Methylmercury is a neurotoxin that bioaccumulates from seawater to high concentrations in marine fish, putting human and ecosystem health at risk. High methylmercury levels have been found in the oxic subsurface waters of all oceans, but only anaerobic microorganisms have been shown to efficiently produce methylmercury in anoxic environments. The microaerophilic nitrite‐oxidizing bacteria Nitrospina have previously been suggested as possible mercury methylating bacteria in Antarctic sea ice. However, the microorganisms responsible for processing inorganic mercury into methylmercury in oxic seawater remain unknown. Here, we show metagenomic and metatranscriptomic evidence that the genetic potential for microbial methylmercury production is widespread in oxic seawater. We find high abundance and expression of the key mercury methylating genes hgcAB across all ocean basins, corresponding to the taxonomic relatives of known mercury methylating bacteria from Deltaproteobacteria, Firmicutes and Chloroflexi. Our results identify Nitrospina as the predominant and widespread microorganism carrying and actively expressing hgcAB. The highest hgcAB abundance and expression occurs in the oxic subsurface waters of the global ocean where the highest MeHg concentrations are typically observed.

中文翻译：

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全球海洋中广泛的微生物汞甲基化基因。

甲基汞是一种神经毒素，会从海水中生物蓄积到海水鱼类中的高浓度，使人类和生态系统健康处于危险之中。在所有海洋的有氧地下水中都发现了高甲基汞含量，但是只有厌氧微生物被证明在缺氧环境中能有效地产生甲基汞。微需氧亚硝酸盐氧化细菌Nitrospina以前曾建议在南极海冰中将汞甲基化细菌作为可能。然而，在含氧海水中负责将无机汞加工成甲基汞的微生物仍然未知。在这里，我们显示了宏基因组学和超转录组学证据，表明微生物甲基汞生产的遗传潜力在含氧海水中广泛存在。我们发现所有海洋盆地中的主要汞甲基化基因hgcAB的丰度和表达都很高，这与来自三角洲变形杆菌，Firmicutes和Chloroflexi的已知汞甲基化细菌的分类学相对应。我们的结果确定了硝基亚种作为携带和积极表达hgcAB的主要和广泛的微生物。最高的hgcAB丰度和表达发生在通常观察到最高的MeHg浓度的全球海洋含氧地下水域中。