Pure-Culture Growth of Fermentative Bacteria, Facilitated by H 2 Removal: Bioenergetics and H 2 Production

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Abstract
We used an H 2 -purging culture vessel to replace an H 2 -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 (Δ G ) in response to changes in the concentrations of reactants and products, the purging rate, and the temperature. In each of these situations, H 2 production changed such that Δ G 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 Δ G 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.