# Patent

## Title
Bacterial cells having a glyoxylate shunt for the manufacture of succinic acid

## Abstract

The present invention is concerned with bacteria for the production of succinic acid. Specifically, the invention relates to a bacterial cell of the genus Pasteurella comprising a heterologous polypeptide having isocitrate lyase activity and a heterologous polypeptide having malate synthase activity. Further, the present invention contemplates a polynucleotide comprising a nucleic acid encoding a polypeptide having isocitrate lyase activity and a nucleic acid encoding a polypeptide having malate synthase activity. Finally, the present invention relates to the use of a bacterial cell of the invention for the manufacture of succinic acid.

## Background
RELATED APPLICATIONS
This application claims benefit under 35 U.S.C. §119(a) of European application 08172793.5, filed Dec. 23, 2008.
SUBMISSION OF SEQUENCE LISTING
The Sequence Listing associated with this application is filed in electronic format via EFS-Web and hereby incorporated by reference into the specification in its entirety. The name of the text file containing the Sequence Listing is SEQUENCE_LISTING—13156—00312_ST25.txt. The size of the text file is 160 kb, and the text file was created on Dec. 21, 2009.
BACKGROUND OF THE INVENTION
Description of Related Art
The fermentative production of succinic acid (SA) from biomass has already drawn much attention because said acid represents an important constituent of synthetic resins or is a source of further valuable low-molecular chemical compounds, in particular tetrahydrofuran (THF), 1,4-butanediol (BDO), gamma-butyrolactone (GBL) and pyrrolidones (WO-A-2006/066839).
A SA-producing bacterium isolated from bovine rumen was described by Lee et al., 2002, Appl Microbiol Biotechnol 58, 663-668. The bacterium is a non-motile, non-spore-forming, mesophilic and capnophilic gram-negative rod or coccobacillus. Phylogenetic analysis based on the 16S rRNA sequence and physiological analysis indicated that the strain belongs to the genus Mannheimia as a novel species, and has been named Mannheimia succiniciproducens MBEL55E. Under 100% CO2 conditions, it grows well in the pH range of 6.0-7.5 and produces SA, acetic acid and formic acid at a constant ratio of 2:1:1. When M. succiniciproducens MBEL55E was cultured anaerobically under CO2-saturation with glucose as carbon source, 19.8 g/L of glucose were consumed and 13.3 g/L of SA were produced in 7.5 h of incubation.
A significant drawback of said organism is, however, its inability to metabolize glycerol, which, as a constituent of triacyl glycerols (TAGs), becomes readily available e. g. as byproduct in the transesterification reaction of Biodiesel production (Dharmadi et al., 2006, Biotech Bioeng 94: 821-829).
The fermentative production of SA from glycerol has been described in the scientific literature (Lee et al., 2001, Biotech Bioeng 72, 41-48; Dharmadi et al., 2006, Biotech Bioeng 94: 821-829) and with glycerol higher yields [mass of SA produced/mass of raw material consumed] than with common sugars like glucose were achieved (Lee et al., 2001, Biotech Bioeng 72, 41-48). However, the space time yield obtained with glycerol was substantially lower than with glucose (0.14 vs. 1.0 g SA/[L h]) and no crude glycerol was used.
Therefore, there is a need for further bacterial strains, which have the ability to produce organic acids, in particular SA, from glycerol. In particular, such strains should produce said acids with high productivity from glycerol, especially if crude glycerol e. g. from biodiesel production can be used without prior purification.
BRIEF SUMMARY OF THE INVENTION
The present invention is concerned with bacteria for the production of succinic acid. Specifically, it relates to a bacterial cell of the genus Pasteurella comprising a heterologous polypeptide having isocitrate lyase activity and a heterologous polypeptide having malate synthase activity. Further, the present invention contemplates a polynucleotide comprising a nucleic acid encoding a polypeptide having isocitrate lyase activity and a nucleic acid encoding a polypeptide having malate synthase activity. Finally, the present invention relates to the use of a bacterial cell of the invention for the manufacture of succinic acid.
The technical problem underlying this invention could be seen as the provision of means and methods for complying with the aforementioned needs. The technical problem is solved by the embodiments described in the claims and herein below.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1: A schematic map of plasmid pSacB.
FIG. 2: A schematic map of plasmid pSacB (delta ldhA) (lactate dehydrogenase).
FIG. 3: A schematic map of plasmid pSacB (delta pflD) (pyruvate formate lyase).
FIG. 4: A schematic map of an expression plasmid pJFF224 (icl ms Y.m.) for the expression of the glyoxylate shunt operon of Yersinia molaretii (isocitrate lyase (icl) and malate synthase (ms)).
FIG. 5: A schematic map of the plasmid pJFF224 (icl/ms S.t.) for the expression of the glyoxylate shunt operon of Salmonella typhimurium. 
FIG. 6: A schematic map of the plasmid pJFF224 (icl ms Y.m.).
FIG. 7: A schematic map of the plasmid pJFF224 (PpckA fdh C.b.)
FIG. 8: A schematic map of the pSacB (delta adhE).
FIG. 9: A schematic map of the pJFF224 (fdh W.s.) for the expression of the W. succiogenes formate dehydrogenase (fdh W.s.).
FIG. 10: A schematic map of an expression plasmid pJFF224 (fdh C.b.) for the expression of the Candida boidinii formate dehydrogenase (fdh C.b.).
FIG. 11: The sequences of SEQ ID No: 1 to 21.



DETAILED DESCRIPTION OF THE INVENTION
The present invention, thus, relates to a bacterial cell of the genus Pasteurella comprising a heterologous polypeptide having isocitrate lyase activity and a heterologous polypeptide having malate synthase activity.
The term “bacterial cell” as used herein refers to a prokaryotic organism, i.e. a bacterium. Bacteria can be classified based on their biochemical and microbiological properties as well as their morphology. These classification criteria are well known in the art. The bacterial cell referred to in accordance with the present invention is from the genus of Pasteurella. The bacteria of the genus Pasteurella are gram-negative and facultative anaerobic. Pasteurella species are non-motile, pleimorphic and most often catalase- and oxidase-positive (Kuhnert and Christensen, 2008, ISBN 978-1-904455-34-9).
Preferably, the bacterial cell is a Pasteurella bacterial cell and, more preferably, a Pasteurella strain DD1 cell. Most preferably, the Pasteurella strain DD1 is the bacterial strain deposited under the Budapest Treaty with DSMZ (Deutsche Sammlung von Mikroorganismen and Zellkulturen, GmbH), Germany, having the deposit number DSM 18541.
Pasteurella bacteria can be isolated from the gastro-intestinal tract of animals and, preferably, mammals. The bacterial strain DD1, in particular, can be isolated from bovine rumen and is capable of utilizing glycerol (including crude glycerol) as a carbon source. Preferably, the said strain has the ability to produce SA from glycerol (including crude glycerol), in particular, under anaerobic conditions. Moreover, the Pasteurella strain DD1 exhibits at least one of the following additional metabolic characteristics:

    a) production of SA from sucrose; in particular, under anaerobic conditions;
    b) production of SA from D-fructose; in particular, under anaerobic conditions;
    c) production of SA from D-galactose; in particular, under anaerobic conditions;
    d) production of SA from D-mannose; in particular, under anaerobic conditions;
    e) production of SA from D-glucose; in particular, under anaerobic conditions;
    f) production of SA from D-xylose; in particular, under anaerobic conditions;
    g) production of SA from L-arabinose; in particular, under anaerobic conditions;
    h) no utilization of of xylitol, inositol and sorbitol;
    i) growth both under aerobic and anaerobic conditions;
    j) growth at initial glucose concentrations of 75 g/L or more;
    k) ammonia tolerance.


In particular, said strain shows at least 2, 3, 4, 5, 6, 7, 8, 9, 10 or all of said metabolic characteristics.
Also preferably, the Pasteurella strain DD1 has a 16S rDNA having a nucleic acid sequence as shown in SEQ ID NO: 7 or a sequence which is at least 96, 97, 98, 99 or 99.9% identical thereto and/or a 23S rDNA having a nucleic acid sequence as shown in SEQ ID NO: 8 or a sequence which shows a sequence homology of at least 95, 96, 97, 98, 99 or 99.9% thereto.
The identity in percentage values referred to in connection with the various polypeptides or polynucleotides to be used for the bacterial cell of the present invention is, preferably, calculated as identity of the residues over the complete length of the aligned sequences, such as, for example, the identity calculated (for rather similar sequences) with the aid of the program needle from the bioinformatics software package EMBOSS (Version 5.0.0, emboss.sourceforge.net/what/) with the default parameters which are, i.e. gap open (penalty to open a gap): 10.0, gap extend (penalty to extend a gap): 0.5, and data file (scoring matrix file included in package): EDNAFUL.
The term “heterologous” as used herein refers to a polypeptide which does not naturally occur in the bacterial cell, i.e. which is not encoded by the endogenous bacterial genes or derived by posttranslational processing from a polypeptide precursor being encoded by the said bacterial genes. A heterologous polypeptide as referred to in accordance with the present invention, thus, can be exogenously introduced into the bacterial cell. Alternatively, the heterologous polypeptide is encoded by a heterologous polynucleotide which has been exogenously introduced into the bacterial cell. In this case, the heterologous polypeptide will be expressed from the heterologous polynucleotide. It will be understood that the heterologous polynucleotide, preferably, comprises in addition to an open reading frame nucleic acid sequence encoding the heterologous polypeptide further sequences which are required for gene expression in bacteria. Such sequences, preferably, include an expression control sequence, e.g., a promoter being active in Pasteurella, and a termination sequence. The heterologous polynucleotide encoding the heterologous polypeptide can be introduced episomally by transformation of an episomal plasmid comprising the heterologous polynucleotide or can be integrated into the bacterial genome by homologous recombination techniques. How to introduce and to achieve expression of heterologous polynucleotides in bacteria and, in particular, Pasteurella is well known to the person skilled in the art and described elsewhere in this specification in detail.
The bacterial cell of the present invention shall comprise a heterologous polypeptide having isocitrate lyase activity. Isocitrate lyase activity as meant herein refers to the capability of a polypeptide to convert isocitrate into succinate and glyoxylate. Polypeptides having isocitrate lyase activity are well known in the art (Robertson E F, 1987, Curr Microbiol 14, 347-350). The enzymatic activity can be determined, preferably, as described in Watanabe et al. (Watanabe et al., 2001, Biosci Biotechnol Biochem 65, 1095-1103) or in the accompanying examples.
Preferably, said heterologous polypeptide having isocitrate lyase activity is encoded by a polynucleotide comprising a nucleic acid selected from the group consisting of:

    
    
        a) a nucleic acid having a nucleotide sequence as shown in SEQ ID NO: 1;
        b) a nucleic acid encoding an amino acid sequence as shown in SEQ ID NO: 2;
        c) a nucleic acid which is at least 70% identical to the nucleic acid of a) or b); and
        d) a nucleic acid encoding an amino acid sequence which is at least 70% identical to the amino acid sequence encoded by the nucleic acid of a) or b).
    
