Adaptive responses of Bacillus cereus ATCC14579 cells upon exposure to acid conditions involve ATPase activity to maintain their internal pH

This study examined the involvement of ATPase activity in the acid tolerance response (ATR) of Bacillus cereus ATCC14579 strain. In the current work, B. cereus cells were grown in anaerobic chemostat culture at external pH (pHe ) 7.0 or 5.5 and at a growth rate of 0.2 h-1 . Population reduction and internal pH (pHi ) after acid shock at pH 4.0 was examined either with or without ATPase inhibitor N,N'-dicyclohexylcarbodiimide (DCCD) and ionophores valinomycin and nigericin. Population reduction after acid shock at pH 4.0 was strongly limited in cells grown at pH 5.5 (acid-adapted cells) compared with cells grown at pH 7.0 (unadapted cells), indicating that B. cereus cells grown at low pHe were able to induce a significant ATR and Exercise-induced increase in ATPase activity. However, DCCD and ionophores had a negative effect on the ability of B. cereus cells to survive and maintain their pHi during acid shock. When acid shock was achieved after DCCD treatment, pHi was markedly dropped in unadapted and acid-adapted cells. The ATPase activity was also significantly inhibited by DCCD and ionophores in acid-adapted cells. Furthermore, transcriptional analysis revealed that atpB (ATP beta chain) transcripts was increased in acid-adapted cells compared to unadapted cells before and after acid shock. Our data demonstrate that B. cereus is able to induce an ATR during growth at low pH. These adaptations depend on the ATPase activity induction and pHi homeostasis. Our data demonstrate that the ATPase enzyme can be implicated in the cytoplasmic pH regulation and in acid tolerance of B. cereus acid-adapted cells.