants have exhibited increased activity, but also because the active site for Class II acyl-ACP thioesterases had been identified as being located more than 100 amino acids away from position 174, using SEQ ID NO:29 reference numbering (see FIG. 1 ), in the area of amino acid residues 293-297 and 304 (see, for example, U.S. Pat. No. 6,150,512).
A mutation at consensus position 174 can be a mutation that changes the amino acid of the naturally-occurring or wild-type gene at that consensus position to any other amino acid. In some embodiments, in which the naturally-occurring or wild-type gene has a methionine residue at amino acid position 174, the mutation can change M174 to any other amino acid, for example, glycine, proline, alanine, valine, leucine, isoleucine, phenylalamine, tyrosine, tryptophan, cysteine, serine, threonine, glutamine, asparagine, lysine, arginine, histidine, glutamate, or aspartate. In some embodiments, a mutation at position 174 changes the amino acid at position 174 of an acyl-ACP thioesterase to an uncharged amino acid, which can be, for example, any of glycine, proline, alanine, valine, leucine, isoleucine, phenylalamine, tyrosine, tryptophan, cysteine, methionine, serine, threonine, glutamine, or asparagine. In some embodiments, the mutation changes the amino acid at position 174 to methionine, leucine, phenylalanine, valine, cysteine, or isoleucine. In some embodiments, the mutation changes the amino acid at position 174 to valine or isoleucine.
Alignment of native plant Class II (FatB-encoded) acyl ACP thioesterases reveals that the amino acid at the position that corresponds to amino acid position 174 of SEQ ID NO:29 is typically a methionine residue. (This position is most often designated as a position between about residue 220 and about residue 250 for thioesterase amino acid sequences that number the first residue of the precursor protein as residue 1.) For example, plant acyl-ACP thioesterases having a methionine at the position corresponding to position 174 of SEQ ID NO:29 include FatB-encoded thioesterases of Cuphea species, such as but not limited to those encoded by Cuphea calophylla FatB genes (e.g., ABB71579, ABB71580, and ABB71581), Cuphea hookeriana FatB1 (Q39513), Cuphea hookeriana FatB1-1 (AAC72882), Cuphea hookeriana FatB2 (AAC49269), Cuphea hookeriana FatB3 (AAC72881), the Cuphea hookeriana 16:0-ACP thioesterase (AAC48990), Cuphea palustris FatB1(AAC49179 and 2208474A), Cuphea palustris FatB2 (AAC49180 and 2208474B), Cuphea wrightii FatB1 (AAC49783) and Cuphea wrightii FatB2 (AAC49784), and Cuphea lanceolata Class II thioesterases (e.g., AAE24875, CAA02760, CAA02766, CAA02765, CAA54060, CAC19934, and CAC19933). Also included are the Class II thioesterases of Diploknema butyracea (e.g., AAX51636), Brassica napus (e.g., ABH11710) and Brassica juncea (e.g., ABI18986). Other Class II thioesterases having a methionine at position 174 are those of Camellia oleifera (e.g., ACQ57190, ACQ63293, ACQ57188, ACQ57189, and ACQ57187), Helianthus annuus (e.g., AAB88824, AAQ08202, AAX19387, AAX19386, AAX19385, AAX19384, AAX19383, AAX19382, AAX19381, AAX19380, AAX19379, AAX19378, AAX19377, CAC80371, and CAC80370), and Jatropha curcas (e.g., ABU96744), as well as Madhuca longifolia FatB (AAX51637), Myristica fragrans FatB2 (AAB71729), Populus tomentosa FatB (ABC47311), Ricinus communis FatB genes (e.g., ABV54795, EEF47013, EEF51750, and EEF36100), Umbellularia califonica FatB genes (M941159, AAC49001, and Q41635), Ulmus Americana FatB (AAB71731), and thioesterases of Arabidopsis thaliana (e.g, AAF22899 and CAA85388). The numbers in parentheses are Genbank accession numbers of representative protein sequences. This list is not intended to be exhaustive, but nonetheless demonstrates that a large number of Class II acyl-ACP thioesterases have a methionine at the amino acid position corresponding to amino acid position 174 of SEQ ID NO:29, indicating that the residue is highly conserved among Class II acyl-ACP thioesterases, and strongly suggesting that its functional role is also conserved.
The invention includes plant FatB acyl-ACP thioesterase genes encoding variant thioesterases, in which the methionine residue corresponding to position 174 of SEQ ID NO:29 is mutated to an uncharged amino acid. In these embodiments, the variant thioesterases preferably have higher activity against an acyl-ACP substrate than the thioesterases encoded by the wild-type genes. The encoded FatB acyl-ACP thioesterases can be of any chain length specificity, such as, for example, C8, C10, C12, C14, C16, or C18. Included in the invention is a plant FatB acyl-ACP thioesterase gene encoding a variant thioesterase in which the methionine at position 174 in the wild-type thioesterase is mutated to leucine, phenylalanine, valine, cysteine, or isoleucine. In some embodiments, a variant plant acyl-ACP thioesterase comprises the mutation M1741, wherein the methionine at position 174 is replaced with isoleucine.
In these embodiments variant thioesterase genes having an M1741 mutation may be variants of any plant FatB (Class II) acyl-ACP thioesterase gene that encodes a methionine at the position corresponding to position 174 of SEQ ID NO:29, including but not limited to genes of any of the Class II thioesterases listed above, including variants thereof having at least 85% identity to the amino acid sequence from about position 65 to about position 355 (using the numbering of SEQ ID NO:29 as a reference) of the thioesterase amino acid sequence of Class II thioesterase genes. The thioesterase genes can have any acyl chain length specificity. Illustrative examples of such thioesterase genes include, for example, an Arabidopsis thaliana FatB thioesterase gene, a Cuphea aequipetala FatB thioesterase gene, a Cuphea calophylla FatB thioesterase gene, a Cuphea hookeriana FatB thioesterase gene, a Cuphea lanceolata FatB thioesterase gene, a Cuphea palustris FatB thioesterase gene, a Cuphea wrightii FatB thioesterase gene, a Diploknema butyracea FatB thioesterase gene, a Brassica napus or Brassica juncea FatB thioesterase gene, a Camellia oleifera FatB thioesterase gene, a Helianthus annuus FatB thioesterase gene, a Jatropha curcas FatB thioesterase gene, a Madhuca longifolia FatB gene,a Myristica fragrans FatB2, a Populus tomentosa FatB gene, a Ricinus communis FatB gene, an Umbellularia californica FatB gene, and an Umbellularia californica FatB gene. The variants having an M1741 mutation can have one or more additional amino acid substitutions with respect to the wild type genes from which they are derived, or can be N-terminally deleted or have variant carboxy termini, provided that the variants have a higher thioesterase activity than the wild-type sequence from which they are derived. The variants having an M1741 mutation in some embodiments are between 80% and 85% identical, between 85% and 90% identical, between 90 and 95% identical, between 95% and 97% identical, between 97% and 99% identical, or between 99% and 100% identical to the wild type mature acyl-ACP thioesterase sequence at the amino acid level from about the amino acid position corresponding to position 65 of SEQ ID NO:29 to about the amino acid position corresponding to position 355 of SEQ ID NO:29. A variant acyl-ACP encoded by a nucleic acid molecule of the invention in some embodiments includes an isoleucine at the amino acid position corresponding to amino acid 103 of SEQ ID NO:29 in addition to the M1741 mutation.
In other embodiments, a variant acyl-ACP thioesterase has an isoleucine at position 103 and the amino acid at position 174 is phenylalanine, cysteine, leucine, or valine.
The invention includes an isolated nucleic acid molecule that encodes a variant plant Class II acyl-ACP thioesterase having at least 80%, at least 85%, at least 90%, or at least 95% identity to the amino acid sequence from position 65 to amino acid 355 of SEQ ID NO:40, SEQ ID NO:43, or SEQ ID NO:45, in which the variant includes a M1741 mutation and has enhanced activity with respect to the plant acyl-ACP thioesterase lacking the mutation at consensus position 174. In some embodiments of the invention, an isolated nucleic acid encoding a variant acyl-ACP thioesterase having an M1741 mutation comprises a sequence encoding the amino acid sequence from position 65 to 355 of SEQ ID NO:40, SEQ ID NO:43, or SEQ ID NO:45.
Also included in the invention is an isolated nucleic acid molecule that encodes a variant plant Class II acyl-ACP thioesterase having at least 80%, at least 85%, at least 90%, or at least 95% identity to the amino acid sequence from position 34 to amino acid 355 of SEQ ID NO:40, SEQ ID NO:43, or SEQ ID NO:45, in which the variant has enhanced activity with respect to the plant acyl-ACP thioesterase lacking the mutation at consensus position 174. In some embodiments of the invention, an isolated nucleic acid encoding a variant acyl-ACP thioesterase having an M1741 mutation comprises a sequence encoding the amino acid sequence from position 34 to 355 of SEQ ID NO:40, SEQ ID NO:43, or SEQ ID NO:45. The isolated nucleic acid molecule in some embodiments comprises a sequence encoding the amino acid sequence of SEQ ID NO:40, SEQ ID NO:43, or SEQ ID NO:45. In some embodiments, the nucleic acid molecule comprises SEQ ID NO:39, SEQ ID NO:42, or SEQ ID NO:44.
A further aspect of the invention is a transgenic organism that includes an exogenous nucleic acid molecule that encodes a variant plant acyl-ACP thioesterase, in which the variant thioesterase has a mutation at the amino acid position corresponding to amino acid position 174 of SEQ ID NO:29 and exhibits increased thioesterase activity. Specifically included are transgenic organisms that include genes encoding any of the aforementioned variants having a mutation at amino acid position 174, including, for example, variants having an isoleucine, methionine, valine, leucine, cysteine, or phenylalanine at positions 174. In some embodiments, the transgenic organism has an exogenous nucleic acid molecule encoding a thioesterase having an isoleucine, valine, leucine, cysteine, or phenylalanine at position 174 and an isoleucine at position 103. In an exemplary embodiment, a transgenic organism has an exogenous gene encoding a thioesterase having an isoleucine at position 174 and an isoleucine at position 103. A transgenic organism is in various embodiments a plant, an alga, or a prokaryote.
For example, in some embodiments, the transgenic organism is a bacterium, such as, but not limited to, an Acetobacter, Acinetobacter, Arthrobacter, Bacillus, Brevibacterium, Chromatium, Chlorobium, Clostridium, Corynebacterium, Deinococcus, Delftia, Desulfovibrio, Enterococcus, Escherichia, Kineococcus, Klebsiella, Lactobacillus, Lactococcus, Micrococcus, Mycobacterium, Jeotgalicoccus, Paenibacillus, Propionibacter, Pseudomonas, Rhodopseudomonas, Rhodobacter, Rhodococcus, Rhodospirillium, Rhodomicrobium, Salmonella, Serratia, Stenotrophomonas, Streptococcus, Vibrio, or Zymomonas species.
In other embodiments, a transgenic organism harboring an acyl-ACP variant having a mutation at amino acid residue 174 is an alga, for example, a microalga such as an Achnanthes, Amphiprora, Amphora, Ankistrodesmus, Asteromonas, Boekelovia, Borodinella, Botryococcus, Bracteococcus, Chaetoceros, Carteria, Chlamydomonas, Chlorococcum, Chlorogonium, Chlorella, Chroomonas, Chrysosphaera, Cricosphaera, Crypthecodinium, Cryptomonas, Cyclotella, Dunaliella, Ellipsoidon, Emiliania, Eremosphaera, Ernodesmius, Euglena, Franceia, Fragilaria, Gloeothamnion, Haematococcus, Halocafeteria, Hymenomonas, Isochrysis, Lepocinclis, Micractinium, Monoraphidium, Nannochloris, Nannochloropsis, Navicula, Neochloris, Nephrochloris, Nephroselmis, Nitzschia, Ochromonas, Oedogonium, Oocystis, Ostreococcus, Pavlova, Parachlorella, Pascheria, Phaeodactylum, Phagus, Platymonas, Pleurochrysis, Pleurococcus, Prototheca, Pseudochlorella, Pyramimonas, Pyrobotrys, Scenedesmus, Schizochytrium, Skeletonema, Spyrogyra, Stichococcus, Tetraselmis, Thalassiosira, Viridiella, or Volvox species. In some embodiments, a transgenic organism is a cyanobacterium, such as an Agmenellum, Anabaena, Anabaenopsis, Anacystis, Aphanizomenon, Arthrospira, Asterocapsa, Borzia, Calothrix, Chamaesiphon, Chlorogloeopsis, Chroococcidiopsis, Chroococcus, Crinalium, Cyanobacterium, Cyanobium, Cyanocystis, Cyanospira, Cyanothece, Cylindrospermopsis, Cylindrospermum, Dactylococcopsis, Dermocarpella, Fischerella, Fremyella, Geitleria, Geitlerinema, Gloeobacter, Gloeocapsa, Gloeothece, Halospirulina, Iyengariella, Leptolyngbya, Limnothrix, Lyngbya, Microcoleus, Microcystis, Myxosarcina, Nodularia, Nostoc, Nostochopsis, Oscillatoria, Phormidium, Planktothrix, Pleurocapsa, Prochlorococcus, Prochloron, Prochlorothrix, Pseudanabaena, Rivularia, Schizothrix, Scytonema, Spirulina, Stanieria, Starria, Stigonema, Symploca, Synechococcus, Synechocystis, Tolypothrix, Trichodesmium, Tychonema, or Xenococcus species.