    


The term “polynucleotide” as used in accordance with the present invention relates to a nucleic acid molecule which encodes a polypeptide having the aforementioned biological activity. A polynucleotide encoding a polypeptide having the aforementioned biological activity has been obtained in accordance with the present invention from Salmonella typhimurium or Yersinia molaretii. Thus, the polynucleotide, preferably, comprises the nucleic acid sequence shown in SEQ ID NO: encoding the polypeptide having an amino acid sequence as shown in SEQ ID NO: 2. It is to be understood that a polypeptide having an amino acid sequence as shown in SEQ ID NO: 2 may be also encoded due to the degenerated genetic code by other polynucleotides as well. Moreover, the term “polynucleotide” as used in accordance with the present invention further encompasses variants of the aforementioned specific polynucleotides. Said variants may represent orthologs, paralogs or other homologs of the polynucleotide of the present invention. The polynucleotide variants, preferably, comprise a nucleic acid sequence characterized in that the sequence can be derived from the aforementioned specific nucleic acid sequences shown in SEQ ID NO: 1 by at least one nucleotide substitution, addition and/or deletion whereby the variant nucleic acid sequence shall still encode a polypeptide having the activity as specified above. Variants also encompass polynucleotides comprising a nucleic acid sequence which is capable of hybridizing to the aforementioned specific nucleic acid sequences, preferably, under stringent hybridization conditions. These stringent conditions are known to the skilled worker and can be found in Current Protocols in Molecular Biology, John Wiley & Sons, N.Y. (1989), 6.3.1-6.3.6. A preferred example for stringent hybridization conditions are hybridization conditions in 6× sodium chloride/sodium citrate (=SSC) at approximately 45° C., followed by one or more wash steps in 0.2×SSC, 0.1% SDS at 50 to 65° C. The skilled worker knows that these hybridization conditions differ depending on the type of nucleic acid and, for example when organic solvents are present, with regard to the temperature and concentration of the buffer. For example, under “standard hybridization conditions” the temperature differs depending on the type of nucleic acid between 42° C. and 58° C. in aqueous buffer with a concentration of 0.1 to 5×SSC (pH 7.2). If organic solvent is present in the abovementioned buffer, for example 50% formamide, the temperature under standard conditions is approximately 42° C. The hybridization conditions for DNA: DNA hybrids are preferably for example 0.1×SSC and 20° C. to 45° C., preferably between 30° C. and 45° C. The hybridization conditions for DNA: RNA hybrids are preferably, for example, 0.1×SSC and 30° C. to 55° C., preferably between 45° C. and 55° C. The abovementioned hybridization temperatures are determined for example for a nucleic acid with approximately 100 by (=base pairs) in length and a G+C content of 50% in the absence of formamide. The skilled worker knows how to determine the hybridization conditions required by referring to textbooks such as the textbook mentioned above, or the following textbooks: Sambrook et al., 1989, “Molecular Cloning”, Cold Spring Harbor Laboratory; Hames and Higgins (Ed.) 1985, “Nucleic Acids Hybridization: A Practical Approach”, IRL Press at Oxford University Press, Oxford; Brown (Ed.) 1991, “Essential Molecular Biology: A Practical Approach”, IRL Press at Oxford University Press, Oxford. Alternatively, polynucleotide variants are obtainable by PCR-based techniques such as mixed oligonucleotide primer-based amplification of DNA, i.e. using degenerated primers against conserved domains of the polypeptides of the present invention. Conserved domains of the polypeptide of the present invention may be identified by a sequence comparison of the nucleic acid sequence of the polynucleotide or the amino acid sequence of the polypeptide of the present invention with sequences of other isocitrate lyases. Oligonucleotides suitable as PCR primers as well as suitable PCR conditions are described in the accompanying Examples. As a template, DNA or cDNA from bacteria, fungi, plants or animals may be used. Further, variants include polynucleotides comprising nucleic acid sequences which are at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least 95%, at least 98% or at least 99% identical to the nucleic acid sequences shown in SEQ ID NO: 1. Moreover, also encompassed are polynucleotides which comprise nucleic acid sequences encoding amino acid sequences which are at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least 95%, at least 98% or at least 99% identical to the amino acid sequences shown in SEQ ID NO: 2. The percent identity values are, preferably, calculated over the entire amino acid or nucleic acid sequence region. A series of programs based on a variety of algorithms is available to the skilled worker for comparing different sequences. In this context, the algorithms of Needleman and Wunsch or Smith and Waterman give particularly reliable results. To carry out the sequence alignments, the program PileUp (Feng & Doolittle, 1987, J Mol Evol 25, 351-360; Higgins & Sharp, 1989, Comput Appl Biosci 5, 151-153) or the programs Gap and BestFit (Needleman & Wunsch, 1970, J Mol Biol 48, 443-453; Smith & Waterman, 1981, J Mol Biol 147, 195-197), which are part of the GCG software packet [Genetics Computer Group, 575 Science Drive, Madison, Wis., USA 53711 (1991)], are to be used. The sequence identity values recited above in percent (%) are to be determined, preferably, using the program GAP over the entire sequence region with the following settings: Gap Weight: 50, Length Weight: 3, Average Match: 10.000 and Average Mismatch: 0.000, which, unless otherwise specified, shall always be used as standard settings for sequence alignments. It is to be understood that the aforementioned variant polynucleotides shall encode polypeptides having isocitrate lyase activity. A polynucleotide comprising a fragment of any of the aforementioned nucleic acid sequences is also encompassed as a polynucleotide of the present invention. The fragment shall encode a polypeptide which still has the activity as specified above. Accordingly, the polypeptide may comprise or consist of the domains of the polypeptide of the present invention conferring the said biological activity. A fragment as meant herein, preferably, comprises at least 50, at least 100, at least 250 or at least 500 consecutive nucleotides of any one of the aforementioned nucleic acid sequences or encodes an amino acid sequence comprising at least 20, at least 30, at least 50, at least 80, at least 100 or at least 150 consecutive amino acids of any one of the aforementioned amino acid sequences. The polynucleotides of the present invention either essentially consist of the aforementioned nucleic acid sequences or comprise the aforementioned nucleic acid sequences. Thus, they may contain further nucleic acid sequences as well. Specifically, the polynucleotides of the present invention may encode fusion proteins wherein one partner of the fusion protein is a polypeptide being encoded by a nucleic acid sequence recited above. Such fusion proteins may comprise as additional part so called “tags” which may serve as a detectable marker or as an auxiliary measure for purification purposes. Tags for the different purposes are well known in the art and comprise FLAG-tags, 6-histidine-tags, MYC-tags and the like. The polynucleotide, preferably, is DNA or RNA. The term encompasses single as well as double stranded polynucleotides. Moreover, comprised are also chemically modified polynucleotides including naturally occurring modified polynucleotides or artificial modified ones.
The bacterial cell of the present invention shall comprise a heterologous polypeptide having malate synthase activity. Malate synthase activity as meant herein refers to the capability of a polypeptide to convert glyoxylate into malate. This enzymatic reaction is dependent on acetyl-CoA. Polypeptides having malate synthase activity are well known in the art (Sundaram et al., 1980, Arch Biochem Biophys 199, 515-525). The enzymatic activity can be determined, preferably, as described in Eggerer & Klette, 1967, Eur J Biochem 1, 447-475 and in Durchschlag et al., 1981, Eur. J. Biochem 114, 255-262 or in the accompanying examples.
Preferably, said heterologous polypeptide having malate synthase activity is encoded by a polynucleotide comprising a nucleic acid selected from the group consisting of:

    
    
        a) a nucleic acid having a nucleotide sequence as shown in SEQ ID NO: 3;
        b) a nucleic acid encoding an amino acid sequence as shown in SEQ ID NO: 4;
        c) a nucleic acid which is at least 70% identical to the nucleic acid of a) or b); and
        d) a nucleic acid encoding an amino acid sequence which is at least 70% identical to the amino acid sequence encoded by the nucleic acid of a) or b).
    
