Wetlands are common sites of active Hg methylation by anaerobic microbes; however, the amount of methylmercury produced varies greatly, as Hg methylation is dependent upon both the availability of Hg and the composition and activity of the microbial community involved. In this study, we identified the major microbial guilds responsible for Hg methylation along a trophic gradient composed of two sites and three different types of wetlands: a bog–fen peatland gradient and a black alder swamp, serving as net sources and a sink for methylmercury respectively. Iron‐reducing bacteria in the Geobacteraceae were important Hg methylators across all wetlands and seasons examined, as evidenced by abundant 16S rRNA and hgcA transcripts clustering with this family. Molybdate inhibited Hg methylation more efficiently in the peatlands than in the swamp, suggesting an increasing role of sulfate‐reducing bacteria and/or related syntrophs in the methylation of Hg with decreasing trophic status. Sulfate addition failed to increase Hg methylation rates in the peatlands, suggesting that SRBs/syntrophs were instead likely metabolizing alternative substrates such as syntrophic fermentation of organic compounds with methanogens. These results highlight the interconnectivity of anaerobic metabolism and importance of community dynamics on the methylation of Hg in wetlands with different trophic status.

中文翻译：

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厌氧行会负责各种营养状态的北方湿地中的甲基化，用作甲基汞的来源或汇。

湿地是厌氧微生物活跃的Hg甲基化的常见场所。但是，甲基汞的产生量相差很大，因为汞的甲基化取决于汞的可用性以及所涉及的微生物群落的组成和活性。在本研究中，我们确定了沿营养梯度（由两个地点和三种不同类型的湿地组成）的主要微生物行会，导致汞甲基化：沼泽-泥炭地梯度和黑色al木沼泽，是甲基汞的净来源和汇。分别。铁减少细菌Geobacteraceae是在所有的湿地和检查赛季重要的汞methylators，通过丰富的16S rRNA和证明HGCA笔录与此家庭聚类。相比于沼泽地，钼酸盐在泥炭地中更有效地抑制Hg甲基化，这表明减少硫酸盐还原细菌和/或相关的同养菌在Hg甲基化中具有越来越强的营养状态。硫酸盐的添加不能增加泥炭地中汞的甲基化率，这表明SRB /同食菌可能代谢了其他底物，例如有机化合物与产甲烷菌的同养发酵。这些结果突出了厌氧代谢的相互关系和社区动力学对营养状态不同的湿地中汞甲基化的重要性。