C-terminal regulatory domain of the ε subunit of FoF1 ATP synthase enhances the ATP-dependent H+ pumping that is involved in the maintenance of cellular membrane potential in Bacillus subtilis

The epsilon subunit of FoF1-ATPase/synthase (FoF1) plays a crucial role in regulating F(o)F(1 )activity. To understand the physiological significance of the epsilon subunit-mediated regulation of F(o)F(1 )in Bacillus subtilis, we constructed and characterized a mutant harboring a deletion in the C-terminal regulatory domain of the epsilon subunit (epsilon( increment C)). Analyses using inverted membrane vesicles revealed that the epsilon( increment C) mutation decreased ATPase activity and the ATP-dependent H+-pumping activity of FoF1. To enhance the effects of epsilon( increment C) mutation, this mutation was introduced into a increment rrn8 strain harboring only two of the 10 rrn (rRNA) operons ( increment rrn8 epsilon( increment C) mutant strain). Interestingly, growth of the increment rrn8 epsilon( increment C) mutant stalled at late-exponential phase. During the stalled growth phase, the membrane potential of the increment rrn8 epsilon( increment C) mutant cells was significantly reduced, which led to a decrease in the cellular level of 70S ribosomes. The growth stalling was suppressed by adding glucose into the culture medium. Our findings suggest that the C-terminal region of the epsilon subunit is important for alleviating the temporal reduction in the membrane potential, by enhancing the ATP-dependent H+-pumping activity of FoF1.