Seasonal dynamics of bacterial communities in a highly polluted coastal lagoon: Dominance of sulfur bacteria in response to elevated H2S levels.

This study aims to evaluate the effects of different environmental gradients and seasonality on the bacterial communities of an impacted coastal lagoon. While the community compositions were homogenous in surface waters with the dominance of Candidatus Pelagibacter, diversity showed high vertical variation due to salinity and dissolved oxygen gradients. Anoxic conditions occurred at deeper parts of the lagoon, particularly at 14 m and 18 m, where nutrient enrichment and high H2S concentration were detected resulting in a shift of bacterial community to anoxic species. Sulfurimonas, Sulfurovum, and Desulfobacula were dominant genera at 14 m and 18 m where the H2S concentration was high. The community composition of the sediment did not change over seasons, dominated by Syntrophus species. The insights gained from this study may contribute to understanding how dissolved oxygen, H2S concentrations and salinity drive bacterial community structure in euxinic ecosystems especially the dominance of anoxic bacteria.