Potassium ion is required for the generation of pH-dependent membrane potential and delta pH by the marine bacterium Vibrio alginolyticus.

The electrochemical potential gradient of protons in the marine bacterium Vibrio alginolyticus was measured as a function of external pH. In K+-containing cells, the membrane potential (delta psi) and delta pH vary with external pH as reported in other bacteria. On the other hand, K+-depleted cells show little pH dependence in the magnitude of delta psi from pH 6.0 to 8.5. The cytoplasmic pH in these cells varies depending on external pH, resulting in the generation of a small delta pH at acidic pH. Addition of K+ to K+-depleted cells leads to partial dissipation of delta psi and concomitant generation of delta pH. Strikingly, this effect of K+ is dependent on external pH. Collapse of delta psi and generation of delta pH by the addition of K+ decrease with increasing external pH. Thus, the delta psi and delta pH obtained after addition of K+ are essentially the same as those determined in K+-containing cells, and cytoplasmic pH becomes less dependent on external pH. The results suggest that the variation of delta psi and delta pH with external pH is controlled by K+ transport.