Oxygen?deficient water zones in the Baltic Sea promote uncharacterized Hg methylating microorganisms in underlying sediments

Human-induced expansion of oxygen-deficient zones can have dramatic impacts on marine systems and its resident biota. One example is the formation potent neurotoxic methylmercury (MeHg) that mediated by microbial methylation inorganic divalent Hg (HgII) under conditions. A negative consequence could be an increase in MeHg production due to shifts communities favor microorganisms methylating Hg. There is, however, limited knowledge about Hg-methylating microbes, i.e., those carrying hgc genes critical for mediating process, from sediments. Here, we aim study presence transcripts metagenomes metatranscriptomes four surface sediments with contrasting concentrations oxygen sulfide Baltic Sea. We show potential methylators differed among depending redox Sediments oxygenated featured hgc-like predominantly associated uncultured Desulfobacterota (OalgD group) Desulfobacterales (including Desulfobacula sp.) while a hypoxic-anoxic included hgc-carrying Verrucomicrobia, unclassified Desulfobacterales, Desulfatiglandales, uncharacterized microbes. Our data suggest may lead compositional change groups sediments, where whose metabolism biology not yet been characterized will promoted expand.