Pure-Culture Growth of Fermentative Bacteria, Facilitated by H2 Removal: Bioenergetics and H2 Production

We used an H₂-purging culture vessel to replace an H₂-consuming syntrophic partner, allowing the growth of pure cultures of Syntrophothermus lipocalidus on butyrate and Aminobacterium colombiense on alanine. By decoupling the syntrophic association, it was possible to manipulate and monitor the single organism's growth environment and determine the change in Gibbs free energy yield (ΔG) in response to changes in the concentrations of reactants and products, the purging rate, and the temperature. In each of these situations, H₂ production changed such that ΔG remained nearly constant for each organism (−11.1 ± 1.4 kJ mol butyrate⁻¹ for S. lipocalidus and −58.2 ± 1.0 kJ mol alanine⁻¹ for A. colombiense). The cellular maintenance energy, determined from the ΔG value and the hydrogen production rate at the point where the cell number was constant, was 4.6 × 10⁻¹³ kJ cell⁻¹ day⁻¹ for S. lipocalidus at 55°C and 6.2 × 10⁻¹³ kJ cell⁻¹ day⁻¹ for A. colombiense at 37°C. S. lipocalidus, in particular, seems adapted to thrive under conditions of low energy availability.