A transgenic organism transformed with a nucleic acid molecule encoding a variant acyl-ACP thioesterase having a mutation at position 174 is in some embodiments a higher plant, such as, for example, Arabidopsis thatliana, Arachis hypogaea, Avena sativa, Brassica species (e.g., Brassica napus, Brassica campestris, Brassica juncea ), Camelina sativa, Carthamus tinctorius, Cocos nucifera, Crambe abyssinica, Cuphea species, an Elaeis species (e.g., Elaeis guineensis, Elaeis oleifera ), Gossypium hirsutum, Glycine max, Helianthus annulus, a Jatropha species, Cucurbita pepo, Oryza satvia, Sesamum indicum, Simmondsia chinensis, Theobroma cacao, Ricinus communis, or Zea mays.
In yet another aspect, the invention provides a method of producing a fatty acid or a fatty acid product, in which the method includes cultivating an organism having an exogenous nucleic acid molecule that includes a sequence encoding a variant acyl-ACP thioesterase having a mutation at the amino acid position corresponding to position 174 of SEQ ID NO:29, and isolating a fatty acid or a fatty acid product from the organism or culture medium. The variant acyl-ACP thioesterase in some embodiments has an isoleucine at position 103 and an isoleucine at position 174. The transgenic host organism can be a bacterium, alga, cyanobacterium, or plant as provided herein, and the sequence encoding the plant acyl-ACP thioesterase in some embodiments is codon-optimized for expression in the host organism. In some preferred embodiments, the nucleic acid molecule encodes a variant of a naturally-occurring medium chain length acyl-ACP thioesterase having a mutation at the amino acid position corresponding to amino acid position 174 in SEQ ID NO:29, in which the variant has enhanced activity towards a C8 acyl substrate with respect to the wild type thioesterase.
The methods can be used for the production and isolation of a fatty acid product such as a triglyceride, a fatty aldehyde, a fatty alcohol, a fatty ester, or a hydrocarbon such as an alkene or alkane. In some embodiments, the fatty acid product is a fatty acid. In exemplary embodiments, the fatty acid product is a C8 fatty acid.
In some preferred embodiments expression of a variant acyl-ACP thioesterase gene as provided herein in a transgenic organism results in an increased percentage of a specific chain length fatty acid product being recovered from the organism and/or culture medium. In some embodiments, at least 5%, at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, or at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the isolated fatty acid products from an organism and/or medium from culturing of an organism having an exogenous nucleic acid molecule encoding a variant acyl-ACP thioesterase of the invention are fatty acid products of a specific chain length. For example, in some embodiments, at least 5%, at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, or at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the isolated fatty acid products from an organism expressing an exogenous variant acyl-ACP thioesterase of the invention are C8 fatty acid products. In some preferred embodiments, the fatty acid product is a C8 fatty acid, and at least 5%, at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, or at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the fatty acids isolated from the organism and/or the growth medium is a C8 fatty acid, such as octanoic acid.
In some illustrative embodiments, the transgenic organism is a prokaryote, such as a bacterium or a cyanobacterium, and the method includes isolating fatty acid products from the culture medium, in which at least 5%, at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, or at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the fatty acid products isolated from the organism or the growth medium are fatty acid products of a specific chain length. For example, in some embodiments, at least 5%, at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, or at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the fatty acid products isolated from the culture medium of a prokaryotic organism transformed with a variant acyl-ACP thioesterase of the invention are C8 fatty acid products. In an illustrative embodiment, at least 5%, at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, or at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the fatty acid products isolated from the culture medium of a prokaryotic organism transformed with a variant acyl-ACP thioesterase of the invention are C8 fatty acid products, such as octanoic acid.
Nucleic acid molecules encoding variant acyl-ACP thioesterases mutated at position 174 that can be expressed in a transgenic host organism can be any disclosed herein. For example, in some embodiments, the variant has a mutation that changes the amino acid at position 174 to an uncharged amino acid. In some embodiments, the amino acid position corresponding to amino acid position 174 of SEQ ID NO:29 is mutated from methionine to any of phenylalanine, cysteine, leucine, valine, or isoleucine. In some embodiments, the variant thioesterase has an isoleucine at position 103, and the amino acid at position 174 is phenylalanine, cysteine, valine, leucine, or isoleucine. In some embodiments, the amino acid position corresponding to amino acid position 103 of SEQ ID NO:29 is isoleucine and the amino acid corresponding to amino acid position 174 of SEQ ID NO:29 is isoleucine. The thioesterase from which the variant sequence is derived can be any plant acyl-ACP thioesterase, such as a plant Class II acyl-ACP thioesterase. In some embodiments, the thioesterase encoded by the exogenous nucleic acid molecule comprises an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 97%, at least 98%, or at least 99% identity to amino acids 65 to 355 of SEQ ID NO:40, SEQ ID NO:43, or SEQ ID NO:45. In some embodiments, the thioesterase encoded by the exogenous nucleic acid molecule comprises amino acids 65 to 355 of SEQ ID NO:40, SEQ ID NO:43, or SEQ ID NO:45. In some embodiments, the thioesterase encoded by the exogenous nucleic acid molecule comprises amino acids 34 to 355 of SEQ ID NO:40, SEQ ID NO:43, or SEQ ID NO:45.
Additional Genes Encoding Enzymes for Synthesizing Fatty Acid Products
Also included in the invention are transgenic host organisms and methods of using transgenic host organisms that include an exogenous acyl-ACP thioesterase as disclosed herein, and further include one or more exogenous genes encoding enzymes that participate in the synthesis of fatty aldehydes, fatty alcohols, fatty esters, or hydrocarbons (e.g., alkanes, alkenes) such as, for example, an acetyl CoA carboxylase, an acyl-CoA synthetase, a ketoacyl-CoA synthase, a fatty acyl-CoA/aldehyde reductase, a fatty acid elongase, a fatty acyl-CoA reductase, a fatty aldehyde reductase, an alcohol acetyl transferase, an acyl-CoA alcohol transacylase, an acyltransferase, a wax synthase, a fatty aldehyde decarbonylase, or a fatty acid decarboxylase.
In some embodiments, genes encoding a fatty acyl-ACP thioesterase and one or more genes encoding other hydrocarbon modification enzymes are transformed into a host organism, and the organism is used for the production of a fatty aldehyde, a fatty alcohol, a fatty ester (including a wax-ester), or a hydrocarbon.
Genes encoding fatty acyl-CoA/aldehyde reductases that can be used include, without limitation, those having Genbank accession numbers AAC45217, YP — 047869, BAB85476, YP — 001086217, YP — 580344, YP — 001280274, YP — 264583, YP — 436109, YP — 959769, ZP — 01736962, ZP — 01900335, ZP — 01892096, ZP — 01103974, ZP — 01915077, YP — 924106, YP — 130411, ZP — 01222731, YP — 550815, YP — 983712, YP — 001019688, YP — 524762, YP — 856798, ZP — 01115500, YP — 001141848, NP — 336047, NP — 216059, YP — 882409, YP — 706156, YP — 001136150, YP — 952365, ZP — 01221833, YP — 130076, NP — 567936, AAR88762, ABK28586, NP — 197634, CAD30694, NP — 001063962, BAD46254, NP — 001030809, EAZ10132, EAZ43639, EAZ07989, NP — 001062488, CAB88537, NP — 001052541, CAH66597, CAE02214, CAH66590, CAB88538, EAZ39844, AAZ06658, CAA68190, CAA52019, and BAC84377. Also included are genes encoding variants of these and other naturally-occurring fatty acyl-CoA/aldehyde reductases having at least 65% identity to the referenced or naturally occurring proteins, in which the activity of the enzyme is not substantially reduced with respect to the wild-type or above referenced enzyme.
Genes encoding fatty acyl-CoA reductases can include genes that encode, without limitation, the fatty acyl-CoA reductases having GenBank accession numbers NP — 187805, ABO14927, NP — 001049083, CAN83375, NP — 191229, EAZ42242, EAZ06453, CAD30696, BAD31814, NP — 190040, AAD38039, CAD30692, CAN81280, NP — 197642, NP — 190041, AAL15288, and NP — 190042. Also included are genes encoding variants of these and other naturally-occurring fatty acyl-CoA reductases having at least 65% identity to the referenced or naturally occurring proteins, in which the activity of the enzyme is not substantially reduced with respect to the wild-type or above referenced enzyme.
Genes encoding fatty aldehyde decarbonylases that can be transformed into an organism harboring an exogenous gene that encodes a plant acyl-ACP thioesterase as disclosed herein include genes that encode the fatty aldehyde decarbonylases listed by GenBank accession numbers. NP — 850932, ABN07985, CAN60676, AAC23640, CAA65199, AAC24373, CAE03390, ABD28319, NP — 181306, EAZ31322, CAN63491, EAY94825, EAY86731, CAL55686, XP — 001420263, EAZ23849, NP — 200588, NP — 001063227, CAN83072, AAR90847, and AAR97643. Also included are genes encoding variants of these and other naturally-occurring fatty aldehyde decarbonylases having at least 65% identity to the referenced or naturally occurring proteins, in which the activity of the enzyme is not substantially reduced with respect to the wild-type or above referenced enzyme.
In particular embodiments, organisms of the present invention are genetically engineered to express a fatty acyl-ACP thioesterase as provided herein, and one or more of an acyl-CoA synthetase, a fatty acyl-CoA/aldehyde reductase, a fatty acyl-CoA reductase, a fatty aldehyde reductase, a fatty aldehyde decarbonylase, or a fatty acid decarboxylase. Suitable expression methods are described below with respect to the thioesterase gene, including, among other methods, inducible expression and tissue-specific expression.
The enzymes described directly above may have a specificity for acting on a substrate having an acyl chain of a specific length. In some embodiments the transgenic host used for producing a fatty acid product contains an acyl-ACP thioesterase as described herein, and one or more exogenous genes that encode enzymes with specificity for substrates of the same acyl chain length. The enzymatic specificity can, in various embodiments, be for a substrate having from 8 to 34 carbon atoms, preferably from 8 to 18 carbon atoms. For example, the nucleic acid molecules introduced into a transgenic host can encode enzymes that have specificity for substrates having 8, 10, 12, 14, 16, or 18 carbon atoms in the acyl chain.
Also included in the invention are embodiments in which a transgenic organism expresses, in addition to a heterologous acyl-ACP thioesterase, a ketoacyl synthase (KAS). In some embodiments, the gene that encodes a β-ketoacyl synthase (KAS) that preferentially produces acyl-ACPs having medium chain lengths. Such KAS enzymes have been described from several plants, including various species of Cuphea (Dehesh et al., 1998; Slabaugh et al., 1998), and would serve to increase the availability of acyl-ACP molecules of the proper length for recognition and cleavage by the heterologous acyl-ACP thioesterase.
Additional embodiments of this invention include transgenic hosts expressing an exogenous plant acyl-ACP thioesterase as provided herein, and optionally one or more additional genes encoding enzymes that function in the synthesis of fatty acid products, in which one or more host genes that encode beta-oxidation pathway enzymes have been inactivated or downregulated. Inactivation of a beta-oxidation enzyme can prevent the degradation of fatty acids released from acyl-ACPs, thus enhancing the yield of accumulated or secreted fatty acids. For example, in cases where the desired products are medium chain fatty acids, the inactivation or downregulation of genes that encode medium chain-specific acyl-CoA synthetase and/or medium chain-specific acyl-CoA oxidase enzymes would be beneficial. Mutations in the genes encoding medium chain-specific acyl-CoA synthetase and/or medium chain-specific acyl-CoA oxidase enzymes such that the activity of the enzymes is diminished would also be effective in increasing the yield of accumulated or secreted fatty acids. Mutations in the genes can be introduced either by recombinant or non-recombinant methods.
