产甲烷古菌/地杆菌协同驱动铁型甲烷厌氧氧化的电子互营机制

甲烷厌氧氧化(AOM)是自然厌氧环境的普遍现象，约占全球甲烷通量的60-80%。铁还原耦合型AOM(即铁-AOM)是近年新发现的AOM类型，主要由产甲烷古菌和伙伴细菌完成。然而，产甲烷古菌伙伴细菌类型、古菌-伙伴细菌间电子如何传递仍是未解之谜。申请人前期发现，铁-AOM富集培养物中产甲烷古菌/地杆菌聚集共生体可驱动甲烷氧化同时还原铁。由此，本项目提出“产甲烷古菌/地杆菌协同催化AOM和铁还原”的假说。以甲烷八叠球菌/地杆菌为对象，甲烷为电子供体，氧化铁为电子受体，采用同位素示踪、FISH-NanoSIMS等手段解析共生体生长特性、甲烷代谢途径和铁还原能力；利用基因敲除、生物电化学、原位光谱等方法系统研究甲烷-共生体-氧化铁间的电子传递机制；结合共生体在自然土壤的空间分布特征，阐明土壤铁-AOM的发生机理，为深入理解AOM与土壤铁循环关系提供新线索，为甲烷温室气体减排提供理论依据和技术支撑。

Anaerobic oxidation of methane (AOM) is a widespread process in natural anaerobic environments, accounting for 60-80% of global methane flux. AOM coupled to iron reduction (Fe-AOM) has recently been identified as a novel AOM, which is mainly catalyzed by methanogens and the parter bacteria. However, the specific types of methanogens and the parter bacteria and how electrons transfer from methanogens to bacteria in the Fe-AOM process remain unknown. Our previous studies indicated that the interactions between methanogens and Geobacter in a Fe-AOM enrichment culture accelerated AOM and Fe(III) reduction. Herein, we propose for the first time a hypothesis that the methanogens/Geobacter symbionts catalyze AOM and iron reduction synergistically. This project aims to investigate systematically the Fe-AOM abilities and cooperation mechanisms by the methanogens/Geobacter symbionts. Using methane as an electron donor and Fe(III) oxides as electron acceptors, the growth property of symbionts, methane metabolism pathway and iron reduction efficiencies will be elucidated via many techniques including 13C isotope tracing and fluorescence in situ hybridization coupled to nanoscale secondary ion mass spectrometry (FISH-NanoSIMS). The EET mechanisms among methane, symbionts and iron oxides will be revealed via gene deletion, bioelectrochemistry and in situ spectroscopy. Combined with the distribution profile of soil symbionts, the role of symbionts in Fe-AOM and its environmental functions will be illuminated. Results of the project will provide new insights into the Fe-AOM principle and its relationship with soil iron redox cycles, and provide a theoretical basis for controlling the methane greenhouse gas emission.