title: Energetics and kinetics of lactate fermentation to acetate and propionate via methylmalonyl-CoA or acrylyl-CoA.
abstract: Fermentation balances and growth yields were determined with various bacteria fermenting lactate to acetate plus propionate either via methylmalonyl-CoA or via acrylyl-CoA. All strains fermented lactate to acetate plus propionate at approximately a 1:2 ratio. Growth yields of Propionibacterium freudenreichii were more than twice as high as those of Clostridium homopropionicum or Veillonella parvula. Hydrogen was formed as a side product to a significant extent only by V. parvula and Pelobacter propionicus; the latter formed hydrogen preferentially when using ethanol as substrate. Acrylyl-CoA reductase of C. homopropionicum and Clostridium neopropionicum was found nearly exclusively in the cytoplasm thus confirming that this reduction step is unlikely to be involved in energy conservation. C. homopropionicum exhibited higher K(S) and higher micro(max) values, as well as higher specific substrate turnover rates than P. freudenreichii. The results allow us to conclude that C. homopropionicum using the acrylyl-CoA pathway with low growth yield obtains its specific competitive advantage compared to P. freudenreichii not through higher substrate affinity or metabolic shift toward enhanced acetate-plus-hydrogen formation but through faster specific substrate turnover.
authors.affiliation: Fakultät für Biologie, Universität Konstanz, D-78457, Konstanz, Germany.
authors.forename: Sabine
authors.initials: S
authors.lastname: Seeliger
authors.forename: Peter H
authors.initials: PH
authors.lastname: Janssen
authors.forename: Bernhard
authors.initials: B
authors.lastname: Schink
mesh_terms: D000085:Acetates / Q000378:metabolism*; D000214:Acyl Coenzyme A / Q000378:metabolism*; D001421:Bacteria, Anaerobic / Q000201:enzymology / Q000254:growth & development / Q000378:metabolism*; D004734:Energy Metabolism; D000431:Ethanol / Q000378:metabolism; D005285:Fermentation; D007700:Kinetics; D007773:Lactates / Q000378:metabolism*; D010088:Oxidoreductases / Q000378:metabolism; D011422:Propionates / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D000085:Acetates; D000214:Acyl Coenzyme A; D007773:Lactates; D011422:Propionates; C015357:methylmalonyl-coenzyme A; D000431:Ethanol; C047011:acryloyl-coenzyme A; D010088:Oxidoreductases