Transformation of Host Organisms
Plants for use in the methods of the invention can be transformed by any feasible means, including, without limitation, the use of Agrobacterium, particle gun-mediated transformation, laser-mediated transformation, or electroporation. Algae and photosynthetic bacteria can be transformed by any suitable methods, including, as nonlimiting examples, natural DNA uptake (Chung et al. (1998) FEMS Microbiol. Lett. 164: 353-361; Frigaard et al. (2004) Methods Mol. Biol. 274: 325-40; Zang et al. (2007) J. Microbiol. 45: 241-245), conjugation, transduction, glass bead transformation (Kindle et al. (1989) J. Cell Biol. 109: 2589-601; Feng et al. (2009) Mol. Biol. Rep. 36: 1433-9; U.S. Pat. No. 5,661,017), silicon carbide whisker transformation (Dunahay et al. (1997) Methods Mol. Biol. (1997) 62: 503-9), biolistics (Dawson et al. (1997) Curr. Microbiol. 35: 356-62; Hallmann et al. (1997) Proc. Natl. Acad. USA 94: 7469-7474; Jakobiak et al. (2004) Protist 155:381-93; Tan et al. (2005) J. Microbiol. 43: 361-365; Steinbrenner et al. (2006) Appl Environ. Microbiol. 72: 7477-7484; Kroth (2007) Methods Mol. Biol. 390: 257-267; U.S. Pat. No. 5,661,017) electroporation (Kjaerulff et al. (1994) Photosynth. Res. 41: 277-283; Iwai et al. (2004) Plant Cell Physiol. 45: 171-5; Ravindran et al. (2006) J. Microbiol. Methods 66: 174-6; Sun et al. (2006) Gene 377: 140-149; Wang et al. (2007) Appl. Microbiol. Biotechnol. 76: 651-657; Chaurasia et al. (2008) J. Microbiol. Methods 73: 133-141; Ludwig et al. (2008) Appl. Microbiol. Biotechnol. 78: 729-35), laser-mediated transformation, or incubation with DNA in the presence of or after pre-treatment with any of poly(amidoamine) dendrimers (Pasupathy et al. (2008) Biotechnol. J. 3: 1078-82), polyethylene glycol (Ohnuma et al. (2008) Plant Cell Physiol. 49: 117-120), cationic lipids (Muradawa et al. (2008) J. Biosci. Bioeng. 105: 77-80), dextran, calcium phosphate, or calcium chloride (Mendez-Alvarez et al. (1994) J. Bacteriol. 176: 7395-7397), optionally after treatment of the cells with cell wall-degrading enzymes (Perrone et al. (1998) Mol. Biol. Cell 9: 3351-3365). Agrobacterium -mediated transformation can also be performed on algal cells, for example after removing or wounding the algal cell wall (e.g., WO 2000/62601; Kumar et al. (2004) Plant Sci. 166: 731-738). Biolistic methods are particularly successful for transformation of the chloroplasts of plant and eukaryotic algal species (see, for example, Ramesh et al. (2004) Methods Mol. Biol. 274: 355-307; Doestch et al. (2001) Curr. Genet. 39: 49-60; U.S. Pat. No. 7,294,506; WO 2003/091413; WO 2005/005643; and WO 2007/133558, all incorporated herein by reference in their entireties).
In some preferred embodiments of the invention, an acyl-ACP thioesterase gene (such as a gene as disclosed herein), is cloned into an expression vector for transformation into a plant, alga, or photosynthetic or nonphotosynthetic bacterium. The vector includes sequences that promote expression of the transgene of interest, e.g., an exogenous acyl-ACP thioesterase gene, such as a promoter, and may optionally include a transit peptide-encoding sequence for directing the expressed thioesterase to the chloroplast of transformed eukaryotic cells, an intron sequence, a sequence having a polyadenylation signal, etc. Alternatively, if the vector does not contain a promoter in operable linkage with the gene of interest, the gene can be transformed into the cells such that it becomes operably linked to an endogenous promoter by homologous recombination or vector integration.
In some embodiments, a vector is designed for integration of the acyl-ACP thioesterase gene into the host genome. For example, vectors used for higher plant transformation include but are not limited to Agrobacterium -based vectors that are designed for integrating transgenes (exogenous genes transformed into the host plant) into the genome of the plant. In other embodiments, vectors can be: 1) targeted for integration into a plant or algal chromosome by including flanking sequences that enable homologous recombination into the chromosome, 2) targeted for integration into endogenous host plasmids by including flanking sequences that enable homologous recombination into the endogenous plasmids, or 3) designed such that the expression vectors replicate within the chosen host.
Artificial chromosome vectors can also be used for the transformation of higher plants, for example, vector constructs that include a centromere sequence and an origin of replication so that the vector and its integrated sequences can be maintained in the plant (see, for example, U.S. Pat. No. 7,456,013 incorporated by reference herein in its entirety). Artificial chromosomes can accommodate more transgenes than can other types of vectors such as, for example, Agrobacterium -based vectors, and therefore can be used in higher plant or algal systems when more than one gene that encodes an enzyme that participates in the synthesis of a fatty acid product is transformed into an organism.
In some cases in which it may be advantageous to transform the chloroplast of a higher plant or alga, vectors can be designed to have regions of sequences flanking the transgene (e.g., the acyl-ACP thioesterase gene or another gene for synthesis of a fatty acid product) that are homologous to chloroplast sequences to promote homologous recombination and integration of the sequence of interest. In these embodiments, the vector preferably includes a promoter for expressing the transgene, in which the promoter functions in the chloroplast.
Vectors that include gene regulatory sequences for transformation of higher plants are well known in the art. Seed specific or inducible promoters can optionally be used in the vectors and constructs transformed into higher plants engineered for synthesis of fatty acid products (for example, U.S. Pat. No. 5,421,034; U.S. Pat. No. 5,608,152; U.S. Pat. No. 6,642,437).
Vectors designed for expression of a gene in microalgae can in some embodiments include a promoter active in microalgae operably linked to the exogenous gene being introduced. A variety of gene promoters and terminators that function in green algae can be utilized in expression vectors, including, but not limited to promoters and terminators from Chlamydomonas and other algae (see, for example, Plant Cell Physiol 49: 625-632 (2008)), promoters and terminators from viruses, and synthetic promoters and terminators.
For transformation of diatoms, a variety of gene promoters that function in diatoms can be utilized in these expression vectors, including, but not limited to: 1) promoters from Thalassiosira and other heterokont algae, promoters from viruses, and synthetic promoters. Promoters from Thalassiosira pseudonana that would be suitable for use in expression vectors include an alpha-tubulin promoter, a beta-tubulin promoter, and an actin promoter. Promoters from Phaeodactylum tricornutum that would be suitable for use in expression vectors include an alpha-tubulin promoter, a beta-tubulin promoter, and an actin promoter. The terminators associated with these genes, other diatom genes, or particular heterologous genes can be used to stop transcription and provide the appropriate signal for polyadenylation.
In some instances it can be advantageous to express a heterologous enzyme, such as but not limited to a thioesterase, at a certain point during the growth of the transgenic host to minimize any deleterious effects on the growth of the transgenic organism and/or to maximize production of the fatty acid product of interest. In these instances one or more exogenous genes introduced into the transgenic organism can be operably linked to an inducible promoter. The promoter can be a lac promoter, a tet promoter (e.g., U.S. Pat. No. 5,851,796), a hybrid promoter that includes either or both of portions of a tet or lac promoter, a hormone-responsive promoter (e.g., an ecdysone-responsive promoter, e.g., U.S. Pat. No. 6,379,945) a metallothionien promoter (U.S. Pat. No. 6,410,828), or a pathogenesis-related (PR) promoter that can be responsive to a chemical such as, for example, salicylic acid, ethylene, thiamine, or BTH (U.S. Pat. No. 5,689,044). An inducible promoter can also be responsive to light or dark (U.S. Pat. No. 5,750,385, U.S. Pat. No. 5,639,952) or temperature (U.S. Pat. No. 5,447,858; Abe et al., Plant Cell Physiol. 49: 625-632 (2008); Shroda et al. Plant J. 21: 121-131 (2000)). The foregoing list is exemplary and not limiting. The promoter sequences can be from any organism, provided that they are functional in the host organism. Inducible promoters as used in the constructs of the present invention can use one or more portions or one or more domains of the aforementioned promoters or other inducible promoters fused to at least a portion of a different promoter that operates in the host organism to confer inducibility on a promoter that operates in the host species.
A variety of gene promoters that function in cyanobacteria can be utilized in expression vectors, including, but not limited to: 1) the lac, tac, and trc promoters that are inducible by the addition of isopropyl β-D-1-thiogalactopyranoside (IPTG), 2) promoters that are naturally associated with transposon- or bacterial chromosome-borne antibiotic resistance genes (neomycin phosphotransferase, chloramphenicol acetyltrasferase, spectinomycin adenyltransferase, etc.), 3) promoters of various heterologous bacterial and native cyanobacterial genes, 4) promoters from viruses and phages, and 5) synthetic promoters. Promoters isolated from cyanobacteria that have been used successfully include the following:
secA (secretion; controlled by the redox state of the cell) rbc (Rubisco operon) psaAB—(PS I reaction center proteins; light regulated) psbA—(D1 protein of PSII; light-inducible)
Likewise, a wide variety of transcriptional terminators can be used for expression vector construction. Examples of possible terminators include, but are not limited to, psbA, psaAB, rbc, secA, and T7 coat protein.
Transformation vectors preferably also include a selectable marker, such as but not limited to a drug resistance gene, an herbicide resistance gene, a metabolic enzyme or factor required for survival of the host (for example, an auxotrophic marker), etc. Transformed cells can be optionally selected based upon the ability to grow in the presence of the antibiotic or other selectable marker under conditions in which cells lacking the resistance cassette or auxotrophic marker would not grow. In some embodiments a non-selectable marker may be present on a vector, such as a gene encoding a fluorescent protein or enzyme that generates a detectable reaction product. In an alternative transformation strategy, selectable or non-selectable markers can be provided on a separate construct, where both the gene-of-interest construct and the selectable marker construct are used together in transformation protocols, and selected transformants are analyzed for co-transformation of the construct that includes the gene-of-interest (see, for example, Kindle (1990) Proc. Natl. Acad. Sci. USA 87: 1228-32; Jakobiak et al. (2004) Protist 155:381-93).
Growth of Transformed Organisms
Plants can be grown on or in culture media or in soil, and can be grown in a greenhouse or growth chamber, or outdoors. Algae and photosynthetic bacteria can be cultured phototrophically, in the absence of a fixed carbon source, or mixotrophically, where the cultures are supplied with light for at least part of the day, and also supplied with a reduced carbon source, such as a (e.g., glucose, fructose, galactose, mannose, rhamnose, arabinose, xylose, lactose, sucrose, maltose), an organic acid (e.g., actetate, citrate, succinate), or glycerol. The photosynthetic organism in some embodiments is cultured mixotrophically, in which the organism is grown in the presence of light for at least a part of the day, and also provided with one or more sources of reduced carbon. A photosynthetic organism can be grown mixotrophically for a period of time, followed by a period of phototrophic growth, or vice versa.
Media for phototrophic or mixotrophic growth of algae are well known, and media can be optimized to enhance growth or production of fatty acid products for a particular species. Artificial light sources can be used as the sole light source or to enhance or extend natural light.
In some embodiments, a transgenic organism contains an exogenous gene for an acyl-ACP thioesterase as described herein (and, optionally one or more additional exogenous genes) that is under the control of an inducible promoter, as described above, and the transgenic organism is grown or cultured for a period of time while the transgene(s) is/are not induced. At a point during the growth period, which can be empirically determined based on production levels of the fatty acid product, the gene can be induced, for example, by a period of dark or light, raising or lowering of the temperature, or addition of one or more nutrients or chemicals to the culture medium. The transgenic organism can be maintained under inducing conditions for any feasible amount of time for production of protein(s) encoded by the transgene(s).
