Continuous monitoring of the cytoplasmic pH in Methanobacterium thermoautotrophicum using the intracellular factor F-420 as indicator

The absorption spectrum of factor F-420 changes depending on the pH and the redox state of the cytoplasm. Specific wavelengths were used to calibrate absorption changes to allow the measurement of changes in the cytoplasmic p h in Methanobacterium thermoautotrophicum. Upon a hydrogen pulse, a rapid e fflux of protons was observed. Under these energized conditions, the Delta pH amounts to 0.2-0.4 pH units at ph 6.6, and 0.6-0.8 pH units at pH 6.0. I t decays within 10-20 s. In parallel, a sodium gradient is formed which has a slightly longer lifetime. Both Delta pH and Delta Psi contribute to the proton-motive force present during methanogenesis. The energy-conversion ra te, as indicated by the decay of the energized state of the cell, is fastes t under growth conditions, i.e. at ph 6.9 and at a temperature of 58 degree sC.