Measurement of ΔpH and electron transport activities in Methanobacterium thermoautotrophicum

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 pH in Methanobacterium thermoautotrophicum. Upon a hydrogen pulse, a rapid efflux of protons was observed. Under these energized conditions, the DeltapH amounts to 0.2-0.4 pH units at pH 6.6, and 0.6-0.8 pH units at pH 6.0. It decays within 10-20 s. In parallel, a sodium gradient is formed which has a slightly longer lifetime. Both DeltapH and DeltaPsi contribute to the proton-motive force present during methanogenesis. The energy-conversion rate, as indicated by the decay of the energized state of the cell, is fastest under growth conditions, i.e. at pH 6.9 and at a temperature of 58 degrees C.