    


The definitions of the term “polynucleotide” made above apply accordingly. Specifically, the polynucleotide shall comprise a nucleic acid sequence which encodes a polypeptide having the aforementioned biological activity. A polynucleotide encoding a polypeptide having the aforementioned biological activity has been obtained in accordance with the present invention from Salmonella typhimurium or Yersinia molaretii. Thus, the polynucleotide, preferably, comprises the nucleic acid sequence shown in SEQ ID NO: 3 encoding the polypeptide having an amino acid sequence as shown in SEQ ID NO: 4. It is to be understood that a polypeptide having an amino acid sequence as shown in SEQ ID NO: 4 may be also encoded due to the degenerated genetic code by other polynucleotides as well. The definitions of variant polynucleotides or polynucleotides comprising a fragment of the aforementioned polynucleotides made before apply accordingly to variant polynucleotides encoding a polypeptide having malate synthase activity.
The aforementioned heterologous polynucleotides may be introduced into the bacterial cell by transformation using a suitable vector. Suitable vectors, preferably, encompass phage or plasmid vectors as well artificial chromosomes, such as bacterial artificial chromosomes. Moreover, the term also relates to targeting constructs which allow for random or site-directed integration of the targeting construct into genomic DNA. Such target constructs, preferably, comprise DNA of sufficient length for either homologous or heterologous recombination with the bacterial genome. The vector, preferably, comprises at least one of the heterologous polynucleotides referred to herein above. It is to be understood that the vector may also comprise both heterologous polynucleotides referred to herein above and, more preferably, even a third polynucleotide as referred to herein below. Preferably, the vector further comprises selectable markers for propagation and/or selection in the bacterial cell. The vector may be incorporated into a host cell by various techniques well known in the art. For example, a plasmid vector can be introduced in a precipitate such as a calcium phosphate precipitate or rubidium chloride precipitate, or in a complex with a charged lipid or in carbon-based clusters, such as fullerens. Alternatively, a vector may be introduced by heat shock or electroporation techniques. The vector, preferably, further comprises an expression control sequences allowing expression in the Pasteurella bacterial cells. Moreover, the vector, preferably, further comprise regulatory sequences ensuring initiation of transcription and, optionally, poly-A signals ensuring termination of transcription and stabilization of the transcript. Possible regulatory elements permitting expression in bacterial cells comprise, e.g., the lac, trp or tac promoters. Preferred vectors to be used for Pasteurella species are selected from the group consisting of: pSacB, pJFF224.
Pasteurella species and, in particular, strain DD1 naturally lack a glyoxylate metabolism. Advantageously, it has been found in the studies underlying the present invention that by introducing an isocitrate lyase in combination with a malate synthase, the production of SA can be significantly increased in a bacterial cell which naturally lacks these enzymes. Thus, by establishing a partial glyoxylate metabolism in such bacterial cells, a so called “glyoxylate shunt”, the bacterial cells can significantly increase their SA production by converting acetyl-CoA into SA whereby losses due to CO2 can be prevented. Such losses would normally occur within the citric acid cycle. In accordance with the present invention, it has been found that a bacterial cell as defined herein can be advantageously used for the manufacture of SA, preferably in an industrial scale.
In a preferred embodiment of the bacterial cell of the present invention, said bacterial cell further comprises a heterologous polypeptide having formate dehydrogenase activity.
The bacterial cell of the present invention shall comprise a heterologous polypeptide having formate dehydrogenase activity. Formate dehydrogenase activity as meant herein refers to the capability of a polypeptide to convert formate into CO2. This enzymatic reaction yields redox-equivalents, i.e. NADH. Polypeptides having formate dehydrogenase activity are well known in the art (Ferry 1990, FEMS Microbiol Rev 7, 377-382). The enzymatic activity can be determined, preferably, as described in Müller et al., 1978, Eur J Biochem 83, 485-498 or in the accompanying Examples.
Preferably, said heterologous polypeptide having formate dehydrogenase activity is encoded by a polynucleotide comprising a nucleic acid selected from the group consisting of:

    
    
        a) a nucleic acid having a nucleotide sequence as shown in SEQ ID NO: 5 or SEQ ID NO: 18;
        b) a nucleic acid encoding an amino acid sequence as shown in SEQ ID NO: 6;
        c) a nucleic acid which is at least 70% identical to the nucleic acid of a) or b); and
        d) a nucleic acid encoding an amino acid sequence which is at least 70% identical to the amino acid sequence encoded by the nucleic acid of a) or b).
    
    


The definitions of the term “polynucleotide” made above apply accordingly. Specifically, the polynucleotide shall comprise a nucleic acid sequence which encodes a polypeptide having the aforementioned biological activity. A polynucleotide encoding a polypeptide having the aforementioned biological activity has been obtained in accordance with the present invention from Candida boidinii or Wolinella succinogenes. Thus, the polynucleotide, preferably, comprises the nucleic acid sequence shown in SEQ ID NO: 5 encoding the polypeptide having an amino acid sequence as shown in SEQ ID NO: 6 or a polynucleotide as shown in SEQ ID NO: 18. It is to be understood that a polypeptide having an amino acid sequence as shown in SEQ ID NO: 6 may be also encoded due to the degenerated genetic code by other polynucleotides as well. The definitions of variant polynucleotides or polynucleotides comprising a fragment of the aforementioned polynucleotides made before apply accordingly to variant polynucleotides encoding a polypeptide having formate dehydrogenase activity.
It has been found in the studies underlying the present invention that the production of SA can even be more increased by further expressing a formate dehydrogenase in the bacterial cell.
In a further preferred embodiment of the bacterial cell of the present invention, said bacterial cell has reduced lactate dehydrogenase activity.
In yet a further preferred embodiment of the bacterial cell of the present invention, said bacterial cell has reduced lactate dehydrogenase and reduced pyruvate formate lyase activity.
The term “reduced lactate dehydrogenase activity” and “reduced lactate dehydrogenase and reduced pyruvate formate lyase activity” encompasses a modified bacterial cell which has no detectable lactate dehydrogenase activity or no detectable lactate dehydrogenase and no detectable pyruvate formate lyase activity. Moreover, the term encompasses a bacterial cell which has a significantly reduced lactate dehydrogenase activity or significantly reduced lactate dehydrogenase and reduced pyruvate lyase activity when compared to a bacterial cell exhibiting physiological lactate dehydrogenase activity levels or significantly reduced lactate dehydrogenase and pyruvate formate lyase activity levels when compared to a bacterial cell exhibiting physiological activity levels of said enzymes. Whether a reduction is significant can be determined by statistical methods well known to those skilled in the art. Bacterial cells being deficient in lactate dehydrogenase or being deficient in lactate dehydrogenase and pyruvate formate lyase activity may occur naturally, i.e. due to spontaneous mutations. A bacterial cell can be modified to lack or to have significantly reduced lactate dehydrogenase activity or significantly reduced lactate dehydrogenase and pyruvate formate lyase activity by various techniques. Preferably, such bacterial cells are obtainable by chemical treatment or radiation. To this end, bacterial cells will be treated by, e.g., a mutagenizing chemical agent, X-rays, or UV light. In a subsequent step, those bacterial cells which lack lactate dehydrogenase or lactate dehydrogenase and pyruvate formate lyase activity or which at least have a reduced lactate dehydrogenase or a reduced lactate dehydrogenase and pyruvate formate lyase activity activity will be selected. Bacterial cells are also obtainable by homologous recombination techniques which aim to mutate, disrupt or excise the lactate dehydrogenase gene or the lactate dehydrogenase and pyruvate formate lyase activity genes in the genome of the bacterial cell. In the following, a preferred technique for recombination, in particular for introducing mutations or for deleting sequences, is described.
This technique is also sometimes referred to as the “Campbell recombination” herein (Leenhouts et al., 1989, Appl Env Microbiol 55, 394-400). “Campbell in,” as used herein, refers to a transformant of an original host cell in which an entire circular double stranded DNA molecule (for example a plasmid) has integrated into a chromosome by a single homologous recombination event (a cross in event), and that effectively results in the insertion of a linearized version of said circular DNA molecule into a first DNA sequence of the chromosome that is homologous to a first DNA sequence of the said circular DNA molecule. “Campbelled in” refers to the linearized DNA sequence that has been integrated into the chromosome of a “Campbell in” transformant. A “Campbell in” contains a duplication of the first homologous DNA sequence, each copy of which includes and surrounds a copy of the homologous recombination crossover point.
“Campbell out,” as used herein, refers to a cell descending from a “Campbell in” transformant, in which a second homologous recombination event (a cross out event) has occurred between a second DNA sequence that is contained on the linearized inserted DNA of the “Campbelled in” DNA, and a second DNA sequence of chromosomal origin, which is homologous to the second DNA sequence of said linearized insert, the second recombination event resulting in the deletion (jettisoning) of a portion of the integrated DNA sequence, but, importantly, also resulting in a portion (this can be as little as a single base) of the integrated Campbelled in DNA remaining in the chromosome, such that compared to the original host cell, the “Campbell out” cell contains one or more intentional changes in the chromosome (for example, a single base substitution, multiple base substitutions, insertion of a heterologous gene or DNA sequence, insertion of an additional copy or copies of a homologous gene or a modified homologous gene, or insertion of a DNA sequence comprising more than one of these aforementioned examples listed above). A “Campbell out” cell is, preferably, obtained by a counter-selection against a gene that is contained in a portion (the portion that is desired to be jettisoned) of the “Campbelled in” DNA sequence, for example the Bacillus subtilis sacB gene, which is lethal when expressed in a cell that is grown in the presence of about 5% to 10% sucrose. Either with or without a counter-selection, a desired “Campbell out” cell can be obtained or identified by screening for the desired cell, using any screenable phenotype, such as, but not limited to, colony morphology, colony color, presence or absence of antibiotic resistance, presence or absence of a given DNA sequence by polymerase chain reaction, presence or absence of an auxotrophy, presence or absence of an enzyme, colony nucleic acid hybridization, antibody screening, etc. The term “Campbell in” and “Campbell out” can also be used as verbs in various tenses to refer to the method or process described above.
It is understood that the homologous recombination events that leads to a “Campbell in” or “Campbell out” can occur over a range of DNA bases within the homologous DNA sequence, and since the homologous sequences will be identical to each other for at least part of this range, it is not usually possible to specify exactly where the crossover event occurred. In other words, it is not possible to specify precisely which sequence was originally from the inserted DNA, and which was originally from the chromosomal DNA. Moreover, the first homologous DNA sequence and the second homologous DNA sequence are usually separated by a region of partial non-homology, and it is this region of non-homology that remains deposited in a chromosome of the “Campbell out” cell.
Preferably, first and second homologous DNA sequence are at least about 200 base pairs in length, and can be up to several thousand base pairs in length. However, the procedure can be made to work with shorter or longer sequences. For example, a length for the first and second homologous sequences can range from about 500 to 2000 bases, and the obtaining of a “Campbell out” from a “Campbell in” is facilitated by arranging the first and second homologous sequences to be approximately the same length, preferably with a difference of less than 200 base pairs and most preferably with the shorter of the two being at least 70% of the length of the longer in base pairs.
It has been found in the studies underlying the present invention that the production of SA is even more increased in bacterial cells lacking lactate dehydrogenase activity or lacking lactate dehydrogenase and pyruvate formate lyase activity.
A preferred lactate dehydrogenase as referred to in accordance with the present invention is encoded by a polynucleotide comprising a nucleic acid selected from the group consisting of:

