Substrates for Sulfate Reduction and Methane Production in Intertidal Sediments

The activity of and potential substrates for methane-producing bacteria and sulfate-reducing bacteria were examined in marsh, estuary, and beach intertidal sediments. Slow rates of methane production were detected in all sediments, although rates of sulfate reduction were 100- to 1,000-fold higher. After sulfate was depleted in sediments, the rates of methane production sharply increased. The addition of methylamine stimulated methanogenesis in the presence of sulfate, and [C]methylamine was rapidly converted to CH(4) and CO(2) in freshly collected marsh sediment. Acetate, hydrogen, or methionine additions did not stimulate methanogenesis. [methyl-C]methionine and [2-C]acetate were converted to CO(2) and not to CH(4) in fresh sediment. No reduction of CO(2) to CH(4) occurred in fresh sediment. Molybdate, an inhibitor of sulfate reduction, inhibited [2-C]acetate metabolism by 98.5%. Fluoracetate, an inhibitor of acetate metabolism, inhibited sulfate reduction by 61%. These results suggest that acetate is a major electron donor for sulfate reduction in marine sediments. In the presence of high concentrations of sulfate, methane may be derived from novel substrates such as methylamine.