Thermodynamics of hydrogen metabolism in methanogenic cocultures degrading ethanol or lactate

Abstract

Pure cultures of Desulfovibrio vulgaris or Pelobacter acetylenicus do not grow with lactate or ethanol, respectively, under obligately proton- reducing conditions. However, a small part of these substrates was oxidized and molecular hydrogen was produced up to 4.2 and 3.2 kPa, respectively. During growth in syntrophic methanogenic cocultures with Methanospirillum hungatei as partner, maximum hydrogen partial pressures were significantly lower (0.7 to 2.5 kPa) than in the corresponding pure cultures. Calculation of Gibbs free energies for the prevailing culture conditions showed that H2 partial pressures were kept in a range at which both, H2-producing and H2-consuming reactions, were thermodynamically permissive in pure as well as in syntrophic mixed cultures. © 1988.