二甲基砷（DMAs）可以诱发水稻直穗病，导致水稻减产。水稻中积累的DMAs源自土壤微生物砷的甲基化产物。申请人前期研究发现水稻土淹水后DMAs含量呈现动态变化，即先积累，随后通过脱甲基消失。因此，水稻土中DMAs脱甲基过程将有助于降低水稻对DMAs的积累。研究还发现产甲烷古菌参与了水稻土中DMAs的脱甲基过程，并且DMAs脱甲基过程很可能需要产甲烷古菌与细菌互作才能完成。目前关于参与DMAs脱甲基过程的产甲烷古菌类型、DMAs脱甲基机制及与细菌互作的机制仍然未知。因此，本项目将分离鉴定参与DMAs脱甲基过程的产甲烷古菌及互作细菌，揭示二者的互作机制；通过转录组分析及酶学纯化等方法探究产甲烷古菌的DMAs脱甲基机制；探究不同水稻土中DMAs脱甲基能力与功能产甲烷古菌丰度之间的关系。本项目旨在进一步明确水稻土中甲基砷脱甲基的微生物学机制，为防治水稻直穗病提供理论依据。

Dimethylarsenic (DMAs) can cause straight-head disease in rice, resulting in large yield losses. DMAs in rice is originated from microbial methylation of arsenic in paddy soils. Upon flooding of paddy soil, DMAs accumulates initially and then disappears due to demthylation. Promoting demthylation of DMAs may therefore reduce its accumulation in rice plants. Based on the previous studies of the applicant, DMAs in paddy soils is produced primarily and subsequently demethylated mainly by methanogenic archaea. Furthermore, demethylation of DMAs requires interactions of methanogens and bacteria. However, methanogens capable of DMAs demethylation have not been isolated from paddy soils. The mechanisms of DMAs demethylation and the interactions between methanogens and bacteria remain to be investigated. In this project, we aim to isolate strains of methanogens and bacteria in paddy soils which are responsible for DMAs demethylation. We will investigate the mode of interactions between methanogens and bacteria during DMAs demethylation. We will elucidate the mechanism of DMAs demethylation via transcriptomic analysis and enzyme reactions in vitro. Finally, we will quantify the ability of DMAs demethylation of different paddy soils and its relationship with the abundance of functional methanogens. This project will improve our knowledge of microbial arsenic demethylation in paddy soils and provide potential solution for the prevention of straight-head disease in rice.