Biosynthetic pathways and methods

This application is the § 371 U.S. National Stage of International Application No. PCT/US2013/076118, filed 18 Dec. 2013, which claims priority to U.S. Provisional Patent Application Ser. No. 61/738,752, filed Dec. 18, 2012 and U.S. Provisional Patent Application Ser. No. 61/821,490, filed May 9, 2013, each of which is incorporated herein by reference.

This disclosure describes, in one aspect, a recombinant microbial cell modified to exhibit increased biosynthesis of a TCA derivative compared to a wild-type control. In some embodiments, the TCA derivative can include 1,4-butanediol. In various embodiments, the microbial cell is a fungal cell or a bacterial cell. In some embodiments, the increased biosynthesis of the TCA derivative can include an increase in xylose dehydrogenase activity, xylonolactonase activity, xylonate dehydratase activity, or 2-keto-3-deoxyaldonic acid dehydratase activity.

In another aspect, this disclosure describes a method that generally includes incubating any embodiments of the recombinant cell summarized above in medium that includes a carbon source under conditions effective for the recombinant cell to produce a TCA derivative. In some embodiments, the TCA derivative can include 1,4-butanediol. In some embodiments, the carbon source can include xylose, arabinose, glucaric acid, galactaric acid, or hydroxyproline. In some embodiments, the increased biosynthesis of the TCA derivative can include an increase in pentose dehydrogenase activity, pentonolactonase activity, aldonic acid dehydratase activity, or 2-keto-3-deoxyaldonic acid dehydratase activity. In other embodiments, the increased biosynthesis of the TCA derivative can include an increase in hexic acid dehydratase activity or 5-dehydro-4-deoxyglucarate dehydratase activity.

In another aspect, this disclosure describes a method that generally includes introducing into a host cell a heterologous polynucleotide encoding at least one polypeptide that catalyzes conversion of a carbon source to a TCA derivative, wherein the at least one polypeptide is operably linked to a promoter so that the modified host cell catalyzes conversion of the carbon source to TCA derivative. In some embodiments, the TCA derivative can include 1,4-butanediol. In some embodiments, the carbon source can include xylose.

The above summary of the present invention is not intended to describe each disclosed embodiment or every implementation of the present invention. The description that follows more particularly exemplifies illustrative embodiments. In several places throughout the application, guidance is provided through lists of examples, which examples can be used in various combinations. In each instance, the recited list serves only as a representative group and should not be interpreted as an exclusive list.

FIG. 1 . The 1,4-butanediol synthetic pathway in E. coli . (A) The synthetic pathway for 1,4-butanediol from glucose and xylose. Abbreviations: G-6P, glucose-6-phosphate; F-6P, fructose-6-phosphate; DHAP, dihydroxyacetone phosphate; GAP, glyceraldehyde-3-phosphate. (B) Synthetic operon for protein overexpression to drive the xylose towards 2,5-dioxopentanoic acid (left), and then drive 2,5-dioxopentanoic acid towards to 1,4-butanediol (right).

FIG. 2 . A, scheme of the organization of conserved genetic clusters involved in the pentose, hexaric acid, and hydroxyproline degradation. Analogous functions are indicated in the same degree of shading. Coding region sizes and distances are not to scale. Protein family numbers are displayed below each coding region according to Clusters of Orthologous Groups of proteins classification system. The coding regions indicated in white or gray encode the following proteins: araA, transcriptional regulator; araF-araH, 1-Ara ABC transporter (periplasmic 1-Ara binding protein, ATP-binding protein, permease); rrnAC3038, heat shock protein X; ycbE, glucarate/galactarate permease; ycbG, transcriptional regulator; PP1249, hydroxyproline permease. B, schematic representation of the convergence of catabolic pathways for pentoses, hexaric acids, and hydroxyproline at the level of 2,5-dioxopentanoate. Enzymatic activities are indicated by their EC number. Dashed lines indicate proposed spontaneous reactions.

FIG. 3 . An engineered 1,4-butanediol synthetic pathway in E. coli.

FIG. 4 . An exemplary engineered metabolic pathway from 2,5-dioxopentanoic acid to 1,4-butanediol.

FIG. 5 . An exemplary engineered metabolic pathway from 2,5-dioxopentanoic acid to 1,4-butanediol.

FIG. 6 . An exemplary engineered metabolic pathway from D-arabinose to 2,5-dioxopentanoic acid.

FIG. 7 . An exemplary engineered metabolic pathway from D-xylose to 2,5-dioxopentanoic acid.

FIG. 8 . An exemplary engineered metabolic pathway from L-arabinose to 2,5-dioxopentanoic acid.

FIG. 9 . An exemplary engineered metabolic pathway from D-glucaric acid to 2,5-dioxopentanoic acid.

FIG. 10 . An exemplary engineered metabolic pathway from D-galactaric acid to 2,5-dioxopentanoic acid.

FIG. 11 . An exemplary engineered metabolic pathway from 4(R)-hydroxy-L-proline to 2,5-dioxopentanoic acid.

FIG. 12 . A plasmid map of YEplac195-xylBCDX (13945 bp).

FIG. 13 . A plasmid map of YEplac11-KivDyqhD (9687 bp).

FIG. 14 . Gas chromatography data showing production of 1,4-butanediol by genetically engineered S. cerevisiae.

This disclosure describes a novel full biosynthetic pathway to biosynthesize high-volume TCA derivatives such as succinate, amino acids, and 1,4-butanediol from xylose by an engineered microbe. The TCA cycle can lead to many commercially important biobased chemicals such as, for example, amino acids (e.g., glutamate, threonine and lysine) and organic acids (e.g., succinate, maleate and fumarate). Here we report the engineering of a shortcut metabolic pathway to TCA cycle. The process from xylose to TCA only involves five steps as compared to conventional published pathways that include more than 20 steps. Because our pathway includes fewer steps from xylose to the TCA cycle, our pathway can produce TCA derivatives with the production of less by-product and, therefore, achieve higher yields than conventional biosynthetic pathways.

