Different Ks values for hydrogen of methanogenic bacteria and sulfate reducing bacteria: An explanation for the apparent inhibition of methanogenesis by sulfate

Desulfovibrio vulgaris (Marburg) and Methanobrevibacter arboriphilus (AZ) are anaerobic sewage sludge bacteria which grow on H₂ plus sulfate and H₂ plus CO₂ as sole energy sources, respectively. Their apparent K_s values for H₂ were determined and found to be approximately 1 M for the sulfate reducing bacterium and 6 M for the methanogenic bacterium. In mixed cell suspensions of the two bacteria (adjusted to equal V_max) the rate of H₂ consumption by D. vulgaris was five times that of M. arboriphilus, when the hydrogen supply was rate limiting. The apparent inhibition of methanogenesis was of the same order as expected from the different K_s values for H₂. Difference in substrate affinities can thus account for the inhibition of methanogenesis from H₂ and CO₂ in sulfate rich environments, where the H₂ concentration is well below 5 M.