Anaerobic Conversion of Lactic Acid to Acetic Acid and 1,2-Propanediol by <i>Lactobacillus buchneri</i>

TLDR

Lactobacillus buchneri and related species can degrade lactic acid under anoxic conditions, a process whose role in cell viability remains unclear. The study proposes a novel anaerobic lactic acid degradation pathway based on stoichiometric analysis and high NAD‑linked 1,2‑propanediol‑dependent oxidoreductase activity. The pathway converts each mole of lactic acid into roughly 0.5 mol acetic acid, 0.5 mol 1,2‑propanediol, and trace ethanol, driven by the enzyme’s high activity. Anaerobic degradation occurs in L.

Abstract

ABSTRACT The degradation of lactic acid under anoxic conditions was studied in several strains of Lactobacillus buchneri and in close relatives such as Lactobacillus parabuchneri , Lactobacillus kefir , and Lactobacillus hilgardii . Of these lactobacilli, L. buchneri and L. parabuchneri were able to degrade lactic acid under anoxic conditions, without requiring an external electron acceptor. Each mole of lactic acid was converted into approximately 0.5 mol of 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-dependent oxidoreductase (530 to 790 nmol min −1 mg of protein −1 ), a novel pathway for anaerobic lactic acid degradation is proposed. The anaerobic degradation of lactic acid by L. buchneri does not support cell growth and is pH dependent. Acidic conditions are needed to induce the lactic-acid-degrading capacity of the cells and to maintain the lactic-acid-degrading activity. 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 certain, but some results indicate that it plays a role in maintaining cell viability.