The contribution of acetate-oxidizing sulfate reduction to decomposition of organic matter in anoxic marine sediments was estimated by the sediment slurry system and the rates of sulfate reduction in the sediment were measured. Acetate and propionate were oxidized completely by sulfate reduction. Formate, however, was decomposed by both sulfate reduction and other processes. Most of lactate was fermented to acetate, propionate, and formate. Half of the added glucose was mineralized by sulfate reduction through fermentation including production of some kinds of low molecular fatty acids. Using fluoroacetate as an inhibitor of acetate metabolism, about 40% of glucose mineralization was estimated to be derived from acetate. The rates of sulfate reduction in an anoxic surface sediment were about 50-60nmol·g^-1·day^-1 during the summer stratified season. Fluoroacetate inhibited this activity by 65-71%. These results suggest that sulfate reduction plays an important role in the mineralization of organic matter and that acetate is a major substrate for sulfate reduction in anoxic sediments.

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The rapid microbial degradation of 2, 4-dichlorophenol (DCP) at 1.0μg DCP-C/ml in a groundwater was observed when the density of responsible degraders, estimated by the most probable number (MPN) method, had increased to 10⁵ cells/ml. However, no degradation of 0.1 or 0.03μg DCP-C/ml was observed even when the density of degraders had increased to 10⁴-10⁵ cells/ml. Rapid degradation of 0.1μg DCP-C/ml occured within a day in the qroundwater in which 1.0μg DCP-C/ml was degraded beforehand, but not in the groundwater which had been precultured with 0.1μg DCP-C/ml. Addition of mineral nutrients enhanced the degradation of 0.1μg DCP-C/ml, but not the growth of degraders. These results suggest that in the groundwater the failure of DCP degradation at low concentration may be attributable to the failure of degraders to express their DCP-degrading activity, such as induction of responsible enzyme(s), and not to the failure to grow or to increase their density.

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