稻田土壤甲基汞降解的微生物生态学机制

Methylmercury (MeHg) is highly neurotoxic, which easily accumulate and magnify in the food chain, threating food safety and human health. Paddy field is one of typical wetland ecosystems and also considered a hotspot for methylation of inorganic Hg. Rice consumption is an important route that human beings exposure to MeHg in Hg-impacted areas, it is thus essential to prevent and control MeHg pollution in paddy fields and its subsequent risks. MeHg can be degraded by a diverse of microorganisms, however little is known regarding the underlying mechanisms of microbial degradation of MeHg in natural paddy ecosystems. This project will integrate metagenomics/metatranscriptomics and Hg isotope technologies to analyse the major taxa involved in MeHg degradation in paddy soils, and also identify the environmental variables that influence microbial processes of MeHg degradation. Dynamics of MeHg degradation and express activities of key microbial groups involved in the demethylation will be monitored, helping to quantify the relative contribution of demethylation microbes to MeHg degradation as well as the influencing factors based on short-term incubation experiments. After that, a large scale of investigation from various geographic conditions in China will be conducted to unravel the soil microbial community composition involved in MeHg degradation. Finally, data resulted from both incubation experiments and field studies will be incorporated to develop biogeochemical models for clarifying the microbial pathways and mechanisms of MeHg degradation in paddy soils, which will be helpful to control and remediate MeHg pollution in paddy ecosystems.

甲基汞(MeHg)具有很强的神经毒性，容易随食物链富集与放大，进而威胁食品安全与人类健康。水稻田是一种典型的湿地生态系统，也是无机(Hg)发生甲基化的热区之一。稻米食用已成为Hg污染区域人群MeHg暴露的重要途径，稻田MeHg的防控刻不容缓。MeHg可以被多种微生物降解，但是目前对于土壤MeHg微生物降解机制不清楚。本项目拟以室内培养试验与野外调查相结合，基于宏基因组/宏转录组和MeHg同位素示踪等手段分析MeHg降解的土壤微生物类群；探究环境因子对稻田土壤MeHg微生物降解过程影响；分析驱动土壤MeHg降解的微生物群落及其活性，阐明稻田土壤微生物对MeHg降解的相对贡献及其主要影响因素；摸清不同地理与环境条件下稻田土壤MeHg降解的微生物群落组成特征。通过对野外调查和室内模拟实验数据进行模型拟合，揭示稻田土壤MeHg降解的微生物生态学机制，为稻田系统MeHg的污染控制与修复提供科学依据。

甲基汞具有极强的神经毒性，容易随食物链富集与放大。稻田土壤是甲基汞产生的热区，食用稻米已成为汞污染区域甲基汞暴露的主要途径，控制稻田土壤甲基汞对于食品安全与人类健康具有重要意义。本项目通过野外调查与实验室分析、利用同位素示踪与多组学等方法开展研究，分析了典型稻田土壤甲基汞降解的降解特征，探究了环境因子对稻田土壤甲基汞微生物降解过程影响，研究了驱动土壤甲基汞降解的微生物群落及其活性。结果发现，微生物是土壤甲基汞降解的重要驱动者，且土壤类型影响微生物对甲基汞降解效率。在高污染土壤中，淹水更有利于甲基汞的微生物降解，特别是微量元素铜的增加可以显著提高甲基汞的微生物降解效率。细菌扩增子和宏转录组测序分析一致表明，Catenulisporaceae、Frankiaceae和Mycobacteriaceae等可能是土壤甲基汞降解主要类群。进一步通过DNA-SIP和高通量测序技术明确了参与稻田土壤甲基汞降解的主要微生物类群。通过接种微生物降解污染土壤发现，接菌量、温度和水分均影响微生物对土壤甲基汞降的去除效率，而层状结构的蒙脱石和水钠锰矿能够促进微生物（Chitinophaga dinghuensis）对甲基汞的降解。项目研究结果揭示了典型稻田土壤甲基汞降解的微生物学机制，为理解甲基汞污染土壤微生物修复提供了理论支撑。