Université de Pau et des Pays de l'Adour, E2S UPPA, CNRS, IPREM, Pau, France.
Independent Researcher, Lourenties, France.
NPJ Biofilms Microbiomes. 2021 Nov 19;7(1):83. doi: 10.1038/s41522-021-00255-y.
Methylmercury, biomagnifying through food chains, is highly toxic for aquatic life. Its production and degradation are largely driven by microbial transformations; however, diversity and metabolic activity of mercury transformers, resulting in methylmercury concentrations in environments, remain poorly understood. Microbial mats are thick biofilms where oxic and anoxic metabolisms cooccur, providing opportunities to investigate the complexity of the microbial mercury transformations over contrasted redox conditions. Here, we conducted a genome-resolved metagenomic and metatranscriptomic analysis to identify putative activity of mercury reducers, methylators and demethylators in microbial mats strongly contaminated by mercury. Our transcriptomic results revealed the major role of rare microorganisms in mercury cycling. Mercury methylators, mainly related to Desulfobacterota, expressed a large panel of metabolic activities in sulfur, iron, nitrogen, and halogen compound transformations, extending known activities of mercury methylators under suboxic to anoxic conditions. Methylmercury detoxification processes were dissociated in the microbial mats with methylmercury cleavage being carried out by sulfide-oxidizing Thiotrichaceae and Rhodobacteraceae populations, whereas mercury reducers included members of the Verrucomicrobia, Bacteroidetes, Gammaproteobacteria, and different populations of Rhodobacteraceae. However most of the mercury reduction was potentially carried out anaerobically by sulfur- and iron-reducing Desulfuromonadaceae, revising our understanding of mercury transformers ecophysiology.
甲基汞通过食物链生物放大，对水生生物具有很高的毒性。其产生和降解在很大程度上受微生物转化的驱动；然而，汞转化器的多样性和代谢活性导致环境中甲基汞浓度仍然知之甚少。微生物垫是一种厚厚的生物膜，其中好氧和缺氧代谢同时发生，为研究在对比氧化还原条件下微生物汞转化的复杂性提供了机会。在这里，我们进行了基因组解析的宏基因组和宏转录组分析，以鉴定受汞严重污染的微生物垫中汞还原菌、甲基化菌和脱甲基菌的潜在活性。我们的转录组结果揭示了稀有微生物在汞循环中的主要作用。汞甲基化菌主要与脱硫菌门有关，在硫、铁、氮和卤素化合物转化中表达了大量的代谢活性，扩展了在亚缺氧到缺氧条件下已知的汞甲基化菌的活性。在微生物垫中，甲基汞解毒过程是分离的，甲基汞的裂解由硫氧化硫杆菌科和红杆菌科的种群进行，而汞还原菌包括疣微菌门、拟杆菌门、γ变形菌纲和不同的红杆菌科种群。然而，大部分汞还原可能是由硫还原菌和铁还原菌门的脱硫单胞菌科在厌氧条件下进行的，这修正了我们对汞转化器生态生理学的理解。
