Sodium-Coupled Energy Transduction in the Newly Isolated

Strain LBS3 is a novel anaerobic thermoalkaliphilic bacterium that grows optimally at pH 9.5 and 50&C. Since a high concentration of Na1 ions is required for growth, we have analyzed the primary bioenergetic mechanism of energy transduction in this organism. For this purpose, a method was devised for the isolation of right-side-out membrane vesicles that are functional for the energy-dependent uptake of solutes. A strict requirement for Na1 was observed for the uptake of several amino acids, and in the case of L-leucine, it was concluded that amino acid uptake occurs in symport with Na1 ions. Further characterization of the leucine transport system revealed that its pH and temperature optima closely match the conditions that support the growth of strain LBS3. The ATPase activity associated with inside-out membrane vesicles was found to be stimulated by both Na1 and Li1 ions. These data suggest that the primary mechanism of energy transduction in the anaerobic thermoalkaliphilic strain LBS3 is dependent on sodium cycling. The implications of this finding for the mechanism of intracellular pH regulation are discussed. The newly isolated strain LBS3 is a gram-positive, spore-forming, anaerobic thermoalkaliphile that grows optimally at 508C and an alkaline pH of 9.5. The strain was isolated from a hot-lake inlet at Lake Bogoria in Kenya and represents a ne