    
    
        a) a nucleic acid having a nucleotide sequence as shown in SEQ ID NO: 20;
        b) a nucleic acid encoding an amino acid sequence as shown in SEQ ID NO: 21;
        c) a nucleic acid which is at least 70% identical to the nucleic acid of a) or b); and
        d) a nucleic acid encoding an amino acid sequence which is at least 70% identical to the amino acid sequence encoded by the nucleic acid of a) or b).
    
    


A preferred pyruvate formate lyase as referred to in accordance with the present invention is encoded by a polynucleotide comprising a nucleic acid selected from the group consisting of:

    
    
        a) a nucleic acid having a nucleotide sequence as shown in SEQ ID NO: 22;
        b) a nucleic acid encoding an amino acid sequence as shown in SEQ ID NO: 23;
        c) a nucleic acid which is at least 70% identical to the nucleic acid of a) or b); and
        d) a nucleic acid encoding an amino acid sequence which is at least 70% identical to the amino acid sequence encoded by the nucleic acid of a) or b).
    
    


The present invention also contemplates a polynucleotide comprising a nucleic acid encoding a polypeptide having isocitrate lyase activity as defined above and a nucleic acid encoding a polypeptide having malate synthase activity as defined above. Moreover, the aforementioned polynucleotide, preferably, also comprises a nucleic acid encoding a polypeptide having formate dehydrogenase activity. Said polynucleotide is, preferably, an isolated polynucleotide.
The term includes all entities of the two or three nucleic acids on a polynucleotide except where the nucleic acids are linked together in their natural context. Accordingly, even the said two or three nucleic acids appear as heterologous nucleic acids linked together in a genome would be regarded as an isolated polynucleotide according to the invention. Moreover, such a polynucleotide comprising a cluster of nucleic acids encoding the two or three enzymes can be incorporated into an bacterial expression vector and used for transformation of bacterial cells (sometimes also referred to as an operon). The advantage of such a polynucleotide or expression vector is that both polypeptides having the aforementioned enzymatic activities will be present in all transfected cells and can be expressed in an equal ratio. Thus, the efficacy for SA production of a bacterial cell can be further improved.
Finally, the present invention relates to a method for manufacturing SA comprising

    
    
        i) cultivating a bacterial cell of the present invention under suitable culture conditions; and
        ii) obtaining SA from the cultured bacterial cells.
    
    


The term “succinic acid” (SA) has to be understood in its broadest sense and also encompasses salts thereof, as for example alkali metal salts, like Na and K salts, or earth alkali salts, like Mg and Ca salts, or ammonium salts; or anhydrides of said acids.
Suitable culture conditions and techniques for obtaining the SA to be applied in the method of the invention, i.e. the fermentative process for the production of SA, are as follows:
The bacterial cell of the present invention is, preferably, incubated in a medium containing an carbon source which can be assimilated and cultivated at a temperature in the range of about 10 to 60 or 20 to 50 or 30 to 45° C. at a pH of 5.0 to 9.0 or 5.5 to 8.0 or 6.0 to 7.0 in the presence of carbon dioxide.
Preferably, SA is produced under anaerobic conditions. Anaerobic conditions may be established by means of conventional techniques, as for example by degassing the constituents of the reaction medium and maintaining anaerobic conditions by introducing carbon dioxide or nitrogen or mixtures thereof and optionally hydrogen at a flow rate of, for example, 0.1 to 1 or 0.2 to 0.5 vvm. Aerobic conditions may be established by means of conventional techniques, as for example by introducing air or oxygen at a flow rate of, for example, 0.1 to 1 or 0.2 to 0.5 vvm. If appropriate, a slight over pressure of 0.1 to 1.5 bar may be applied in the process.
The assimilable carbon source is preferably selected from glycerol, D-glucose, D-xylose, L-arabinose, D-galactose, D-mannose and mixtures thereof or compositions containing at least one of said compounds, or is selected from decomposition products of starch, cellulose, hemicellulose and/or lignocellulose.
The initial concentration of the assimilable carbon source is, preferably, adjusted to a value in a range of 5 to 100 g/l and may be maintained in said range during cultivation.
The pH of the reaction medium may be controlled by addition of suitable bases as for example, ammonium hydroxide in the form of an at least 5% (w/v) or more concentrated (up to saturation) aqueous solution or gaseous ammonia or other bases.
Particularly Preferred Conditions for Producing SA are:


    Carbon source: Glucose or glycerol (including crude glycerol)
    Temperature: 30 to 45° C.
    pH: 5.5 to 7.0
    supplied gas: CO2 


The term “crude glycerol” has to be understood as untreated glycerol-containing stream as it accrues in processes in which glycerol is a by product, as for example the production of bio diesel or bio ethanol. Unless otherwise stated the term “glycerol” as used herein also encompasses “crude glycerol”.
Further preferred conditions will be derivable from the attached examples and figures.
Succinic acid and/or SA salts produced are, preferably, obtained by methods known in the art, as for example crystallization, filtration, electrodialysis, chromatography. For example, they may be isolated by precipitating as a calcium succinate product in the fermenter during the fermentation by using calcium hydroxide, -oxide, -carbonate or hydrogen carbonate for neutralization and filtration of the precipitate.
The desired SA product is recovered from the precipitated calcium or succinate by acidification of the succinate with sulfuric acid followed by filtration to remove the calcium sulfate (gypsum) or which precipitates. The resulting solution may be further purified by means of ion exchange chromatography in order to remove undesired residual ions.
Another embodiment of the invention relates to a process for the production of SA and/or SA salts, in particular ammonium salts, which method comprises the fermentative production of SA as defined above and controlling the pH with a suitable base, in particular inorganic base, like ammonia, or an aqueous solution thereof.
Another embodiment of the invention relates to a process for the production of tetrahydrofuran (THF) and/or 1,4-butanediol (BDO) and/or gamma-butyrolactone (GBL) which comprises

    a) the fermentative production of SA and/or SA salts, e. g. ammonium salts as defined above, and
    b1) either the direct catalytic hydrogenation of the obtained free acid to THF and/or BDO and/or GBL or
    b2) the chemical esterification of obtained free SA and/or SA ammonium salts to its corresponding di-loweralkyl ester and subsequent catalytic hydrogenation of said ester to THF and/or BDO and/or GBL.


Lower alkyl preferably represent a straight chain or branched C1-C6-, preferably C1-C4-alkyl residue, in particular methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, as well as n-pentyl and n-nexyl and branched analogues thereof.
Another embodiment of the invention relates to a process for the production of pyrrolidones which comprises

    a) the fermentative production of SA ammonium salts as defined above, and
    b) the chemical conversion of SA ammonium salts to pyrrolidones in a manner known per se, for example as described in WO-A-2006/066839 (which document is herewith incorporated by reference).


In a preferred embodiment, said glycerol, which is used as assimilable carbon source, is crude glycerol.
More Details on Direct Hydrogenation of SA:
Suitable experimental conditions for performing direct catalytic hydrogenation are well known, and for example, described in U.S. Pat. No. 4,550,185, incorporated herewith by reference.
The SA is hydrogenated in a manner known per se using processes, apparatus and assistants, such as solvents, familiar to the person skilled in the art. In particular, a continuous or batch wise liquid phase hydrogenation is carried out in the presence of a heterogeneous catalyst suitable for the acid hydrogenation. The optimal process parameters can be established by the person skilled in the art without unacceptable effort. For example, the reaction temperature is in the range from about 100 to about 300° C., preferably in the range from about 130 to 285° C., and the pressure is from about 20 to 350 bar, for example from 100 to 250 bar. Catalysts usable for the hydrogenation reaction are known to the person skilled in the art. For example, various palladium/rhenium/carbon catalysts may be used. Solvents usable for the hydrogenation reaction are known to the person skilled in the art. For example, an aqueous solvent medium may be used.
More Details on Esterification of SA Followed by Hydrogenation:
Suitable experimental conditions for performing the chemical esterification, followed by direct catalytic hydrogenation are well known, and for example, described in European Patent application 06007118.0 incorporated herewith by reference.

    a) Esterification process:


