H2 Consumption by Various Acetogenic Bacteria Follows First-Order Kinetics up to H2 Saturation

Acetogenic bacteria play an important role in various biotechnological processes, because of their chemolithoautotrophic metabolism converting carbon dioxide with molecular hydrogen (H-2) as electron donor into acetate. As the main factor limiting acetogenesis is often H-2, insights into the H-2 consumption kinetics of acetogens are required to assess their potential in biotechnological processes. In this study, initial H-2 consumption rates at a range of different initial H-2 concentrations were measured for three different acetogens. Interestingly, for all three strains, H-2 consumption was found to follow first-order kinetics, i.e. the H-2 consumption rate increased linearly with the dissolved H-2 concentration, up to almost saturated H-2 levels (600 mu M). This is in contrast with Monod kinetics and low half-saturation concentrations, which have commonly been assumed for acetogens. The obtained biomass specific first-order rate coefficients (k(1)(X)) were further validated by comparison with values obtained by fitting first-order kinetics on previous time-course experimental results. The latter method was also used to determine the k(1)(X) value of five additional acetogens strains. Biomass specific first-order rate coefficients were found to vary up to six-fold, with the highest k(1)(X) for Acetobacterium wieringae and the lowest for Sporomusa sphaeroides. Overall, our results demonstrate the importance of the dissolved H-2 concentration to understand the rate of acetogenesis in biotechnological systems.