Amino acid transport in the thermophilic anaerobe Clostridium fervidus is driven by an electrochemical sodium gradient

Amino acid transport was studied in membranes of the peptidolytic, thermophilic, anaerobic bacterium Clostridiumfervidus. Uptake of the negatively charged amino acid L-glutamate, the neutral amino acid L-serine, and the positively charged amino acid L-arginine was examined in membrane vesicles fused with cytochrome c-containing liposomes. Artificial ion diffusion gradients were also applied to establish the specific driving forces for the individual amino acid transport systems. Each amino acid was driven by the AW and AiiNa+/F and not by the ZApH. The Na+ stoichiometry was estimated from the amino acid-dependent 22Na+ efflux and Na+-dependent 3H-amino acid efflux. Serine and arginine were symported with 1 Na+ and glutamate with 2 Na+. C. fervidus membranes contain Na+/Na+ exchange activity, but Na+/H+ exchange activity could not be demonstrated. Bacteria growing in nonextreme environments pump out H ' to keep the intracellular pH around 7 to 8 and maintain an inwardly directed Na ' concentration gradient and an outwardly directed K+ gradient (1, 15, 32, 41). These H ' and Na+ concentration gradients in turn can be used for ener-getically unfavorable reactions, such as motility and uphil