The esterification process which may comprise a reactive distillation can be performed using an apparatus known per se in various designs.
For example an esterification plant which is operated in continuous mode can be used which comprises a rectification column with an appropriate number of theoretical stages achieved by installation of trays or packings. The aqueous charge comprising the ammonium salt of SA is fed into the top of the column from a reservoir vessel as soon as a steady-state temperature profile has formed in the column as a result of feeding-in alkanol that is evaporated in the evaporator loop adherent to the sump of the column. The reaction forms a countercurrent flow of descending, ammonium salt-containing liquid and condensate, and ascending, alkanol-containing vapor phase. To catalyze the esterification reaction, a homogeneous catalyst may be added to the ammonium salt initial charge. Alternatively, heterogeneous catalysts may be provided in the column internals. The carboxylic ester formed is liquid under the process conditions and passes via the lower end of the column into the sump of the distillation column and is continuously withdrawn from the sump. Gaseous components, for example azeotropic mixtures comprising alkanol-water and/or ammonia, are removed from the reaction column and hence from the reaction equilibrium at the top of the column.
Further modifications of the above-described specific embodiments can be implemented by the person skilled in the art without unacceptable effort.
Suitable process parameter ranges for the esterification process according to the invention can be determined easily by the person skilled in the art depending on the configuration of the apparatus used, for example type of column internals used, type and amount of the reactants, type and amount of the catalyst used if appropriate. For instance, without being restrictive thereto, individual parameters may be set within the following parameter ranges:

    Column temperature: 0-300° C., in particular 40-250° C., or 70-200° C.
    Pressure: from 0.1 to 6 bar, in particular standard pressure
    Residence time: a few seconds (for example from 1 to 60) up to days (for example from 1 to 5), in particular from a few minutes (for example from 1 to 60) to a few hours (for example from 1 to 15), more preferably from a few minutes (for example from 5 to 20) to 2 h.
    b) Hydrogenation process


The SA esters prepared in accordance with the invention are hydrogenated in a manner known per se using processes, apparatus and assistants, such as catalysts, familiar to the person skilled in the art.
In particular, a continuous or batch wise gas phase hydrogenation is carried out in the presence of a heterogeneous catalyst suitable for the ester hydrogenation. The optimal process parameters can be established by the person skilled in the art for the particular ester without unacceptable effort. For example, the reaction temperature is in the range from about 100 to about 300° C., preferably in the range from about 200 to 280° C., and the pressure is from about 5 to 100 bar, for example from 10 to 50 bar. The molar ratio of reactant to hydrogen is set within the range from about 1:100 to about 1:2000, for example from 1:800 to 1:1500.
Catalysts usable for the inventive hydrogenation reaction are known to the person skilled in the art. For example, various copper catalysts may be used. The prior art describes, for example, the use of reduced copper chromite catalysts which are obtainable under the name 85/1 from Davy Process Technology Ltd., England. However, catalysts particularly suitable in accordance with the invention are supported copper oxide catalysts, the copper oxide being applied to alumina or silica support materials. The examples of the hydrogenation of succinic esters to BDO (1,4-Butanediol)/GBL (gamma-butyrlactone)/THF with copper catalysts are also well known in the art.
Fermentation as used according to the present invention can be performed in stirred fermenters, bubble columns and loop reactors. The possible method types including stirrer types and geometric designs are well known in the art and can be found in standard text books. In the process, typical variants available are the following variants known to those skilled in the art or explained, for example, in a standard textbook (Chmiel H, Hammes W P, Bailey J E, 1987, “Biochemical engineering. A challenge for interdisciplinary cooperation.”, ISBN: 3-437-30574-3.), such as batch, fed batch, repeated fed batch or else continuous fermentation with and without recycling of the biomass. Depending on the production strain, sparging with air, oxygen, carbon dioxide, hydrogen, nitrogen or appropriate gas mixtures can/must be effected in order to achieve good yields.
Before the chemical conversion in the fermentation broth in the process according to the invention, the fermentation broth can be pretreated; for example, the biomass of the broth can be removed. Processes for removing the biomass are known to those skilled in the art, for example filtration, sedimentation and flotation. Consequently, the biomass can be removed, for example, with centrifuges, separators, decanters, filters or in flotation apparatus. For maximum recovery of the product of value, washing of the biomass is often advisable, for example in the form of a diafiltration. The selection of the method is dependent upon the biomass content in the fermenter broth and the properties of the biomass, and also the interaction of the biomass with the product of value. In one embodiment, the fermentation broth can be sterilized or pasteurized.
In a further embodiment, the fermentation broth is concentrated. Depending on the requirement, this concentration can be done batch wise or continuously. The pressure and temperature range should be selected such that firstly no product damage occurs, and secondly minimal use of apparatus and energy is necessary. The skillful selection of pressure and temperature levels for a multistage evaporation in particular enables saving of energy.
The term “fermentation broth” is understood to mean an aqueous solution which is based on a fermentative process and has not been worked up or has been worked up, for example, as described herein.
In apparatus terms, stirred tanks, falling-film evaporators, thin-film evaporators, forced-flash circulation evaporators and other evaporator types can be utilized in natural or forced circulation mode.
All references cited in this specification are herewith incorporated by reference with respect to their entire disclosure content and the disclosure content specifically mentioned in this specification.
The invention will be now described by the following examples which shall not be construed, whatsoever, as a limitation of its scope.
EXAMPLES
Example 1
Transformation of DD1







TABLE 1







Nomenclature of the DD1 wildtype and mutants referred to in


the Examples.








Strain
Description





LU13843
Wildtype DD1 (deposit DSM18541)


LU15050
DD1 delta ldh


LU15224
DD1 delta ldh pflD


LU15224 pJFF224 (icl ms Y. m.)
DD1 delta ldh pflD pJFF224



(icl ms Y. m.)


LU15224 pJFF224
DD1 delta ldh pflD pJFF224


LU13843 pJFF224
DD1 pJFF224


LU13843 pJFF224 (icl ms S. t.)
DD1 pJFF224 (icl ms S. t.)


LU 15050 pJFF224
DD1 delta ldh pJFF224


LU15050 pJFF224 (icl ms S. t.)
DD1 delta ldh pJFF224



(icl ms S. t.)


LU 15050 pJFF224 (icl ms Y. m.)
DD1 delta ldh pJFF224



(icl ms Y. m.)


LU 13843 pJFF224 (PpckA fdh
DD1 pJFF224


C. b.)
(PpckA fdh C. b.)


LU 15050 pJFF224 (PpckA fdh
DD1 delta ldh pJFF224


C. b.)
(PpckA fdh C. b.)


LU 13843 pJFF224 (PpckA fdh
DD1 pJFF224 (PpckA fdh C. b.,


C. b., PEFTU icl ms Y. m.)
PEFTU icl ms Y. m.)


LU15050 delta adhE.
DD1 delta ldh delta adhE


LU15050 delta adhE. pJFF224
DD1 delta ldh delta adhE pJFF224


(PpckA fdh C. b.)
(PpckA fdh C. b.)


LU 13843 pJFF224 (fdh W. s.)
DD1 pJFF224 (fdh W. s.)


LU 15050 pJFF224 (fdh W. s.)
DD1 delta ldh pJFF224 (fdh W. s.)


LU 15050 delta adhE pJFF224
DD1 delta ldh delta adhE pJFF224


(fdh W. s.)
(fdh W. s.)









Pasteurella strain LU13843 was transformed with DNA by electroporation using the following protocol:
Pre-Culture:
LU 13843 was inoculated from a freshly grown BHI-Agar plate into 40 ml BHI (brain heart infusion, Difco) in 100 ml shake flask. Incubation was performed over night at 30° C.; 200 rpm.
Main-Culture:


    50 ml BHI in 100 ml shake flask
    Inoculated to a final OD(610) of 0.4
    Incubation: approximately 1.5 h at 30° C., 200 rpm
    The cells were harvested at an OD of approximately 1.3
    Pellet washed once with 10% cold glycerol at 4° C.
    Resuspended in 1.7 ml 10% glycerol (4° C.)


100 μl of competent cells were mixed with 5-10 μg DNA (10-20 μl) and kept on ice for 2 min in an electroporation cuvette with a width of 0.2 cm.

    Electroporation conditions: 800 Ω; 25 μF; 2 kV (Gene Pulser, Bio-Rad)
    Addition of 1 ml of BHI immediately after electroporation
    Incubation for 2 h at 30° C.


Cells were plated on BHI with 5 mg/L chloramphenicol and incubated for 2-5 d at 30° C. until the colonies of the transformants were visible. Clones were isolated and restreaked onto BHI with 5 mg/L chloramphenicol until purity of clones was obtained.
Example 2
Generation of Deletion Constructs
Deletion plasmids were constructed based on the vector pSacB (SEQ ID NO 9). FIG. 1 shows a schematic map of plasmid pSacB. 5′- and 3′-flanking regions of the chromosomal fragment which should be deleted were amplified by PCR from chromosomal DNA of LU 13843 and introduced into the vector using standard techniques. Normally, at least 80% of the ORF were targeted for a deletion. In such a way, the deletion plasmids for lactate dehydrogenase ldhA, pSacB (delta ldhA), and for the pyruvate formate lyase pflD, pSacB (delta pflD) were constructed. FIGS. 2 and 3 show schematic maps of plasmid pSacB (delta ldhA) and pSacB (delta pflD).
Example 3
Generation of Improved Succinate Producing Strains
LU 13843 was transformed as described above with the pSacB (delta ldh) and “Campbelled in” to yield a “Campbell in” strain. Transformation and integration into the genome of LU 13843 was confirmed by PCR yielding bands for the integrational event of the plasmid into the genome of LU 13843. The “Campbell in” strain was then “Campbelled out” using agar plates containing sucrose as a counter selection medium, selecting for the loss (of function) of the sacB gene. Therefore, the “Campbell in” strains were incubated in 25-35 ml of non selective medium (BHI containing no antibiotic) at 37° C., 220 rpm over night. The overnight culture was then streaked onto freshly prepared BHI containing sucrose plates (10%, no antibiotics) and incubated overnight at 37° C. (“first sucrose transfer”). Single colony obtained from first transfer were again streaked onto freshly prepared BHI containing sucrose plates (10%) and incubated overnight at 37° C. (“second sucrose transfer”). This procedure was repeated until a minimal completion of five transfers (“third, forth, fifth sucrose transfer”) in sucrose. The term “first to fifth sucrose transfer” refers to the transfer of a strain after chromosomal integration of a vector containing a sacB levansucrase gene onto sucrose and growth medium containing agar plates for the purpose of selecting for strains with the loss of the sacB gene and the surrounding plasmid sequences. Single colony from the fifth transfer plates were inoculated onto 25-35 ml of non selective medium (BHI containing no antibiotic) and incubated at 37° C., 220 rpm over night. The overnight culture was serially diluted and plated onto BHI plates to obtain isolated single colonies. The “Campbelled out” strains containing the deletion of the ldhA gene were confirmed by chloramphenicol sensitivity. The deletion mutants among these strains were identified and confirmed by PCR analysis. This led to the ldhA deletion mutant LU15050.
LU15050 was transformed with pSacB (delta pflD) as described above and “Campbelled in” to yield a “Campbell in” strain. Transformation and integration was confirmed by PCR. The “Campbell in” strain was then “Campbelled out” as described previously. The deletion mutants among these strains were identified and confirmed by PCR analysis. This led to the ldhA pflD double deletion mutant LU15224.
LU15224 was transformed with pJFF224 (icl ms Y.m.) expressing the gyloxylate shunt operon from Yersinia molaretii and pJFF224 as a vector control. Resulting transformants were used for further experiments. LU15050 was transformed with pJFF224 (icl ms S.t.) expressing the gyloxylate shunt operon from Salmonella typhimurium. Resulting transformants were used for further experiments.
Example 4
Cell Bank Preparation
1. Media Preparation
Composition of the cultivation media is described in table 3.







