Effects of methanogenesis and sulfate-reduction on acetogenetic oxidation of propionate and further decomposition of acetate in paddy soil

Under laboratory conditions, submerged paddy soil with the addition of propionate was incubated anaerobically. Propionate oxidation was suppressed by the addition of H2, and the specific inhibitor for methanogenesis (2-bromoethane-sulfonate; BES). The inhibition with H2 can be associated to the negative feedback of endergonic propionate oxidation with H2. The BES inhibition on propionate oxidation can be attributed to the uncoupling of propionate oxidation and methanogenesis. When sulfate was added, propionate oxidation was not suppressed by the addition of H2, but it was suppressed by the addition of the specific inhibitor for sulfate-reduction (molybdate). These findings suggest the occurrence of preferential coupling of propionate oxidation with sulfate reduction. During the oxidation of propionate after the addition of sulfate, acetate hardly accumulated in the absence of BES, but accumulated in the presence of BES. Propionate oxidation proceeded irrespective of the addition of BES. These findings indicate that the decomposition of acetate, which was produced from propionate, was associated with methanogenesis even in the presence of sulfate, and that electrons flowed through methanogenesis and sulfate-reduction without competition as long as propionate was present.