Mercury Methylation Genes Identified across Diverse Anaerobic Microbial Guilds in a Eutrophic Sulfate-Enriched Lake
Mercury Methylation Genes Identified across Diverse Anaerobic Microbial Guilds in a Eutrophic Sulfate-Enriched Lake
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DOI：
10.1021/acs.est.0c05435
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发表时间：
2020-12-15
影响因子：
11.4
通讯作者：
McMahon, Katherine D.
中科院分区：
文献类型：
--
作者：
Peterson, Benjamin D.;McDaniel, Elizabeth A.;McMahon, Katherine D.
汞甲基化是一种微生物介导的过程，将无机汞转化为具有生物蓄积性和神经毒性的甲基汞（MeHg）。甲基化生物的代谢活性高度依赖于生物地球化学条件，从而影响甲基汞的产生。然而，我们对自然生态系统中甲基化反应的生态生理认识仍然有限。在这里，我们确定了在一个淡水湖的缺氧、硫化物低浓度环境中MeHg生产的潜在位置。在这些位点，我们使用散弹枪宏基因组学来表征含有hg甲基化基因hgcA的微生物。假设的甲基化体主要由hgcA序列主导，这些序列与经过充分研究和证实的甲基化体不同。利用基因组解析的宏基因组学，我们在拟杆菌门和最近描述的Kiritimatiellaeota门中鉴定了具有hgcA （hgcA+）的生物体。我们确定了来自硫酸盐还原细菌的hgcA+基因组，但这些基因组仅占hgcA+基因组覆盖率的22%。最丰富的hgcA+基因组来自发酵罐，占hgcA基因覆盖率的一半以上。许多这些生物体也介导多糖的水解，可能来自蓝藻华。这项工作强调了hg甲基化基因在微生物代谢行业中的分布，并表明多糖的初级降解和发酵可能在淡水湖缺氧低铁中MeHg的产生中起着重要但未被认识到的作用。
Mercury (Hg) methylation is a microbially mediated process that converts inorganic Hg into bioaccumulative, neurotoxic methylmercury (MeHg). The metabolic activity of methylating organisms is highly dependent on biogeochemical conditions, which subsequently influences MeHg production. However, our understanding of the ecophysiology of methylators in natural ecosystems is still limited. Here, we identified potential locations of MeHg production in the anoxic, sulfidic hypolimnion of a freshwater lake. At these sites, we used shotgun metagenomics to characterize microorganisms with the Hg-methylation gene hgcA. Putative methylators were dominated by hgcA sequences divergent from those in well-studied, confirmed methylators. Using genome-resolved metagenomics, we identified organisms with hgcA (hgcA+) within the Bacteroidetes and the recently described Kiritimatiellaeota phyla. We identified hgcA+ genomes derived from sulfate-reducing bacteria, but these accounted for only 22% of hgcA+ genome coverage. The most abundant hgcA+ genomes were from fermenters, accounting for over half of the hgcA gene coverage. Many of these organisms also mediate hydrolysis of polysaccharides, likely from cyanobacterial blooms. This work highlights the distribution of the Hg-methylation genes across microbial metabolic guilds and indicate that primary degradation of polysaccharides and fermentation may play an important but unrecognized role in MeHg production in the anoxic hypolimnion of freshwater lakes.