We have selected the TCA derivative 1,4-butanediol as a model product to demonstrate the generality of our novel biosynthetic pathway. 1,4-butanediol is a major commodity chemical; 2.5 million tons of 1,4-butanediol are used per year to make, for example, plastics, polyesters, and spandex fibers. 1,4-butanediol also can react, for example, with dicarboxylic acids to yield polyesters, with diisocyanates to yield polyurethanes, and with phosgene to yield chloroformates. Because our pathway permits the biosynthesis of 1,4-butanediol from, for example, xylose in only six steps from xylose to 1,4-butanediol, 1,4-butanediol may be biosynthesized with less by-product being formed and, therefore, a higher yield. For example, our pathway can produce 1.0 g/L 1,4-butanediol from 20 g/L xylose.

1,4-butanediol currently is manufactured from petroleum-based feedstocks such as acetylene, butane, propylene, and butadiene. Given the industrial importance of 1,4-butanediol as a chemical intermediate and the issues associated with petroleum feedstocks, alternative low-cost renewable biosynthetic routes from sugars have been sought. However, the highly reduced nature of 1,4-butanediol relative to carbohydrates has thwarted attempts thus far to develop effective pathways and organisms for direct production.

1,4-butanediol has been reported to be synthesized from glucose and xylose by engineered E. coli in which the succinyl-CoA intermediate was converted into succinate semialdehyde, 4-hydroxybutyrate, 4-hydroxybutyryl-CoA, 4-hydroxybutyraldehyde, and 1,4-butanediol by multiple enzymes from various organisms. This process involves around 20 chemical steps that include the pentose phosphate pathway, glycolysis, the TCA cycle, and designed artificial downstream metabolic steps. In contrast, this disclosure describes a shortcut pathway that requires only six steps ( FIG. 1A ).

D-xylose is converted by Caulobacter crescentus sequentially to D-xylonolactone, D-xylonate (D-xylonoic acid), 2-keto-3-deoxy-xylonate (2-oxo-4(S),5-dihydroxy-pentanoic acid), then α-ketoglutaric semialdehyde (2,5-dioxopentanoic acid) by, respectively, xylose dehydrogenase (xylB), xylonolactonase (xylC), xylonate dehydrogenase (xylD), Kda dehydratase (xylX). We cloned the coding regions of these enzymes into a single plasmid (pBDO-1), which was then transformed into an E. coli host cell. The host cell was then further modified to include a second plasmid that included a decarboxylase and an alcohol dehydrogenase. The decarboxylase converts the α-ketoglutaric semialdehyde to succinaldehyde; the alcohol dehydrogenase reduces the succinaldehyde to 1,4-butanediol ( FIG. 1A ). In some embodiments, the second plasmid was identified as pBDO-3 and included the coding regions of benzoylformate decarboxylase BFD ( Pseudomonas putida ) and an alcohol dehydrogenase of yqhD ( E. coli ). In other embodiments, the second plasmid was identified as pBDO-4 and included the decarboxylase of KIVD ( Lactococcus lactis ) and alcohol dehydrogenase of yqhD ( E. coli ).

The E. coli host cell possesses an endogenous xylose metabolism pathway that includes xylA, yjhH and yagE. To improve the product yield from xylose to 1,4-butanediol, expression of these three coding regions were inhibited. The host cell strain SBDO-1 is based on E. coli BW25113 in which xylA, yjhH, and yagE are knocked out so that SBDO-1 cannot metabolize xylose. Strain SBDO-2, carrying plasmid pBDO-1, also cannot metabolize xylose.

The strain SBDO-3, which is based on SBDO-2 but carries plasmid pBDO-2 that expresses α-ketoglutaric semialdehyde dehydrogenase xylA, can consume xylose quickly. These results indicate that the endogenous xylose utilization pathway in E. coli was blocked fully by the ΔxylA, ΔyjhH, and ΔyagE deletions in SBDO-1. Moreover, these results demonstrate that the C. crescentus enzymes function in E. coli . Consequently, xylose metabolism observed in SBDO-4 and SBDO-5 is attributable to the xylose pathway from C. crescentus that we engineered into the host cell. To produce 1,4-butanediol, plasmids pBDO-3 or pBDO-4, each of which expresses the same alcohol dehydrogenase but a different decarboxylase, were introduced into strain SBDO-2 strain. After two days of fermentation, strain SBDO-4 (carrying pBDO-3) produced 0.25 g/L 1,4-butanediol with 0.1 g/L 1,2,4-butanetriol (a by-product); strain SBDO-5 (carrying pBDP-4) produced 1.0 g/L 1,4-butanediol with 4.0 g/L 1,2,4-butanetriol. Thus, the kivD encoded on pBDO-4 and carried by strain SBDO-5 provides better yield of 1,4-butanediol than BFD. Other than 1,2,4-butanetriol, no other byproducts were detected in significant amounts in the fermentation broth, suggesting that our new 1,4-butanediol producing pathway has higher 1,4-butanediol yield as compared with the published pathway (Yim et al., 2011. Nat. Chem. Biol. 7:445-452).

Thus, in one aspect, the invention provides recombinant microbial cell modified to exhibit increased biosynthesis of a TCA derivative compared to a wild-type control.

