Identifying different populations of sulfate-reducing bacteria within marine sediment systems, using fatty-acid biomarkers

SUMMARY: The distribution of lipid fatty acids was studied in marine sediment slurries in which sulphate reduction had been stimulated by the addition of acetate, propionate, lactate or hydrogen. Acetate was directly oxidized to carbon dioxide at the expense of sulphate, propionate was incompletely oxidized to acetate at the expense of sulphate, and lactate was largely fermented (approximately 75%) to propionate and acetate, with the propionate subsequently utilized for sulphate reduction. Changes in the lipid fatty acids within these slurries were interpreted by comparison with the lipid fatty acid profiles of pure cultures of Desulfovibrio desulfuricans, Desulfobacter sp. and Desulfobulbus sp. Desulfobacter sp. seems to be the main acetate-utilizing sulphate-reducing bacterium, as in both the slurry and the original sediment the lipid fatty acids in the C12-C18range (where bacterial contributions would be expected) were dominated by even chain fatty acids similar to the lipid fatty acid distribution of Desulfobacter sp. Desulfobulbus sp. appears to be responsible for propionate oxidation and also for hydrogen consumption as its biomarker fatty acid n-C17:1 was increased significantly by the addition of either propionate or hydrogen. Surprisingly, the biomarker for Desulfovibrio desulfuricans (br-C17:1) was not stimulated in any of the sediment slurries. The results demonstrate that there are at least two functional groups of sulphate-reducing bacteria in marine systems, and that lipid fatty acid analysis is a useful technique for investigating bacterial distributions within a complex sedimentary environment