Peatlands are generally important sources of methylmercury (MeHg) to adjacent aquatic ecosystems, increasing the risk of human and wildlife exposure to this highly toxic compound. While microorganisms play important roles in mercury (Hg) geochemical cycles where they directly and indirectly affect MeHg formation in peatlands, potential linkages between net MeHg formation and microbial communities involving these microorganisms remain unclear. To address this gap, microbial community composition and specific marker gene transcripts were investigated along a trophic gradient in a geographically constrained peatland chronosequence. Our results showed a clear spatial pattern in microbial community composition along the gradient that was highly driven by peat soil properties and significantly associated with net MeHg formation as approximated by MeHg concentration and %MeHg of total Hg concentration. Known fermentative, syntrophic, methanogenic and iron-reducing metabolic guilds had the strong positive correlations to net MeHg formation, while methanotrophic and methylotrophic microorganisms were negatively correlated. Our results indicated that sulfate reducers did not have a key role in net MeHg formation. Microbial activity as interpreted from 16S rRNA sequences was significantly correlated with MeHg and %MeHg. Our findings shed new light on the role of microbial community in net MeHg formation of peatlands that undergo ontogenetic change.

泥炭地通常是邻近水生生态系统甲基汞 (MeHg) 的重要来源，增加了人类和野生动物接触这种剧毒化合物的风险。虽然微生物在汞 (Hg) 地球化学循环中发挥重要作用，它们直接和间接影响泥炭地中甲基汞的形成，但净甲基汞形成与涉及这些微生物的微生物群落之间的潜在联系仍不清楚。为了解决这一差距，在地理上受限的泥炭地时间序列中，沿着营养梯度研究了微生物群落组成和特定标记基因转录物。我们的研究结果表明，沿梯度的微生物群落组成具有清晰的空间模式，该模式高度受泥炭土壤特性的驱动，并且与净 MeHg 形成显着相关，近似于 MeHg 浓度和总 Hg 浓度的 %MeHg。已知的发酵、共养、产甲烷和铁还原代谢群与净甲基汞形成有很强的正相关，而甲烷营养微生物和甲基营养微生物则呈负相关。我们的结果表明硫酸盐还原剂在净甲基汞形成中没有关键作用。从 16S rRNA 序列解释的微生物活性与 MeHg 和 %MeHg 显着相关。我们的研究结果揭示了微生物群落在经历个体发生变化的泥炭地的净甲基汞形成中的作用。