PROTON-TRANSLOCATING ADENOSINE-TRIPHOSPHATASE ACTIVITY IN LACTIC-ACID BACTERIA

Streptococcus thermophilus 19258 and 573, Lactococcus lactis ssp. lactis C2, Lactococcus lactis ssp. cremoris HP, and Lactobacillus casei 685 were grown in various media and assayed for proton-translocating ATPase (H+-ATPase) activity. The H+-ATPase was extracted from the membrane fractions of protoplasted cells using a French pressure cell, and activity was measured by the release of inorganic phosphate from ATP. The pH optima for the H+-ATPase, assayed in vitro, were 7.5 for S. thermophilus and Lactococcus lactis ssp. cremoris HP and 5.0 for Lactobacillus casei 685. In contrast, for cells grown in batch culture the H+-ATPase activity was always greatest when the cytoplasmic pH was less than the optimum for the enzyme. The H+-ATPase activity generally increased as the pH decreased until an extracellular pH of 5.0 was reached. Below an extracellular pH of 5.0, activities of this enzyme dropped markedly. The aciduric lactic acid bacterium, Lactobacillus casei 685, had higher basal levels of this enzyme than the streptococci and lactococci. Results suggest that this enzyme may be involved in regulation of the intracellular pH in lactic acid bacteria.