Kinetic characterization of Methanobacterium bryantii M.o.H.

H2 is a key electron donor for many anaerobic microorganisms; thus, keen competition for H2 occurs among H2-utilizing microbial groups. Monod kinetic parameters provide essential information for kinetic analysis of competition for H2. In this study, we estimated Monod kinetic parameter values for a methanogen that consumes only H2 as its electron donor, Methanobacterium bryantii M.o.H. Utilization of a single electron donor is an advantage in this study, because complications from alternate metabolic pathways are avoided. Using a set of batch experiments designed to provide the best estimates of each parameter, we obtained these values: maximum specific growth rate (mumax) = 0.77/ day, maximum substrate consumption rate (qmax) = 2.36 mol-H2/gcells/day, true yield (Y) = 0.325 gcell/mol H2, fraction of donor electrons to synthesis (fs degrees) = 0.03 e-cell/e- donor, half-maximum-rate substrate concentration (Ks) = 18 000 nM = 18 microM H2, and endogenous decay rate (b) = 0.088/ day. This self-consistent set of parameters indicates that, when H2 is not limiting, M. bryantii M.o.H. is a slow grower (low mumax) compared to other H2-oxidizing methanogens and sulfate reducers, and this is mainly due to its low true Y, not a low qmax. The relatively high Ks and b values suggest that M. bryantii also may not be a strong competitor when H2 is limiting.