水稻土落干期遗存类咕啉启动淹水期多氯联苯厌氧脱氯的机制

In tidal flats, paddy fields and other periodic dry-wet alternate environment, active redox biogeochemical processes drive the anaerobic reduction coupled to aerobic degradation removal of organic pollutant, such as polychlorinated biphenyls (PCBs). Because of reductive dehalogenase’s dependence on exogenous corrinoid and the short supply of corrinoid in anaerobic environment, reductive dechlorination is extremely difficult to start, while alternating aerobic and anaerobic condition makes dechlorination quick started. So efficient aerobic biosynthesized corrinoid remaining to anaerobic period may be an important mechanism. In this study, a gradual progressive system will be established as paddy soil isolated pure cultures, paddy soil enriched mixed cultures, paddy soil microcosms to clear the rules of corrinoid biosynthesized by aerobic bacteria and released under anaerobic stress, analyze the key functional members involved in the vestigial corrinoid from areobic period starting PCBs anaerobic dechlorination process and the molecular event pathways of aerobic corrinoid biosynthsis, corrinoid salvaging and remodeling by dechlorination bacteria and dechlorination respiratory. The stability of this mechanism will be investigated through multiple alternating anaerobic-aerobic operation, and verified by collecting paddy soil samples differs in seasons, types and farming methods in a typical PCBs contaminated area, to indicate the mechanism of legacy corrinoid from drying period starting anaerobic dechlorination of PCBs during flooding period in paddy soil. The results of the study will make us more profoundly understand the self-purification mechanism of organic pollution in dry-wet alternate environment on earth and provide the theory basis for in situ bioremediation of halogenated organic compounds, to serve the current pressing soil pollution prevention and control work in China.

地球存在滩涂、稻田等多种周期性干湿交替环境，氧化还原过程活跃，驱动了多氯联苯（PCBs）等有机污染物厌氧还原-好氧降解耦合去除。PCBs还原脱氯辅酶类咕啉的外源依赖及厌氧环境类咕啉供应不足导致脱氯极难启动，而好氧-厌氧交替则可快速启动脱氯，好氧合成类咕啉遗存至厌氧期可能是重要机制。本研究将采用“水稻土分离纯培-水稻土来源混培-水稻土微宇宙”体系，明确好氧菌产类咕啉及其受厌氧胁迫释放规律，解析好氧遗存类咕啉启动厌氧脱氯的关键功能种群及好氧类咕啉合成-脱氯菌类咕啉装配-脱氯呼吸等关联分子事件通路，通过多次厌氧-好氧交替考察机制稳定性，并在典型污染地区采集多季不同类型与耕作方式水稻土进行验证，阐明水稻土落干期遗存类咕啉启动淹水期PCBs厌氧脱氯的机制。研究结果将使我们更深刻认识地球干湿交替环境有机污染自净机理，为卤代有机物污染修复提供理论依据，以服务我国当前迫切的土壤污染防治工作。

环境中的高氯代多氯联苯需要经过微生物的厌氧脱氯-好氧降解才能彻底矿化，干湿交替环境如稻田土壤中多氯联苯可发生微生物还原脱氯-好氧开环降解耦合去除。然而，微生物还原脱氯辅酶类咕啉的外源依赖、厌氧环境中类咕啉竞争导致的供应不足使得脱氯极难启动，而好氧-厌氧交替则可快速启动脱氯，但具体机制不明。本研究采用“水稻土分离纯培-水稻土来源混培-水稻土微宇宙-野外小区”体系，通过构建好氧产类咕啉菌-厌氧脱氯菌组合，研究水稻土落干期遗存类咕啉启动淹水期多氯联苯厌氧脱氯的机制，得到以下主要结果：.1. 明晰了水稻土中优势微生物红球菌能在好氧条件下合成类咕啉，在厌氧胁迫下绝大部分菌体死亡从而可释放类咕啉，常规培养体系中类咕啉浓度约为4 μg/L，超过脱卤拟球菌脱氯启动约1 μg/L的阈值；落干水稻土中存在好氧合成的类咕啉，浓度可达4.96 μg/kg，具有启动脱氯的潜力；.2. 红球菌所产类咕啉可以启动脱卤拟球菌纯培或混培对多氯联苯等氯代有机污染物的脱氯。29天左右，多氯联苯浓度从21.84 mg/L降低至11.66 mg/L，六氯、七氯同系物大量转化为四氯同系物，相应地，红球菌合成的类咕啉被脱卤拟球菌吸收并利用；而无红球菌对照组长达141天脱氯尚未启动。脱氯菌细胞产率可达2.07 × 10^11 16S rRNA基因拷贝数/mmol Cl-，比无好氧红球菌对照组高204.4%，高于文献报道组合培养物中脱氯菌细胞产率；.3. 通过厌氧-好氧交替实验考察了好氧遗存类咕啉启动厌氧脱氯机制的稳定性，并在典型污染地区水稻土小区、中试实验中进行了验证，阐明了水稻土落干期遗存类咕啉启动淹水期多氯联苯厌氧脱氯、并实现多氯联苯脱氯-降解彻底去除的机制。水稻土经过淹水-落干交替处理6个月后，多氯联苯的累积去除率可达38.2%。.本项目的研究结果将使我们更深刻认识干湿交替环境中卤代有机污染物的微生物自净机理，为土壤与地下水中卤代有机物污染的绿色可持续修复提供理论依据。