GRIL, Département de Sciences Biologiques, Université de Montréal, Montréal, Québec, Canada.
GRIL, Département de Sciences Biologiques, Université du Québec à Montréal, Montréal, Québec, Canada.
mSphere. 2021 Mar 17;6(2):e00021-21. doi: 10.1128/mSphere.00021-21.
Periphytic biofilms have the potential to greatly influence the microbial production of the neurotoxicant monomethylmercury in freshwaters although few studies have simultaneously assessed periphyton mercury methylation and demethylation rates and the microbial communities associated with these transformations. We performed a field study on periphyton from a river affected by run-of-river power plants and artificial wetlands in a boreal landscape (Québec, Canada). incubations were performed on three sites using environmental concentrations of isotopically enriched monomethylmercury (MMHg) and inorganic mercury (Hg) for demethylation and methylation rate measurements. Periphytic microbial communities were investigated through 16S rRNA gene analyses and metagenomic screenings for the gene, involved in mercury methylation. Positive mercury methylation rates ([5.9 ± 3.4] × 10 day) were observed only in the wetlands, and demethylation rates averaged 1.78 ± 0.21 day for the three studied sites. The 16S rRNA gene analyses revealed as the most abundant phylum across all sites (36.3% ± 1.4%), from which families associated with mercury methylation were mostly found in the wetland site. Metagenome screening for HgcA identified 24 different sequences in the constructed wetland site only, associated with 8 known families, where the iron-reducing were the most abundant. This work brings new information on mercury methylation in periphyton from habitats of impacted rivers, associating it mostly with putative iron-reducing bacteria. Monomethylmercury (MMHg) is a biomagnifiable neurotoxin of global concern with risks to human health mostly associated with fish consumption. Hydroelectric reservoirs are known to be sources of MMHg many years after their impoundment. Little is known, however, on run-of-river dams flooding smaller terrestrial areas, although their numbers are expected to increase considerably worldwide in decades to come. Production of MMHg is associated mostly with anaerobic processes, but Hg methylation has been shown to occur in periphytic biofilms located in oxic zones of the water column. Therefore, in this study, we investigated production of MMHg by periphytic communities in habitats impacted by the construction of a run-of-river dam by combining transformation rate measurements with genomic approaches targeting genes, responsible for mercury methylation. These results provide extended knowledge on mercury methylators in river ecosystems impacted by run-of-river dams in temperate habitats.
底栖生物膜有可能极大地影响淡水中神经毒素一甲基汞的微生物产量，尽管很少有研究同时评估底栖生物汞甲基化和去甲基化速率以及与这些转化相关的微生物群落。我们在加拿大（魁北克）受河流上的径流式水电站和人工湿地影响的河流底栖生物中进行了一项野外研究。在三个地点进行了用环境浓度的同位素富集一甲基汞（MMHg）和无机汞（Hg）进行的孵育，以测量去甲基化和甲基化速率。通过 16S rRNA 基因分析和涉及汞甲基化的 基因的宏基因组筛选研究了底栖微生物群落。仅在湿地中观察到阳性的汞甲基化速率（[5.9±3.4]×10-1 天-1），而三个研究地点的去甲基化速率平均为 1.78±0.21 天-1。16S rRNA 基因分析表明，在所有地点中，均以 为最丰富的门（36.3%±1.4%），其中与汞甲基化有关的科主要存在于湿地地点。针对 HgcA 的宏基因组筛选仅在构建的湿地地点中鉴定出 24 种不同的 序列，与 8 个已知家族相关，其中铁还原菌最为丰富。这项工作提供了有关受影响河流生境中底栖生物汞甲基化的新信息，将其主要与假定的铁还原菌联系起来。一甲基汞（MMHg）是一种具有生物放大作用的神经毒素，全球范围内都存在对人类健康的风险，主要与鱼类消费有关。水力发电水库在蓄水多年后已知是 MMHg 的来源。然而，对于淹没较小陆地面积的径流式水坝，人们知之甚少，尽管预计在未来几十年内，它们的数量将在全球范围内大幅增加。MMHg 的产生主要与厌氧过程有关，但已经表明，在水柱好氧区的底栖生物膜中会发生 Hg 甲基化。因此，在这项研究中，我们通过结合转化速率测量和针对负责汞甲基化的 基因的基因组方法，研究了受径流式水坝建设影响的生境中底栖生物群落对 MMHg 的 生产。这些结果为受径流式水坝影响的温带河流生态系统中汞甲基化菌提供了更广泛的知识。