Growth of algae can be in open areas, such as, for example, ponds, canals, channels, raceways, or tanks, or can be in bioreactors. Bioreactors are preferred for mixotrophic growth, and can also be used for phototrophic growth. The bioreactors can be of any sizes and form, and can include inlets for providing nutrients, additives, or gases, such as but not limited to air or CO 2 . A bioreactor preferably also has an outlet for sampling of the culture. A bioreactor can be configured such that the algal culture is mixed during the growth period, for example, by stirring, rocking, shaking, inverting, bubbling of gases through the culture, etc. Outdoor ponds, raceways, tanks, canals, etc. can also be designed for mixing of cultures through, for example, paddles, pumps, hoses or jets for circulation of the culture media, or tubes, hoses or inlets for supplying air or CO 2 to the culture.
Production of Fatty Acid Products
Where cultures of algae or photosynthetic bacteria are employed in the methods, the fatty acid products can be isolated from the culture medium, from the cells, or from whole culture (culture medium plus cells). In some embodiments the fatty acid products include a C8 fatty acid product, such as octanoic acid, triglycerides that include octanoic acid, or a fatty aldehyde, fatty alcohol, fatty ester, or hydrocarbon derived from octanoic acid. In some embodiments the fatty acid products include a C10 fatty acid product, such as decanoic acid, triglycerides that include decanoic acid, or a fatty aldehyde, fatty alcohol, fatty ester, or hydrocarbon derived from decanoic acid.
In embodiments in which a fatty acid product such as a triglyceride, a fatty aldehyde, a fatty alcohol, a fatty ester, or a hydrocarbon are produced by the transgenic organism, the transgenic organism optionally includes an additional exogenous gene, in which the additional transgene encodes another enzyme that functions in the synthesis of a fatty acid product. In embodiments in which the fatty acid product is a fatty aldehyde, for example, a C8 fatty aldehyde or a C10 fatty aldehyde, the transgenic host organism can further comprise an exogenous nucleic acid molecule that encodes an acyl-CoA reductase. Where the isolated fatty acid product is a fatty alcohol, the transgenic photosynthetic organism in some embodiments comprises, in addition to the transgene that encodes a C8-preferring or a C10-preferring acyl-ACP thioesterase, an exogenous nucleic acid molecule encoding an acyl-CoA reductase. In embodiments in which the fatty acid product is a fatty ester, such as a wax ester, the transgenic organism used for production of the wax ester can include a fatty acyl-CoA reductase and an exogenous nucleic acid molecule encoding a wax ester synthase (which may or may not also have diacylglycerol acyltransferase activity). Nucleic acid molecules encoding additional enzymes for the synthesis of fatty acid products can be provided in expression constructs. The genes can be codon-optimized for expression in the host.
In embodiments in which a fatty acid is isolated or separated from the cells and/or culture medium, the isolated or separated fatty acid can be converted to one or more of a fatty aldehyde, fatty alcohol, fatty ester, or hydrocarbon through chemical or enzymatic methods.
In some preferred embodiments, the method includes culturing a photosynthetic organism transformed with a nucleic acid molecule encoding a Class II acyl-ACP thioesterase, and isolating one or more fatty acid products of specific chain length(s) from the culture. In preferred embodiments, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, at least 45%, or at least 50% of the fatty acid product isolated from the culture is a fatty acid product of a specific chain length. In some preferred embodiments, between 50% and 55%, between 55% and 60%, between 60% and 65%, between 65% and 70%, between 70% and 75%, between 75% and 80%, between 80 and 85%, between 85% and 90%, between 90% and 95%, between 95% and 97%, between 97% and 99%, or between 99% and 100% of the fatty acid product isolated from the culture is one or more fatty acids of specific chain length(s). In some embodiments of these methods, a prokaryotic photosynthetic organism transformed with a nucleic acid molecule encoding an acyl-ACP thioesterase is grown in culture, and one or more fatty acids is isolated from the culture media, where at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, between 80% and 85%, between 85% and 90%, between 90% and 95%, between 95% and 97%, between 97% and 99%, or between 99% and 100% of the fatty acids isolated from the culture are fatty acids of specific chain lengths.
Isolation of Fatty Acid Products
Fatty acids and fatty acid products can be extracted from the seeds, fruit, or nuts of higher plants by grinding, crushing, or pressing the seeds, fruit or nuts. In some preferred embodiments, the seeds, nuts, or fruit are heated prior to or during the extraction process to soften plant tissues and improve solubility of the fatty acid product. Algae that produce fatty acid products can also be subject to extraction procedures in which the cells are ground, sonicated, or otherwise disrupted and pressed to separate the oil and other liquids from solid cell or tissue components. Fatty acids can be extracted with an organic solvent, for example, triglycerides and fatty acids can be extracted with hexane.
Extracellular hydrocarbons can also be extracted from living microalgae cells which are then returned to a bioreactor by exposure of the cells, in an otherwise sterile environment, to a non-toxic extraction solvent, followed by separation of the living cells and the hydrophobic fraction of extraction solvent and hydrocarbons, in which the separated living cells are then returned to a culture container such as a stainless steel fermentor or photobioreactor (see Biotechnol Bioeng. 2004 Dec. 5; 88(5):593-600 and Biotechnol Bioeng. 2004 Mar. 5; 85(5):475-81).
Fatty acid products (e.g., lipids, fatty acids, aldehydes, alcohols, alkenes, and alkanes) produced by cells of the invention can be harvested, or otherwise collected, by any convenient means. For example, hydrocarbons secreted from cells can be centrifuged to separate the hydrocarbons in a hydrophobic layer from contaminants in an aqueous layer and optionally from any solid materials as a precipitate in after centrifugation. Material containing cell or cell fractions can be treated with proteases to degrade contaminating proteins before or after centrifugation. In some instances the contaminating proteins are associated, possibly covalently, to hydrocarbons or hydrocarbon precursors which form hydrocarbons upon removal of the protein. In other instances the hydrocarbon molecules are in a preparation that also contains proteins. Proteases can be added to hydrocarbon preparations containing proteins to degrade proteins (for example, the protease from Streptomyces griseus can be used (SigmaAldrich catalog number P5147). After digestion, the hydrocarbons are preferably purified from residual proteins, peptide fragments, and amino acids. This purification can be accomplished, for example, by methods listed above such as centrifugation and filtration.
In some embodiments, fatty acid products are isolated from algal cells or whole culture that includes cells by generating a cell lysate. The cells are first disrupted, for example, by heat, treatment with an acid or base, treatment with enzymes, osmotic shock, mechanical disruption, sonication, freeze-thaw, etc., and then intracellular and cell membrane/cell wall-associated fatty acids can be collected from the lysed cells.
The fatty acid products can be extracted with a hydrophobic solvent such as hexane (see Frenz et al. 1989, Enzyme Microb. Technol., 11:717) or by liquefaction (see for example Sawayama et al. 1999, Biomass and Bioenergy 17:33-39 and Inoue et al. 1993, Biomass Bioenergy 6(4):269-274); oil liquefaction (see for example Minowa et al. 1995, Fuel 74(12):1735-1738); or supercritical CO 2 extraction (see for example Mendes et al. 2003, Inorganica Chimica Acta 356:328-334). Cells can also be freeze dried and pulverized followed by extraction with n-hexane (Miao and Wu, Biosource Technology (2006) 97:841-846).
In embodiments in which algae or microorganisms secrete fatty acid products, the cells can be removed from the culture medium, for example, by centrifugation, sedimentation, flocculation, or filtering, and the culture medium can be extracted with a solvent such as hexane.
Capture and recovery of fatty acids or fatty acid products that are secreted into the culture medium by recombinant bacteria and algae, such as cyanobacteria, as described above, can also be performed by adsorbing the fatty acids secreted into the culture medium to small, easily harvested objects. In this method, small objects that are able to bind free fatty acids and other lipids, referred to for purposes of this specification as “fat adsorbing objects,” are circulated in the culture medium for an appropriate amount of time and then collected by physical separation. The fatty acids are then eluted from the fat adsorbing objects by the use of an appropriate non-polar solvent. Evaporation of the solvent, followed by further processing of the isolated fatty acids and lipids can then be carried out to yield chemicals and fuels that can be used for a variety of commercial purposes.
The fat adsorbing objects (for example, spheres ranging from 1 mm to 30 mm) can be manufactured from various materials including, but not limited to, polymers including, for example, polyethylene and derivatives, polystyrene and derivatives, polyamide and derivatives, polyester and derivatives, polyurethane and derivatives, polyacrylates and derivatives, silicone and derivatives, and polysaccharide and derivatives. Certain glass and ceramic materials can also be used as the solid support component of the fat adsorbing objects. The surfaces of the fat adsorbing objects are modified so that they are able to bind fatty acids and lipids. An example of such modification is the introduction of ether-linked alkyl groups having various chain lengths, preferably 10-30 carbons. In another example, acyl chains of various lengths can be attached to the surface of the fat adsorbing objects via ester, thioester, or amide linkages.
In another embodiment of this invention, the fat adsorbing objects are coated with inorganic compounds known to bind fatty acids and lipids. Examples of such compounds include but are not limited to aluminum hydroxide, graphite, anthracite, and silica.
To capture secreted fatty acids from the culture medium used to cultivate the photosynthetic microorganisms, the fat adsorbing objects are circulated in the culture medium for an appropriate period of time, and then removed from the culture by the use of filters or screens or other physical separation devices. Alternatively, the fat absorbing objects can be provided in a column or tube through which the algal culture can be passed.
The fatty acids bound to the fat adsorbing objects are then eluted by the use of an appropriate non-polar solvent such as hexane, after which the fat adsorbing objects can be dried and returned to the culture medium so that more fatty acids can be bound and removed. The hexane containing the dissolved fatty acids is then evaporated, leaving the fatty acids in a purified state for further conversion to chemicals and fuels. The fat adsorbing objects can be designed to be neutrally buoyant or positively buoyant to enhance circulation in the culture medium. It is anticipated that a continuous cycle of fatty acid removal and recovery using the fat adsorbing objects can be implemented by utilizing the steps outlined above.
The following examples are offered to illustrate but not to limit the invention.
EXAMPLE 1
Isolation of a Gene that Encodes a Novel Acyl-ACP Thioesterase (Ca1FatB2) from Cuphea Aequipetala
To isolate a gene encoding a medium chain acyl-ACP thioesterase, seeds of Cuphea aequipetala (Accession No. PI561477) were obtained from the USDA National Plant Germplasm System through the North Central Regional Plant Introduction Station in Ames, Iowa. Genomic DNA was isolated from the seeds as follows: 50 seeds were transferred to a microfuge tube and incubated for one hour at 50-55° C. in 0.35 mL of Extraction Buffer (200 mM Tris-HCl pH 8.0, 200 mM NaCl, 25 mM EDTA, 0.5% SDS, and 20 mg/mL proteinase K). The hydrated and lysed seeds were then ground using a plastic pestle. 0.35 mL of CTAB solution (2% w/v CTAB, 100 mM Tris-HCl, pH 8.0, 20 mM EDTA, 1.4 M NaCl, 1% PVP) was added and incubated at room temperature for one hour. The mixture was then centrifuged at 14000×g for 5 minutes and the supernatant solution was transferred to a Phase Lock Gel tube (5 Prime, Inc.). DNA was extracted with one volume of phenol:chloroform (1:1) and the aqueous phase was transferred to a new tube; this step was repeated twice. DNA was precipitated in 1/10 volume of 3 M sodium acetate, pH 5.5, and 0.8 volumes of isopropanol. The pellet was rinsed with 70% ethanol and the genomic DNA was resuspended in water.
A nested polymerase chain reaction (PCR) approach was used to amplify a large portion of the Ca1FatB2 gene using degenerate oligonucleotide primers. The primary PCR was performed with primers ‘fatB degen1 2F’ (SEQ ID NO:1) and ‘fatB degen6 1R’ (SEQ ID NO:2). The secondary PCR was performed with primers ‘fatB degen7 1F’ (SEQ ID NO:3) and ‘fatB degen8 1R’ (SEQ ID NO:4) that were nested inside the ‘fatB degen1 2F’ and ‘fatB degen6 1R’ primer sequences. A mixture of Phusion DNA polymerase (New England Biolabs, Ipswich, Mass.) plus RedTaq DNA polymerase (Sigma, St. Louis, Mo.) was used for both PCR reactions under the following thermocycler conditions: 94° C. for 5 min; 40 cycles of (94° C. for 30 s; 55° C. for 30 s; 72° C. for 4 min); 72° C. for 5 min. After electrophoresis through 1% agarose gels, 1.7- to 3-kbp amplicons from the secondary PCR were excised and purified using the ZYMOCLEAN™ Gel DNA Recovery Kit (Zymo Research, Orange, Calif.). The isolated DNA was subsequently incubated for 15 min at 72° C. with Taq DNA polymerase and dNTPs, followed by insertion into the pCR4-TOPO vector (Invitrogen, Carlsbad, Calif.), which was used to transform chemically competent E. coli TOP10 cells (Invitrogen). Transformants were colony-screened using the primers ‘fatB degen7 1F’ (SEQ ID NO:3) and ‘fatB seq2 R’ (SEQ ID NO:5) to confirm the presence of the Ca1FatB2 gene. Positive clones were then sequenced.
