BIOENERGETIC STUDIES OF METHANOSPHAERA-STADTMANAE, AN OBLIGATE H(2)-METHANOL UTILIZING METHANOGEN

In Methanosphaera stadtmanae producing methane from the reduction of m ethanol with H-2, sodium (>0.3 mM Na+) was not required for methanogen esis or ATP synthesis. The ATPase inhibitor N,N'-dicyclohexylcarbodiim ide inhibited both ATP synthesis and methanogenesis, but was only effe ctive in the presence of low Na+ (<1 mM). The observed N,N'-dicyclohex ylcarbodiimide inhibition of methanogenesis was relieved by the additi on of the protonophore 3,3',4',5-tetrachlorosalicylanilide. 3,3',4',5- Tetrachlorosalicylanilide itself caused a rapid decrease in the intrac ellular ATP concentration and stimulated methanogenesis. This stimulat ion was enhanced when the cells were incubated in the presence of NaCl . The effects of Na+ on the effectiveness of N,N'-dicyclohexylcarbodii mide and 3,3',4',5-tetrachlorosalicylanilide cannot yet be explained. Ionophores (3,3',4',5-tetrachlorosalicylanilide, SF6847, monensin, and gramicidin) caused decreases in the membrane potential and the intrac ellular ATP concentration while stimulating methanogenesis. The data p resented are consistent with the coupling of the last step of methanog enesis to ATP synthesis via a proton motive force in a representative of the Methanobacteriales.