Protonmotive Force and ATP Generation During Malolactic Fermentation

Malate catabolism by Lactobacillus plantarum formed a Δp at external pH of 3.5 to 6.5. Observed ATP concentrations increased as a result of malate catabolism, but decreased in the presence of the ionophores monensin, nigericin, and tetrachlorosalicylanilide at a concentration of 1 to 2 µ M . The ΔpH and ATP concentrations determined during malate catabolism were higher below pH 4.5 than above pH 4.5. Malate catabolism generated a Δψ at pH 4.5 and above, but not at pH 3.5. It was concluded that the Δp formed as a result of malate catabolism was ΔpH dependent for cells growing at pH values below 5.5. Loading cells of L. plantarum with 100 m M D- or L-lactate produced a diffusion generated ΔpH, but no ATP was produced when cells were treated with IAA to inhibit glycolysis. However, ATP was produced in the absence of IAA. Adding lactate into the MES buffer with cells loaded with lactate decreased the amount of ATP produced due to lactic acid diffusion. Based on the available information, we suggest that energy from malolactic fermentation is produced by malate -1 transport and lactic acid diffusion.