Lactic acid excretion by Streptococcus mutans

Abstract

Lactic acid is the major end-product of glycolysis by Streptococcus mutans under conditions of sugar excess or low environmental pH. However, the mechanism of lactic acid excretion by S. mutans is unknown. To characterize lactic acid efflux in S. mutans the transmembrane movement of radiolabelled lactate was monitored in de-energized cells. Lactate was found to equilibrate across the membrane in accordance with an artificially imposed transmembrane pH gradient (ΔpH). The imposition of a transmembrane electrical potential (Δψ) upon de-energized cells did not cause an accumulation of lactate within the cell. The efflux of lactate from lactate-loaded, de-energized cells created a ΔpH, but did n..