While described above in the context of an exemplary embodiment in which the TCA derivative is a 1,4-butanediol, the recombinant cells and methods described herein can provide TCA derivatives other than 1,4-butanediol. Exemplary alternative TCA derivatives include, for example, succinate, fumarate, malate, glutamate, lysine, threonine, 4-hydroxybutyrate, and products synthesizable from a product of the TCA cycle in one, two, three, four, or five enzymatic steps. In some of these embodiments, one or more enzymes involved in the synthesis of the TCA derivative may be heterologous to the host cell and, therefore, provided recombinantly. Exemplary TCA derivative products and exemplary enzymes involved in the synthesis of the exemplary TCA derivative products are listed in Table 1. For any embodiment in which the identified enzyme is not endogenous to a host cell, the enzyme may be introduced into the host cell to produce a recombinant cell as described herein.

In addition to the enzymes listed in Table 1, homologs of the listed enzymes may be used. Thus, as an alternative to AraDH (SEQ ID NO:1), one may use, for example, any of the polypeptides depicted in SEQ ID NO:2-5; as an alternative to AraD (SEQ ID NO:6), one may use, for example, any of the polypeptides depicted in SEQ ID NO: 7-10; as an alternative to Kda (SEQ ID NO:11), one may use, for example, any of the polypeptides depicted in SEQ ID NO: 12-15; as an alternative to DopDH (SEQ ID NO:16), one may use, for example, any of the polypeptides depicted in SEQ ID NO:17-20; as an alternative to YcbD (SEQ ID NO:21), one may use, for example, any of the polypeptides depicted in SEQ ID NO:22-25; as an alternative to XylB (SEQ ID NO:26), one may use, for example, any of the polypeptides depicted in SEQ ID NO:27-30; as an alternative to XylC (SEQ ID NO:31), one may use, for example, any of the polypeptides depicted in SEQ ID NO:32-35; as an alternative to XylD (SEQ ID NO:36), one may use, for example, any of the polypeptides depicted in SEQ ID NO:37-40; as an alternative to XylX (SEQ ID NO:41), one may use, for example, any of the polypeptides depicted in SEQ ID NO:42-45; as an alternative to AraE (SEQ ID NO:46), one may use, for example, any of the polypeptides depicted in SEQ ID NO:47-50; as an alternative to AraI (SEQ ID NO:51), one may use, for example, any of the polypeptides depicted in SEQ ID NO:52-55; as an alternative to AraB (SEQ ID NO:56), one may use, for example, any of the polypeptides depicted in SEQ ID NO:57-60; as an alternative to AraD (SEQ ID NO:61), one may use, for example, any of the polypeptides depicted in SEQ ID NO:62-65; as an alternative to YcbF (SEQ ID NO:66), one may use, for example, any of the polypeptides depicted in SEQ ID NO:67-70; as an alternative to YcbH (SEQ ID NO:71), one may use, for example, any of the polypeptides depicted in SEQ ID NO:72-75; as an alternative to YcbC (SEQ ID NO:76), one may use, for example, any of the polypeptides depicted in SEQ ID NO:77-80; as an alternative to HypE (SEQ ID NO:81), one may use, for example, any of the polypeptides depicted in SEQ ID NO:82-85; as an alternative to PP_1245 (SEQ ID NO:86), one may use, for example, any of the polypeptides depicted in SEQ ID NO:87-90; as an alternative to PP_1247 (SEQ ID NO:91), one may use, for example, the polypeptide depicted in SEQ ID NO:92; as an alternative to PP_1246 (SEQ ID NO:93), one may use, for example, any of the polypeptides depicted in SEQ ID NO:94-97; as an alternative to alpha-ketoisovalerate decarboxylase (SEQ ID NO:98), one may use, for example, any of the polypeptides depicted in SEQ ID NO:99-102; as an alternative to YqhD (SEQ ID NO:103), one may use, for example, any of the polypeptides depicted in SEQ ID NO:104-107.

In some cases, the wild-type control may be unable to produce the TCA derivative and, therefore, an increase in the biosynthesis of a particular product may reflect any measurable biosynthesis of that product. In certain embodiments, an increase in the biosynthesis of a TCA derivative can include biosynthesis sufficient for a culture of the microbial cell to accumulate the TCA derivative to a predetermine concentration.

The predetermined concentration may be any predetermined concentration of the product suitable for a given application. Thus, a predetermined concentration may be, for example, a concentration of at least 0.1 g/L such as, for example, at least 0.25 g/L, at least 0.5 g/L, at least 1.0 g/L, at least 2.0 g/L, at least 3.0 g/L, at least 4.0 g/L, at least 5.0 g/L, at least 6.0 g/L, at least 7.0 g/L, at least 8.0 g/L, at least 9.0 g/L, at least 10 g/L, at least 20 g/L, at least 50 g/L, at least 100 g/L, or at least 200 g/L.

While described above in the context of an exemplary embodiment in which the host cell is E. coli , the recombinant cells described herein can be constructed, and the methods of making and using the recombinant cells can be performed, using any suitable host cell.

Thus, the recombinant cell can be, or be derived from, any suitable microbe including, for example, a prokaryotic microbe or a eukaryotic microbe. As used herein, the term “or derived from” in connection with a microbe simply allows for the “host cell” to possess one or more genetic modifications before being modified to exhibit the indicated increased biosynthetic activity. Thus, the term “recombinant cell” encompasses a “host cell” that may contain nucleic acid material from more than one species before being modified to exhibit the indicated biosynthetic activity.

In some embodiments, the host cell may be selected to possess one or more natural physiological activities. For example, the host cell may be photosynthetic (e.g., cyanobacteria) or may be cellulolytic (e.g., Clostridium cellulolyticum ).

In some embodiments, the recombinant cell may be, or be derived from, a eukaryotic microbe such as, for example, a fungal cell. In some of these embodiments, the fungal cell may be, or be derived from, a member of the Saccharomycetaceae family such as, for example, Saccharomyces cerevisiae, Candida rugosa , or Candida albicans.

