Interactions between Pyruvate and Lactate Metabolism in Propionibacterium freudenreichii subsp. shermanii : In Vivo 13 C Nuclear Magnetic Resonance Studies

Abstract

ABSTRACT In vivo 13 C nuclear magnetic resonance spectroscopy was used to elucidate the pathways and the regulation of pyruvate metabolism and pyruvate-lactate cometabolism noninvasively in living-cell suspensions of Propionibacterium freudenreichii subsp. shermanii . The most important result of this work concerns the modification of fluxes of pyruvate metabolism induced by the presence of lactate. Pyruvate was temporarily converted to lactate and alanine; the flux to acetate synthesis was maintained, but the flux to propionate synthesis was increased; and the reverse flux of the first part of the Wood-Werkman cycle, up to acetate synthesis, was decreased. Pyruvate was consumed at apparent initial rates of 148 and 90 μmol · min −1 · g −1 (cell dry weight) when it was the sole substrate or cometabolized with lactate, respectively. Lactate was consumed at an apparent initial rate of 157 μmol · min −1 · g −1 when it was cometabolized with pyruvate. P. shermanii used several pathways, namely, the Wood-Werkman cycle, synthesis of acetate and CO 2 , succinate synthesis, gluconeogenesis, the tricarboxylic acid cycle, and alanine synthesis, to manage its pyruvate pool sharply. In both types of experiments, acetate synthesis and the Wood-Werkman cycle were the metabolic pathways used most.