Competition between sulfate-reducing and methanogenic bacteria for H2 under resting and growing conditions

The basis for the outcome of competition between sulfidogens and methanogens for H2 was examined by comparing the kinetic parameters of representatives of each group separately and in co-culture. Michaelis-Menten parameters (Vmax and Km) for four methanogens and five sulfate-reducing bacteria were determined from H2-depletion data. Further, Monod growth parameters (μmax, Ks, YH2) for Desulfovibrio sp. G11 and Methanospirillum hungatei JF-1 were similarly estimated. H2Km values for the methanogenic bacteria ranged from 2.5 μM (Methanospirillum PM1) to 13 μM for Methanosarcina barkeri MS; Methanospirillum hungatei JF-1 and Methanobacterium PM2 had intermediate H2Km estimates of 5 μM. Average H2Km estimates for the five sulfidogens was 1.2 μM. No consistent difference among the Vmax estimates for the above sulfidogens (mean=100 nmol H2 min-1 mg-1 protein) and methanogens (mean=110 nmol H2 min-1 mg-1 protein) was found. A two-term Michaelis-Menten equation accurately predicted the apparent H2Km values and the fate of H2 by resting co-cultures of sulfate-reducers and methanogens. Half-saturation coefficients (Ks) for H2-limited growth of Desulfovibrio sp. G11 (2–4 μM) and Methanospirillum JF-1 (6–7 μM) were comparable to H2Km estimates obtained for these organisms. Maximum specific growth rates for Desulfovibrio sp. G11 (0.05 h-1) were similar to those of Methanospirillum JF-1 (0.05–0.06 h-1); whereas G11 had an average yield coefficient 4 x that of JF-1. Calculated μmax and Vmax/Km values for the methanogens and sulfidogens studied predict that the latter bacterial group will process more H2 whether these organisms are in a growing or resting state, when the H2 concentration is in the first-order region.