, Volume 132, Issue 3, pp 285-288

Kinetic mechanism for the ability of sulfate reducers to out-compete methanogens for acetate

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Methanosarcina barkeri and Desulfobacter postgatei are ubiquitous anaerobic bacteria which grow on acetate or acetate plus sulfate, respectively, as sole energy sources. Their apparent K s values for acetate were determined and found to be approximately 0.2 mM for the sulfate-reducing bacterium and 3 mM for the methanogenic bacterium. In mixed cell suspensions of the two bacteria (adjusted to equal V max) the rate of acetate consumption by D. postgatei approached 15-fold the rate of M. barkeri at low acetate concentrations. The apparent inhibition of methanogenesis was of the same order as expected from the different K s value for acetate. Difference in substrate affinities can thus account for the inhibition of methanogenesis from acetate in sulfate-rich environments, where the acetate concentration is well below 1 mM.