C‐terminal regulatory domain of the ε subunit of F o F 1 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 o F 1 ‐ATPase/synthase (F o F 1 ) plays a crucial role in regulating F o F 1 activity. To understand the physiological significance of the ε 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 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 o F 1 . 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 o F 1 .