ENERGY TRANSDUCTION IN THE THERMOPHILIC ANAEROBIC BACTERIUM CLOSTRIDIUM-FERVIDUS IS EXCLUSIVELY COUPLED TO SODIUM-IONS

The thermophilic, peptidolytic, anaerobic bacterium Clostridium fervid us is unable to generate a pH gradient in the range of 5.5-8.0, which limits growth of the organism to a narrow pH range (6.3-7.7). A signif icant membrane potential (DELTApsi almost-equal-to -60 mV) and chemica l gradient of Na+ (-ZDELTApNa almost-equal-to -60 mV) are formed in th e presence of metabolizable substrates. Energy-dependent Na+ efflux is inhibited by the Na+/H+ ionophore monensin but is stimulated by uncou plers, suggesting that the Na+ gradient is formed by a primary pumping mechanism rather than by secondary Na+/H+ antiport. This primary sodi um pump was found to be an ATPase that has been characterized in insid e-out membrane vesicles and in proteoliposomes in which solubilized AT Pase was reconstituted. The enzyme is stimulated by Na+, resistant to vanadate, and sensitive to nitrate, which is indicative of an F/V-type Na+-ATPase. In the proteoliposomes Na+ accumulation depends on the pr esence of ATP, is inhibited by the ATPase inhibitor nitrate, and is co mpletely prevented by the ionophore monensin but is stimulated by prot onophores and valinomycin. These and previous observations, which indi cated that secondary amino acid transport uses solely Na+ as coupling ion, demonstrate that energy transduction at the membrane in C. fervid us is exclusively dependent on a Na+ cycle.