GENERATION OF A PROTON MOTIVE FORCE BY THE ANAEROBIC OXALATE-DEGRADING BACTERIUM OXALOBACTER-FORMIGENES

The generation of transmembrane ion gradients by Oxalobacter formigene s cells metabolizing oxalate was studied. The magnitudes of both the t ransmembrane electrical potential (Delta psi) and the pH gradient (int ernal alkaline) decreased with increasing external pH; quantitatively, the Delta psi was the most important component of the proton motive f orce, As the extracellular pH of metabolizing cells was increased, int racellular pH increased and remained alkaline relative to the external pH, indicating that O. formigenes possesses a limited capacity to reg ulate internal pH, The generation of a Delta psi by concentrated suspe nsions of O. formigenes cells was inhibited by the K+ ionophore valino mycin and the protonophore carbonyl cyanide-m-chlorophenylhydrazone, b ut not by the Na+ ionophore monensin. The H+ ATPase inhibitor N,N'-dic yclohexyl-carbodiimide inhibited oxalate catabolism but did not dissip ate the Delta psi. The results support the concept that energy from ox alate metabolism by O. formigenes is conserved not as a sodium ion gra dient but rather, at least partially, as a transmembrane hydrogen ion gradient produced during the electrogenic exchange of substrate (oxala te) and product (formate) and from internal proton consumption during oxalate decarboxylation.