Prevalence of Heterotrophic Methylmercury Detoxifying Bacteria across Oceanic Regions.

Microbial reduction of inorganic divalent mercury (Hg) and methylmercury (MeHg) demethylation is performed by the operon, specifically by and genes, respectively, but little is known about the mercury tolerance capacity of marine microorganisms and its prevalence in the ocean. Here, combining culture-dependent analyses with metagenomic and metatranscriptomic data, we show that marine bacteria that encode genes are widespread and active in the global ocean. We explored the distribution of these genes in 290 marine heterotrophic bacteria ( and spp.) isolated from different oceanographic regions and depths, and assessed their tolerance to diverse concentrations of Hg and MeHg. In particular, the sp. ISS312 strain presented the highest tolerance capacity and a degradation efficiency for MeHg of 98.2% in 24 h. Fragment recruitment analyses of sp. genomes (ISS312 strain and its associated reconstructed metagenome assembled genome MAG-0289) against microbial bathypelagic metagenomes confirm their prevalence in the deep ocean. Moreover, we retrieved 54 and 6 genes variants related to the sp. ISS312 strain from global metagenomes and metatranscriptomes from Oceans. Our findings highlight the biological reductive MeHg degradation as a relevant pathway of the ocean Hg biogeochemical cycle.