Bacterial populations and processes involved in acetate and propionate consumption in anoxic brackish sediment.

Bacterial populations and pathways involved in acetate and propionate consumption were studied in anoxic brackish sediment from the Grosser Jasmunder Bodden, German Baltic Sea. Uptake of acetate and propionate from the porewater was studied using stable carbon isotope-labeled compounds. Labeled acetate was not produced as an intermediate during propionate uptake experiments, and propionate consumption was not affected by the addition of acetate. In parallel, incorporation of labeled acetate and propionate into phospholipid-derived fatty acids (PLFA) was studied to indicate bacterial populations involved in the consumption of these substrates. The (13)C-acetate label was mainly recovered in even-numbered PLFA (16:1omega7c, 16:0 and 18:1omega7c). In contrast, primarily odd-numbered PLFA (a15:0, 15:0, 17:1omega6 and 17:0) and the even-numbered i16:0 were labeled after incubation with (13)C-propionate. Although single PLFA labeled with propionate are commonly found in sulfate reducers, the complete PLFA-labeling pattern does not resemble any of the know strains. However, the acetate-labeling pattern is similar to Desulfotomaculum acetoxidans and Desulfofrigus spp., two acetate-consuming, sulfate reducers. In conclusion, our data suggest that acetate and propionate were predominantly consumed by different, specialized groups of sulfate-reducing bacteria.