Enzyme activities in and energetics of acetate metabolism by the mesophilic syntrophically acetate-oxidizing anaerobe Clostridium ultunense

The metabolism of the syntrophically acetate-oxidizing Clostridium ultunense was investigated with cell extracts of the pure culture and the methanogenic triculture from which C. ultunense was isolated. Enzyme measurements indicated that: (1) the CO dehydrogenase (Wood) pathway was used both during acetate formation and during acetate oxidation; (2) methylene-tetrahydrofolate reductase activity was not detected during acetate oxidation; (3) two different methylene-tetrahydrofolate dehydrogenase enzymes were active, depending on the direction in which the Wood pathway was used. The hydrogen partial pressure in the headspace of a growing triculture varied between 1.6 and 6.8 Pa, indicating that C. ultunense and the methanogenic partner each get about −17 kJ per mol reaction in this syntrophic cooperation, thus operating at the lowermost range of energy to be exploited by a living organism.