Dataset Information

Re-citrate synthase from Clostridium kluyveri is phylogenetically related to homocitrate synthase and isopropylmalate synthase rather than to Si-citrate synthase.

ABSTRACT: The synthesis of citrate from acetyl-coenzyme A and oxaloacetate is catalyzed in most organisms by a Si-citrate synthase, which is Si-face stereospecific with respect to C-2 of oxaloacetate. However, in Clostridium kluyveri and some other strictly anaerobic bacteria, the reaction is catalyzed by a Re-citrate synthase, whose primary structure has remained elusive. We report here that Re-citrate synthase from C. kluyveri is the product of a gene predicted to encode isopropylmalate synthase. C. kluyveri is also shown to contain a gene for Si-citrate synthase, which explains why cell extracts of the organism always exhibit some Si-citrate synthase activity.

SUBMITTER: Li F

PROVIDER: S-EPMC1913417 | biostudies-literature | 2007 Jun

REPOSITORIES: biostudies-literature

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Re-citrate synthase from Clostridium kluyveri is phylogenetically related to homocitrate synthase and isopropylmalate synthase rather than to Si-citrate synthase.

Li Fuli F Hagemeier Christoph H CH Seedorf Henning H Gottschalk Gerhard G Thauer Rudolf K RK

Journal of bacteriology 20070330 11

The synthesis of citrate from acetyl-coenzyme A and oxaloacetate is catalyzed in most organisms by a Si-citrate synthase, which is Si-face stereospecific with respect to C-2 of oxaloacetate. However, in Clostridium kluyveri and some other strictly anaerobic bacteria, the reaction is catalyzed by a Re-citrate synthase, whose primary structure has remained elusive. We report here that Re-citrate synthase from C. kluyveri is the product of a gene predicted to encode isopropylmalate synthase. C. klu ...[more]

PMID: 17400742

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Project description:BackgroundThe product of current syngas fermentation systems is an ethanol/acetic acid mixture and the goal is to maximize ethanol recovery. However, ethanol currently has a relatively low market value and its separation from the fermentation broth is energy intensive. We can circumvent these disadvantages of ethanol production by converting the dilute ethanol/acetic acid mixture into products with longer carbon backbones, which are of higher value and are more easily extracted than ethanol. Chain elongation, which is the bioprocess in which ethanol is used to elongate short-chain carboxylic acids to medium-chain carboxylic acids (MCCAs), has been studied with pure cultures and open cultures of microbial consortia (microbiomes) with several different substrates. While upgrading syngas fermentation effluent has been studied with open cultures, to our knowledge, no study exists that has performed this with pure cultures.ResultsHere, pure cultures of Clostridium kluyveri were used in continuous bioreactors to convert ethanol/acetic acid mixtures into MCCAs. Besides changing the operating conditions in regards to substrate loading rates and composition, the effect of in-line product extraction, pH, and the use of real syngas fermentation effluent on production rates were tested. Increasing the organic loading rates resulted in proportionally higher production rates of n-caproic acid, which were up to 40 mM day-1 (4.64 g L-1 day-1) at carbon conversion efficiencies of 90% or higher. The production rates were similar for bioreactors with and without in-line product extraction. Furthermore, a lower ethanol/acetic acid ratio (3:1 instead of 10:1) enabled faster and more efficient n-caproic acid production. In addition, n-caprylic acid production was observed for the first time with C. kluyveri (up to 2.19 ± 0.34 mM in batch). Finally, the use of real effluent from syngas fermentation, without added yeast extract, but with added defined growth factors, did maintain similar production rates. Throughout the operating period, we observed that the metabolism of C. kluyveri was inhibited at a mildly acidic pH value of 5.5 compared to a pH value of 7.0, while reactor microbiomes perform successfully at mildly acidic conditions.ConclusionsClostridium kluyveri can be used as a biocatalyst to upgrade syngas fermentation effluent into MCCAs at pH values above 5.5.

Dataset Information

Re-citrate synthase from Clostridium kluyveri is phylogenetically related to homocitrate synthase and isopropylmalate synthase rather than to Si-citrate synthase.

Publications

Re-citrate synthase from Clostridium kluyveri is phylogenetically related to homocitrate synthase and isopropylmalate synthase rather than to Si-citrate synthase.

Similar Datasets

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