基于铬同位素分馏的六价铬微生物还原机制解析

The process of microbial Cr(VI) reduction play an important role in the transport and transformation of Cr(VI) in the contaminated soils and groundwater. Microbial Cr(VI) reduction occurred on the cell surface or inside the cell. However, due to lack of accurate quantitative methods, the mechanism of microbial Cr(VI) reduction is still unclear and it is still difficult to quantitatively evaluate the contributions of intracellular and extracellular Cr(VI) reduction. Cr isotope fractionation can be applied to distinguish the occurrence of Cr in different process and various conditions. Thus, the relative contributions of intracellular and extracellular Cr(VI) reduction can be evaluated by Cr isotope fractionation. In this study, the Cr isotope fractionation factors will be measured during Cr(VI) reduction by different reductase or with different electron transfer pathways. The Cr isotope fractionation analysis is a promising tool to investigate the mechanism of intracellular and extracellular Cr(VI) reduction. In addition, based on the elementary reactions, the quantitative kinetic model will be established to describe microbial Cr(VI) reduction. The results from the kinetic model will be compared with the results of Cr isotope fractionation to quantitatively investigate the contributions of intracellular and extracellular Cr(VI) reduction. This study will further our understanding of Cr biogeochemical cycling in the soil and will provide a theoretical basis for the application of Cr isotope fractionation in bioremediation of Cr(VI). This study has important significance in research area of soil chemistry.

微生物还原六价铬的过程对于铬在土壤及地下水中的迁移、转化具有重要的影响。微生物还原六价铬的过程可以发生在细胞表面或内部，但由于缺乏准确的定量方法，难以对微生物胞内与胞外还原六价铬的相对贡献进行定量解析。利用铬同位素分馏可以有效区分不同条件、不同过程产生的铬，从而定量解析微生物胞内、胞外还原铬的反应机制。本申请旨在测定不同的还原酶和不同电子传输途径还原六价铬过程中的铬同位素分馏系数，通过铬同位素分馏揭示微生物胞内、胞外六价铬的还原机制。进一步结合各过程的基元反应方程，建立六价铬还原动力学模型，与铬同位素分馏方法进行对比验证，明确微生物胞内与胞外还原六价铬的相对贡献。本申请将加深对铬在土壤中的生物地球化学循环的理解，为铬同位素分馏在六价铬生物修复过程中的应用提供理论依据，具有重要的土壤化学意义。

微生物还原六价铬的过程对于土壤中铬的迁移转化具有重要影响。本申请选择了希瓦氏菌MR-1为研究对象，研究了不同环境因素对微生物还原六价铬过程中的铬同位素分馏的影响机制；通过添加还原酶抑制剂的实验方法，构建了微生物胞内、胞外六价铬的实验体系，利用铬同位素分馏揭示微生物胞内、胞外六价铬的还原机制；由于微生物介导的硝酸盐还原与亚铁氧化耦合过程可以通过吸附或共沉淀的方式进一步有效固定土壤中的铬，本项目利用氮氧同位素分馏和反应动力学模型研究了硝酸盐还原与亚铁氧化耦合过程的反应机制；硝酸盐还原过程会生成中间产物亚硝酸盐，亚硝酸盐可以和亚铁发生化学反硝化过程，进一步有效固定土壤中的铬，本项目利用利用氮氧同位素分馏研究了亚硝酸盐和亚铁之间发生化学反硝化的反应机理；进一步结合各过程的基元反应方程，建立反应动力学模型，评估了生物过程和化学过程的相对贡献。本项目为铬同位素分馏在土壤中铬生物修复过程中的应用提供理论依据。