In other embodiments, the recombinant cell may be, or be derived from, a prokaryotic microbe such as, for example, a bacterium. In some of these embodiments, the bacterium may be a member of the phylum Protobacteria. Exemplary members of the phylum Protobacteria include, for example, members of the Enterobacteriaceae family (e.g., Escherichia coli ) and, for example, members of the Pseudomonaceae family (e.g., Pseudomonas putida ). In other cases, the bacterium may be a member of the phylum Firmicutes. Exemplary members of the phylum Firmicutes include, for example, members of the Bacillaceae family (e.g., Bacillus subtilis ), members of the Clostridiaceae family (e.g., Clostridium cellulolyticum ) and, for example, members of the Streptococcaceae family (e.g., Lactococcus lactis ). In other cases, the bacterium may be a member of the phylum Cyanobacteria.

In some embodiments, the increased biosynthesis of the TCA derivative compared to a wild-type control can include an increase in activity of one or more enzymes involved in the metabolism of the carbon source (e.g., xylose or arabinose). Such enzymes may be found in the proteome of microbes such as, for example, Sulfolobus solfataricus, Caulobacter crescentus, Burkholderia thailandensis, Haloarcula marismortui, Bacillus subtilis , and Pseudomonas putida . Exemplary enzymes, shown in the context of their native metabolic pathways, are shown in FIG. 2 . So, for example, increased biosynthesis of the TCA derivative can include an increase in activity of one or more enzymes involved in the metabolism of D-xylose in Caulobacter crescentus such as, for example, xylose dehydrogenase ( FIG. 2 , CC0821) activity, xylonolactonase ( FIG. 2 , CC0819) activity, xylonate dehydrogenase ( FIG. 2 , CC0822) activity, and 2-keto-3-deoxyaldonic acid dehydratase ( FIG. 2 , CC0823) activity compared to the wild-type control.

In some embodiments, the increased biosynthesis of the TCA derivative compared to a wild-type control can further include an increase in benzoylformate decarboxylase activity and an increase in alcohol dehydrogenase activity. In some of these embodiments, the benzoylformate decarboxylase can include BFD of Pseudomonas putida . In some of these embodiments, the alcohol dehydrogenase can include yqhD of E. coli.

In some embodiments, the increased biosynthesis of the TCA derivative compared to a wild-type control can further include an increase in decarboxylase activity and an increase in alcohol dehydrogenase activity. In some of these embodiments, the decarboxylase can include KIVD of Lactococcus lactis . In some of these embodiments, the alcohol dehydrogenase can include yqhD of E. coli . See, e.g., Example 2 and FIGS. 12-14 .

In some embodiments, the recombinant cell can include an engineered metabolic pathway designed to permit the recombinant cell to increase its consumption of a particular carbon source compared to a wild-type control. Exemplary metabolic pathways are illustrated in, for example, FIG. 6 through FIG. 11 . Accordingly, exemplary carbon sources include, for example, arabinose, xylose, arabinose, glucaric acid, galactaric acid, or hydroxyproline. In other embodiments, the recombinant cell may be designed to consume a uronic acid such as, for example, galacturonic acid and/or glucuronic acid as a carbon source. In such embodiments, a heterologous polynucleotide that encodes a uronate dehydrogenase enzyme may be introduced into the recombinant cell to confer to the recombinant cell the ability to convert uronic acid to aldonic acid. In still other embodiments, the recombinant cell can utilize a carbon source that includes, for example, glucose, cellulose, galacturonic acid, glucuronic acid, CO 2 , or glycerol. In some of these embodiments, the recombinant cell may be further modified to convert the carbon source (e.g., glucose) to one or more of the carbon sources (e.g., xylose and/or a hexaric acid such as, e.g., glucaric acid) that is an entry point to one or more of the engineered pathways described herein.

FIG. 6 shows an exemplary metabolic pathway that permits a recombinant cell to use D-arabinose as a carbon source for the production of 2,5-dioxopentanoic acid. In this example, the recombinant cell can include an enzyme that can convert D-arabinose into D-arabinolactone such as, for example, a pentose dehydrogenase. One example of a suitable pentose dehydrogenase includes AraDH from Sulfolobus solfataricus . The pentose dehydrogenase can provide catalytic conversion of D-arabinose into D-arabinolactone that is, for example, at least 110% greater than that exhibited by a wild-type control.

The exemplary metabolic pathway illustrated in FIG. 6 also includes an enzyme that can convert D-arabinonic acid to 2-oxo-4(S),5-dihydroxy-pentanoic acid such as, for example, an aldonic acid dehydratase. One example of a suitable aldonic acid dehydratase includes AraD from Sulfolobus solfataricus . The aldonic acid dehydratase can provide catalytic conversion of D-arabinonic acid into 2-oxo-4(S),5-dihydroxy-pentanoic acid that is, for example, at least 110% greater than that exhibited by a wild-type control.

The exemplary metabolic pathway illustrated in FIG. 6 also includes an enzyme that can convert 2-oxo-4(S),5-dihydroxy-pentanoic acid to 2,5-dioxopentanoic acid such as, for example, a 2-keto-3-deoxyaldonic acid dehydratase. On example of a suitable 2-keto-3-deoxyaldonic acid dehydratase includes KdaD from Sulfolobus solfataricus . The 2-keto-3-deoxyaldonic acid dehydratase can provide catalytic conversion of 2-oxo-4(S),5-dihydroxy-pentanoic acid to 2,5-dioxopentanoic acid that is, for example, at least 110% greater than that exhibited by a wild-type control.

FIG. 7 shows an exemplary metabolic pathway that permits a recombinant cell to use D-xylose as a carbon source for the production of 2,5-dioxopentanoic acid. In this example, the recombinant cell can include an enzyme that can convert D-xylose to D-xylonolactone such as, for example, a pentose dehydrogenase. Exemplary suitable pentose dehydrogenases include XylB from Caulobacter crescentus or rrnAC3034 from Haloarcula marismortui . The pentose dehydrogenase can provide catalytic conversion of D-xylose to D-xylonolactone that is, for example, at least 110% greater than that exhibited by a wild-type control.

