根瘤菌强化紫花苜蓿根际降解多氯联苯的分子机制研究

Polychlorinated biphenyls (PCBs) are on the list of 12 prior controlled persistent organic pollutants (POPs) by UNEP. PCBs in soils can be bioaccumulated and biomagnified through food chains, subsequently posing risks to human health. Therefore, it is of great theoretical and practical significance to understand the mechanisms behind the bioremediation of PCBs contaminated soils. Legume-Rhizobium is the most common symbiont between plants and microbes in the nature. Our previous research showed that free-living Sinorhizobium meliloti could degrade PCBs in soils directly, and the alfalfa-rhizobium symbiont could significantly enhance the remediation of PCBs contaminated soils. However, the mechanism is still not well understood. In this study, microbes, metabolic intermediates and key enzymes involved in the rhizosphere degradation of PCBs will be isolated from alfalfa-rhizobium symbiont. The effects of symbiont root exudates on the community structures of PCBs-degrading microbes and their degrading-gene diversities will be investigated using stable isotope probing and pyrosequencing techniques. This project aims at revealing the molecular mechanisms under the rhizobium enhanced rhizosphere degradation of PCBs by legumes, and providing the scientific basis for developing bioremediation technologies for POPs contaminated soils.

多氯联苯（PCBs）是被联合国环境规划署列为首批需要削减和控制的12种持久性有机污染物之一。土壤中PCBs可以通过食物链的生物富集进而危害人体健康。因此，研究PCBs污染土壤的生物修复机理具有重要的科学与现实意义。豆科植物与根瘤菌是自然界最常见的植物-微生物共生体系，我们前期研究发现游离态根瘤菌可以降解土壤中的PCBs，而根瘤菌接种紫花苜蓿所形成的固氮共生体可以显著提高对PCBs污染土壤的修复效率,但有关机理尚不明确。本项目深入研究根瘤菌-紫花苜蓿共生体及其根际微生物对土壤中PCBs的代谢产物、代谢途径以及关键代谢酶活性，并结合稳定性同位素探针以及超高通量基因测序等分子生物学技术进一步确定共生体根际PCBs降解菌的类群，探明根系分泌物对降解菌及其降解基因分子多样性的影响机制。该研究将为揭示根瘤菌强化豆科植物根际降解PCBs的分子机制、发展POPs污染土壤的生物修复技术提供理论依据。

豆科植物与根瘤菌是自然界最常见的植物-微生物共生体系，我们前期研究发现，根瘤菌接种紫花苜蓿所形成的固氮共生体可以显著提高对PCBs 污染土壤的修复效率，但有关机理尚不明确。本项目以豆科植物紫花苜蓿和中华苜蓿根瘤菌为研究对象，以三氯联苯PCB 28 和四氯联苯PCB 77为目标污染物，建立并优化了适用于根际微域试验中少量土壤样品的多氯联苯（PCBs）快速检测方法；采用三室根箱法揭示了PCB在紫花苜蓿-根瘤菌共生体根际土壤不同微域中的消减动态；鉴定了PCB的代谢产物与潜在代谢途径；阐明了根际土壤中PCBs代谢相关酶的活性及根际微生物群落结构与功能多样性的变化特征；鉴定了2种主要的紫花苜蓿根系分泌物，盆栽试验验证了根系分泌物对PCBs的降解促进机制；采用13C 标记PCB稳定同位素探针和PCR-DGGE等技术鉴定了共生体及其根际土壤中的联苯降解菌。研究成果可为揭示根瘤菌强化豆科植物根际降解PCBs的分子机制、发展有机污染土壤的生物修复技术提供理论依据。