ATP synthesis in Methanobacterium thermoautotrophicum coupled to CH4 formation from H2 and CO2 in the apparent absence of an electrochemical proton potential across the cytoplasmic membrane

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Abstract
Methanogenic bacteria are considered to couple methane formation with the synthesis of ATP by a chemiosmotic mechanism. This hypothesis was tested with M. thermoautotrophicum. Methane formation from H2 and CO2 (2.5-3 .mu.mol .times. min-1 mg cells-1) by cell suspensions of this organism resulted in the formation of an electrochemical proton potential (.DELTA.~.mu.H+) across the cytoplasmic membrane of 230 mV (inside negative) and in the synthesis of ATP up to an intracellular concentration of 5-7 nmol/mg. The addition of ionophores at concentrations which completely dissipated .DELTA.~.mu.H+ without inhibiting methane formation did not result in an inhibition of ATP synthesis. It thus appears that .DELTA.~.mu.H+ across the cytoplasmic membrane is not the driving force for the synthesis of ATP in M. thermoautotrophicum.

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