The exemplary metabolic pathway illustrated in FIG. 7 also includes an enzyme that can convert D-xylonolactone to D-xylonic acid such as, for example, a pentonolactonase. Exemplary suitable pentonolactonases include XylC from Caulobacter crescentus or rrnAC3033 from Haloarcula marismortui . The pentonolactonase can provide catalytic conversion of D-xylonolactone to D-xylonic acid that is, for example, at least 110% greater than that exhibited by a wild-type control.

The exemplary metabolic pathway illustrated in FIG. 7 also includes an enzyme that can convert D-xylonic acid to 2-oxo-4(S),5-dihydroxy-pentanoic acid such as, for example, an aldonic acid dehydratase. Exemplary suitable aldonic acid dehydratases include XylD front Caulobacter crescentus or rrnAC3032 from Haloarcula marismortui . The aldonic acid dehydratase can provide catalytic conversion of D-xylonic acid into 2-oxo-4(S),5-dihydroxy-pentanoic acid that is, for example, at least 110% greater than that exhibited by a wild-type control.

The exemplary metabolic pathway illustrated in FIG. 7 also includes an enzyme that can convert 2-oxo-4(S),5-dihydroxy-pentanoic acid to 2,5-dioxopentanoic acid such as, for example, a 2-keto-3-deoxyaldonic acid dehydratase. Exemplary suitable 2-keto-3-deoxyaldonic acid dehydratases include XylX from Caulobacter crescentus or rrnAC3039 from Haloarcula marismortui . The 2-keto-3-deoxyaldonic acid dehydratase can provide catalytic conversion of 2-oxo-4(S),5-dihydroxy-pentanoic acid to 2,5-dioxopentanoic acid that is, for example, at least 110% greater than that exhibited by a wild-type control.

FIG. 8 shows an exemplary metabolic pathway that permits a recombinant cell to use L-arabinose as a carbon source for the production of 2,5-dioxopentanoic acid. In this example, the recombinant cell can include an enzyme that can convert L-arabinose to L-arabinolactone such as, for example, a pentose dehydrogenase. One example of a suitable pentose dehydrogenase includes AraE from Burkholderia thailandensis . The pentose dehydrogenase can provide catalytic conversion of L-arabinose to L-arabinolactone that is, for example, at least 110% greater than that exhibited by a wild-type control.

The exemplary metabolic pathway illustrated in FIG. 8 also includes an enzyme that can convert L-arabinolactone to L-arabinonic acid such as, for example, a pentonolactonase. One example of a suitable pentonolactonase includes AraI from Burkholderia thailandensis . The pentonolactonase can provide catalytic conversion of L-arabinolactone to L-arabinonic acid that is, for example, at least 110% greater than that exhibited by a wild-type control.

The exemplary metabolic pathway illustrated in FIG. 8 also includes an enzyme that can convert L-arabinonic acid to 2-oxo-4(R),5-dihydroxy-pentanoic acid such as, for example, an aldonic acid dehydratase. One example of a suitable aldonic acid dehydratase includes AraB from Burkholderia thailandensis . The aldonic acid dehydratase can provide catalytic conversion of L-arabinonic acid to 2-oxo-4(R),5-dihydroxy-pentanoic acid that is, for example, at least 110% greater than that exhibited by a wild-type control.

The exemplary metabolic pathway illustrated in FIG. 8 also includes an enzyme that can convert 2-oxo-4(R),5-dihydroxy-pentanoic acid to 2,5-dioxopentanoic acid such as, for example, a 2-keto-3-deoxyaldonic acid dehydratase. One example of a suitable 2-keto-3-deoxyaldonic acid dehydratase includes AraD from Burkholderia thailandensis . The 2-keto-3-deoxyaldonic acid dehydratase can provide catalytic conversion of 2-oxo-4(R),5-dihydroxy-pentanoic acid to 2,5-dioxopentanoic acid that is, for example, at least 110% greater than that exhibited by a wild-type control.

FIG. 9 shows an exemplary metabolic pathway that permits a recombinant cell to use D-glucaric acid as a carbon source for the production of 2,5-dioxopentanoic acid. In this example, the recombinant cell can include an enzyme that can convert D-glucaric acid to 4-deoxy-5-keto-D-glucaric acid such as, for example, an aldonic acid dehydratase. Suitable exemplary aldonic acid dehydratases include YcbF from Bacillus subtilis . The aldonic acid dehydratase can provide catalytic conversion of D-glucaric acid to 4-deoxy-5-keto-D-glucaric acid that is, for example, at least 110% greater than that exhibited by a wild-type control.

The exemplary metabolic pathway illustrated in FIG. 9 also includes an enzyme that can convert 4-deoxy-5-keto-D-glucaric acid to 2,5-dioxopentanoic acid such as, for example, a 2-keto-3-deoxyaldonic acid dehydratase. One example of a suitable 2-keto-3-deoxyaldonic acid dehydratase includes YcbC from Bacillus subtilis . The 2-keto-3-deoxyaldonic acid dehydratase can provide catalytic conversion of 4-deoxy-5-keto-D-glucaric acid to 2,5-dioxopentanoic acid that is, for example, at least 110% greater than that exhibited by a wild-type control.

FIG. 10 shows an exemplary metabolic pathway that permits a recombinant cell to use D-galactaric acid as a carbon source for the production of 2,5-dioxopentanoic acid. In this example, the recombinant cell can include an enzyme that can convert D-galactaric acid to 4-deoxy-5-keto-D-glucaric acid such as, for example, an aldonic acid dehydratase. Suitable exemplary aldonic acid dehydratases include YcbH from Bacillus subtilis . The aldonic acid dehydratase can provide catalytic conversion of D-galactaric acid to 4-deoxy-5-keto-D-glucaric acid that is, for example, at least 110% greater than that exhibited by a wild-type control.

