稻田土壤砷甲基化过程的分子碳源分异机制

稻田土壤砷甲基化可诱导水稻直穗病发生，严重影响水稻产量与品质。砷甲基化亦是土壤砷向大气挥发的驱动力，调控全球砷生物地球化学循环过程。研究已证明，不同有机物料施用可差异性激发稻田土壤砷甲基化，进一步发现以脂肪族碳链及高丰度非稳态基团如烷基、氮烷基、羧基等为特征的分子碳源更易促进稻田砷甲基化，然而相关机制仍不清楚。本项目聚焦碳链形态及碳基团稳态性显著差异的分子碳源，基于13C示踪和核酸探针（SIP）技术验证目标分子碳源调控稻田砷甲基化效率的分异规律；基于稻田淹水和落干过程中优势菌群富集培养与表征，从砷甲基化、去甲基化微生物平衡角度，阐明不同分子碳源调控砷甲基化进程的微生物机制；通过构建工程菌株，进一步从微生物胞内分子13C源同化诱导甲基供体13C-SAM差异性合成方面揭示相关机理。项目研究成果将为预防水稻直穗病发生和保障水稻安全生产、调控砷生物地球化学循环过程提供科学策略。

Arsenic (As) methylation in paddy soil can induce the occurrence of the straight head disease and seriously affect the rice yield and quality. Arsenic methylation is also the driving force of soil As volatilization into the atmosphere, which is known to regulate the global As biogeochemical cycle. Studies have shown that the application of different organic materials can stimulate As methylation in paddy soils at different extent. It is further found that the molecular carbon source characterized by aliphatic carbon chain and the high abundance of labile carbon such as alkyl-C, N-alkyl-C and carboxyl-C can promote As methylation in paddy soils. However, the relevant mechanism is still unclear. This project will focus on the molecular carbon sources which significant different in carbon chain morphology and labile carbon abundance. The 13C tracing and stable isotope probe (SIP) technology will be applied to verify the differentiation of the different molecular carbon sources dominating As methylation efficiency in paddy soils. The culture experiments of the dominant flora during flooding and drying in paddy soils will be setup, and the microbial balance controlling As methylation and demethylation process will be concerned to clarify the microbial mechanism of the special molecular carbon regulating As methylation efficiency. With the constructed engineering strains capable of As methylation and SAM synthesis, the differential synthesis of 13C-SAM as the potential methyl donor in microbial cells will be revealed. The project can provide scientific strategies for ensuring the safe production of rice and the future regulation of microbial process during As biogeochemical cycle.