Sulfate-reducing bacteria in littoral sediment of Lake Constance

The viable population of sulfate-reducing bacteria (SRB) in littoral sediments of Lake Constance was investigated using enrichment and enumeration techniques. Enrichment studies established that most types of SRB grew best in media with low salt concentrations (max. 0.4 g Cl−/1), consistent with the low salinity of the freshwater habitat. Enumerations were based on an adequate medium with the following electron donors: H2, lactate, acetate, propionate, butyrate, caprylate, succinate, benzoate, or S2O32− for thiosulfate-disproportionating bacteria. Cultures were incubated for 6 weeks to obtain maximum counts. A maximum cell density of 6.3 × 106 cells per ml sediment was estimated, which is the highest number of SRB ever reported for anoxic sediments. A comparison with measured sulfate reduction rates showed that the enumeration techniques were about 10–100-fold more efficient than those previously used. The population of SRB had a characteristic structure consisting of 87.7% H2-utilizing SRB (physiologically resembling the classical Desulfovibrio species); 12.0% propionate utilizers (tentatively identified as Desulfobulbus species); 0.3% long chain fatty acid-oxidizing Desulfovibrio sapovorans species. Acetate-utilizing SRB (Desulfotomaculum acetoxidans) constituted ≤ 0.05% of the total estimated population. Moreover, the latter species was only present as inactive spores. Benzoate-degrading SRB were not detected.