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 (H2) as electron donor into acetate. As the main factor limiting acetogenesis is often H2, insights into the H2 consumption kinetics of acetogens are required to assess their potential in biotechnological processes. In this study, initial H2 consumption rates at a range of different initial H2 concentrations were measured for three different acetogens. Interestingly, for all three strains, H2 consumption was found to follow first-order kinetics, i.e. the H2 consumption rate increased linearly with the dissolved H2 concentration, up to almost saturated H2 levels (600 µM). 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 (k1 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 k1 X value of five additional acetogens strains. Biomass specific first-order rate coefficients were found to vary up to six-fold, with the highest k1 X for Acetobacterium wieringae and the lowest for Sporomusa sphaeroides. Overall, our results demonstrate the importance of the dissolved H2 concentration to understand the rate of acetogenesis in biotechnological systems.