铁生物成矿过程促进土壤镉钝化的化学-微生物机制

The heavy metal cadmium (Cd) is one of the most widely distributed contaminants in agricultural soils worldwide and poses a great threat to food safety and human health. Iron(III) oxides affect the mobility of contaminants including Cd in the environment by providing reactive surfaces for sorption or complexation. In fact, the mobility of mineral-associated contaminants is altered during biotic and abiotic Fe redox reactions including formation, transformation, and dissolution. The reverse reaction, that is, the reduction of Fe(III) to Fe(II), is mainly mediated by Fe(III)-reducing bacteria who oxidize organic or inorganic electron donors and reduce Fe(III) oxides. However, it is not well understood how the interrelation between Fe and Cd changes under Fe(III)-reducing conditions. In this project, a hypothesized mechanism is proposed on soil Cd immobilization mediated by Fe(III) mineral dissolution and secondary Fe mineral formation in red soil where Fe(III)-reducing processes occur actively. Cadmium-contaminated paddy soil collected from South China will be used to investigate the interrelation between Cd mobility and the reduction and dissolution of Fe minerals and the formation of Fe(II) and secondary Fe minerals. Molecular biological, bio-electrochemical and soil mineralogical methods and techniques will be employed. An Fe(III)-reducing bacteria-Fe(III) oxides-Cd coexisting system will be set up. The mechanism for soil Cd immobilization mediated by Fe(III) mineral dissolution and secondary Fe mineral formation will be clarified. Results from this project are expected to provide scientific basis for soil Cd immobilization and technical support for the development of in situ bioremediation technologies for Cd-contaminated soil.

农业土壤中镉污染引发的粮食安全问题备受关注。铁是土壤中最为重要的氧化还原活性元素，铁氧化物形态与镉的迁移转化密切相关。长期以来的研究认为镉与铁氧化物结合取决于吸附/络合作用，土壤还原条件下铁氧化物的还原溶解与二次成矿过程对镉转化的影响，则少见报道。为此，本项目针对华南红壤铁还原强烈发生的有利条件，将“铁还原－铁生物成矿过程”与“土壤镉的转化过程”联系起来，提出“铁生物成矿过程耦合土壤镉钝化机制”假说，并以镉污染水稻土为研究对象，综合运用分子生态学、生物电化学与土壤矿物学等手段，系统研究“铁还原菌－铁氧化物－镉”的共存体系中铁氧化物还原溶解与二次成矿过程，探讨铁氧化物晶型转变与土壤中镉转化的关系，明确铁还原菌、Fe(II)、铁氧化物、镉等要素的角色与功能，揭示铁生物成矿过程耦合土壤镉钝化的化学-微生物机制，拓宽对土壤镉形态转化机理的认识，为镉污染土壤原位修复提供理论依据。

本项目以镉污染水稻土为对象，以水铁矿为铁氧化物模型，围绕铁还原菌-Cd(II)-土壤铁氧化物互作体系，研究铁氧化物生物成矿影响下的土壤Cd(II)的钝化机制。主要成果包括：（1）发现并命名GSS12T和GSS14T等2株微生物新种，为研究镉污染土壤Fe(III)还原与Cd(II)钝化的微生物-化学协同机制提供了新的研究手段；（2）考察铁还原模式菌Geobacter soli GSS01T参与的铁二次成矿与Cd(II)钝化耦合过程，并利用转录组学和蛋白组学技术解析了GSS01还原铁氧化物的分子机制；（3）考察铁氧化物二次成矿过程对镉污染稻田Cd(II)钝化过程的影响效应，阐明了Cd(II)钝化与铁生物成矿过程的响应关系及关键微生物菌群。本项目初步揭示了铁氧化物二次成矿与Cd(II)钝化交互过程的内在驱动机制，为深入理解土壤镉钝化的微生物-化学耦合机制提供科学依据，为镉污染土壤的高效治理提供技术支撑。项目发现并命名2株微生物新种，发表SCI论文7篇，获授权专利2项；培养硕士2名。