The sequence of the isolated Cuphea aequipetala FatB2 genomic fragment is provided as SEQ ID NO:6. The first 22 and last 21 nucleotides of SEQ ID NO:6 correspond to the amplification primer sequences that were based on homology to other acyl-ACP thioesterases. Intron locations were predicted by comparison of the translated sequences from all three reading frames with known FatB protein sequences along with examination for consensus intron/exon boundaries, allowing the coding regions of the gene and deduced amino acid sequence of the encoded protein to be determined. The sequence was found to be highly homologous at the amino acid level to FatB genes of other Cuphea species, and the corresponding gene was designated “Ca1FatB2”. The cloned region lacked sequences encoding the complete chloroplast transit peptide and the carboxy terminus since the primers used to isolate the sequence annealed to sequences within the coding region.
EXAMPLE 2
Expression of a Synthetic Ca1FatB2 Gene in E. Coli
A synthetic acyl-ACP thioesterase gene based on the coding sequences of the isolated Ca1FatB2 genomic clone was constructed for expression studies. The nucleotide sequence of this synthetic version of the Ca1FatB2 gene is indicated as SEQ ID NO:7, and the amino acid sequence derived from this synthetic gene is indicated as SEQ ID NO:8. The plasmid containing the synthetic gene is referred to as pJ201:24592.
The synthetic gene was truncated at the 5′ end to eliminate sequences encoding the putative chloroplast transit peptide. Although the site of processing of plant acyl-ACP thioestease precursors is not known with certainty, it is believed that the truncation of the synthetic gene excludes all or most of the plastid transit peptide-encoding region at the amino-terminus of the Ca1FatB2 thioesterase. Furthermore, as the gene sequence obtained by PCR lacked a carboxy-terminus-encoding region, a consensus carboxy-terminus sequence was designed based on published acyl-ACP thioesterase sequences in order to complete the 3′ region of the gene (amino acid positions 356-362 of SEQ ID NO:8). The gene was synthesized using the codon usage preference of Synechocystis for functional testing of the gene product via expression in E. coli and Synechocystis 6803 (kazusa.or.jp/codon/cgi-bin/showcodon.cgi?species=1148).
In order to produce an expression vector, the synthetic Ca1FatB2 gene was amplified from pJ201:24592 using primers ‘fatB GLA162 SYopt NT F’ (SEQ ID NO:9) and ‘fatB GLA162 SYopt R’ (SEQ ID NO:10), and the IN-FUSION™ Dry-Down PCR Cloning Kit (Clontech, Mountain View, Calif.) was used to insert the gene into pTrcHisB (Invitrogen, Carlsbad, Calif.) having the TrcE promoter, which was then introduced into TOP10 E. coli cells to create plasmid GLA256 in strain PE-0284. Plasmid GLA256 was then transformed into the E. coli strain K27, which has a mutation in the fadD (acyl-CoA synthetase) gene (Overath et al., Eur. J. Biochem. 7:559-574), to create strain PE-0285. During the cloning process, an inadvertent elongation of the 3′ consensus sequence by 15 nucleotides occurred, such that the last 2 amino acids (IS, i.e., isoleucine and serine) were replaced by KLGCFGG (SEQ ID NO: 11). The substrate preference and protein function of this thioesterase having a variant C-terminus (SEQ ID NO:12) were not significantly altered by this change in the carboxy-terminus when compared to the native sequence (the activity of the native sequence is shown as “Variant I” in Table 2 of Example 4). The Synechocystis codon-optimized nucleic acid sequence encoding this carboxy terminus variant is provided as SEQ ID NO:13.
Transformed E. coli K27 cells were inoculated into 4 mL of LB medium at OD 600 =0.2 and induced with 0.5 mM IPTG during log phase; E. coli Top10 strains did not require induction. The cells were cultured in 15 mL Falcon round-bottom tubes for 24 hours and assayed for free fatty acid (FFA) production and secretion into the medium by the use of gas chromatography as follows: Cultures were centrifuged at 3,000×g and the supernatant solutions were filtered through 0.7 μm WHATMAN™ glass microfiber filters using a Millipore vacuum filter manifold. Two mL of the filtrate were transferred to glass tubes with Teflon-lined caps. Each 2-mL sample was extracted with a mixture of 40 μL internal standard solution (C11:0, 2 mg/mL), 50 μL phosphoric acid (1 M), 100 μL NaCl (5 M) and 2 mL hexane. After incubation for one hour with gentle rocking at room temperature, the organic phase was transferred to a GC vial. A 1 μL sample was injected into an Agilent Model 7890A gas chromatograph using a 40:1 split ratio onto a DB-FFAP column (J&W Scientific, 15 m×250 μm×0.25 μm), with a temperature profile starting at 150° C. for 0.5 min, then heating at 15° C./min to 230° C. and holding for 7.1 min (1.1 mL/min He). As shown in Table 1, octanoic acid was the predominant fatty acid secreted into the medium by the E. coli cells containing the Ca1FatB2 gene. No fatty acids were detected in the media of control cells lacking the Ca1FatB2 gene (but containing plasmid pTrcHisB).
TABLE 1
Production and Secretion of FFAs in E. coli
Cells Expressing a Synthetic Ca1FatB2 Gene
FFA levels (mg/L)
Strain ID
Plasmid
8:0
10:0
12:0
14:0
16:0
16:1
18:0
18:1
Ca1FatB2 in E.
GLA256
9.3
0.2
0.0
0.0
0.0
0.0
0.0
0.0
coli Top 10 cells
(Strain PE-0284)
Ca1FatB2 in E.
GLA256
39.8
1.8
1.2
0.0
0.0
0.0
0.0
0.0
coli K27 cells
(Strain PE-0285)
Empty vector
pTrcHisB
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
control
(Strain PE-0286)
Example 3
Completion of the 3′ End of the Native Ca1FatB2 Gene
Genome walking was performed to determine the complete actual sequence at the 3′ end of the Ca1FatB2 coding region. An adaptor ‘GW ad’ was constructed by annealing oligos ‘GW adL’ (SEQ ID NO:14) and ‘GW adS’ (SEQ ID NO:15) at a final concentration of 100 mM each in 1× DNA ligase buffer (Invitrogen Corp., Carlsbad, Calif.). The GW adS oligomer was phosphorylated at the 5′ end and included a 3′ amino modifier. The following incubation conditions were used: 95° C. for 3 min; followed by 55° C. for 3 min; 45° C. for 3 min; 35° C. for 3 min; 25° C. for 3 min; 15° C. for 3 min; and then 4° C. hold. Single endonuclease digests were performed on C. aequipetala genomic DNA (gDNA) with PmlI, SnaBI, MscI, and StuI (New England Biolabs, Ipswich, Mass.) with overnight incubation at 37° C. The reactions were heat inactivated at 80° C. and the DNA was purified by standard phenol/chloroform procedures. Adaptor ‘GW ad’ was then ligated to the digested gDNA at 16° C. overnight with T4 DNA ligase (Invitrogen Corp., Carlsbad, Calif.). A nested PCR approach was used to amplify the 3′ end of Ca1FatB2 gene. The primary PCR was performed with primers ‘adP1’ (SEQ ID NO:16) and ‘GLA162-1F’ (SEQ ID NO:17). The secondary PCR was performed with ‘adP2’ (SEQ ID NO:18) and ‘GLA162-2BF’ (SEQ ID NO:19). Phusion DNA polymerase (New England Biolabs, Ipswich, Mass.) was used for both PCRs using the following thermocycler conditions: 98° C. for 3 min; 10 cycles (98° C. for 10 sec; 67° C. for 30 sec; 72° C. for 4 min); 30 cycles (98° C. for 10 sec; 70° C. for 30 sec; 72° C. for 4 min); 72° C. for 5 min; 4° C. hold. dNTPs were added to the secondary amplicons and incubated with Taq polymerase at 72° C. for 5 min. The PCR products were cloned into the pCR4-TOPO vector by use of the TOPO TA Cloning kit (Invitrogen Corp., Carlsbad, Calif.) and sequenced. Sequence alignments were performed with Sequencher (Gene Codes Corp., Ann Arbor, Mich.).
The sequence of the resulting isolated Cuphea aequipetala FatB2 genomic DNA fragment is provided as SEQ ID NO:20. The predicted native Ca1FatB2 coding nucleotide sequence is indicated as SEQ ID NO:21. A small portion of the region of the gene that encodes the plastid transit peptide is not included in this sequence, although the entire sequence could be obtained by additional 5′ genome walking The deduced protein sequence that is encoded by this Ca1FatB2 gene, assembled by PCR of genomic DNA with primers designed to hybridize within the coding region of a Class II acyl-ACP thioesterase followed by removal of intron sequences and gene walking to obtain sequences C-terminal sequences downstream of the amplified region of the gene is indicated as SEQ ID NO:22 ( FIG. 1 ).
In order to confirm the absence of a chimeric assembly in the gene sequence extended by genome walking, a one-piece amplicon was obtained using primers ‘GLA162 seq1F’ (SEQ ID NO:23) and ‘GLA162-290R’ (SEQ ID NO:24). The 2.1 kb amplicon was gel purified and TOPO cloned into the pCRII-Blunt vector (Invitrogen Corp., Carlsbad, Calif.). The one-piece amplicon differed slightly within the coding regions of the version originally amplified from the seed DNA at two residues: M67I (methionine at residue 67 replaced by isoleucine) and L103I (leucine at residue 103 replaced by isoleucine). These amino acid substitutions were incorporated as a variant of the gene. These amino acid changes are present in “Variant III”; the nucleotide sequence of this variant is provided as SEQ ID NO:25 and the protein translation is provided as SEQ ID NO:26. The protein functionality of Variant III was not found to be affected to a significant extent (see Example 4).
EXAMPLE 4
Production of Ca1FatB2 Gene Variants and Expression in E. Coli
As described above, genome walking was performed to determine the 3′ DNA sequence of the native Ca1FatB2 gene. The region encoding the hybrid carboxy-terminus consensus sequence present in plasmid GLA256 was replaced by a codon-optimized version of the native 3′ end of the Ca1FatB2 gene using primers ‘fatB GLA162 SYopt NT F’ (SEQ ID NO:9) and ‘fatB GLA162 SYopt 2R’ (SEQ ID NO:27). The resulting amplicon (SEQ ID NO:28) encoded the protein indicated as SEQ ID NO:29 (“Variant I”) and was inserted into the Synechocystis expression vector pSGI-YC28 using the InFusion system to create plasmid PR2B. pSGI-YC28 contains the TrcE promoter from pTrcHisA (Invitrogen Corp) the lacI q gene, and the homology arms that enable integration of the expression cassette into the “RS1” site of the Synechocystis PCC 6803 genome (Williams, Methods Enzymol. 167:766-778). This vector replicates autonomously in E. coli and allows gene expression in both E. coli and Synechocystis sp. PR2B was transformed into E. coli K27 to create strain PE-0238.
As described below, additional variants of the Ca1FatB2 gene were produced in order to assess potential structure-function relationships. Results of expression analyses normalized to optical density at 600 nm (OD600) are provided in Table 2.
Variant II: The encoded gene product has an isoleucine at amino acid position 103 rather than a leucine. The gene was produced from the Variant I gene via overlap PCR using the primers ‘fatB GLA162 SYopt NT F’ (SEQ ID NO:9), ‘GLA162 SYopt mut2 R’ (SEQ ID NO:68), ‘GLA162SYopt mut2 F’ (SEQ ID NO:69), and ‘fatB GLA162 SYopt 2R’ (SEQ ID NO:65). The nucleotide sequence of the Variant II gene product is given as SEQ ID NO:70, and the amino acid sequence of the Variant II gene product is given as SEQ ID NO:71.
Variant III: The encoded gene product has an isoleucine at amino acid position 103 rather than a leucine and an isoleucine at amino acid position 67 rather than a methionine. The gene was produced from the Variant II gene via overlap PCR using the primers ‘fatB GLA162 SYopt NT F’ (SEQ ID NO:9), ‘GLA162SYopt mut3 R’ (SEQ ID NO:30), ‘GLA162SYopt mut3 F’ (SEQ ID NO:31), and ‘fatB GLA162 SYopt 2R’ (SEQ ID NO:27). The nucleotide sequence of the Variant III gene is given as SEQ ID NO:25, and the amino acid sequence of the Variant III gene product is given as SEQ ID NO:26.
