In natural environments, the production of neurotoxic and bioaccumulative methylmercury (MeHg) is mediated by microorganisms carrying the genes hgcA and hgcB. However, the contribution of these microorganisms to mercury (Hg) methylation or MeHg accumulation in the ocean is poorly understood. Here we determined the total Hg (THg) and MeHg concentrations in seawater samples and conducted a metagenomic survey of the hgcAB genes and functional modules involved in metabolic pathways in the East China Sea (ECS). In the metagenomic analyses, we used paired-end reads and assembled contigs for hgcAB enumeration and phylogenetic analyses in the seawater column. To evaluate the relative abundance of hgcAB in the metagenomic data, we estimated the abundance of recA (single-copy gene of bacteria) as well and then compared them. Moreover, the profiles of prokaryotic community composition were analyzed by 16S rRNA gene (V4 region) deep-sequencing. In the mesopelagic layers, the hgcA sequences were detected, and there was a positive correlation between hgcA abundance relative to the recA and MeHg concentrations. Thus, the quantification of the hgcA sequences could provide valuable information to evaluate the potential environments of microbial MeHg accumulation in the seawater column. A phylogenetic analysis using the assembled contigs revealed that all of the hgcA sequences in the mesopelagic layers were affiliated with Nitrospina-like sequences. The 16S rRNA gene analysis revealed that Nitrospinae were abundant in the mesopelagic layers. Although the lineages of Deltaproteobacteria, Firmicutes, and Spirochaetes were detected in the seawater column, their hgcAB sequences were not detected in our metagenomes, despite the fact that they are closely related to previously identified Hg methylators. The metabolic pathway analysis revealed that the modules related to sulfur and methane metabolism were prominent in the mesopelagic layers. However, no hgcA sequences affiliated with sulfate-reducing bacteria (SRB) or methanogens were detected in these layers, suggesting that these bacteria could not be strongly involved in the Hg accumulation in the seawater column. Our results indicate that Nitrospina-like bacteria with hgcAB genes could play a critical role in microbial Hg accumulation in the oxygenated mesopelagic layers of the ECS.

在自然环境中，神经毒性和生物蓄积性甲基汞（MeHg）的产生是由携带该基因的微生物介导的 糖化血红蛋白 和 抗体。但是，这些微生物对海洋中汞（Hg）甲基化或MeHg积累的贡献知之甚少。在这里，我们确定了海水样品中的总Hg（THg）和MeHg浓度，并对海藻样品进行了宏基因组学调查。抗体东海（ECS）代谢途径中涉及的基因和功能模块。在宏基因组学分析中，我们使用了双末端阅读和组装的重叠群用于抗体海水柱的计数和系统发育分析。评估...的相对丰度抗体 在宏基因组学数据中，我们估计了 记录（细菌的单拷贝基因），然后对其进行比较。此外，通过16S rRNA基因（V4区）深度测序分析了原核生物的组成。在近中生层，糖化血红蛋白 检测到序列，并且之间存在正相关 糖化血红蛋白 相对于 记录和甲基汞浓度。因此，糖化血红蛋白这些序列可以提供有价值的信息，以评估海水柱中微生物MeHg积累的潜在环境。使用组装的重叠群的系统发育分析表明，所有糖化血红蛋白 近视层中的序列与 硝化菌类序列。16S rRNA基因分析表明，中旋弹性层中富含硝基刺。尽管在海水柱中检测到了Deltaproteobacteria，Firmicutes和Spirochaetes的血统，抗体尽管我们的基因组与先前鉴定的Hg甲基化因子密切相关，但并未在我们的基因组中检测到这些序列。代谢途径分析表明，与硫和甲烷代谢有关的模块在中弹性层中突出。但是，没有糖化血红蛋白在这些层中检测到了与硫酸盐还原细菌（SRB）或产甲烷菌相关的序列，这表明这些细菌不会强烈参与海水柱中的Hg积累。我们的结果表明硝化菌样细菌 抗体 这些基因可能在ECS的中氧弹性层中微生物Hg积累中起关键作用。