珠江口汞甲基化细菌群落及其在甲基汞原位生成中的作用

Studies on mercury (Hg) methylation in the estuary, which is an important sink of terrestrial Hg, are essential to understanding of biogeochemical cycle of Hg in the regional environment. In situ bacterial methylation of inorganic Hg is the major pathway of MeHg production in the aquatic environments. The Pearl River Estuary (PRE) has been seriously polluted with Hg due to the rapid economic development and urbanization. However, there is still a lack of knowledge on characterization of bacterial community of Hg methylation and its influencing factors in the PRE, as well as their relationships with methylation rate of inorganic Hg. Therefore, this proposed project aims to provide an in-depth understanding towards bacterial methylation of inorganic Hg in the PRE. By using multiple sophisticated techniques, including Hg speciation analysis, isotope dilution, isotope tracer and high throughput DNA sequencing-based bacterial community analysis, the following specific goals will be achieved: 1) To reveal temporal-spatial distribution of Hg methylation bacterial community in the sediments and water of the PRE; 2) To estimate the contributions of dominant bacterial species to in situ production of MeHg; 3) To seek the main environmental factors related to bacterial community of Hg methylation and to elucidate the solid relationships between these factors and Hg methylation rate. The above accomplishments of this project could be especially helpful to accurate evaluation of health risk of Hg pollution in the PRE.

河口是陆地汞排放的一个重要的“汇”，研究河口汞甲基化过程对于认识区域环境中汞生物地球化学循环具有重要意义。汞细菌甲基化是水环境中甲基汞产生的主要途径。我国珠江口汞污染日趋严重，但目前对于珠江口汞甲基化细菌群落结构特征及其主要影响因素，以及两者对汞甲基化速率的影响尚缺乏基本的认识。本申请将围绕珠江口汞的细菌甲基化过程与机制这一核心问题，综合运用汞形态分析、同位素示踪及基于高通量测序的微生物群落分析等研究手段，揭示珠江口典型环境沉积物和水体中汞甲基化细菌群落的组成和时空变化规律；评价不同菌群对甲基汞原位生成的贡献；明确影响汞甲基化细菌群落的主要环境因子，探明环境因子对甲基化细菌群落、汞的甲基化速率影响机制，为合理评估珠江口区域汞污染引起的环境与健康风险提供科学依据。

我国珠江口及近海的汞污染日趋严重，其环境生态与健康风险备受关注。本项目以珠江口及近海区域为研究对象，围绕珠江口汞的细菌甲基化过程与机制这一核心问题，综合运用汞形态分析、同位素示踪及基于高通量测序的生物信息学分析等研究手段，揭示了珠江口及近海沉积物中汞甲基化细菌群落和功能基因的组成和时空变化规律，评价养殖环境中不同汞甲基化群落对甲基汞原位生成的贡献，探明了甲基汞污染、汞原位甲基化过程及汞甲基化细菌群落之间的关系。主要研究结果如下：1）与国内外其他河口相比，珠江口及近海沉积物中总汞污染水平较高，甲基汞污染水平相对较低，总汞与甲基汞的空间分布不同，说明两者的污染源不同；2）与其他国内外河口相比，珠江口及近海沉积物中汞甲基化速率较小而去甲基化速率较大，河口及近海环境中甲基汞水平受汞原位甲基化和去甲基化过程共同调控，汞净甲基化效率是反应水环境中甲基汞原位生成的一个有效指标；3）珠江口及近海沉积物中变形菌门的硫酸盐还原菌是主要的汞甲基化细菌，其与汞甲基化速率显著相关；4）珠江口及近海沉积物中hgcAB基因水平与汞甲基化速率显著相关，其很好的指示沉积物中汞原位甲基化过程。本项目的研究结果明确表明了珠江口及近海汞的原位甲基化是甲基汞污染的重要来源，为合理评估和控制珠江口及近海区域甲基汞污染引起的环境与健康风险提供了一定科的学依据。