Potential sulfur metabolisms and associated bacteria within anoxic surface sediment from saline meromictic Lake Kaiike (Japan)

The effects of light and of added electron donors and sulfur compounds on sulfur metabolisms in the microbial mat dilutions from the saline meromictic Lake Kaiike were investigated. Sulfide concentrations in the mat dilution without any electron donor gradually increased by ≈0.6-1 mM in the dark. Additions of lactate, acetate, H2/CO2, propionate and iso-butylate stimulated sulfide production, whereas benzoate did not, indicating the limitation of sulfate reduction by available electron donor concentrations. More sulfide was produced, without a decrease of sulfate, in an elemental sulfur-amended dilution than in a non-amended control. In contrast, the addition of a high concentration of sulfide slowed down sulfide production. After enrichment under various conditions, microbial communities in the dilutions were characterized by a denaturing gradient gel electrophoresis of PCR-amplified 16S rRNA gene and sequencing. As a result, microorganisms affiliated with mesophilic sulfate-reducing bacteria group within the Deltaproteobacteria and the Epsilonproteobacteria were mainly enriched by the addition of electrons used in this study, suggesting that these microorganisms might play an important role in sulfur metabolisms within the surficial sediment of Lake Kaiike.