产甲烷古菌介导(类)金属转化的研究进展

Advances and prospects in metal(loid) transformation driven by methanogenic archaea

摘要:

产甲烷古菌是缺氧环境中碳循环的核心驱动者。近年的研究表明，产甲烷古菌还参与了(类)金属的生物地球化学循环，但其介导的金属转化机制尚未得到系统的总结。本文综合了最新的研究成果，重点解析了产甲烷古菌对铁(Fe)、汞(Hg)、钒(V)、铬(Cr)、镉(Cd)、砷(As)、硒(Se)等典型(类)金属的氧化、还原、甲基化及去甲基化过程。(1) Fe(Ⅲ)还原对甲烷生成具有双向调控作用，当胞外Fe(Ⅲ)还原不能耦合能量代谢时，会显著抑制产甲烷古菌的生长及产甲烷过程，例如巴氏甲烷八叠球菌(Methanosarcina barkeri)；而当胞外Fe(Ⅲ)还原耦合能量代谢时，则会促进产甲烷古菌的生理代谢活性，例如噬乙酸甲烷八叠球菌(Methanosarcina acetivorans)；(2) 在汞甲基化机制方面，产甲烷古菌通过hgcAB基因簇编码的甲基转移酶实现Hg(Ⅱ)向甲基汞(methylmercury, MeHg)的转化，且部分菌株，如卢米尼甲烷马赛球菌(Methanomassiliicoccus luminyensis)的甲基化活性与死细胞释放的酶活性相关；(3) 砷转化机制呈现多样性，M. acetivorans通过As(Ⅲ)S-腺苷甲硫氨酸甲基转移酶(arsenic methyltransferase, ArsM)催化As(Ⅲ)甲基化，同时可利用砷酸盐还原酶(arsenate reductase, ArsC)还原As(V)为As(Ⅲ)，而稻田古菌群落还表现出有机胂的去甲基化能力；(4) 硒的生物转化具有双重性，低浓度硒纳米颗粒(selenium nanoparticles, SeNPs)能够促进产甲烷活性并诱导有机硒合成，而高浓度则会引发氧化应激。在环境效应方面，(类)金属通过改变氧化还原电位、竞争电子受体或诱导毒性胁迫，显著影响产甲烷古菌的代谢活性与群落结构。本文系统地揭示了产甲烷古菌在(类)金属循环中的多功能性，并提出未来需要结合宏组学与代谢组学技术解析关键酶的分子机制，同时探索基于产甲烷古菌的(类)金属污染生物修复新策略。

关键词:产甲烷古菌;(类)金属转化;还原;甲基化;去甲基化

Abstract:

Methanogenic archaea are pivotal drivers of carbon cycling in anoxic environments. Growing evidence shows that they also participate in the biogeochemical cycling of metal(loid)s, yet the underlying transformation mechanisms have not been systematically summarized. This review integrates the latest findings to dissect how methanogenic archaea oxidize, reduce, methylate, and demethylate representative metal(loid)s, including iron (Fe), mercury (Hg), vanadium (V), chromium (Cr), cadmium (Cd), arsenic (As), and selenium (Se). The research findings are summarized as follows: (1) Fe(Ⅲ) reduction exerts bidirectional control over methanogenesis. When extracellular Fe(Ⅲ) reduction is not coupled to energy metabolism, it markedly suppresses the growth and methane production of methanogenic archaea (e.g., Methanosarcina barkeri). Conversely, when extracellular Fe(Ⅲ) reduction is coupled to energy metabolism, it stimulates the physiological and metabolic activities of methanogenic archaea (e.g., Methanosarcina acetivorans). (2) For mercury methylation, methanogenic archaea convert Hg(Ⅱ) to methylmercury (MeHg) via a methyltransferase encoded by the hgcAB gene cluster. In some species (e.g., Methanomassiliicoccus luminyensis), the observed methylation activity is associated with enzymes released from lysed cells. (3) Arsenic transformation runs with diverse mechanisms. Methanosarcina acetivorans methylates As(Ⅲ) via the arsenic methyltransferase (ArsM) and concurrently reduces As(V) to As(Ⅲ) through arsenate reductase (ArsC), whereas archaeal communities in paddy soils are capable of demethylating organic arsine. (4) Selenium biotransformation exhibits dual effects: low concentrations of selenium nanoparticles (SeNPs) enhance methanogenic activity and induce organoselenium synthesis, whereas high concentrations trigger oxidative stress. Environmentally, metal (loid)s markedly affect the metabolic activity and community structure of methanogenic archaea by altering redox potential, competing for electron acceptors, or imposing toxic stress. This review highlights the multifunctionality of methanogenic archaea in metal (loid) cycling and proposes that future work should combine meta-omics and metabolomics approaches to elucidate enzyme-level mechanisms, while exploring methanogenic archaea-based strategies for the bioremediation of metal (loid) contamination.

Key words:methanogenic archaea;metal(loid) transformation;reduction;methylation;demethylation