Enrichment of sulfate‐reducing bacteria and resulting mineral formation in media mimicking pore water metal ion concentrations and p H conditions of acidic pit lakes

Acid mine drainage sites are extreme environments with high acidity and metal ion concentrations. Under anoxic conditions, microbial sulfate reduction may trigger the formation of secondary minerals as a result of H 2 S production and p H increase. This process was studied in batch experiments with enrichment cultures from acidic sediments of a pit lake using growth media set at different pH values and containing elevated concentrations of Fe 2+ and Al 3+ . At initial p H values of 5 and 6, sulfate reduction occurred shortly after inoculation. Sulfate‐reducing bacteria affiliated to the genus D esulfosporosinus predominated the microbial communities as shown by 16 S r RNA gene analysis performed at the end of the incubation. At initial p H values of 3 and 4, sulfate reduction and cell growth occurred only after an extended lag phase, however, at a higher rate than in the less acidic assays. At the end of the growth phase, enrichments were dominated by T hermodesulfobium spp. suggesting that these sulfate reducers were better adapted to acidic conditions. Iron sulfides in the bulk phase were common in all assays, but specific aluminum precipitates formed in close association with cell surfaces and may function as a detoxification mechanism of dissolved Al species at low p H .