TABLE 3







Composition of solid and liquid media for the preparation of


cell banks.











Concentration



Concentration
of stock


Compound
[g/L]
solution [g/L]












Glucose
varyinga
650


Bacto yeast extrakt (Becton Dickinson)
5
—


Bacto peptone (Becton Dickinson)
5
—


(NH4)2SO4
1
500


CaCl2*2H2O
0.2
20


MgCl2*6H2O
0.2
20


NaCl
1
100


K2HPO4
3
500


MgCO3
varyingb
—


Bacto-Agar (for solid media only)
12






aGlucose concentrations were 15 g/L (in plates) and 20 or 50 g/L (in liquid media).


bMgCO3 (Riedel-de Haen, product number: 13117 by Sigma-Aldrich Laborchemikalien GmbH) concentrations were 5 g/L (in plates) and 0 or 30 g/L (in liquid media).






5 g yeast extract, 5 g peptone, MgCO3 and (for solid media) 12 g Bacto-Agar were mixed in 900 mL distilled water and autoclaved (20 min). After cooling down to about 65° C. the missing components were added as sterile stock solutions. Glucose, ammonium sulfate and K2HPO4 were all separately autoclaved. Ca-, Mg- and Na-chlorides were autoclaved together.
2. MCB Preparation
Two agar plates were freshly inoculated with the desired strain and incubated at 37° C. in an anaerobic jar (Anaerocult A, Merck) over night. The biomass was taken off the plates and resuspended in the MgCO3-free liquid medium with 20 g/L glucose to adjust OD600≈1.0. Inoculation was performed with 0.5 mL of this cell suspension. Cultivations were performed in 100 mL-serum bottles with gas tight butyl rubber stoppers (Ochs GmbH, Bovenden/Lenglern, Germany) containing 50 mL of the liquid medium with 20 g/L glucose and 30 g/L MgCO3 and a CO2-atmosphere with 0.8 bar overpressure. The serum bottles (in total 10) were incubated at 37° C., a rotary speed of 160 rpm and a shaking diameter of 2.5 cm.
To monitor glucose consumption the cultivation of one bottle was stopped and sampling and HPLC analysis were performed after 0, 3, 4, 5, 7, 8 and 8.5 h. After 8.5 h (the glucose concentration was 3.4 g/L) the cultivation was stopped. Aliquots of 0.5 mL cell suspension and 0.5 mL sterile glycerol were filled in cryovials, mixed and stored for 13 h at −20 and afterwards at −80° C. as MCB. The MCB was tested for purity by streaking a loop of the last cryovial on agar plates for contamination control and checking in liquid culture (media as described table 8) the product spectrum and for contamination (by microscopy).
Consumption of glucose and formation of SA and by-products were quantified via HPLC analyses of the undiluted cell free supernatants of the cultivation broth using RI-detection. Broth samples were taken with a sterile syringe through the butyl rubber plug, cell separation was performed by filtration (0.22 μm). A 300×7.8 mm I. D. Column Aminex HPX-87 H (Biorad) and 5 mm H2SO4 were used as stationary and mobile phase, respectively. The column temperature was 30° C., the flow rate was 0.5 mL min−1.
3. WCB Preparation
One vial of the MCB was used to inoculate a 100 mL-serum bottle with gas tight butyl rubber stopper (see above) containing 50 mL of the liquid medium with 50 g/L glucose. Incubation was performed for 10 h at 37° C. in a shaking incubator (rotary speed: 180 rpm, shaking diameter: 2.5 cm). At the end of the cultivation the glucose concentration was 20 g/L and the pH around 6.5. Aliquots of 0.5 mL cell suspension and 0.5 mL sterile glycerol were filled in cryovials, mixed and stored at −80° C. as WCB. Purity checks were the same as for the MCB. HPLC conditions were the same as those described above.
Example 5
Fermentation of Mutant Strains LU15224 pJFF224 (icl ms Y.m.) and LU15224 pJFF224
The mutant strain of DD1 LU15224 pJFF224 (icl ms Y.m.), which is a double knockout for Δldh and ΔpflD and over-expresses the plasmid pJFF224 (icl ms Y.m.), containing the glyoxylate shunt operon genes, was analyzed by anaerobic fermentation experiments in comparison to the plasmid control strain LU15224 pJFF224, containing the same genetic background as LU15224 pJFF224 (icl ms Y.m.) but only an empty expression plasmid pJFF224. Mutant strains were generated as described in example 1 to 3.
1. Medium Preparation
The composition of the cultivation medium is described in the following table 4.







TABLE 4







Medium composition for batch cultivations of DD1-mutants with over-


expression plasmids.











Concentration



Concentration
of stock


Compound
[g/L]
solution [g/L]












Glucose-Monohydrat
50
722


Bacto yeast extrakt (Becton Dickinson)
5
100


(NH4)2SO4
1
500


CaCl2*2H2O
0.2
20


MgCl2*6H2O
0.2
20


NaCl
1
100


K2HPO4
3
500


Chloramphenicol
0.005
5


MgCO3a
50
—





aMgCO3 was used as buffering agent in serum bottle experiments only.






MgCO3 was supplemented with ddH2O and autoclaved in serum bottles. Yeast extract, glucose, ammonium sulfate and potassium phosphate were all separately autoclaved. Ca-, Mg- and Na-chlorides were autoclaved together. After cooling down the ddH2O autoclaved fermenters and serum bottles the missing components were added as sterile stock solutions. For the seed cultures the same medium was used.
2. Cultivations and Analytics
The seed culture was grown anaerobically in a 100 mL-serum bottle with gas tight butyl rubber stoppers containing 50 mL medium at 37° C. in a shaking incubator (rotary speed: 170 rpm, shaking diameter: 2.5 cm). Inoculation of the seed culture was performed with 1 mL of the WCB (as described in example 4) under sterile conditions. Immediately after the inoculation the aerobic gas atmosphere was substituted by pure CO2 with an overpressure of about 0.8 bar. After 11 h and 17 h of incubation for LU15224 pJFF224 (icl ms Y.m.) and LU15224 pJFF224, respectively, the fermenter was inoculated with 20 mL to start the cultivation in the 500 mL fermenter (Sixfors, Infors Switzerland) containing 380 mL of cultivation medium which had been gassed over night with CO2 to ensure oxygen-free conditions. The cultivation temperature was maintained at 37° C. and the pH at 6.5 with 25% NH4OH. The CO2-gas stream was adjusted to 0.4 l*min−1. The stirrer speed was adjusted to 500 rpm.

    Consumption of glucose and formation of SA and by-products were quantified via HPLC as described in example 4.

3. Results



The results are summarized in table 5 showing values after glucose depletion.
Heterologous over-expression of the glyoxylate shunt genes lead to a significant increase of the succinate yield compared to the control strain LU15224 pJFF224. It is also detected that acetate is produced with a lower titer in LU15224 pJFF224 (icl ms Y.m.) compared to the control, hinting to an improved flux from pyruvate via acetyl-CoA, isocitrate, malate, fumarate to succinate introduced by the heterologous glyoxylate shunt operon.







TABLE 5







Production of succinate by the mutant LU15224 pJFF224 (icl ms Y. m.)


and the plasmid control LU15224 pJFF224 after glucose depletion


in a SixFors fermentation broth.










LU15224




pJFF224
LU15224


Parameter
(icl ms Y.m.)
pJFF224












Final volume of fermentation broth [ml]
432
435


consumed glucose [g]
22.98
23.17


produced succinate [g]
20
19.16


succinate yield [g/g]
0.87
0.83


produced lactate [g]
0
0


produced pyruvate [g]
0
0


produced acetate [g]
3.12
3.26


produced formate [g]
0
0









Example 6
Cloning and Expression of the Glyoxylate Shunt Operon From Salmonella typhimurium LT2
In another embodiment the glyoxylate shunt operon from Salmonella typhimurium (S. typhimurium) LT2 ATCC 15277 is amplified by PCR cloned from chromosomal DNA of from S. typhimurium LT2 ATCC 15277 using the PfuTurboTM DNA polymerase (Roche) and is inserted into the vector pJFF224. The expression of the genes in this construct is driven by the native promoter of the operon as well as by a T4 promoter located on the vector pJFF224. FIG. 5 shows a schematic map of the resulting plasmid termed pJFF224 (icl ms S.t). The strain DD1 (termed LU13843) was transformed with the plasmid pJFF224 (icl ms S.t.) as described above. A serum bottle experiment was performed and analyzed as described above. It can be found that upon overexpression of the glyoxylate shunt operon from S. typhimurium the succinic acid production was increased over the control. The yield of glucose converted to succinic was increased from 0.42 g SA/g glucose to 0.51 g SA/g glucose.







