基于DNA-稳定同位素探针技术的原位植物根际PCBs降解功能微生物的探查及降解机理研究

The biodegradation is the major way for polychlorinated biphenyls (PCBs) to dissipate in the soil. Rhizosphere is the most active region for PCBs degradation in soil and it plays a very important role in the dissipation of PCBs. Investigating the effects of rhizosphere on the degradation of PCBs，exploring the potential high efficient PCBs-degrading microbes and clarifying the mechanism of degradation are of great significance for the bioremediation of PCBs contaminated soils. DNA-based stable isotope probing (DNA-SIP) technique can link directly unknown microbes and their functions without isolation and pure culturing procedures and it has proved to be a powerful tool of identifying microbes that can degrade contaminants in situ. In the present study, using typical PCBs contaminated soils and clean agricultural soil, with the aid of in situ labeling of soils from rhizosphere and non-rhizosphere, the degradation of typical PCBs will be studied in the field and pot experiment study. By analyzing the difference of PCBs degradation dynamics, the effects of rhizosphere on the PCBs metabolizing will be elaborated. The possible pathway and mechanism underlying PCBs degradation is going to be revealed by analyzing the composition of functional microbial community, intermediates and functional genes. In the rhizosphere, treatments of soil flooding and the addition of the root exudates collected from different growth stage will be performed to study the effects of soil water controlling and root exudates on the functional microbial community and PCBs degradation. Potential microbial species and insights on the rhizoremediation of PCBs contaminated soils are hoped to be provided.

微生物降解是土壤中多氯联苯（PCBs）消减的主要途径。植物根际是土壤PCBs降解最旺盛的区域，对PCBs在自然界的消减有重要作用。研究根际效应对PCBs降解的影响、发掘潜在高效的PCBs降解微生物物种、明确其降解机制对污染土壤的生物修复具有重要意义。DNA-稳定同位素探针技术脱离了传统分离培养的限制，可以将未知的微生物种群和其功能直接联系起来。本研究拟以典型的PCBs污染土壤以及干净的农田土为研究对象，采用根际土壤与非根际土壤同位素同步原位标记的方法，研究典型PCBs在植物根际与非根际土壤降解的动力学差异，厘清植物根际效应对PCBs降解的影响；明确PCBs降解过程中功能微生物种群的动态变化，结合中间产物及降解功能基因分析，揭示其降解过程和降解机制；阐明土壤水分调控及植物不同生长阶段根系分泌活动对功能微生物以及PCBs降解过程的影响，为PCBs降解污染土壤的根际修复提供微生物资源和理论依据。

微生物降解是土壤中多氯联苯（PCBs）消减的主要途径。植物根际是土壤PCBs降解最旺盛的区域，对PCBs在自然界的消减有重要作用。研究根际效应对PCBs降解的影响、发掘潜在高效的PCBs降解微生物物种、明确其降解机制对污染土壤的生物修复具有重要意义。本研究深入探究了根际效应对PCBs降解的影响，并通过稳定性同位素探针技术原位鉴定PCBs降解功能菌及功能基因，揭示了根际效应的作用机制。研究结果表明，根际环境能够通过改变PCBs降解功能微生物的种类、丰度、多样性及之间的相互关系，显著提升PCBs降解效率。根系分泌物添加实验及原位根际代谢组结果表明，外源添加根系分泌物对PCBs降解影响较小，但种植植物处理中根系分泌的延胡索酸等碳水化合物能够重塑功能微生物群落结构，提高降解基因丰度，加速PCBs降解。根系腐烂实验则证明是关键化合物种类而非数量参与了功能微生物群落建构并促进PCBs降解效率的提升。为了进一步提高PCBs降解能力，我们进行了根际土壤淹水实验，淹水处理能够通过改变根际氧化还原电位，富集脱氯菌群，并通过富集产甲烷菌为脱氯提供电子供体，促进高氯PCBs脱氯；此外，根际的含氧微区能够为脱氯后的低氯PCBs矿化提供适宜环境，从而让高氯PCBs得以完全降解。本研究还鉴定获得了多种新型PCBs降解菌，并明确了根际与非根际PCBs降解机制及代谢途径，解析了降解基因的起源。本项目为PCBs降解污染土壤的根际修复提供微生物资源、理论依据和可行性手段。