A novel type of energetics in a marine alkali-tolerant bacterium. Δ μ -_Na-driven motility and sodium cycle

Motility of a marine alkali-tolerant bacterium, Vibrio alginolyticus, can be observed in the presence of high concentrations of a protonophorous uncoupler, CCCP. Motility in the CCCP-containing media is completely inhibited by decrease in extracellular [Na⁺] or by monensin-induced increase in intracellular [Na⁺]. A mutant has been selected that grows only in media supplemented with a substrate such as acetate requiring no Δ μ -_Na to be transported into the cell. Motility of the mutant was found to be completely inhibited by CCCP. Cyanide, CCCP and vanadate added separately or in twos inhibit motility only partially. The three poisons added together completely paralyse the cells. In this inhibitor cocktail, arsenate can substitute for CCCP + vanadate; cyanide can be replaced by anaerobiosis. It is concluded that (i) Δ μ -_Na rather than Δ μ -_NH powers the flagellar motor of V. alginolyticus in the presence of CCCP, and (ii) in addition to the Na⁺-motive respiratory chain [Tokuda, H. and Unemoto, T. (1982) J. Biol. Chem. 257, 10007-10014] there is a vanadate and arsenate-sensitive oxygen-independent mechanism of Δμ_Na generation, presumably an ion-motive ATPase. A suggestion is put forward that circulation of Na⁺ can replace that of H⁺ in V. alginolyticus, Δ μ -_Na being formed by the Na⁺-motive respiratory chain and utilized by Na⁺-solute symporters, the Na⁺-driven flagellar motor and maybe by a reverse ion-motive ATPase.