Kinetic characterization of Methanobacterium bryantii M.o.H.

H-2 is a key electron donor for many anaerobic microorganisms; thus, keen competition for H-2 occurs among utilizing microbial groups. Monod kinetic parameters provide essential information for kinetic analysis of competition for H-2. In this study, we estimated Monod kinetic parameter values for a methanogen that consumes only H-2 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 (mu(max)) = 0.77/day, maximum substrate consumption rate (q(max)) = 2.36 mol-H-2/gcells/day, true yield (Y) = 0.325 gcell/mol H-2, fraction of donor electrons to synthesis (f(S)degrees) = 0.03 e(-)cell/e(-)donor, half-maximum-rate substrate concentration (K-S) = 18 000 nM = 18 mu M H-2, and endogenous decay rate (b) = 0.088/day. This self-consistent set of parameters indicates that, when H-2 is not limiting, M. bryantii M.o.H. is a slow grower (low mu(max)) compared to other H-2-oxidizing methanogens and sulfate reducers, and this is mainly due to its low true Y, not a low q(max). The relatively high K-S and b values suggest that M. bryantii also may not be a strong competitor when H-2 is limiting.