TABLE 6







Results after expression of the glyoxylate shunt operon from


S. typhimurium LT2 in LU13843.

















yield







succinic







acid g



succinic
lactic
formic
acetic
SA/g


Strain
acid
acid
acid
acid
substrate















LU13843 pJFF224
15.1
10.1
6.8
7.5
0.42


LU13843 pJFF224 (icl ms
18.1
6.5
6
8.1
0.51


S. t.)









Example 7
Strain Expression of the Glyoxylate Shunt Operon From S. Typhimurium LT2 in the Strain DD1 Delta LDH (LU15050)
The strain DD1 delta ldh (LU15050) was transformed with the plasmid pJFF224 (icl ms S.t.) as described above. A serum bottle experiment was performed and analyzed as described above. Cells were grown overnight on BHI agar plates with chloramphenicol, added to 4 μg/ml. Cells were scraped off the agar plate and inoculated with an OD 600 nm of 0.1. It can be found that upon overexpression of the glyoxylate shunt operon from S. typhimurium in LU15050 the succinic acid production was increased over the control. The yield of glucose converted to succinic was increased from 0.62 g SA/g glucose to 0.72 g SA/g glucose.







TABLE 7







Results after expression of the glyoxylate shunt operon from


S. typhimurium LT2 in LU15050.

















yield succinic



Succinic
Formic
Acetic

acid, SA/g



acid
acid
acid
ethanol
substrate





LU15050
31.10
6.40
7.11
0.98
0.62


LU15050
35.90
5.60
7.50
1.15
0.72


pJFF224 (icl







ms S. t.)









Example 8
Cloning and Expression of the Glyoxylate Shunt Operon From Yersinia Molaretii ATCC 43969
In another embodiment the glyoxylate shunt operon from Yersinia molaretii (Y. molaretii) ATCC 43969 is amplified by PCR cloned from chromosomal DNA of Y. molaretii ATCC 43969 using the PfuTurboTM DNA polymerase (Roche) and is inserted into the vector pJFF224. The expression of the genes in this construct is driven by the native promoter of the operon as well as by a T4 promoter located on the vector pJFF224. FIG. 6 shows a schematic map of the resulting plasmid termed pJFF224 (icl ms Y.m.). The strain DD1 delta ldh (LU15050) was transformed with the plasmid pJFF224 (icl ms Y.m.) as described above. A serum bottle experiment using 48 g/l glucose was performed and analyzed as described above. Cells were grown overnight on BHI agar plates with chloramphenicol, added to 4 μg/ml. Cells were scraped off the agar plate and inoculated with an OD 600 nm of 0.1. It can be found that upon overexpression of the glyoxylate operon from Y. molaretii in LU15505 the succinic acid production was significantly increased over the control. The yield of glucose converted to succinic was increased from 0.60 g SA/g glucose for LU15050 to 0.69 g SA/g glucose for LU15050 pJFF224 (icl ms Y.m.).







TABLE 8







Results from expression of the glyoxylate operon from


Y. molaretii ATCC 43969 in LU 15050.

















yield succinic




succinic
formic
acetic
acid, g SA/g




acid
acid
acid
substrate
















LU 15050
28.7
5.2
7.3
0.60



LU 15050
33.0
5.5
6.7
0.69



pJFF224







(icl ms Y. m.)









Example 9
Cloning and Expression of the Formate Dehydrogenase Gene From Candida Boidinii 
The formate dehydrogenase gene (fdh) from Candida boidinii (C. boidinii) ATCC 18810 was amplified by PCR from chromosomal DNA from C. boidinii ATCC 18810 using the PfuTurboTM DNA polymerase (Roche). The gene was fused to the PpckA promoter from the strain DD1 and was inserted into the vector pJFF224. The expression of the genes in this construct is driven by the PpckA promoter as well as by a T4 promoter located on the vector pJFF224. FIG. 7 shows a schematic map of the resulting plasmid termed pJFF224 (PpckA fdh C.b.). The strains DD1 (LU13843) and DD1 delta ldh (LU 15050) were transformed with the plasmid pJFF224 pJFF224 (PpckA fdh C.b.) as described above.
The resulting strains were selected on agar containing 4 μg/ml chloramphenicol. The succinic acid productivity was analyzed as described above. It was found that upon overexpression of fdh the amount of succinic acid was increased from 27.5 to 30.3 g/l, while the amount of formate as a side product was reduced to either lower than 0.1 g/l or 0.16 g/l in LU 15050. The yield of succinic acid was increased from 0.57 to 0.63 in LU 13843 or from 0.67 to 0.68 for LU 15050.







TABLE 9







Results after expression of fdh from C. boidinii in


LU 13843 and LU 15050.

















yield succinic



succinic
lactic
formic
acetic
acid, g SA/g


strain
acid
acid
acid
acid
substrate















LU 13843 pJFF224
27.5
7.80
4.74
7.32
0.57


LU 13843 pJFF224
30.3
5.82
—
6.39
0.63


(PpckA fdh C. b.)







LU 15050 pJFF224
32.40
0.26
4.51
7.19
0.67


LU 15050 pJFF224
32.61
0.25
0.16
6.59
0.68


(PpckA fdh C. b.)









Example 10
Simultaneous Over Expression of the Formate Dehydrogenase Gene From C. Boidinii and the Glyoxylate Shunt Operon From Y. Molaretii 
The formate dehydrogenase gene from C. boidinii ATCC 18810 under the control of the PpckA promoter and the glyoxylate shunt operon from Y. molaretii under the control of the EFTU promoter from DD1 were inserted into the vector pJFF224 to yield pJFF224 (PpckA fdh C.b., PEFTU icl ms Y.m.). The expression of the genes in this construct is driven by the PpckA promoter, the PEFTU promoter as well as by a T4 promoter located on the vector pJFF224. FIG. 7 shows a schematic map of the resulting plasmid termed pJFF224 (PpckA fdh C.b., PEFTU icl ms Y.m.). The strains LU13843 and LU 15050 were transformed with the plasmid pJFF224 and pJFF224 (PpckA fdh C.b., PEFTU icl ms Y.m.) as described above.
The resulting strains were selected on agar containing 4 μg/ml chloramphenicol. The succinic acid productivity was analyzed as described above except that xylose was added as the carbon source instead of glucose. It was found that upon overexpression of fdh the amount of succinic acid was increased from 35.6 g/l to 36.4 g/l, while the amount of lactic acid as a side product was reduced from 2.1 g/l to 1.7 g/l in LU 13843.
The yield of succinic acid was increased from 0.75 in LU 13843 to 0.76 in LU 13843 pJFF224 (PpckA fdh C.b., PEFTU icl ms Y.m.).







TABLE 10







Results after expression of fdh from C. boidinii and the glyoxylate shunt


operon from Y. molaretii in LU 13843 after growth in xylose.

















yield succinic



succinic
lactic
formic
acetic
acid, g SA/g


strain
acid
acid
acid
acid
substrate





LU 13843 pJFF224
35.6
2.1
3.4
10.2
0.75


LU 13843 pJFF224
36.4
1.7
3.9
10.4
0.76


(PpckA fdh C. b.,







PEFTU icl ms Y. m.)









Example 11
Deletion of adhE Gene From DD1 and DD1 Mutant Strains
The adhE gene was identified on the chromosome of the DD1 genome by sequence analysis using the know adhE gene from E. coli and analyzing for homologues in DD1. A gene deletion fragment for the adhE gene is obtained through PCR amplification of 1500 bp covering the upstream region and the respective downstream region of the adhE gene from DD1 with forward and reverse primers carrying the restriction sequences for XhoI and XbaI. The fragment is purified and digested with XhoI and XbaI, as well as the vector which is additionally dephosphorylated. The ligated vector carrying the fragment of the DD1 genome with the adhE up- and downstream regions is propagated in E. coli and is used for the transformation of DD1. The strain LU15050 DD1 delta ldh is transformed as described above with the pSacB (delta adhE) and “Campbelled in” to yield a “Campbell in” strain. FIG. 8 shows a schematic map of the pSacB (delta adhE). Transformation and integration into the genome of LU15050 is confirmed by PCR yielding bands for the integrational event of the plasmid into the genome of LU15050. The “Campbell in” strain is then “Campbelled out” using agar plates containing sucrose as a counter selection medium, selecting for the loss (of function) of the sacB gene. Therefore, the “Campbell in” strains are incubated in 25-35 mL of non selective medium (BHI containing no antibiotic) at 37° C., 220 rpm over night. The overnight culture is then streaked onto freshly prepared BHI containing sucrose plates (10%, no antibiotics) and incubated overnight at 37° C. (“first sucrose transfer”). Single colony obtained from first transfer are again streaked onto freshly prepared BHI containing sucrose plates (10%) and are incubated overnight at 37° C. (“second sucrose transfer”). This procedure is repeated until a minimal completion of five transfers (“third, forth, fifth sucrose transfer”) in sucrose. The term “first to fifth sucrose transfer” refers to the transfer of a strain after chromosomal integration of a vector containing a sacB levansucrase gene onto sucrose and growth medium containing agar plates for the purpose of selecting for strains with the loss of the sacB gene and the surrounding plasmid sequences. Single colony from the fifth transfer plates are inoculated onto 25-35 ml of non selective medium (BHI containing no antibiotic) and are incubated at 37° C., 220 rpm over night. The overnight culture was serially diluted and plated onto BHI plates to obtain isolated single colonies. The “Campbelled out” strains containing the deletion of the adhE gene are confirmed by chloramphenicol sensitivity. The deletion mutants among these strains are identified and confirmed by PCR analysis. This led to the adhe deletion mutant LU15050 delta adhE. LU15050 delta adhE is transformed with pJFF224 (PpckA fdh C.b.) expressing the formate dehydrogenase from Candida boidinii pJFF224 as a vector control. Resulting transformants are used for further experiments. After growth in serum bottles as described above the strains are found to contain significantly increased amounts of succinic acid if compared to the plasmid control not containing a fdh gene. Also the amount of side products such as ethanol is significantly reduced in the DD1 delta adhE strain over expressing a formate dehydrogenase.
Example 12
Cloning and Expression of the Wolinella succinogenes fdh in DD1 and DD1 Mutant Strains
In another embodiment of formate dehydrogenase operon encoding the genes: fdhA, fdhB, fdhC and fdhD from Wolinella succinogenes (W. succinogenes) DSMZ 1714 is amplified by PCR cloned from chromosomal DNA of W. succinogenes DSMZ 1714 using the PfuTurboTM DNA polymerase (Roche) and is inserted into the vector pJFF224. The expression of the genes in this construct is driven by a promoter fragment amplified from the 5′-region of the phosphoenolypyruvate carboxykinase (pck) gene from DD1 and by a T4 promoter located on the vector. FIG. 9 shows a schematic map of the resulting plasmid termed pJFF224 (fdh W.s.).

