Metabolic Regulation of End Product Distribution in Lactobacilli: Causes and Consequences

This review examines the regulation of end product distribution in Lactobacillus plantarum and other lactobacilli, the factors that influence this distribution, and the bioenergetic consequences of end product distribution. Similarities to and differences from other genera in the lactic acid bacteria are described. Lactobacilli use many different transport systems to obtain nutrients. Carbohydrates and organic acids are transported in cells by specific phosphoenolpyruvate phosphotransferases (PEP—PTS) or permeases. The carbohydrates are then metabolized to different end products through a common key intermediate, pyruvate. The ability of lactobacilli to produce various end products depends on species, strains, genetic capacity, expression of enzyme activity, sugar structure, and environmental conditions. The regeneration of the NAD⁺ required for continued glycolysis is a key regulatory factor of end product distribution. The excretion of protons with acidic end products can directly generate a proton motive force and it also contributes to intracellular pH homeostasis. Anionic precursor—product exchange systems can also generate a proton motive force if the exchange is not electroneutral.