南湖新闻网讯（通讯员 陈亢华）近日，我校资源与环境学院土壤微生物生态与环境健康课题组在土壤甲基汞（CH3Hg+）的微生物降解研究方面取得新进展，相关成果以“Microbial potential to mitigate neurotoxic methylmercury accumulation in farmlands and rice”为题发表于Nature Communications。

CH3Hg+是一种强神经毒性污染物，常在水稻土等缺氧环境中由无机汞在微生物作用下转化生成，极易在稻米中富集，并通过食物链放大，对人类健康（尤其是胎儿神经系统发育）和野生动物构成严重威胁。尽管微生物去甲基化被认为是CH3Hg+降解的关键途径，但土壤中降解CH3Hg+的主要微生物类群及其代谢通路仍不明确。

本研究首次合成了13CH3Hg+化合物，并成功应用13CH3Hg+-DNA稳定同位素探针技术（13CH3Hg+-DNA-SIP）结合宏基因组测序，系统解析了土壤中参与CH3Hg+降解的微生物类群及其代谢途径。研究结果表明，假节杆菌属（Pseudarthrobacter）、甲基嗜菌科（Methylophilaceae, MM2类群）和脱氯单胞菌属（Dechloromonas）在高汞污染稻田土壤中显著富集，可能是主要的CH3Hg+降解类群（图1）。进一步纯培养实验证实，隶属于甲基嗜菌科的Methylovorus menthalis和脱氯单胞菌属的Dechloromonas denitrificans具有CH3Hg+降解能力。

图1 参与土壤甲基汞降解的主要微生物类群

宏基因组分析发现，这些候选微生物大多携带与Wood-Ljungdahl途径、二羧酸-羟基丁酸循环、产甲烷和反硝化作用相关的功能基因，但普遍缺乏传统CH3Hg+还原去甲基化所需的merA和merB基因（图2），表明非mer介导途径（例如氧化去甲基化）可能在土壤CH3Hg+降解中起主要作用。此外，基于全国主要稻区典型土壤的估算结果表明，土壤中微生物降解过程可导致稻米中CH3Hg+积累量降低0.08-0.64倍，相应减少居民健康风险0.62%-13.75%，新生儿智商（IQ）损失减少0.13-2.84%。

图2 土壤微生物降解甲基汞的潜在代谢途径

本研究系统揭示了土壤中降解CH3Hg+的关键微生物及其代谢路径，量化了微生物降解对降低稻米CH3Hg+积累及相关健康风险的贡献，凸显了微生物在稻田土壤中CH3Hg+降解中的重要作用，为发展基于微生物的汞污染修复策略提供了重要的理论依据和微生物资源基础。

我校资源与环境学院已毕业博士研究生周心劝和陈亢华为论文共同第一作者，刘玉荣教授为论文通讯作者。美国德克萨斯大学泰勒分校余日清副教授、中国科学院广州地球化学研究所李继兵副研究员、美国橡树岭国家实验室顾宝华教授、华中农业大学冯娇副研究员、谭文峰教授、黄巧云教授、杨曼、刘琴、郝芸芸、刘慧文也参与了该项研究。本研究得到了国家自然科学基金和华中农业大学人才项目资助。

审核人 刘玉荣

论文链接：https://www.nature.com/articles/s41467-025-60458-1

【英文摘要】

Toxic methylmercury (CH3Hg+) is produced by microbial conversion of inorganic mercury in hypoxic environments such as rice paddy soils, and can accumulate in rice grains. Although microbial demethylation has been recognized as a crucial pathway for CH3Hg+ degradation, the identities of microbes and pathways accountable for CH3Hg+ degradation in soil remain elusive. Here, we combine 13CH3Hg+-DNA stable-isotope probing experiments with shotgun metagenomics to explore microbial taxa and associated biochemical processes involved in CH3Hg+ degradation in paddy and upland soils. We identify Pseudarthrobacter, Methylophilaceae (MM2), and Dechloromonas as the most significant taxa potentially engaged in the degradation of 13CH3Hg+ in paddy soil with high mercury contamination. We confirm that strains affiliated with two of those taxa (species Dechloromonas denitrificans and Methylovorus menthalis) can degrade CH3Hg+ in pure culture assays. Metagenomic analysis further reveals that most of these candidate 13CH3Hg+ degraders carry genes associated with the Wood-Ljungdahl pathway, dicarboxylate-hydroxybutyrate cycle, methanogenesis, and denitrification, but apparently lack the merB and merA genes involved in CH3Hg+ reductive demethylation. Finally, we estimate that microbial degradation of soil CH3Hg+ contributes to 0.08–0.64 fold decreases in CH3Hg+ accumulation in rice grains across China (hazard quotient (HQ) decrements of 0.62–13.75%). Thus, our results provide insights into microorganisms and pathways responsible for CH3Hg+ degradation in soil, with potential implications for development of bioremediation strategies.