    The resulting plasmid is transformed into the strains LU 13843 and LU 15050 and DD1 delta (ldh adhE). The resulting strains selected for plasmid content by the addition of 4 μg/ml chloramphenicol are analyzed for succinic acid production in serum bottle experiments as described above. It is found that the expression of the formate dehydrogenase operon encoding the genes: fdhA, fdhB fdhC and fdhD from Wolinella succinogenes DSMZ 1714 increases the succinic acid yield as well as decreasing amount of the side product formate.


REFERENCES


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## Claims

1. A bacterial cell of the genus Pasteurella comprising a heterologous polypeptide having isocitrate lyase activity and a heterologous polypeptide having malate synthase activity, wherein the bacterial cell has increased succinic acid production relative to a corresponding control bacterial cell,
wherein the heterologous polypeptide having isocitrate lyase activity is encoded by a nucleic acid selected from the group consisting of:
a. a nucleic acid having the nucleotide sequence of SEQ ID NO: 1;
b. a nucleic acid encoding the amino acid sequence of SEQ ID NO: 2;
c. a nucleic acid which is at least 98% identical to the nucleic acid of a) or b); and
d. a nucleic acid encoding a polypeptide comprising an amino acid sequence which is at least 98% identical to the amino acid sequence encoded by the nucleic acid of a) or b), and
wherein the heterologous polypeptide having malate synthase activity is encoded by a nucleic acid selected from the group consisting of:
a. a nucleic acid having the nucleotide sequence of SEQ ID NO: 3;
b. a nucleic acid encoding the amino acid sequence of SEQ ID NO: 4;
c. a nucleic acid which is at least 98% identical to the nucleic acid of a) or b); and
d. a nucleic acid encoding a polypeptide comprising an amino acid sequence which is at least 98% identical to the amino acid sequence encoded by the nucleic acid of a) or b).

2. The bacterial cell of claim 1, wherein the bacterial cell further comprises a heterologous polypeptide having formate dehydrogenase activity.

3. The bacterial cell of claim 2, wherein the heterologous polypeptide having formate dehydrogenase activity is encoded by a nucleic acid selected from the group consisting of:
a. a nucleic acid having the nucleotide sequence of SEQ ID NO: 5 or 18;
b. a nucleic acid encoding the amino acid sequence of SEQ ID NO: 6;
c. a nucleic acid which is at least 90% identical to the nucleic acid of a) or b); and
d. a nucleic acid encoding a polypeptide comprising an amino acid sequence which is at least 90% identical to the amino acid sequence encoded by the nucleic acid of a) or b).

4. The bacterial cell of claim 1, wherein the bacterial cell has reduced lactate dehydrogenase activity relative to a corresponding wildtype bacterial cell.

5. A method for manufacturing succinic acid comprising
i) cultivating the bacterial cell of claim 1 under suitable culture conditions; and
ii) obtaining succinic acid from the cultured bacterial cells.

6. A bacterial cell of strain DD1 of the genus Pasteurella as deposited under DSM18541 with the DSMZ Germany comprising a heterologous polypeptide having isocitrate lyase activity and a heterologous polypeptide having malate synthase activity, wherein the bacterial cell has increased succinic acid production relative to a corresponding control bacterial cell,
wherein the heterologous polypeptide having isocitrate lyase activity is encoded by a nucleic acid selected from the group consisting of:
a. a nucleic acid having the nucleotide sequence of SEQ ID NO: 1;
b. a nucleic acid encoding the amino acid sequence of SEQ ID NO: 2;
c. a nucleic acid which is at least 90% identical to the nucleic acid of a) or b); and
d. a nucleic acid encoding a polypeptide comprising an amino acid sequence which is at least 90% identical to the amino acid sequence encoded by the nucleic acid of a) or b), and
wherein the heterologous polypeptide having malate synthase activity is encoded by a nucleic acid selected from the group consisting of:
a. a nucleic acid having the nucleotide sequence of SEQ ID NO: 3;
b. a nucleic acid encoding the amino acid sequence of SEQ ID NO: 4;
c. a nucleic acid which is at least 90% identical to the nucleic acid of a) or b); and
d. a nucleic acid encoding a polypeptide comprising an amino acid sequence which is at least 90% identical to the amino acid sequence encoded by the nucleic acid of a) or b).

7. The bacterial cell of claim 6, wherein the heterologous polypeptide having isocitrate lyase activity is encoded by a nucleic acid selected from the group consisting of:
a. a nucleic acid having the nucleotide sequence of SEQ ID NO: 1;
b. a nucleic acid encoding the amino acid sequence of SEQ ID NO: 2;
c. a nucleic acid which is at least 95% identical to the nucleic acid of a) or b); and
d. a nucleic acid encoding a polypeptide comprising an amino acid sequence which is at least 95% identical to the amino acid sequence encoded by the nucleic acid of a) or b), and
wherein the heterologous polypeptide having malate synthase activity is encoded by a nucleic acid selected from the group consisting of:

a. a nucleic acid having the nucleotide sequence of SEQ ID NO: 3;
b. a nucleic acid encoding the amino acid sequence of SEQ ID NO: 4;
c. a nucleic acid which is at least 95% identical to the nucleic acid of a) or b); and
d. a nucleic acid encoding a polypeptide comprising an amino acid sequence which is at least 95% identical to the amino acid sequence encoded by the nucleic acid of a) or b).

8. The bacterial cell of claim 6, wherein the bacterial cell further comprises a heterologous polypeptide having formate dehydrogenase activity.

9. The bacterial cell of claim 8, wherein the heterologous polypeptide having formate dehydrogenase activity is encoded by a nucleic acid selected from the group consisting of:
a. a nucleic acid having the nucleotide sequence of SEQ ID NO: 5 or 18;
b. a nucleic acid encoding the amino acid sequence of SEQ ID NO: 6;
c. a nucleic acid which is at least 90% identical to the nucleic acid of a) or b); and
d. a nucleic acid encoding a polypeptide comprising an amino acid sequence which is at least 90% identical to the amino acid sequence encoded by the nucleic acid of a) or b).

10. The bacterial cell of claim 6, wherein the bacterial cell has reduced lactate dehydrogenase activity relative to a corresponding wildtype bacterial cell.

11. A method for manufacturing succinic acid comprising
i) cultivating the bacterial cell of claim 6 under suitable culture conditions; and
ii) obtaining succinic acid from the cultured bacterial cells.

12. An isolated polynucleotide comprising a first nucleic acid encoding a heterologous polypeptide having isocitrate lyase activity operably linked to heterologous regulatory sequences, wherein the polypeptide is encoded by:
a. a nucleic acid having the nucleotide sequence of SEQ ID NO: 1;
b. a nucleic acid encoding the amino acid sequence of SEQ ID NO: 2;
c. a nucleic acid which is at least 98% identical to the nucleic acid of a) or b); or
d. a nucleic acid encoding a polypeptide comprising an amino acid sequence which is at least 98% identical to the amino acid sequence encoded by the nucleic acid of a) or b).

13. The isolated polynucleotide of claim 12, further comprising a second nucleic acid encoding a polypeptide having malate synthase activity operably linked to heterologuous regulatory sequences, wherein the polypeptide having malate synthase activity is encoded by:
a. a nucleic acid having the nucleotide sequence of SEQ ID NO: 3;
b. a nucleic acid encoding the amino acid sequence of SEQ ID NO: 4;
c. a nucleic acid which is at least 98% identical to the nucleic acid of a) or b); or
d. a nucleic acid encoding a polypeptide comprising an amino acid sequence which is at least 98% identical to the amino acid sequence encoded by the nucleic acid of a) or b).

14. The isolated polynucleotide of claim 13, further comprising a third nucleic acid encoding a polypeptide having formate dehydrogenase activity, wherein the polypeptide having formate dehydrogenase activity is encoded by:
a. a nucleic acid having the nucleotide sequence of SEQ ID NO: 5 or 18;
b. a nucleic acid encoding the amino acid sequence of SEQ ID NO: 6;
c. a nucleic acid which is at least 98% identical to the nucleic acid of a) or b); or
d. a nucleic acid encoding a polypeptide comprising an amino acid sequence which is at least 98% identical to the amino acid sequence encoded by the nucleic acid of a) or b).