Department of Ecology and Genetics, Limnology and Science for Life Laboratory, Uppsala University, Uppsala, Sweden
Department of Marine Biology and Oceanography, Institut de Ciències del Mar, Consejo Superior de Investigaciones Científicas, Barcelona, Catalonia, Spain.
Appl Environ Microbiol. 2018 Nov 15;84(23). doi: 10.1128/AEM.01774-18. Print 2018 Dec 1.
Methylmercury is a potent human neurotoxin which biomagnifies in aquatic food webs. Although anaerobic microorganisms containing the gene potentially mediate the formation of methylmercury in natural environments, the diversity of these mercury-methylating microbial communities remains largely unexplored. Previous studies have implicated sulfate-reducing bacteria as the main mercury methylators in aquatic ecosystems. In the present study, we characterized the diversity of mercury-methylating microbial communities of boreal lake sediments using high-throughput sequencing of 16S rRNA and genes. Our results show that in the lake sediments, and also represent abundant members of the mercury-methylating communities. In fact, incubation experiments with a mercury isotopic tracer and molybdate revealed that only between 38% and 45% of mercury methylation was attributed to sulfate reduction. These results suggest that methanogens and iron-reducing bacteria may contribute to more than half of the mercury methylation in boreal lakes. Despite the global awareness that mercury, and methylmercury in particular, is a neurotoxin to which millions of people continue to be exposed, there are sizable gaps in the understanding of the processes and organisms involved in methylmercury formation in aquatic ecosystems. In the present study, we shed light on the diversity of the microorganisms responsible for methylmercury formation in boreal lake sediments. All the microorganisms identified are associated with the processing of organic matter in aquatic systems. Moreover, our results show that the well-known mercury-methylating sulfate-reducing bacteria constituted only a minor portion of the potential mercury methylators. In contrast, methanogens and iron-reducing bacteria were important contributors to methylmercury formation, highlighting their role in mercury cycling in the environment.
甲基汞是一种强效的人类神经毒素，在水生食物网中具有生物放大作用。尽管含有基因的厌氧微生物有可能在自然环境中形成甲基汞，但这些汞甲基化微生物群落的多样性在很大程度上仍未得到探索。先前的研究表明，硫酸盐还原菌是水生生态系统中主要的汞甲基化菌。在本研究中，我们使用 16S rRNA 和基因的高通量测序来描述北方湖泊沉积物中汞甲基化微生物群落的多样性。我们的结果表明，在湖泊沉积物中，和也代表了汞甲基化群落中的丰富成员。事实上，用汞同位素示踪剂和钼酸盐进行的孵育实验表明，只有 38%到 45%的汞甲基化归因于硫酸盐还原。这些结果表明，产甲烷菌和铁还原菌可能对北方湖泊中超过一半的汞甲基化有贡献。尽管人们普遍认识到汞，特别是甲基汞，是一种神经毒素，数以百万计的人仍在继续接触，但对于水生生态系统中形成甲基汞的过程和生物体的理解仍存在很大差距。在本研究中，我们揭示了北方湖泊沉积物中形成甲基汞的微生物多样性。所有鉴定出的微生物都与水生系统中有机物的处理有关。此外，我们的结果表明，众所周知的汞甲基化硫酸盐还原菌只构成了潜在汞甲基化菌的一小部分。相比之下，产甲烷菌和铁还原菌是甲基汞形成的重要贡献者，突出了它们在环境中汞循环中的作用。