Variant IV: The encoded gene product has an isoleucine at amino acid position 103 rather than a leucine. In addition, the amino-terminus of the gene product was truncated by an additional 33 amino acids. The gene was produced from Variant II via PCR using the primers ‘fatB GLA162 SYopt NT2 F’ (SEQ ID NO:36) and ‘fatB GLA162 SYopt 2R’ (SEQ ID NO:27). The nucleotide sequence of Variant IV is provided as SEQ ID NO:37, and the amino acid sequence of the Variant IV gene product is given as SEQ ID NO:38.
Variant V: The encoded gene product has an isoleucine at amino acid position 103 rather than a leucine, an asparagine at amino acid position 184 rather than a serine, and an isoleucine at amino acid position 174 rather than a methionine. The gene was produced from Variant II via PCR. The nucleotide sequence of Variant V is provided as SEQ ID NO:39, and the amino acid sequence of the Variant V gene product is given as SEQ ID NO:40. This variant unexpectedly led to a much higher rate of octanoic acid secretion compared to the other variants and produced a higher proportion of octanoic acid. This result was surprising not only because mutants demonstrating increased activity toward the enzyme's preferred substrate have been unattainable until now, but also because other researchers have identified the active site of the enzyme as encompassing amino acids at least 100 residues away from the region of the protein exhibiting these mutations (see for example, U.S. Pat. No. 6,150,512, identifying amino acids YRREC (SEQ ID NO:41) as being at the active site (corresponding to amino acids 293-297 of SEQ ID NO:29 ( FIG. 1 )).
TABLE 2
Production and Secretion of FFAs in E. coli K27-Derived
Cells Expressing Variants of a Synthetic Ca1FatB2 Gene
Production
% total FFA
mg
Variant
Encoded protein
Vector
Strain ID
C8:0
C10:0
C12:0
C8:0/L/OD600
I (native)
Original sequence
PR2B
PE-0238
87
6
3
15
SEQ ID NO: 28
of CaFatB1 mature
protein
SEQ ID NO: 29
II
L103I
GLA518
PE-0288
87
6
3
19
SEQ ID NO: 32
SEQ ID NO: 33
III
M67I, L103I
GLA700
PE-0295
92
6
2
19
SEQ ID NO: 25
SEQ ID NO: 26
IV
L103I
GLA513
PE-0292
89
5
2
19
SEQ ID NO: 37
96-bp 5′ deletion
SEQ ID NO: 38
V
S184N, L103I,
GLA648
PE-0049
95
4
1
65
SEQ ID NO: 39
M174I
SEQ ID NO: 40
EXAMPLE 5
Synthesis and Assay of Additional Thioesterase Variants
Based on the above results, additional variants of the FatB acyl-ACP thioesterase were constructed by overlap PCR amplification in which the mutations were incorporated into primer sequences. A first set of mutants is based on the wild-type C. aequipetala sequence, in which the mutants have various substitutions at amino acid position 174. A second set of mutants was constructed in which the mutants had substitutions at position 174, in addition to the mutations L103I and S184N. Two isolates of each variant were selected for determining the level of production and secretion of various chain length fatty acids in E. coli K27 according to the methods provided in Example 2. The results are provided in the tables of FIGS. 2A-2D and FIGS. 3A-3D , and depicted graphically in FIGS. 4A-4B ).
Results of the fatty acid determination of samples from single amino acid position mutants indicate that isoleucine at position 174 results in the highest levels of production of C8 fatty acid. The M174I mutant (isolates 37 and 38 in FIGS. 2A-2D and FIGS. 3A-3D , having the nucleotide sequence provided as SEQ ID NO:42 and the amino acid sequence provided as SEQ ID NO:43) produces more than twice the octanoic acid produced by the isolates having the wild type gene (isolates 33 and 34 in FIGS. 2A-2D and FIG. 3A-3D ). A mutant having valine at position 174 (isolates 23 and 24) also produced higher than wild-type levels of C8 fatty acid, and mutants having phenylalanine (isolates 15 and 16), cysteine (isolates 27 and 28), or leucine (isolates 11 and 12) at position 174 produced high levels and high percentages of octanoic acid as well. This was true for the cultures as a whole ( FIG. 4A ) and when the values were normalized for cell density ( FIG. 4B ).
The production of octanoic acid was enhanced even further when additional mutations were combined with the mutations at position 174. The highest producing isolates, isolates 71 and 72, which included the S184N and L103I mutations in addition to the M174I mutation, yielded almost three-fold the amount of octanoic acid as did the wild-type strain (isolates 33 and 34), confirming the results shown in Table 2, in which the S184N, L103I, M174I mutant (“Variant V” having the nucleotide sequence SEQ ID NO:39, encoding amino acid sequence of SEQ ID NO:40) produced about four-fold the amount of octanoic acid as did the native C. aequipetala sequence (“Variant I”). Mutations of M174 to valine, phenylalanine, or leucine in combination with the L103I and S184N mutations (variants 49 and 50, 63 and 64, and 59 and 60, respectively) also showed enhancement of C8 fatty acid production with respect to transformants expressing the M174V, M174F, and M174L mutations on their own (isolates 23 and 24, 15 and 16, and 11 and 12, respectively).
EXAMPLE 6
Synthesis and Assay of Additional Thioesterase Variants
To complete the set of single site mutants having different substitutions at position 174 that was provided in Example 5, the single site mutant M174R was constructed. The triple site mutants L103I, M174C, S184N and L103, M174P, S184N were also constructed to determine the effect of the L103I and S184N substitutions on a moderately high-producing mutant (M174C, having activity comparable to wild-type) and a low-producing mutant (M174P). Finally, to elucidate the relative contribution of the mutations at positions 103 and 184 to the increased activity of the L103I, M174I, S184N triple site mutant over the M174I single site mutant, the double mutant L103I, M174I was also constructed by PCR amplification.
E. coli K27 cells were transformed with each of the constructs, and as a control, cells were transformed with empty vector. Additional isolates of cells transformed with constructs containing the M174I thioesterase mutant gene and triple L103I, M174I, S184N thioesterase mutant gene used in the experiments of Example 5 were also obtained for comparison of the results to previous experiments. Two isolates were obtained for each of the mutants and the empty vector control. The sequences of the thioesterase constructs in isolated TOP10 E. coli transformants were confirmed by sequencing prior to transforming the constructs into the K27 expression strain.
The thioesterase mutant-containing cells and empty vector-containing cells were cultured and induced for thioesterase expression, and fatty acids were isolated from the media after culturing the isolates overnight and assayed as provided in Example 5. Due to co-eluting contaminating peaks, C12 fatty acid amounts could not be determined; however, based on Example 2, the amount of C12 fatty acid in the samples was likely to be less than 3% of the total fatty acids in the samples.
The data presented in the table of FIG. 5A shows that the amounts of C8 and total fatty acids produced by the wild-type, M174I mutant, and L103I, M174I, S184N mutant were comparable to the levels seen in FIGS. 2A-2D (compare isolates 37, 38, 71, and 72 of FIGS. 2A-2D with isolates of 81, 82, 79, and 80 of FIGS. 5A-5B ), demonstrating the reproducibility of the results. Isolates 83 and 84 of FIG. 5 (nucleotide and amino acid sequences provided as SEQ ID NO:44 and SEQ ID NO:45, respectively), which include the L103I and M174I mutations (but lack the S184N mutation), produce levels of C8 fatty acid and total fatty acid that are essentially the same as that of the triple mutant L103I, M174I, S184N, indicating that a mutant thioesterase that includes the L103I mutation in addition to the M174I mutation has enhanced fatty acid production with respect to a mutant thioesterase that includes only the M174I mutation, while the S184N mutation has no discernible affect on fatty acid production. Normalized fatty acid production is provided in the table of FIG. 5B and presented graphically in FIG. 6 .
This result also indicates that the mutation of position M174, alone or in combination with a mutation at position 103, is tolerant of at least some mutations at other amino acid positions in the protein, as the S184N mutation did not affect the yield.
The data also demonstrate that modifying the gene such that an isoleucine is encoded at position 103 (here, in combination with S184N) increases the activity of a thioesterase mutant having a C or P at position 174 (comparing the higher production levels of isolates 87-90 of FIGS. 5A-5B with those of isolates 27, 28, 35, and 36 of FIGS. 2A-2D ). A variant having isoleucine at position 103 and cysteine at position 174 also showed enhancement of C8 fatty acid production with respect to wild-type bearing isolates.
EXAMPLE 7
Expression of the Ca1FatB2 Gene in the Cyanobacterium Synechocystis Sp.
Plasmid PR2B of Example 4 was also transformed into Synechocystis sp. PCC 6803 to create strain PH-0094. The transformation protocol used was essentially as described by Zang et al. ( Microbiology 45:241-245). To test for the production of free fatty acids in phototrophically grown Synechocystis, the Ca1FatB2-containing cells were pre-cultivated in 100 mL of BG-11 medium supplied with kanamycin (20 mg/L) to late-log phase (OD 730 nm =1.0) on a rotary shaker (150 rpm) at 30° C. with constant illumination (60 μE·m −2 ·sec −1 ). Cultures were then subcultured at initial OD 730 nm =0.4-0.5 in BG-11 and cultivated overnight to OD 730 nm =0.7-0.9. For time-course studies, 50-mL aliquots of the culture were transferred into 250-mL flasks and induced by adding IPTG (final conc.=1 mM). Cultures were sampled at various time points after IPTG induction and then filtered through WHATMAN™ GF/B glass microfiber filters using a MILLIPORE® vacuum filter manifold (Millipore, Billerica, Mass.). Filtrates were collected in screw top culture tubes for gas chromatographic (GC) analysis. Free fatty acids (FFA) were separated from the filtered culture supernatant solutions by liquid-liquid extraction. For each sample, 2 mL filtered culture was extracted with a mixture of 40 μL internal standard solution (C11:0, 2 mg/mL), 50 μl phosphoric acid (1 M), 100 μl NaCl (5 M) and 2 mL hexane. A 1 μl sample was injected using a 40:1 split ratio on to a DB-FFAP column (J&W Scientific, 15 m×250 μm×0.25 μm), with a temperature profile starting at 150° C. for 0.5 min, then heating at 15° C./min to 230° C. and holding for 7.1 min (1.1 mL/min He). The level of secreted FFAs in the medium 10 days after IPTG induction is provided in Table 3. The results demonstrate that the high activity thioesterase variants also result in higher fatty acid production by a photosynthetic organism.
TABLE 3
Production and Secretion of FFAs in Synechocytis Cells Expressing a Synthetic Ca1FatB2 Gene
Total
Strain ID
Plasmid
C8:0
C10:0
C12:0
C14:0
C16:0
C16:1
C18:0
C18:1
FFA (mg/L)
Vector control
YC27
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
(Strain PH-0019)
Ca1FatB2
PR2B
54.8
6.4
0.0
0.0
0.0
0.0
0.0
0.0
61.2
native gene
(Strain PH-0094)
Ca1FatB2
GLA648
156.4
11.4
0.2
0.0
0.0
0.0
0.0
0.0
167.8
S184N, L103I,
M174I gene
(Strain PH-0095)
EXAMPLE 8
Isolation of Additional Novel Acyl-ACP Thioesterase (FatB) Genes from Various Cuphea Species
An additional seventeen novel FatB genes, listed in Table 4, were also isolated from Cuphea samples by extracting genomic DNA from Cuphea seeds or vegetative tissues. Nested degenerate primers were used to clone individual FatB genes from the DNA samples. This approach results in gene sequences lacking complete 5′ and 3′ ends of the genes. The genes obtained by amplification of genomic DNA provided sequences that started from within the plastid transit peptide, therefore it was unnecessary to complete the terminal 5′ nucleotide sequence in order to obtain a functional gene. (The activity of the thioesterase is unaffected by the presence or the absence of this transit peptide (Jones et al. (1995) The Plant Cell 7: 359-371; Voelker et al. (1992) Science 257:72-74).) The 3′ ends of many of the novel thioesterase genes were completed via genome walking For those genes whose 3′ ends were not determined, a consensus hybrid sequence was appended based on known Cuphea FatB protein sequences prior to expressing the genes in vivo. We have found that altering the 3′ sequence does not significantly modify substrate preference or function of FatB genes.