The exemplary metabolic pathway illustrated in FIG. 9 also includes an enzyme that can convert 4-deoxy-5-keto-D-glucaric acid to 2,5-dioxopentanoic acid such as, for example, a 2-keto-3-deoxyaldonic acid dehydratase. One example of a suitable 2-keto-3-deoxyaldonic acid dehydratase includes YcbC from Bacillus subtilis . The 2-keto-3-deoxyaldonic acid dehydratase can provide catalytic conversion of 4-deoxy-5-keto-D-glucaric acid to 2,5-dioxopentanoic acid that is, for example, at least 110% greater than that exhibited by a wild-type control.

FIG. 11 shows an exemplary metabolic pathway that permits a recombinant cell to use 4(R)-hydroxy-D-proline as a carbon source for the production of 2,5-dioxopentanoic acid. In this example, the recombinant cell can include an enzyme that can convert 4(R)-hydroxy-D-proline to 4(R)-hydroxy-D-proline. One suitable exemplary enzyme for this embodiment includes, amino acid transporter LysE (HypE) from Pseudomonas . The enzyme can provide catalytic conversion of 4(R)-hydroxy-D-proline to 4(R)-hydroxy-D-proline that is, for example, at least 110% greater than that exhibited by a wild-type control.

The exemplary metabolic pathway illustrated in FIG. 11 also includes an enzyme that can convert 4(R)-hydroxy-D-proline to 2-carboxy-4(R)-hydroxy-δ-pyrroline. One suitable exemplary enzyme for this embodiment includes, for example, HypOX from Pseudomonas . The enzyme can provide catalytic conversion of 4(R)-hydroxy-D-proline to 2-carboxy-4(R)-hydroxy-δ-pyrroline that is, for example, at least 110% greater than that exhibited by a wild-type control.

The exemplary metabolic pathway illustrated in FIG. 11 also includes an enzyme that can convert 2-oxo-4(R)-5-aminopentanoic acid to 2,5-dioxopentanoic acid such as, for example, a 2-keto-3-deoxyaldonic acid dehydratase. One exemplary 2-keto-3-deoxyaldonic acid dehydratase includes PP1247 from Pseudomonas . The 2-keto-3-deoxyaldonic acid dehydratase can provide catalytic conversion of 2-oxo-4(R)-5-aminopentanoic acid to 2,5-dioxopentanoic acid that is, for example, at least 110% greater than that exhibited by a wild-type control.

The recombinant cell can be engineered to convert the 2,5-dioxopentanoic acid to any desirable TCA derivative. In some embodiments, the recombinant cell can include an α-ketoglutaric semialdehyde dehydrogenase to shunt the 2,5-dioxopentanoic acid into the TCA cycle. In this manner, TCA cycle derivatives such as, for example, succinate, fumarate, malate, glutamate, lysine, threonine, 4-hydroxybutyrate may be produced.

In some embodiments, however, the recombinant cell may be further modified to possess a metabolic pathway for the conversion of 2,5-dioxopentanoic acid to 1,4-butanediol. Exemplary metabolic pathways are illustrated, for example, in FIG. 4 and FIG. 5 . The exemplary pathway illustrated in FIG. 4 includes an enzyme that can convert 2,5-dioxopentonoic acid to succinaldehyde such as, for example, a 2-ketoacid decarboxylase or a 2-oxoglutarate decarboxylase. Suitable exemplary enzymes include, for example, Kivd, BFD, and IPDC. The exemplary pathway illustrated in FIG. 4 also includes an enzyme that can convert succinaldehyde to 1,4-butanediol such as, for example, an alcohol dehydrogenase. Suitable exemplary alcohol dehydrogenases include YqhD, ADH6, YjgB, and YahK.

The exemplary pathway illustrated in FIG. 5 includes an enzyme that can convert 2,5-dioxopentonoic acid to 2-keto-5-hydroxy-pentonate such as, for example, an alcohol dehydrogenase. Here again, suitable exemplary alcohol dehydrogenases include, for example, YqhD, ADH6, YjgB, and YahK. The exemplary pathway illustrated in FIG. 5 includes an enzyme that can convert 2-keto-5-hydroxy-pentonate to 4-hydroxy-1-butyraldehyde such as, for example, a 2-ketoacid decarboxylase or a 2-oxoglutarate decarboxylase. Suitable exemplary enzymes include, for example, Kivd, BFD, and IPDC. The exemplary pathway illustrated in FIG. 5 includes conversion of 4-hydroxy-1-butyraldehyde into 1,4-butanediol. This conversion may be catalyzed by an alcohol dehydrogenase such as, for example, YqhD, ADH6, YjgB, and YahK. For the metabolic pathway illustrated in FIG. 5 , therefore, the recombinant cell can include one or more alcohol dehydrogenases.

In some embodiments, the host cell can include one or more genetic modifications to reduce endogenous metabolism of the carbon source so that metabolism of the carbon source is directed toward the production of the TCA derivative. For example, in embodiments in which the carbon source is xylose and the host cell is E. coli , the host cell can include one or more modifications to decrease endogenous metabolism of xylose. In the case of E. coli , such modifications can include for example, a decrease in α-ketoglutaric semialdehyde dehydrogenase activity, aldolase activity, and/or 2-keto-3-deoxy gluconate aldolase activity. Such modifications can include modifications to coding regions of, or regulatory regions that control expression of, xylA, yjhH, and/or yagE. Such modifications can include, for example, a deletion of a sufficient amount of one or more coding regions that the enzymatic activity is reduced.

