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.