Metagenomic evidence for climate-associated variation in microbial methylmercury production across peatlands

Peatlands are major global mercury (Hg) reservoirs and are highly sensitive to warming, yet climate effects on microbial controls of neurotoxic methylmercury (MeHg) formation remain unclear. Here, we combined global synthesis with new measurements to assess climate-associated variation in net MeHg production. Metagenomes from 144 peat soils revealed higher relative abundance of the Hg-methylation gene hgcA but lower relative abundance of the demethylation gene merB at high latitudes, consistent with their opposing correlations with mean annual temperature. The ratio of nitrogen-fixation to denitrification genes ( nifH / nosZ ) covaried with hgcA and merB , suggesting links between nitrogen cycling and Hg transformation. Genome-resolved analyses further showed expanded denitrification pathways in hgcA -bearing taxa from warmer peatlands. Together, these findings indicate that warmer climates may be associated with microbial community restructuring and lower net MeHg production. A space-for-time framework therefore suggests reduced MeHg yields under future warming, informing Hg-risk assessment under the Minamata Convention.