Membrane H Conductance of Clostridium thermoaceticum and Clostridium acetobutylicum: Evidence for Electrogenic Na/H Antiport in Clostridium thermoaceticum.

H conductance in de-energized cells of Clostridium thermoaceticum and Clostridium acetobutylicum was determined from the rate of realkalinization of the medium after an acid pulse. In both organisms, cell membrane proton permeability was increased by fermentation end products and ionophores. In C. thermoaceticum, H conductance was increased by Na ions compared with K as counterions. In these cells, addition of Na, but not K, elicited efflux of H; H efflux was stimulated by SCN and decreased by various ionophores. We concluded that C. thermoaceticum possesses an electrogenic Na/H antiporter. In contrast, C. acetobutylicum cells did not have an electrogenic Na/H antiporter.