F-type proton-pumping atpase mediates acid tolerance in Streptococcus mutans

Abstract Aims Streptococcus mutans is highly sensitive to inhibitors of proton-pumping F-type ATPase (F-ATPase) under acidic conditions. Herein, we investigated the role of S. mutans F-ATPase in acid tolerance using a bacterium expressing the F-ATPase β subunit at lower levels than the wild-type strain. Methods and results We generated a mutant S. mutans expressing the catalytic β subunit of F-ATPase at lower levels than the wild-type bacterium. The mutant cells exhibited a significantly slower growth rate at pH 5.30, whereas the rate was essentially the same as that of wild-type cells at pH 7.40. In addition, the colony-forming ability of the mutant was decreased at pH < 4.30, but not at pH 7.40. Thus, the growth rate and survival of S. mutans expressing low levels of the β subunit were reduced under acidic conditions. Conclusions Together with our previous observations, this study indicates that F-ATPase is involved in the acid tolerance mechanism of S. mutans by secreting protons from the cytoplasm.