水稻土中多氯联苯微生物脱氯的外源类咕啉依赖机制研究

Polychlorinated biphenyls (PCBs) is a typical widespread persistant organic polltant all over the world. The vast area of paddy soil is an important sink for these compounds. High-chlorinated PCBs in environment is extremely difficult to be degraded, needing to be reductively dechlorinated to lower chlorinated PCBs before it could be carried out for aerobic mineralization. It has been proved that PCBs could be reductively dechlorinated effectively in paddy soil, though the mechanisms are still unknown. In this study, based on PCBs obligate dechlorination bacteria are bacteria can not synthesis itself dechlorination of important coenzyme corrinoid, we will investigate collaborative dechlorination of PCBs by obligate bacteria with corrinoid producing strains which involved in soil carbon cycle in paddy soil. Different mechanism of different corrinoid action on obligate dechlorination will be studied. And environmental factors affect the corrinoid synthesis, secretion, thus affecting the obligate dechlorination will also be focus on. Corrinoid transported by transporter protein regulated by ribosomal switching, which affects the dechlorination is also going to be researched. This work will provide theoretical supporting for the accelerated natural attenuation of PCBs in paddy soil or other natural wetland all over the world, as well as for the remediation of PCBs contaminated site applying artificial wetland.

持久性有机污染物多氯联苯（PCBs）在全球范围内广泛迁移，面积广大的水稻土是其重要的受纳体。高氯代PCBs在环境中极难降解，须脱氯为低氯代PCBs后方可进行矿化。已有研究表明水稻土还原条件下PCBs可较快脱氯，但具体机理不明。本研究依据PCBs脱氯菌均为专性脱氯菌无法自身合成重要脱氯辅酶类咕啉的制约因素，考察水稻土中大量存在的参与碳循环的类咕啉产生菌与PCBs专性脱氯菌的协同脱氯作用机制。重点研究不同微生物合成的不同类咕啉对专性脱氯的作用机制；环境因子影响类咕啉合成、分泌，从而影响专性脱氯的机制；核糖体开关响应类咕啉、PCBs，调控类咕啉转运蛋白从而影响脱氯的机制。希望能为阐明水稻田等湿地厌氧环境下氯代有机物自然衰减机理提供新的思路，也为氯代有机物污染场地的人工湿地修复提供理论依据。

环境中典型的卤代有机污染物长期持留，关键在于很多有机卤化物如高氯代多氯联苯（PCBs）必须先脱卤才能彻底好氧降解。专性脱氯菌自身无法合成而又是其脱卤酶必须辅因子——类咕啉的缺乏，可能是导致土壤等环境中氯代有机物脱氯缓慢的瓶颈因子。本研究以水稻土等来源的脱氯菌-产类咕啉菌组合为研究对象，系统研究了类咕啉合成菌与脱氯菌协同脱氯的作用机制。主要得到了以下结果：.（1）从水稻土中富集得到依赖外源类咕啉的脱氯培养物XS、不依赖外源类咕啉的脱氯培养物PS等；稀释减绝获得一个PCBs专性厌氧脱氯菌Dehalococcoides mccartyi含量为91%的无沉积物培养物。同时，从水稻土中分离得到一株能够产类咕啉的Rhodococcus biphenylivorans TG9，另获得产甲烷产类咕啉菌Methanosarcina mazei，建立了并优选了多个产类咕啉-脱氯培养体系。结果表明，维生素B12、TG9及M.mazei生产的类咕啉都可以满足Dehalococcoides mccartyi的脱氯呼吸需求。.（2）在M.mazei-PSCC、TG9-PSCC组合中，产类咕啉过程起到了主导作用，限制脱氯反应速率。M.mazei还可为脱氯菌提供氢气作为电子供体。.（3）有机氯代物对产类咕啉菌M.mazei有毒害，进而影响脱氯。重金属离子对脱氯菌和产甲烷产类咕啉菌均有影响，通过本研究，得出了组合培养物最适宜的重金属离子浓度。有机质能促进培养物脱氯，但对培养物产类咕啉没有明显影响。.（4）体系中产类咕啉菌释放到胞外的类咕啉不断被脱氯菌捕获并利用。脱氯菌体内较低的类咕啉浓度使类咕啉核糖开关打开，调控周质类咕啉转运进胞内进行脱氯，从而为产类咕啉菌M.mazei解除氯代有机物的毒性。.（5）污染物添加实验和修复工程小试实验均表明，环境培养物缺乏足够的类咕啉来支持土著菌脱氯，提高体系类咕啉含量有利于环境氯代有机物污染修复。. 本研究结果将有助于阐明环境中产类咕啉菌与脱氯菌的共生机制，为氯代有机物污染土壤与地下水的生物修复提供理论依据和技术支撑。

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