As used herein, the terms “activity” with regard to particular enzyme refers to the ability of a polypeptide, regardless of its common name or native function, to catalyze the conversion of the enzyme's substrate to a product, regardless of whether the “activity” as less than, equal to, or greater than the native activity of the identified enzyme. Methods for measuring the biosynthetic activities of cells are routine and well known to those of ordinary skill in the art.

As used herein, an increase in catalytic activity can be quantitatively measured and described as a percentage of the catalytic activity of an appropriate wild-type control. The catalytic activity exhibited by a genetically-modified polypeptide can be, for example, at least 110%, at least 125%, at least 150%, at least 175%, at least 200% (two-fold), at least 250%, at least 300% (three-fold), at least 400% (four-fold), at least 500% (five-fold), at least 600% (six-fold), at least 700% (seven-fold), at least 800% (eight-fold), at least 900% (nine-fold), at least 1000% (10-fold), at least 2000% (20-fold), at least 3000% (30-fold), at least 4000% (40-fold), at least 5000% (50-fold), at least 6000% (60-fold), at least 7000% (70-fold), at least 8000% (80-fold), at least 9000% (90-fold), at least 10,000% (100-fold), or at least 100,000% (1000-fold) of the activity of an appropriate wild-type control.

Alternatively, an increase in catalytic activity may be expressed as at an increase in k cat such as, for example, at least a two-fold increase, at least a three-fold increase, at least a four-fold increase, at least a five-fold increase, at least a six-fold increase, at least a seven-fold increase, at least an eight-fold increase, at least a nine-fold increase, at least a 10-fold increase, at least a 15-fold increase, or at least a 20-fold increase in the k cat value of the enzymatic conversion.

An increase in catalytic activity also may be expressed in terms of a decrease in K m such as, for example, at least a two-fold decrease, at least a three-fold decrease, at least a four-fold decrease, at least a five-fold decrease, at least a six-fold decrease, at least a seven-fold decrease, at least an eight-fold decrease, at least a nine-fold decrease, at least a 10-fold decrease, at least a 15-fold decrease, or at least a 20-fold decrease in the K m value of the enzymatic conversion.

A decrease in catalytic activity can be quantitatively measured and described as a percentage of the catalytic activity of an appropriate wild-type control. The catalytic activity exhibited by a genetically-modified polypeptide can be, for example, no more than 95%, no more than 90%, no more than 85%, no more than 80%, no more than 75%, no more than 70%, no more than 65%, no more than 60%, no more than 55%, no more than 50%, no more than 45%, no more than 40%, no more than 35%, no more than 30%, no more than 25%, no more than 20%, no more than 15%, no more than 10%, no more than 5%, no more than 4%, no more than 3%, no more than 2%, no more than 1% of the activity, or 0% of the activity of a suitable wild-type control.

Alternatively, a decrease in catalytic activity can be expressed as an appropriate change in a catalytic constant. For example, a decrease in catalytic activity may be expressed as at a decrease in k cat such as, for example, at least a two-fold decrease, at least a three-fold decrease, at least a four-fold decrease, at least a five-fold decrease, at least a six-fold decrease, at least a seven-fold decrease, at least an eight-fold decrease, at least a nine-fold decrease, at least a 10-fold decrease, at least a 15-fold decrease, or at least a 20-fold decrease in the k cat value of the enzymatic conversion.

A decrease in catalytic activity also may be expressed in terms of an increase in K m such as, for example, an increase in K m of at least two-fold, at least three-fold, at least four-fold, at least five-fold, at least six-fold, at least seven-fold, at least an eight-fold, at least nine-fold, at least 10-fold, at least 15-fold, at least 20-fold, at least 25-fold, at least 30-fold, at least 35-fold, at least 40-fold, at least 45-fold, at least 50-fold, at least 75-fold, at least 100-fold, at least 150-fold, at least 200-fold, at least 230-fold, at least 250-fold, at least 300-fold, at least 350-fold, or at least 400-fold.

Thus, in another aspect, we describe herein methods for biosynthesis of a TCA derivative. Generally, the methods includes incubating a recombinant cell as described herein in medium that includes a carbon source under conditions effective for the recombinant cell to produce the TCA derivative. The carbon source can include, for example, saccharides (e.g., xylose, arabinose, glucose, cellulose), a uronic acid (e.g., galacturonic acid or glucuronic acid), CO 2 , glycerol, or a native substrate of an enzyme that is part of the engineered metabolic pathway. Exemplary native substrates of exemplary enzymes are shown in Table 1 and include, for example, glucaric acid, galactaric acid, hydroxyproline, arabinonic acid, 2-oxo-4(S),5-dihydroxy-pentanoic acid, 2-oxo-4(R),5-dihydroxy-pentanoic acid, 2,5-dioxopentanoic acid, xylonolactone, xylonic acid, arabinonolactone, 4-deoxy-5-keto-D-glucaric acid, 4(R)-hydroxy-L-proline, 4(R)-hydroxy-D-proline, 2-carboxy-4(R)-hydroxy-pyrroline, 2,5-dioxopentanoic acid, succinaldehyde.

In yet another aspect, we describe herein methods for introducing a heterologous polynucleotide into cell so that the host cell exhibits an increased ability to convert a carbon source to a TCA derivative. The heterologous polynucleotide can encode a polypeptide operably linked to a promoter so that modified cell catalyzes conversion of the carbon source to the TCA derivative. In some of these embodiments, the carbon source can include xylose. The host cells for such methods can include, for example, any of the microbial species identified above with regard to the recombinant cells described herein.

