Proton circulation in Vibrio costicola.

The importance of proton movements was assessed in the moderate halophile Vibrio costicola. When anaerobic cells in acidic buffer (pH 6.5) were given an O2 pulse, protons were extruded regardless of the presence of Na+. At pH 8.5, however, V. costicola produced an acidic response to an O2 pulse in the absence of Na+ and an alkaline response when Na+ was present. An Na+/H+ antiport activity was confirmed at pH 8.5. All of these effects were prevented by protonophores or butanol treatment. Growth in complex medium at pH 8.5 was prevented by a high concentration (50 microM) of carbonyl cyanide m-chlorophenyl-hydrazone (CCCP) or a low concentration (5 microM) of another protonophore, 3,3',4',5-tetrachlorosalicylanilide (TCS). The relative ineffectiveness of the former protonophore was caused by the proteose peptone and tryptone ingredients of the complex medium, since 5 microM completely prevented growth in their absence. The results are explained by a primary respiratory-linked proton efflux coupled to a secondary Na+/H+ antiport operating at alkaline pH. Evidence was seen for a role of Na+ in stimulating proton influx at alkaline pH, presumably via the pH homeostasis mechanism.