基于纳米导线研究还原脱氯和产甲烷生物电化学耦合机制

In anaerobic environment (e.g. flooded paddy soil), reductive dechlorination is currently the crucial biodegradation way for Chlorinated organic pollutants (COPs). However, this anaerobic redox reaction generally occurs synchronously with methanogenesis. Hence, the COPs degradation through reductive dechlorination might lead to an increasing risk for a secondary pollution of methane emission. We assumed this was due to the electron syntrophism between dechlorination bacteria and methanogens, whose inner mechanism stays unknown. Therefore, this project is proposed based on the theory of extracellular nanowires electron-syntrophic system. The strict dechlorination bacteria Dehalococcoides spp. and syntrophy methanogen Methanosarcina. Barkeri. are chosen as the experimental material strains. Technologies such as scanning electron microscope, mutant screening and bioelectrochemical systems are all applied in this research. By biologic and genetic analysis, the nanowires characteristics and extracellular electronic transportation of the two experimental strains will be firstly explored. The coupling bioelectrochemical mechanism between reductive dechlorination and methanogenesis is then revealed by comparing the influences of single and multi- bacteria on COPs coupled with methane bioelectrochemical system. Influences of exogenous functional microorganisms on the protogenous soil microbial community, COPs remediation and methanogenesis can be also elucidated by the microbial inoculating method. By these findings, this research proposes a new effective approach that soil organic pollutants (threatening Eco-environmental safety) are biodegraded with methane mitigation (associating with global warming) synchronously.

还原脱氯是目前研究淹水稻田等厌氧环境氯代有机污染物（COPs）生物降解的主要途径，但在厌氧条件下产甲烷过程常与之协同耦联，导致COPs还原降解可能会引发甲烷增排的次生污染风险。研究猜测这是脱氯呼吸菌和产甲烷菌进行了电子互营，本项目以纳米导线胞外电子传递为理论切入点，选取专性脱氯呼吸菌Dehalococcoides spp.和兼性产甲烷菌Methanosarcina barkeri为模式菌，利用电镜扫描、突变体筛选和生物电化学系统等技术，探索脱氯呼吸菌和产甲烷菌的纳米导线及其胞外电子传递特征；通过分析单菌和复合菌对COPs耦联产甲烷生物电化学系统的影响，揭示还原脱氯和产甲烷生物电化学耦合机制；基于稻田土壤接种脱氯呼吸菌和产甲烷菌，阐明外源功能微生物对原生土壤菌落、COPs修复和甲烷排放的影响。通过研究为寻求环境污染物降解同步甲烷减排途径提供新思路，以此更好地应对有机污染和气候变暖问题。

无论是历史遗留还是新型氯代有机污染物（COPs）都是危害自然生态系统健康的全球性环境问题，据报道，在湿地、稻田、地下水等厌氧环境中，还原脱氯和甲烷（CH4）排放常协同伴生，但其一般耦合特征和作用机理尚不清楚。本项目以产甲烷菌潜在还原脱氯功能挖掘为切入点，结合Meta-analysis、淹水土壤和纯菌培养等研究方法，研究了产甲烷和还原脱氯的耦合关系、及产甲烷菌在COPs降解过程中的潜在脱氯功能。主要结果如下：.1、Meta-analysis发现，产甲烷与还原脱氯整体表现为正向协同，COPs污染生境中产甲烷菌相对丰度较高的菌群是Methanobacterium、Methanoregula和Methanosarcina，其相对丰度分别为1.66%、1.42%和1.26%；同时产甲烷菌与其他潜在脱氯功能微生物（如Dehalococcoides、Desulfitobacterium和Geobacter等）正相关关系显著（p<0.01），在微生物网络中有重要的节点作用。.2、淹水土壤试验表明，添加CH4可以加速不灭菌土壤中有机氯林丹的脱氯降解；灭菌导致了土壤微生物多样性降低，但林丹降解速率、CH4排放、产甲烷菌及其mcrA基因相对丰度并未受到抑制，反而被促进，比如，不灭菌（NS）、灭菌（S）、不灭菌+甲烷（NSC）、灭菌+甲烷（SC）的林丹最终残留量分别为8.30、1.11、1.16和1.03 mg kg-1，与NS相比，S、SC和NSC的林丹降解率分别提高了33.1%、33.5%和32.9%。.3、纯菌培养试验表明，Methanosarcina barkeri促进林丹还原脱氯，相关脱氯产物和差异代谢产物的脱氯功能显著上调；结合热力学动力学密度泛函理论模型模拟在分子水平上探索了产甲烷关键辅酶因子F430对林丹还原脱氯的影响，相对于林丹的自解离反应，F430酶催化介导的脱氯反应能降低25%的反应能垒。.综上，本项目重点解析了产甲烷菌作为潜在脱氯功能微生物的作用机理，突出了挖掘COPs污染环境中占据重要生态位的产甲烷菌的多样性环境功能，为深入理解还原脱氯与产甲烷的耦合关系提供了基础数据支撑，并对后续进一步探索持久性COPs污染加速自净协同甲烷减排的环境微生态条件具有重要指导意义。