Unrecognized microbial sources of methyl mercury in freshwater lakes

甲基汞是一种有毒的环境污染物，在鱼类中含量很高。这导致了大量的鱼类消费建议。虽然我们知道这种化学物质可以由微生物产生，这些微生物可以将汞从无毒的形式变成有毒的形式，但是关于这种情况在环境中的什么地方发生还有很多问题。该项目的目标是确定哪些微生物可以在湖泊中进行这种反应。这项研究将集中在高分辨率的地图上，在这些微生物活跃的湖泊中，有高水平的甲基汞。这些图谱将与将活性与甲基汞生产联系起来的最先进的宏基因组学技术进行比较。水资源管理者、监管机构、苗族自给渔民和其他利益相关者将参与进来，以增进对甲基汞构成的潜在威胁的了解。这项工作的成功完成将有助于更好地了解仁慈甲基化，并导致更明智的决策，以尽量减少人类接触受污染的鱼类。甲基汞（MeHg）是一种令人关注的环境污染物，它是一种神经毒素，可在水生食物网中生物积累，导致人类通过食用鱼类接触到甲基汞。无机汞主要由于人类活动进入生态系统后，微生物负责将其转化为毒性更大的甲基汞。初步数据表明，汞甲基化基因分布在不同的微生物谱系内和之间，包括那些很少或没有培养代表的微生物谱系。这些新生物体在甲基化中的作用几乎完全没有被探索过。现场研究将与美国地质调查局合作，在两个不同的现场进行：威斯康星州麦迪逊的Mendota湖和爱达荷州地狱峡谷的Snake河沿岸的一系列水库。两者都是高度富营养化的，初级生产由农业养分投入推动。迄今为止的研究表明，甲基汞在这两个地点的温跃层下方积聚。拟议的工作将建立在这些观察的基础上，通过追求三个具体目标：目标1是使用从研究地点收集的样品测量水柱中时空氧化还原梯度的甲基化和去甲基化率。目标2是利用元基因组学和元转录组学将甲基化行会与原位生物地球化学联系起来，使用鸟枪测序社区DNA和cDNA以及计算分析来恢复群体基因组，同时将基因表达与个体功能群联系起来。关键群体将使用qPCR进行量化，以提供更多的时间和空间甲基化分布的定量和复制视图。目的3是利用汞同位素和假设抑制或促进甲基化的靶向修饰物的中胚层孵育来确定甲基化的代谢限制。成功地确定水柱中汞甲基化的存在将改变我们对甲基汞动力学的理解，因为我们目前的理解是这通常发生在厌氧沉积物中。通过对汞甲基化动力学的详细分析，有可能找到控制甲基化和/或防止汞在鱼类体内吸收的新方法。与当地苗族渔民社区的接触将增加对甲基汞如何被鱼类吸收的了解，从而增加潜在的效益。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The chemical methylmercury is toxic environmental pollutant that can be found in high concentrations in fish. This has led to numerous fish consumption advisories. While we know that this chemical can be produced by microorganisms that change mercury from a non-toxic form into a toxic form, there are many questions concerning where this occurs in the environment. The goal of this project is to identify which microorganisms can perform this reaction in lakes. The study will focus on high resolution mapping where these microorganisms are active in lakes that have fish with high levels of methylmercury. These maps will be compared with state-of-the-science metagenomics techniques link activity to methylmercury production. Water managers, regulatory agencies, Hmong subsistence fishers, and other stakeholders will be engaged to increase understanding of the potential threat methylmercury poses. Successful completion of this work will lead to a better understanding of mercy methylation and lead to more informed decision making to minimize human exposure to contaminated fish.Methylmercury (MeHg) is an environmental pollutant of major concern due to its role as a neurotoxin that bioaccumulates in aquatic food webs, leading to human exposure through fish consumption. After inorganic mercury enters ecosystems due mainly to human activity, microbes are responsible for transforming it into the much more toxic MeHg. Preliminary data suggests that mercury methylation genes are distributed within and across divergent microbial lineages, including those with few or no cultured representatives. The role of these novel organisms in methylation is almost completely unexplored. Filed studies will be performed in collaboration with the US Geological Survey at two contrasting field sites: Lake Mendota in Madison, WI and a series of reservoirs along the Snake River in Hell's Canyon, Idaho. Both are highly eutrophic with primary production being fueled by agricultural nutrient input. Work to date has shown that MeHg accumulates just below the thermocline at both sites. The proposed work will build on these observations by pursuing three specific aims: Aim 1 is to measure methylation and demethylation rates across spatial and temporal redox gradients in the water column using samples collected from the study sites. Aim 2 is to link methylator guilds to in situ biogeochemistry using metagenomics and metatranscriptomics using shotgun sequencing community DNA and cDNA and computational analysis to recover population genomes while linking gene expression to individual functional groups. Key populations will be quantified using qPCR to provide a more quantitative and replicated view of the methylator distributions in time and space. Aim 3 is to define metabolic constraints on methylation using mesocosm incubations with mercury isotopes and targeted amendments hypothesized to inhibit or promote methylation. Successfully establishing the presence of mercury methylation in the water column would be transformative to our understanding of MeHg dynamics, as our current understanding is that this normally occurs in anaerobic sediments. By providing detailed analysis of Hg methylation dynamics, new approaches to controlling methylation and/or preventing uptake in fish may be possible. Outreach to a local Hmong community of fishers will increase the potential benefits by increasing understanding of how MeHg is take up by fish.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.