Fermentation of 2,3-butanediol by Pelobacter carbinolicus sp. nov. and Pelobacter propionicus sp. nov., and evidence for propionate formation from C2 compounds

From anaerobic enrichments with 2,3-butanediol as sole substrate pure cultures of new Gram-negative, strictly anaerobic, non-sporeforming bacteria were isolated. Similar isolates were obtained with acetoin as substrate. From marine muds in saltwater medium a short rod (strain Gra Bd 1) was isolated which fermented butanediol, acetoin and ethylene glycol to acetate and ethanol. The DNA base ratio of this strain was 52.3 mol% guanine plus cytosine.From freshwater sediments and sewage sludge, a different type of short rod (strain Ott Bd 1) was isolated in freshwater medium, which fermented butanediol, acetoin, ethanol, lactate and pyruvate stoichiometrically to acetate and propionate. Propanol and butanol were oxidized to the respective fatty acids with concomitant reduction of acetate and bicarbonate to propionate. The DNA base ratio of strain Ott Bd 1 was 57.4 mol% guanine plus cytosine. No other substrates were used by the isolates, and no other products could be detected. In cocultures with Acetobacterium woodii or Methanospirillum hungatei, strain Gra Bd 1 also grew on ethanol, propanol, and butanol by fermenting these alcohols to the respective fatty acids and molecular hydrogen. Cytochromes could not be detected in any of the new isolates. Since both types of bacteria can not be affiliated to any of the existing genera and species, the new species Pelobacter carbinolicus and Pelobacter propionicus are proposed. The mechanism of butanediol degradation and propionate formation from acetate as well as the ecological importance of both processes are discussed.