Effect of 2-bromo-ethane sulfonate, molybdate and chloroform on acetate consumption by methanogenic and sulfate-reducing populations in freshwater sediment

The relative importance of methanogenesis and sulfate reduction in freshwat er sediment supplemented with acetate was investigated. Addition of acetate stimulated both methane formation and sulfate reduction. indicating that a n active aceticlastic population of methanogens and sulfate reducers was pr esent in the sediment. Sulfate reducers were most important in the consumpt ion of acetate. However, when sulfate reducers were inhibited, acetate was metabolised at a similar rate by methanogens. Acetate, propionate and valer ate accumulated only when both processes were inhibited by the combined add ition of 2-bromo-ethane sulfonate and molybdate. The relative amounts of ac etate, propionate and valerate were 93, 6 and 1 mol%, respectively. These r esults demonstrate the role of acetate as a key intermediate in the termina l step of organic matter mineralisation in the sediment. Addition of chloro form inhibited both methanogenesis and sulfate reduction. We studied the in hibitory effect of CHCl3 on homoacetogenic bacteria, sulfate-reducing bacte ria and methanogens. The results showed that inhibition by CHCl3 correlates with microorganisms, which operate the acetyl-CoA cleavage pathway. We pro pose that chloroform can be used to elucidate the role of different metabol ic types of sulfate reducers to sulfate reduction in natural environments. (C) 2000 Federation of European Microbiological Societies. Published by Els evier Science B.V. All rights reserved.