Functional discrepancy between F-type and A-type rotary ion-translocating ATPases in acid tolerance of Streptococcus anginosus.

Streptococcus anginosus, a gram-positive anaerobe found in the oral cavity and gastrointestinal tract, causes serious purulent abscesses in various tissues and is also associated with the occurrence of esophageal and gastric tumors. Mechanisms underlying the highly evolved acid tolerance are vital for bacterial growth and survival under acidic environments in the upper gastrointestinal tract or dental plaque. We previously observed that proton-pumping F-type ATPase (F-ATPase) of S. mutans plays a vital role in acid tolerance. Unlike S. mutans, S. anginosus possesses A-type ATPase (A-ATPase) in addition to F-ATPase. In other organisms, A-ATPases function as either proton- or sodium-translocating enzymes. In the present study, we investigated which ATPases are involved in the acid tolerance mechanism of S. anginosus and found that both ATPases were expressed in S. anginosus cells, with an increased expression level of F-ATPase under acidic conditions. Knockout cells of the F-ATPase catalytic β subunit gene demonstrated no growth at pH 5.30, whereas growth was detected at pH 7.40. Moreover, the colony-forming ability of the β-knockout cells significantly decreased at pH < 4.70 compared with that of wild-type cells, but it was similar at pH 7.40. These defects of the β-knockout cells in growth and survival under acidic conditions were recovered in the knockout cells expressing the β subunit. Conversely, knockout cells of the A-ATPase catalytic B subunit gene exhibited similar growth and survival under acidic conditions as those of wild-type cells. These results demonstrate that F-ATPase but not A-ATPase is essential for the acid tolerance mechanism of S. anginosus.