Anaerobic conversion of lactic acid to acetic acid and 1,2-propanediol by Lactobacillus buchneri

The degradation of lactic acid under anoxic conditions was studied in sever al strains of Lactobacillus buchneri and in close relatives such as Lactoba cillus parabuchneri, Lactobacillus kefir, and Lactobacillus hilgardii. Of t hese lactobacilli, L. buchneri and L. parabuchneri were able to degrade lac tic acid under anoxic conditions, without requiring an external electron ac ceptor. Each mole of lactic acid was converted into approximately 0.5 mol o f acetic acid, 0.5 mol of 1,2-propanediol, and traces of ethanol. Based on stoichiometry studies and the high levels of NAD-linked 1,2-propanediol-dep endent oxidoreductase (530 to 790 nmol min(-1) mg of protein(-1)), a novel pathway for anaerobic lactic acid degradation is proposed. The anaerobic de gradation of lactic acid by L. buchneri does not support cell growth and is pH dependent. Acidic conditions are needed to induce the lactic-acid-degra ding capacity of the cells and to maintain the lactic-acid-degrading activi ty. At a pH above 5.8 hardly any lactic acid degradation was observed. The exact function of anaerobic lactic acid degradation by L. buchneri is not c ertain, but some results indicate that it plays a role in maintaining cell viability.