pH-mediated regulation of pyruvate catabolism in Lactobacillus plantarum chemostat cultures

While the ability of lactobacilli to catabolize pyruvate to a variety of industrially important catabolites is well known, the mechanisms which regulate pyruvate distribution among alternative catabolic pathways is unclear. This paper demonstrates that environmental acidity regulates the catabolic activities of Lactobacillus plantarum cells in chemostat cultures. L. plantarum cells grown in medium containing 100 mM exogenous pyruvate, diverted pyruvate away from lactate to acetoin. Pyruvate uptake and acetoin generation increased under acidic conditions; on a molar basis, pyruvate utilization increased twice as fast as acetoin production, reflecting the 2:1 stoichiometry of pyruvate incorporation into acetoin. Lactate production increased under alkaline conditions when glucose was fermented to provide endogenous pyruvate. Acetate was formed only at pH 7.5 and 8.0, although acetoin production decreased at elevated pH values. These data indicate that L. plantarum adjusts to changes in environmental pH by altering its distribution of pyruvate among various catabolites.