Bioenergetic studies of Methanosphaera stadtmanae, an obligate H2–methanol utilising methanogen

In Methanosphaera stadtmanae producing methane from the reduction of methanol with H2, sodium (> 0.3 mM Na+) was not required for methanogenesis or ATP synthesis. The ATPase inhibitor N,N′-dicyclohexylcarbodiimide inhibited both ATP synthesis and methanogenesis, but was only effective in the presence of low Na+ (< 1 mM). The observed N,N′ -dicyclohexylcarbodiimide inhibition of methanogenesis was relieved by the addition of the protonophore 3,3′,4′,5-tetrachlorosalicylanilide. 3,3′,4′,5-Tetrachlorosalicylanilide itself caused a rapid decrease in the intracellular ATP concentration and stimulated methanogenesis. This stimulation was enhanced when the cells were incubated in the presence of NaCl. The effects of Na+ on the effectiveness of N,N′-dicyclohexylcarbodiimide 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 intracellular ATP concentration while stimulating methanogenesis. The data presented are consistent with the coupling of the last step of methanogenesis to ATP synthesis via a proton motive force in a representative of the Methanobacteriales.Key words: methanogenesis, proton motive force, membrane potential.