C-terminal regulatory domain of the ε subunit of F_oF₁ ATP synthase enhances the ATP-dependent H⁺ pumping that is involved in the maintenance of cellular membrane potential in Bacillus subtilis

The ε subunit of F_oF₁-ATPase/synthase (F_oF₁) plays a crucial role in regulating F_oF₁activity. To understand the physiological significance of the ε subunit-mediated regulation of F_oF₁in Bacillus subtilis, we constructed and characterized a mutant harboring a deletion in the C-terminal regulatory domain of the ε subunit (ε^∆C). Analyses using inverted membrane vesicles revealed that the ε^∆C mutation decreased ATPase activity and the ATP-dependent H⁺-pumping activity of F_oF₁. To enhance the effects of ε^∆C mutation, this mutation was introduced into a ∆rrn8 strain harboring only two of the 10 rrn (rRNA) operons (∆rrn8 ε^∆C mutant strain). Interestingly, growth of the ∆rrn8 ε^∆C mutant stalled at late-exponential phase. During the stalled growth phase, the membrane potential of the ∆rrn8 ε^∆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 ε subunit is important for alleviating the temporal reduction in the membrane potential, by enhancing the ATP-dependent H⁺-pumping activity of F_oF₁.