草酸青霉作用下土壤中铬的形态转化机制研究

Chromium pollution is one of the serious environmental problems in China. Reduction of Cr(VI) to Cr(III) is an important way to promote the soil chromium pollution treatment. Compared with the chemical reduction of Cr(VI), microbial treatment has emerged to be a cost effective, efficient, and environment friendly remediation technology, which presents a promising alternative for in situ cleanup of large field application. A strain with highly Cr(VI) reducing ability named Penicillium oxalicum SL2 (SL2) was isolated in our lab, it shows high capacity to adapt the complex environments, such as high salt and heavy metal pollution, which gives it a brilliant prospect to bioremediation. Our study aims to explore the mechanism of chromium transformation in soil induced by SL2. Based on the combination of synchrotron radiation analysis technique and electrochemical techniques, the Cr(VI) tolerant ability and transformation efficiency induced by SL2 will be demonstrated, and the effects of soil factors such as sulphate and iron on the response of Cr influenced by SL2 will be confirmed. To reveal the molecular mechanism for chromium transformation in soil influenced by SL2, we will illustrate the interaction between the surface groups of mycelium and chromium, the functional components of SL2, electron transfer in the microbial reduction, Cr(VI)-reducing site of SL2 and the fate of Cr(VI)-reduction products. Our study will provide key information on Cr(VI) pollution control and governance in soil.

土壤铬污染是我国面临的突出环境问题之一。将Cr(VI)还原为Cr(III)是土壤铬污染治理的重要途径，微生物还原Cr(VI)具有成本低、无二次污染等优点。本课题组在前期研究中筛选出了一株高效Cr(VI)还原真菌草酸青霉菌（Penicillium oxalicum SL2），能适应高盐、高重金属等复杂环境，具有良好的应用前景。本项目拟以阐明SL2作用下土壤中铬的分子形态转化机制为目标，利用SL2和泥浆反应器构成的试验体系模拟实际土壤铬污染修复，应用XAFS和XRF等同步辐射技术联合电化学技术研究SL2对Cr(VI)污染土壤的耐性及转化作用，探索土壤中硫酸盐和铁离子等因素对SL2耐性和转化铬形态的影响，从菌丝体表面基团与铬的相互作用、Cr(VI)还原功能组分、电子传递模式、还原位置与产物归趋等角度揭示草酸青霉作用下土壤中铬的分子形态转化机制，为土壤Cr(VI)污染控制和修复提供理论依据。

微生物修复Cr(VI)污染技术具有成本低、环境友好等优点，可以和传统的物理化学方法形成互补。本项目以高效Cr(VI)还原真菌草酸青霉菌（Penicillium oxalicum SL2）为材料，通过室内实验，结合X射线吸收精细结构光谱（XAFS）等技术探究SL2对Cr(VI)的耐性及转化作用，考察硫酸盐、钙离子等对菌株SL2耐性和铬形态转化的影响，探究菌株SL2作用下土壤中铬的分子形态转化机制。主要发现：1）Cr(VI)对菌株SL2的最小抑制浓度大于1000 mg/L，Cr(VI)胁迫下菌株SL2的生长规律可用Gompertz模型模拟。低土水配比（2.5%）、分步淋洗及水洗预处理均有利于铬污染土壤浸出液中Cr(VI)的去除。通过扫描透射X射线显微技术（STXM）发现生物淋洗后SL2胞内铬形态主要为与磷酸铬、草酸铬钾、及半胱氨酸结合态铬（Cr(III)-Cys）相似的物质。2）硫酸盐的添加促进了菌株SL2的生长，加速了Cr(VI)还原，通过X射线近边吸收结构谱学（XANES）分析发现，SL2菌丝体内产生半胱氨酸、谷胱甘肽等物质，提高了Cr(VI)去除效率。钙离子可通过维持细胞壁的完整性减小Cr(VI)对SL2细胞的损伤。3）菌株SL2主要通过产生草酸等有机酸代谢物间接还原Cr(VI)，此外，SL2菌丝体表面可吸附少量的Cr(VI)，其表面的羟基、氨基、羧基等官能团参与了菌株SL2与Cr(VI)的相互作用。通过XANES分析发现，菌株SL2体内的铬元素形态在初期主要为Cr(III)-Cys和磷酸铬，随后向草酸铬钾转化。Cr(VI)胁迫下菌株 SL2有机酸代谢、能量代谢、应激反应和DNA修复等基因差异表达，其耐Cr(VI)分子机制主要体现在能量调控、铬离子转运调控、信号通路调控和氧化还原作用四个方面。研究成果为土壤铬污染控制和修复提供理论依据。