金属还原菌还原转化Cr(VI)的动力学模型及其界面反应机制

The soil microorganisms have important influences on the transport and transformation of heavy metals in the contaminated soils. The interaction between microorganisms and metal ions, including adsorption, surface complexation and redox reaction, is a complicated biogeochemical process. In this study, the kinetic model of Cr(VI) reduction by dissimilatory metal reducing bacteria (DMRB) will be investigated, and the interfacial processes are expected to be disclosed on a basis of the kinetic model and thermodynamic analysis. By investigating the adsorption/complexation of Cr(VI)/Cr(III) on the cell surface of metal reducing bacteria and the redox reaction rates between Cr(VI) and outer membrane cytochromes of DMRB, the key parameters of adsorption, complexation and redox reactions will be obtained. The effects of electron shuttles on the Cr(VI) reduction will be investigated as well with aims of indentifing the critical reactions and the crucial species for the Cr(VI) bioreduction processes. Based on the elementary reactions, the quantitative kinetic model will be established to describe the Cr(VI) redcution by DMRB. The effects of different factors on Cr(VI) reduction by DMRB will be further investigated to disclose the comprehensive mechanism of the whole processes of adsorption/complexation/electron transfer during Cr(VI) reduction. This study will provide a comprehensive understanding of the bioreduction of heavy metals in contaminated soils and will be useful to develop new strategies for bioremediation of heavy metal contaminated soils.

土壤微生物对于土壤重金属离子的迁移、转化具有重要的影响，土壤金属还原菌与金属离子间相互作用包括吸附、络合与氧化还原反应，是一个复杂的生物地球化学过程，其反应动力学模型的研究较为欠缺。本申请以金属还原菌与六价铬为模型反应体系，旨在建立其动力学原理模型，并解析金属还原菌还原六价铬的微观界面反应机制。重点研究六价铬/三价铬在金属还原菌表面的吸附/络合作用、微生物外膜金属还原酶细胞色素c与六价铬的氧化还原反应，获得吸附/络合/氧化还原反应的动力学参数；基于各过程的基元反应方程，获得六价铬还原动力学的具体参数；结合外源电子穿梭体对六价铬还原动力学的影响，明确金属还原菌还原六价铬的关键反应步骤和关键活性物种。阐明金属还原菌还原转化六价铬的吸附/络合/电子传递的微观机制。预期成果可为深入阐明土壤中微生物与重金属形态转化相互作用的微观机制，开发重金属生物修复技术提供理论依据。

微生物外膜细胞色素c在异化金属还原过程中起了重要作用，以往研究主要采用提纯蛋白的方式研究细胞色素c的离体反应性质，然而对于活体细胞内细胞色素c的性质仍缺乏研究。在本项目中，我们采用了漫透射光谱法成功测试了活体细菌中的外膜细胞色素c，并采用此方法研究了活体细菌中细胞色素c与六价铬的反应动力学。建立了细胞色素c还原转化Cr(VI)的量化动力学模型，揭示了细胞色素c还原转化Cr(VI)过程中的分子反应机制，并且首次将毒性指标引入反应动力学模型，揭示了铬毒性导致细菌还原六价铬活性降低的原因。项目总共发表SCI论文五篇，其中两篇分别发表在Environmental Science & Technology、Soil Science Society of America Journal等环境类和土壤类顶级杂志上。