In some embodiments, the heterologous polynucleotide may be inserted into a vector. A vector is a replicating polynucleotide such as, for example, a plasmid, phage, or cosmid, to which another polynucleotide may be inserted so as to bring about the replication of the inserted polynucleotide. Construction of vectors containing a polynucleotide of the invention employs standard ligation techniques known in the art. See, e.g., Sambrook et al, Molecular Cloning: A Laboratory Manual ., Cold Spring Harbor Laboratory Press (1989). A vector can permit, for example, further cloning—i.e., a cloning vector—or expression of the polypeptide encoded by the coding region—i.e., an expression vector. The term vector includes, but is not limited to, plasmid vectors, viral vectors, cosmid vectors, or artificial chromosome vectors. In one embodiment, the vector is a plasmid. Selection of a vector can depend upon a variety of desired characteristics in the resulting construct, such as a selection marker, vector replication rate, and the like.

An expression vector optionally includes regulatory sequences operably linked to the coding region. The polynucleotides described herein are not limited by the use of any particular promoter, and a wide variety of promoters are known. Promoters act as regulatory signals that bind RNA polymerase in a cell to initiate transcription of a downstream (3′ direction) coding region. The promoter used can be a constitutive or an inducible promoter. It can be, but need not be, heterologous with respect to the host cell. Exemplary promoters include, for example, trp, tac, and T7.

“Coding sequence” or “coding region” refers to a nucleotide sequence that encodes a polypeptide and, when placed under the control of appropriate regulatory sequences, expresses the encoded polypeptide. The boundaries of a coding region are generally determined by a translation start codon at its 5′ end and a translation stop codon at its 3′ end. As used herein, the term “polypeptide” refers broadly to a polymer of two or more amino acids joined together by peptide bonds. The term “polypeptide” also includes molecules that contain more than one polypeptide joined by disulfide bonds, ionic bonds, or hydrophobic interactions, or complexes of polypeptides that are joined together, covalently or noncovalently, as multimers (e.g., dimers, tetramers). Thus, the terms peptide, oligopeptide, and protein are all included within the definition of polypeptide and these terms are used interchangeably. The term “polypeptide” does not connote a specific length of a polymer of amino acids, nor does it imply or distinguish whether the polypeptide is produced using recombinant techniques, chemical or enzymatic synthesis, or is naturally occurring.

“Regulatory sequence” refers to a nucleotide sequence that regulates expression of a coding region to which it is operably linked. Nonlimiting examples of regulatory sequences include, for example, promoters, transcription initiation sites, translation start sites, translation stop sites, and terminators. “Operably linked” refers to a juxtaposition wherein the components are in a relationship permitting them to function in their intended manner. A regulatory sequence is “operably linked” to a coding region when it is joined in such a way that expression of the coding region is achieved under conditions compatible with the regulatory sequence.

As used in the preceding description, the term “and/or” means one or all of the listed elements or a combination of any two or more of the listed elements; the term “comprises” and variations thereof do not have a limiting meaning where these terms appear in the description and claims; unless otherwise specified, “a,” “an,” “the,” and “at least one” are used interchangeably and mean one or more than one; and the recitations of numerical ranges by endpoints include all numbers subsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc.).

In the preceding description, particular embodiments may be described in isolation for clarity. Unless otherwise expressly specified that the features of a particular embodiment are incompatible with the features of another embodiment, certain embodiments can include a combination of compatible features described herein in connection with one or more embodiments.

For any method disclosed herein that includes discrete steps, the steps may be conducted in any feasible order. And, as appropriate, any combination of two or more steps may be conducted simultaneously.

The present invention is illustrated by the following examples. It is to be understood that the particular examples, materials, amounts, and procedures are to be interpreted broadly in accordance with the scope and spirit of the invention as set forth herein.

incubating a recombinant cell of any preceding Embodiment in medium that comprises a carbon source under conditions effective for the recombinant cell to produce a TCA derivative.

Embodiment 128. The method of Embodiment 126 wherein the carbon source comprises xylose, arabinose, glucaric acid, galactaric acid, or hydroxyproline.

Embodiment 129. The method of any one of Embodiments 126-128 wherein the increased biosynthesis of the TCA derivative comprises an increase in pentose dehydrogenase activity, pentonolactonase activity, aldonic acid dehydratase activity, or 2-keto-3-deoxyaldonic acid dehydratase activity.

Embodiment 130. The method of any one of Embodiments 126-129 wherein the increased biosynthesis of the TCA derivative comprises an increase in hexic acid dehydratase activity or 5-dehydro-4-deoxyglucarate dehydratase activity.

introducing into a host cell a heterologous polynucleotide encoding at least one polypeptide that catalyzes conversion of a carbon source to a TCA derivative, wherein the at least one polypeptide is operably linked to a promoter so that the modified host cell catalyzes conversion of the carbon source to TCA derivative.

Embodiment 134. The method of Embodiment 131 wherein the TCA derivative comprises succinate, fumarate, malate, glutamate, lysine, threonine, 4-hydroxybutyrate.

The complete disclosure of all patents, patent applications, and publications, and electronically available material (including, for instance, nucleotide sequence submissions in, e.g., GenBank and RefSeq, and amino acid sequence submissions in, e.g., SwissProt, PIR, PRF, PDB, and translations from annotated coding regions in GenBank and RefSeq) cited herein are incorporated by reference in their entirety. In the event that any inconsistency exists between the disclosure of the present application and the disclosure(s) of any document incorporated herein by reference, the disclosure of the present application shall govern. The foregoing detailed description and examples have been given for clarity of understanding only. No unnecessary limitations are to be understood therefrom. The invention is not limited to the exact details shown and described, for variations obvious to one skilled in the art will be included within the invention defined by the claims.

Unless otherwise indicated, all numbers expressing quantities of components, molecular weights, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless otherwise indicated to the contrary, the numerical parameters set forth in the specification and claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. All numerical values, however, inherently contain a range necessarily resulting from the standard deviation found in their respective testing measurements.

All headings are for the convenience of the reader and should not be used to limit the meaning of the text that follows the heading, unless so specified.