Energetic analysis of the growth of Methanobrevibacter arboriphilus A2 in hydrogen-limited continuous cultures.

Hydrogen-limited chemostat cultures of Methanobrevibacter arboriphilus A2 were carried out. The available electron balance and carbon balance in M. arboriphilus A2 and other methanogenic strains grown on various substrates were well satisfied. This indicates that no extracellular organic products were formed during methanogenic growth. The molar growth yields for methane (Y(X/CH(4) )) were calculated as 1.06-1.42 g cell/mol CH(4) at dilution rate (0.21-0.43 day(-1)). The smaller Y(X/CH(4) ) of M. arboriphilus A2 compared with that of the other methanogenic strains was probably owing to the low growth rate of M. arboriphilus A2. The low value of Y(X/CH(4) ) may be favorable for methane fermentation because less sludge accumulation is expected. The efficiency of free energy transduction to ATP during methane formation from H(2) + CO(2) was 12-17% at the dilution rate (0.21-0.43 day(-1)) assuming that Y(ATP) was 6.5 g/mol and the free energy change of CO(2) reduction to methane with H(2) was -62.8 kJ/mol under physiological conditions.