Genomic DNA Isolation from Cuphea Samples
Genomic DNA was isolated from Cuphea avigera, Cuphea carthagenesis, Cuphea decandra, Cuphea inflate, Cuphea paucipetala, and Cuphea leptopoda tissues as follows: 2 cm stem and leaf cuttings ( Cuphea avigera ) or 40-50 seeds (other species) from each Cuphea sample were transferred to separate microfuge tubes and incubated for one hour at 55° C. in 350 μl of Extraction Buffer (200 mM Tris-HCl pH 8.0, 200 mM NaCl, 25 mM EDTA, 0.5% SDS, and 20 mg/ml proteinase K). The hydrated and lysed tissues were then ground using a plastic pestle. 350 μl of CTAB solution (2% w/v CTAB, 100 mM Tris-Cl, pH 8.0, 20 mM EDTA, 1.4 M NaCl, 1% PVP) were added and incubated at room temperature for one hour. The mixture was then centrifuged at 14000×g for 5 minutes and the supernatant solution was transferred to a Phase Lock Gel tube (5 Prime, Inc., Gaithersburg, Md.). DNA was extracted with one volume of phenol:chloroform (1:1) and the aqueous phase was transferred to a new tube; this step was repeated 2-3 times. DNA was precipitated in 1/10 volume of 3 M sodium acetate, pH 5.5, and 0.8 volumes of isopropanol. The pellet was rinsed with 70% ethanol and the genomic DNA was resuspended in water.
Gene Isolation and Cloning
A nested PCR approach was employed to amplify FatB genes using degenerate primers as described below. The primary PCR was performed with primers fatB degen1 2F (5′-ATGGTGGCTRCYGMWGCAAG; SEQ ID NO:1) and fatB degen6 1R (5′-CTAAGAKAYMGAGTYTCCAKKTSARGTC; SEQ ID NO:2). The secondary PCR was performed with primers fatB degen7 1F (5′-GCAGCAAGTTCHGCATKCTTCC; SEQ ID NO:3) and fatB degen8 1R (5′-CAKTCTTSGGYCKCCACTCAG; SEQ ID NO:4). A mixture of Phusion DNA polymerase (New England Biolabs, Ipswich, Mass.) plus RedTaq (Sigma, St. Louis, Mo.) was used for both PCRs under the following thermocycler conditions: 94° C. for 5 min; 40 cycles (94° C. for 30 s; 55° C. for 30 s; 72° C. for 4 min); 72° C. for 5 min. 1.7- to 3-kbp amplicons from the secondary PCR were excised and purified after electrophoresis through 1% agarose gels (Bio-Rad, Hercules, Calif.). The isolated DNA was subsequently incubated for 15 min at 72° C. with Taq DNA polymerase and dNTPs, followed by cloning into the pCR4-TOPO vector (Invitrogen, Carlsbad, Calif.) and transformed into chemically competent E. coli TOP10 cells (Invitrogen). Selected E. coli clones that were positive for gene insertions were then sequenced. Intron locations were predicted by comparison of the translated sequences from all three reading frames with known FatB protein sequences, allowing the coding regions of the genes and deduced amino acid sequences of the encoded proteins to be determined.
Genome Walking to Determine 3′ Carboxy Terminus Coding Sequence
Genome walking was performed on the Cc1FatB1, Ci1FatB1, Cl1FatB1, Cl3FatB1, Cd1FatB1, Cl4FatB1 and Ca2FatB2 genes to complete the sequences at the 3′ ends of the coding regions. An adaptor ‘GW ad’ was constructed by annealing oligos ‘GW adL’ (GTAATACGACTCACTATAGGGCACGCGTGGTCGACGGCCCGGGCT GGTT; SEQ ID NO:14) and ‘GW adS’ (AACCAGCCCG; SEQ ID NO:15) at a final concentration of 100 μM each in 1× ligase buffer (Invitrogen Corp.). The following thermocycler conditions were used: 95° C. for 3 min; 55° C. for 3 min; 45° C. for 3 min; 35° C. for 3 min; 25° C. for 3 min; 15° C. for 3 min; 4° C. hold. Single endonuclease digests were performed on the Cuphea genomic DNAs with PmlI, SnaBI, MscI, EcoRV, and/or StuI (Fermentas, Glen Burnies, Md.; New England Biolabs, Ipswich, Mass.) with overnight incubation at 37° C. The reactions were heat inactivated at 80° C. and were followed by standard phenol/chloroform cleanup. Adaptor ‘GW ad’ was then ligated to the digested genomic DNA at 16° C. overnight with T4 DNA ligase (Invitrogen). A nested PCR approach was used to amplify the genomic 3′ ends of the FatB genes. Phusion DNA polymerase (New England Biolabs) was used for both PCRs using the following thermocycler conditions: 98° C. for 3 min; 10 cycles (98° C. for 10 sec; 67° C. for 30 sec; 72° C. for 4 min); 30 cycles (98° C. for 10 sec; 70° C. for 30 sec; 72° C. for 4 min); 72° C. for 5 min; 4° C. hold. dNTPs were added to the secondary amplicons and incubated with Taq at 72° C. for 5 min. The PCR products were cloned into the pCR4 vector (Invitrogen Corp.) and sequenced (Bio Applied Technologies Joint, Inc., San Diego, Calif.). Alignments were performed with the Sequencher program (Gene Codes Corp., Ann Arbor, Mich.).
Cloning of Codon-Optimized Synthetic FatB Genes
The Synechocystis sp. PCC 6803 codon usage table was utilized to codon optimize the coding regions for most of the novel thioesterase genes. Gene constructs encoding the sequences of SEQ ID NO:55 was synthesized to include the carboxy-terminus consensus sequence ANGAISTGKTSNGNSIS (SEQ ID NO:46), gene constructs encoding the sequences of SEQ ID NO:30 and SEQ ID NO:36 were synthesized to include the carboxy-terminus consensus sequence TNGAISTTKTSPGNSVS (SEQ ID NO:47), and genes encoding the sequences of SEQ ID NO:51, SEQ ID NO:59, SEQ ID NO:63, SEQ ID NO:79, SEQ ID NO:85, SEQ ID NO:89, and SEQ ID NO:99 were cloned with the native 3′ sequences that were determined by genome walking Both consensus sequences were based on published acyl-ACP thioesterase 3′ DNA sequences. The synthetic gene constructs for expression were made with a truncation of the 5′ end to exclude the predicted plastid transit peptide-encoding region at the amino-terminus.
References to the disclosed sequences (SEQ ID NOs) of these synthetic genes are indicated in Table 4. The CiFatB1 gene was synthesized by Integrated DNA Technologies (Coralville, Iowa); all other genes were synthesized by DNA 2.0 (Menlo Park, Calif.). All genes were cloned into a Synechocystis sp. PCC 6803 integration vector pSGI-YC28 with the exception of Ca1FatB1, which was cloned into the pTrcHisB vector (Invitrogen), and Cl3FatB1 and Ca2FatB2, which were cloned into the pJexpress plasmid at the time of synthesis. pSGI-YC28 contains the “TrcE” trc promoter from pTrcHisA, the lacI q gene, and the homology arms that enable integration of the expression cassette into the “RS1” site of the Synechocystis PCC 6803 genome (Williams, Methods Enzymol. 167:766-778). This vector replicates autonomously in E. coli and allows gene expression in both E. coli and Synechocystis sp. 6803. pJexpress is an E. coli expression system developed at DNA2.0 in which a modified inducible T5 promoter drives gene expression. Gene inserts were either cloned using the InFusion system (Clontech, Mountainview, Calif.) or double-digested with BamHI and NcoI (New England Biolabs) and ligated with T4 DNA ligase (New England Biolabs). An alignment of the amino terminal regions of the proteins encoded by the expression constructs is provided as FIG. 7 .
TABLE 4
Novel FatB Genes Isolated from Various Cuphea Species
NGPR
Isolated
Isolated gene,
Codon-optimized
Amino acid
Acc.
genomic DNA
amino acid
gene sequence,
Sequence,
Number
Cuphea Species
Gene
sequence
sequence
expression constructs
Expression constructs
PI 534673
C. carthagenensis
Cc1FatB1
SEQ ID NO: 48
SEQ ID NO: 49
SEQ ID NO: 50
SEQ ID NO: 51
PI 561477
C. aequipetala
Ca1FatB1
SEQ ID NO: 52
SEQ ID NO: 53
SEQ ID NO: 54
SEQ ID NO: 55
PI 534687
C. inflata
Ci1FatB1
SEQ ID NO: 56
SEQ ID NO: 57
SEQ ID NO: 58
SEQ ID NO: 59
PI 534694
C. leptopoda
Cl1FatB1
SEQ ID NO: 60
SEQ ID NO: 61
SEQ ID NO: 62
SEQ ID NO: 63
PI 534694
C. leptopoda
Cl1FatB2
SEQ ID NO: 64
SEQ ID NO: 65
PI 561495
C. paucipetala
Cp1FatB1
SEQ ID NO: 66
SEQ ID NO: 67
SEQ ID NO: 68
SEQ ID NO: 69
PI 561487
C. leptopoda
Cl2FatB1
SEQ ID NO: 70
SEQ ID NO: 71
PI 561487
C. leptopoda
Cl2FatB2
SEQ ID NO: 72
SEQ ID NO: 73
SEQ ID NO: 74
SEQ ID NO: 75
PI 578175
C. leptopoda
Cl3FatB1
SEQ ID NO: 76
SEQ ID NO: 77
SEQ ID NO: 78
SEQ ID NO: 79
PI 578175
C. leptopoda
Cl3FatB2
SEQ ID NO: 80
SEQ ID NO: 81
PI 594928
C. decandra
Cd1FatB1
SEQ ID NO: 82
SEQ ID NO: 83
SEQ ID NO: 84
SEQ ID NO: 85
PI 650910
C. leptopoda
Cl4FatB1
SEQ ID NO: 86
SEQ ID NO: 87
SEQ ID NO: 88
SEQ ID NO: 89
PI 650910
C. leptopoda
Cl4FatB2
SEQ ID NO: 90
SEQ ID NO: 91
PI 650910
C. leptopoda
Cl4FatB3
SEQ ID NO: 92
SEQ ID NO: 93
Ames 17868
C. avigera
Ca2FatB1
SEQ ID NO: 94
SEQ ID NO: 95
Ames 17868
C. avigera
Ca2FatB2
SEQ ID NO: 96
SEQ ID NO: 97
SEQ ID NO: 98
SEQ ID NO: 99
Ames 17868
C. avigera
Ca2FatB3
SEQ ID NO: 100
SEQ ID NO: 101
EXAMPLE 9
Expression of FatB Thioesterases in E. Coli and Analysis Of FFA Products
Constructs of Example 8 were transformed into E. coli strain K27, which has a mutation in the fadD (acyl-CoA synthetase) gene (Overath et al., Eur. J. Biochem. 7:559-574), to create the indicated strains. Ca2FatB2 and Cl3FatB1 were under the control of the inducible T5 promoter; all other thioesterase genes were driven by the inducible pTrcE promoter. These strains were inoculated into 10 mL of LB medium supplemented with 50 mg/L kanamycin at OD 600 =0.2 and induced with 0.5 mM IPTG during log phase.
The cultures were grown in 25 mL glass vials for 24 hours and assayed for free fatty acid (FFA) production and secretion into the medium by the use of gas chromatography as follows: Extractions were performed on 7.2 mL whole culture with a mixture of 40 μl internal standard solution (C9:0, C13:0, and C17:0, final concentration of 50 μg/mL), 0.6 mL of 50% sulfuric acid, 1.2 mL NaCl (5 M), and 10.8 mL hexane. Samples were vortexed vigorously to emulsify, incubated at room temperature for one hour, and vortexed again. The mixture was spun at 1800 rpm for 5 minutes, and the organic phase was transferred to a GC vial. A 1 μL sample was injected into an Agilent Model 7890A gas chromatograph using a 40:1 split ratio onto a DB-FFAP column (J&W Scientific, 15 m×250 μm×0.25 μm), with a temperature profile starting at 180° C. for 0.5 minute, then heated at a rate of 30° C. per minute to 230° C., and holding for 3.9. minutes (1.8 mL/min He). Free fatty acid peaks were detected on an FID instrument.
Table 5 shows the predominant fatty acids produced by the various strains.
The E. coli strain transformed with the Ca2FatB2 thioesterase predominantly synthesized C8 free fatty acids, which made up 40% of the C8-C18 free fatty acids produced by the strain.
