The lactate metabolism of the oral bacterium Veillonella from human saliva

Lactate is metabolized by Veillonella via the methylmalonyl-coenzyme A (CoA) pathway to propionate and, by further pathways, to acetate. Whereas pyruvate and oxaloacetate are metabolized via the pyruvate-formate lyase reaction, lactate acts as a donor of hydrogen allowing the reduction of oxaloacetate to malate in the methylmalonyl-CoA pathway. Succinate, believed to be an intermediate in lactate metabolism of Veillonellae is readily decarboxylated to propionate by these organisms, but a severe, progressive substrate inhibition occurs at concentrations above 12–16 mmol/l.