Soil and Water Science Department, University of Florida, Gainesville, Florida, USA.
DB Environmental, Rockledge, Florida, USA.
Appl Environ Microbiol. 2019 Jun 17;85(13). doi: 10.1128/AEM.00156-19. Print 2019 Jul 1.
Mercury (Hg) methylation in the Florida Everglades is of great environmental concern because of its adverse effects on human and wildlife health through biomagnification in aquatic food webs. Periphyton and flocculant materials (floc) overlaying peat soil are important ecological compartments producing methylmercury (MeHg) in this ecosystem. These compartments retain higher concentrations of MeHg than did soil at study sites across nutrient and/or sulfate gradient(s). To better understand what controls Hg methylation in these compartments, the present study explored the structures and abundances of Hg methylators using genes as biomarkers. The sequences indicated that these compartments hosted a high diversity of Hg methylators, including , , , and , with community compositions that differed between these habitats. The copy numbers of quantified by quantitative PCR revealed that floc and soil supported higher numbers of Hg methylators than periphyton in the Everglades ecosystem. The abundance of Hg methylators was strongly positively correlated with concentrations of carbon and nutrients (e.g., phosphorus and nitrogen) according to redundancy analysis. Strong correlations were also observed among numbers of sulfate reducers, methanogens, and the dominant -carrying groups, suggesting that would spread primarily through the growth of those assemblages. The abundances of Hg methylators were weakly negatively correlated to MeHg concentrations, suggesting that the size of this population would not solely determine the final concentrations of MeHg in the ecological compartments studied. This study extends the knowledge regarding the distribution of diverse potential mercury methylators in different environmental compartments in a wetland of national concern. Methylmercury is a potent neurotoxin that impacts the health of humans and wildlife. Most mercury in wetlands such as the Florida Everglades enters as inorganic mercury via atmospheric deposition, some of which is transformed to the more toxic methylmercury through the activities of anaerobic microorganisms. We investigated the numbers and phylogenetic diversity of , genes that are linked to mercury methylation, in the soil, floc, and periphyton in areas of the Everglades with different sulfate and nutrient concentrations. Soil harbored relatively high numbers of cells capable of methylating mercury; however, little detectable methylmercury was present in soil. The greatest concentrations of methylmercury were found in floc and periphyton. The dominant methylators in those compartments included methanogens and This work provides significant insight into the microbial processes that control methylation and form the basis for accumulation through the food chain in this important environment.
佛罗里达州大沼泽地的汞（Hg）甲基化是一个非常令人关注的环境问题，因为它通过水生食物网中的生物放大作用对人类和野生动物的健康产生了不利影响。附生藻类和覆盖在泥炭土上的絮凝材料（floc）是在这个生态系统中产生甲基汞（MeHg）的重要生态区室。这些区室比研究地点的土壤保留了更高浓度的 MeHg，无论是在养分还是硫酸盐梯度下。为了更好地了解这些区室中汞甲基化的控制因素，本研究使用基因作为生物标志物探索了 Hg 甲基化菌的结构和丰度。这些序列表明，这些区室中存在着丰富的 Hg 甲基化菌，包括、、、和，它们的群落组成在这些生境中存在差异。通过定量 PCR 定量的拷贝数显示，在大沼泽地生态系统中，floc 和土壤支持的 Hg 甲基化菌数量高于附生藻类。根据冗余分析，Hg 甲基化菌的丰度与碳和营养物质（如磷和氮）的浓度呈强烈正相关。硫酸盐还原菌、产甲烷菌和主要携带组之间也观察到强烈的相关性，这表明将主要通过这些组合的生长来传播。Hg 甲基化菌的丰度与 MeHg 浓度呈弱负相关，这表明该种群的大小不会单独决定所研究的生态区室中 MeHg 的最终浓度。本研究扩展了关于不同环境区室中不同潜在汞甲基化菌分布的知识，这些区室位于一个国家关注的湿地中。甲基汞是一种强有力的神经毒素，会影响人类和野生动物的健康。湿地中的大部分汞（如佛罗里达州大沼泽地）以无机汞的形式通过大气沉降进入，其中一些通过厌氧微生物的活动转化为更具毒性的甲基汞。我们调查了 Everglades 不同硫酸盐和养分浓度区的土壤、floc 和附生藻类中与汞甲基化相关的、基因的数量和系统发育多样性。土壤中含有相对较多的能够甲基化汞的细胞；然而，土壤中几乎没有可检测到的甲基汞。甲基汞浓度最大的是在 floc 和附生藻类中。那些区室中的主要甲基化菌包括产甲烷菌和。这项工作提供了对控制甲基化的微生物过程的重要见解，并为在这个重要环境中通过食物链积累提供了基础。