The E. coli strains transformed with the Cl2FatB2 and Cl4FatB1 thioesterases predominantly synthesized C10 free fatty acids, which made up 42.6% and 37.7% of the total C8-C18 free fatty acids produced by Cl2FatB2 and Cl4FatB1 strains, respectively, but the transformed strains also made a significant amount of C16 fatty acids, which made up 25.4% and 27.7% of the total C8-C16 free fatty acids produced by Cl2FatB2 and Cl4FatB1 strains, respectively.
The Cc1FatB1-containing E. coli strain produced mainly C12, C14, and C16 free fatty acids, with a greater percentage of C14 and C16 free fatty acids that C12 free fatty acids being produced by the E. coli host. Cp1FatB1, Cl1FatB1, Cd1FatB1, and Cl3FatB1-containing strains produced predominantly C14 and C16 free fatty acids, with 80% to greater than 90% of the free fatty acids being produced being C14 or C16 fatty acids. Although more than 50% of the free fatty acids produced by the Ci1FatB1-carrying strain were C16 fatty acids, this strain also produces some C18 fatty acids (>20% of the fatty acids produced). The results are depicted graphically in FIG. 8 , FIG. 9 , and FIG. 10 .
TABLE 5
Production and Secretion of Free Fatty Acids by E. coli Expressing FatB Genes
Total
OD
FFAs
Genotype
600
C8:0
C10:0
C10:1
C12:0
C12:1
C14:0
C14:1
C16:0
C16:1
C18:0
C18:1
mg/L/OD
Experiment #1
empty vector
4.8
0.2
0.1
0.0
0.1
0.0
0.4
0.1
1.3
0.3
0.4
0.3
3.2
Cc1FatB1
1.3
3.5
1.2
0.4
46.8
8.6
29.3
56.4
5.9
73.4
1.6
6.8
234.1
Cp1FatB1
2.3
0.0
0.2
0.0
1.4
0.0
84.2
3.0
10.5
74.9
0.4
11.3
185.9
Cl2FatB2
3.2
3.2
30.4
17.0
5.1
7.9
11.3
2.1
9.1
19.2
0.2
6.0
111.4
Cl4FatB1
3.9
1.8
16.3
7.8
3.0
4.8
7.2
1.3
5.9
11.8
0.1
4.0
63.9
Cl1FatB1
3.6
0.2
0.2
0.0
0.3
0.0
22.4
0.4
9.4
12.4
0.2
5.3
50.6
Ci1FatB1
4.5
0.0
0.1
0.0
0.0
0.0
0.4
0.0
1.0
0.4
0.0
0.6
2.6
Cd1FatB1
1.1
0.7
0.5
0.0
0.8
0.0
78.4
2.1
24.8
131.5
0.3
13.6
252.6
Experiment #2
empty vector
4.3
0.0
0.1
0.0
0.1
0.0
0.5
0.2
1.8
0.7
0.0
0.2
3.6
Cl3FatB1
2.1
0.5
0.3
0.0
0.3
0.0
36.7
0.7
13.3
44.3
0.0
6.1
102.3
Ca2FatB2
4.1
4.4
0.6
0.0
0.2
0.0
1.3
0.2
2.0
1.2
0.3
0.8
11.0
Experiment #3
empty vector
3.3
0.2
0.3
0.0
0.3
0.0
0.7
0.0
4.2
1.8
0.0
0.0
7.4
Ca1FatB1
0.9
0.0
0.0
0.0
8.6
0.0
80.2
9.3
7.8
49.9
0.0
0.0
155.8
EXAMPLE 10
Expression of FatB Thioesterases in the Cyanobacterium Synechocystis Sp.
The plasmid constructs were also transformed into Synechocystis sp. PCC 6803. The transformation protocol used was essentially as described by Zang et al. ( Microbiology 45:241-245). To test for the production of free fatty acids in the various cyanobacterial isolates, the strains were pre-cultivated in 30 mL of BG-11 medium supplemented with kanamycin (20 mg/L) to late-log phase (OD 730 nm =1.0) on a rotary shaker (150 rpm) at 30° C. with constant illumination (60 μE·m −2 ·sec −1 ). Cultures were then subcultured into 125 mL glass flasks with silicone stoppers at initial OD 730 nm =0.4-0.5 in BG-11 and cultivated overnight to OD 730 nm =0.7-0.9, and induced by addition of IPTG (final concentration, 1 mM).
Free fatty acid (FFA) analyses were performed on extractions of 20 mL whole cell culture with a mixture of internal standard solution (C9:0, C13:0, and C17:0, final concentration of 50 μg/mL), 1.7 mL 50% sulfuric acid, 3.4 mL NaCl (5M), and 30 mL hexane. Samples were vortexed vigorously to emulsify, incubated at room temperature for one hour, and vortexed again. The mixture was transferred to 50 mL glass centrifuge tubes and spun at 1800 rpm for 5 minutes, and the organic phase was transferred to a GC vial. A 1 ul sample was injected into an Agilent model 7890A gas chromatograph using a 40:1 split ration onto a DB-FFAP column (J&W Scientific, 15 m×250 μm×0.25 μm), with a temperature profile starting at 180° C. for 0.5 minute, then heating at 30° C./minute to 230° C. and holding for 3.9 minutes (1.8 mL/min He). Free fatty acid peaks were detected on an FID instrument.
The levels of secreted FFAs produced six days after IPTG induction are provided in Table 6 and Table 7, and depicted graphically in FIG. 11 , FIG. 12 , and FIGS. 13A-13B ). The Synechocystis isolate transformed with Cd1FatB1, depicted in FIG. 11 , produced essentially no free fatty acids and was later found by DNA sequencing to have incurred a premature stop codon within the reading frame. An alternate Cd1FatB1-carrying Synechocystis isolate, was found to be one of the highest free fatty acid producers tested, as shown in Table 7 and depicted in FIGS. 13A-13B .
TABLE 6
Production and Secretion of Free Fatty Acids by Synechocystis Expressing FatB Genes
Total
OD
FFAs
Genotype
730
C8:0
C10:0
C12:0
C14:0
C16:0
C16:1
C18:0
C18:1
mg/L/OD
Experiment #1
empty vector
6.2
0.0
0.0
0.0
0.0
0.3
0.2
0.4
0.3
1.3
Cc1FatB1
4.5
0.2
0.2
6.8
23.2
32.9
1.0
3.2
1.7
69.4
Cp1FatB1
6.8
0.0
0.0
0.1
2.0
8.7
0.1
0.6
0.2
11.7
Cl2FatB2
6.8
0.2
8.1
0.3
0.7
7.3
0.1
0.5
0.1
17.3
Cl4FatB1
6.4
0.4
14.9
0.6
1.5
13.5
0.3
0.9
0.2
32.3
Cl1FatB1
6.5
0.0
0.2
0.0
0.0
0.8
0.0
0.1
0.0
1.1
Cd1FatB1
8.0
0.0
0.0
0.1
0.1
0.5
0.0
0.2
0.0
0.9
Experiment #2
empty vector
5.2
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
Ca2FatB2
4.1
27.2
6.8
0.0
0.0
0.5
0.0
0.0
0.0
34.5
TABLE 7
Production and Secretion of Free Fatty Acids by Synechocystis Expressing FatB Genes
Total
OD
C18:1
C18:1
C18:2
FFAs
Genotype
730
C8:0
C10:0
C12:0
C14:0
C16:0
C16:1
C18:0
cis9
cis11
cis9, 12
mg/L
empty vector
7.3
0.7
0.0
0.0
0.0
1.3
0.0
0.0
0.0
0.0
0.0
1.9
ChFatB2
8.6
67.0
60.6
0.7
0.0
2.7
0.0
1.5
0.0
0.0
1.3
133.7
Cc1FatB1
6.5
1.3
1.6
30.4
107.1
139.9
1.9
9.5
2.0
0.0
4.7
298.3
Cd1FatB1
4.4
0.0
0.9
0.6
15.0
247.6
1.1
11.3
1.4
0.0
3.3
281.2
Total
OD
C18:1
C18:1
C18:2
FFAs
Genotype
730
C8:0
C10:0
C12:0
C14:0
C16:0
C16:1
C18:0
cis9
cis11
cis9, 12
mg/L/OD
empty vector
7.3
0.1
0.0
0.0
0.0
0.2
0.0
0.0
0.0
0.0
0.0
0.3
ChFatB2
8.6
7.8
7.0
0.1
0.0
0.3
0.0
0.2
0.0
0.0
0.1
15.6
Cc1FatB1
6.5
0.2
0.2
4.7
16.5
21.5
0.3
1.5
0.3
0.0
0.7
45.9
Cd1FatB1
4.4
0.0
0.2
0.1
3.4
56.3
0.2
2.6
0.3
0.0
0.8
63.9
As seen in Table 6 and Table 7, Synechocystis transformed with the Ca2FatB2 thioesterase gene makes predominantly C8 free fatty acids, and also produces some C10 free fatty acids: 78.84% of the free fatty acids secreted into the media are C8 free fatty acids, and 19.71% are C10 free fatty acids. Synechocystis transformed with the Cl2FatB2 thioesterase gene and Synechocystis transformed with the Cl4FatB1 thioesterase gene synthesize predominantly C10 and C16 fatty acids, with slightly more C10 than C16 being produced: The Cl2FatB2 strain produced 46.8% C10 FFAs and 42.7% C16 FFAs, and the Cl4FatB1 strain produced 46.8% C10 FFAs and 42.1% C16 FFAs. Synechocystis cyanobacterial cells transformed with the Cp1FatB1 gene, the Cl1FatB1 gene, the Ci1FatB1 gene, the Cd1FatB1 gene, the Cl3FatB1 gene, and the Ca1FatB1 gene produced predominantly C14 and C16 free fatty acids, while Synechocystis transformed with Cc1FatB1 produced a majority of C14 and C16 fatty acids along with some C12 fatty acids.
EXAMPLE 11
Production of Wax Ester by E. Coli Expressing Cuphea Acyl-ACP Thioesterases
To demonstrate that a microorganism transformed with one of the Cuphea thioesterases disclosed herein could produce a fatty acid product derived from one or more fatty acids, E. coli cells were transformed with a construct containing three exogenous genes: a Cuphea thioesterase (either the C8 and C10-preferring Cuphea hookeriana Ch1FatB2 gene (Dehesh, K. et al., The Plant Journal 9:167-172 (1996)) or the Cc1FatB1 gene (SEQ ID NO:51) disclosed herein), a Mus musculus wax synthase gene (NCBI Genbank GI:49854217) and an Arabidopsis thaliana fatty acyl-CoA reductase gene, FAR6 (NCBI Genbank GI:67633703). All three genes were cloned on the same expression plasmid, in which all three genes were driven by separate trc promoters.
The FAR6 gene did not appear to be active in E. coli, probably due to the presence of the chloroplast transit peptide in the expressed protein, which likely interfered with enzyme activity. However, the cells did produce esters when provided with 5 mM decanol in the culture medium.
To test for wax ester formation, E. coli cells were grown at 30° C. with shaking until they reached an OD 600 of 0.7 to 0.9, at which time the transgenes were induced by the addition of 0.5 mM IPTG. At the same time IPTG was added, decanol was added to a final concentration of 5 mM, and the cultures were incubated overnight. The cells were then harvested, washed once with PBS and then resuspended in water and transferred to a glass vial. An equal volume of 2:1 chloroform:methanol was added to each sample, and the suspension was vortexed vigorously and then centrifuged to separate the phases. The organic layer was transferred to a 2 mL glass GC vial and the contents were evaporated under nitrogen. The residue was resuspended in chloroform: methanol for GC analysis.
The results are depicted in FIGS. 14A-14B . FIG. 14B shows the analysis of products isolated from E. coli cells transformed with the C. hookeriana ChFatB2 thioesterase. The wax esters produced by the cells were predominantly decyl octanoate and decyl decanoate (expected from the C10-preference of the ChFatB2 thioesterase) and decyl hexadecanoate (reflecting the preference of the E. coli host for generating C16 fatty acids). FIG. 14A shows the analysis of products isolated from the media of E. coli cells transformed with the Cc1FatB1 thioesterase, demonstrated in Example 9 to generate free C14 and C16 fatty acids in E. coli. Consistent with the substrate preference of this thioesterase, co-expression of the Cc1FatB1 thioesterase with the Mus musculus wax synthase resulted in the most prevalent wax ester isolated from the cells being decyl tetradecanoate, followed by decyl hexadecenoate.
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