厌氧砷氧化菌对水稻土砷生物有效性的影响及机制研究

Arsenic is recognized as carcinogenic; chronic exposure to arsenic results in a wide range of adverse health effects. Some paddy areas in Southern China have been seriously contaminated by Arsenic, threatening agricultural production, food safety and human health. Arsenic species affects the absorption and transfer of arsenic in rice root, microbe-mediated anaerobic oxidation of arsenite plays an important role in arsenic mobilization and detoxification in paddy soil. In this proposal, we focus on the effect of the anaerobic arsenite-oxidizing process on arsenic mobility and transformation, aiming to isolate anaerobic arsenite-oxidizing bacteria from paddy soils,the diversity and physiological characteristics of arsenite-oxidizers will be investigated. We will employ in-situ analysis of arsenic contaminated paddy soils and simulation in lab to study arsenic transformation and the relationship between arsenite-oxidizing and nitrate-reducing process. In addition, the effects of nitrate application on the key functional genes controlling arsenic transformation in paddy soils will be determined, and the contribution of functional microbe to arsenic transformation will be evaluated. Furthermore, the effect of bioaugmenting arsenite-oxidizers in the rhizosphere on arsenic bioavailability will be investigated, the dynamic processes of arsenic mobilization in soil and arsenic accumulation in rice grains will be investigated. The project will provide a theoretical basis for developing practical measures to reduce arsenic accumulation by rice.

砷污染是一个全球性的环境问题。我国南方水稻产区砷污染现象较严重，危害农产品安全和人体健康。水稻土中的砷形态直接影响到水稻根系对砷的吸收及转移，微生物是影响砷形态转化的重要因素。本项目申请从微生物介导的厌氧砷氧化机理及影响因素入手，采用分离培养和分子生态学技术相结合，筛选依赖于硝酸盐还原的厌氧砷氧化菌，研究水稻土厌氧砷氧化菌的多样性及砷氧化酶基因多样性；研究不同梯度硝酸盐对土壤溶液中砷形态转化的影响，表征硝酸盐还原强度对土壤中砷氧化的影响；揭示淹水水稻土中微生物介导的砷氧化与硝酸盐还原之间的内在联系；探讨通过强化水稻土砷氧化过程降低砷的生物有效性及其具体协同途径和机制；为提出阻控水稻砷吸收的实用措施提供理论指导。

本研究以南方砷污染水稻土为研究对象，研究了稻田土中三价砷、二价铁氧化与反硝化过程偶联的机理，并以分离的厌氧砷氧化菌为研究对象，通过基因敲除和回补等实验手段，明确反硝化菌驱动亚铁和三价砷厌氧氧化的机制。本文的主要结果归纳如下：(1)首次发现淹水土壤中添加硝酸盐能够促进三价砷和二价铁的厌氧氧化，降低了土壤中砷的生物有效性，提高了砷氧化酶基因的丰度；并显著改变了厌氧砷氧化菌群落结构，揭示了与反硝化过程耦合的厌氧砷氧化菌在稻田土壤砷氧化的生物地球化学循环中的重要性；(2)本研究探讨了砷氧化菌对三价砷的厌氧氧化机理，结果显示：砷氧化酶Aio参与了厌氧砷氧化过程，并且该过程与反硝化过程偶联，三价砷氧化酶基因的厌氧表达受三价砷的诱导；(3) 本研究通过亚硝酸盐还原酶nirK基因敲除和回补等手段，阐明了反硝化菌驱动亚铁和三价砷厌氧氧化的机制，研究结果表明微生物三价砷和二价铁的厌氧氧化是两个相互独立的过程，微生物氧化二价铁的本质是反硝化过程产生并累积的亚硝酸盐与二价铁发生的化学反应。..