我国典型水稻土胞外呼吸菌多样性、格局及其元素生物地球化学耦合机制

Extracellular respiring microbes (ERM) widely distribute and play essential roles in the biogeochemical cycles of iron (Fe) and trace elements. In anaerobic condition, bacteria can breathe soluble ions (e.g. nitrate, sulfate) and insoluble minerals (e.g. Fe oxides) instead of oxygen. When solid oxides serve as the electron accepter, the bacteria have to transfer the electrons, which are generated from the oxidation of organic matters, out of the membrane through various mechanisms, including redox membrane protein, electron shuttles, and conductive pili. Paddy soil is one of the most important soil types in agricultural system. During the rice growth season, the soil is flooded and the redox potential rapidly shifts to negative. The unique redox condition in paddy field provides suitable habit for ERM growth. Rice is the staple food for Asia people and covers approximate 30 million hectare in our country. Although the ERM dominate the reduction of iron minerals in paddy soils, it remains unclear that who consist of the ERM community, how the ERM interact with the iron and other trace elements, such on nitrogen (N), phosphorus (P) and arsenic (As). In the proposal, we will focus on the paddy soils all over China and aim to : 1) identify the ERM diversity and metabolic pathway by using novel enrichment methods (e.g. microbial fuel cells) and cutting-edge technologies for single-cell sequence; 2) uncover the dominating environmental parameters that influence the pattern of ERM by large-scale and long-term experiments; 3) explain the Fe(III) reduction kinetics of ERM feeding with difference electron donors; 4) reveal the mechanisms that ERM interact with iron oxides and other elements of significant environmental concerns, namely N, As, and P, by using isolated species. The results from this project will significantly enhance our understanding that how the ERM in paddy soils influence the biogeochemical behaviors of elements and contribute to build a sustainable agriculture for the future.

胞外呼吸菌是环境中广泛存在的，通过胞外电子传递进行呼吸的一类微生物，在生物地球化学循环中发挥重要作用，特别是在水稻土元素循环中起到关键的作用。本项目以我国典型水稻土为主要对象，拟开展研究的主要内容包括：1）通过新型富集培养技术，建立若干表征典型土壤胞外呼吸菌群的方法，并在富集的基础上结合单细胞分选和测序技术，深度挖掘胞外呼吸菌的多样性和新的代谢途径。2）通过典型区域、时间序列和长期定位实验开展系统研究，解析典型水稻土胞外呼吸菌的多样性及其区域分布特征，结合相关化学和统计分析，明确影响土壤胞外呼吸菌组成和区域变异的主控因子。3）选择典型土壤序列，以水铁矿为底物，探明不同电子供体的土壤胞外呼吸菌多样性与铁还原动力学之间的耦联关系。4）在上述三方面研究的基础上，通过构建模式体系，研究胞外呼吸纯菌或菌群如何通过介导铁的还原对氮磷砷转化的影响机制，解析在胞外呼吸菌介导下铁与氮磷砷转化的耦合机制。

胞外呼吸菌是环境中广泛存在的，通过胞外电子传递进行呼吸的一类微生物，在生物地球化学循环中发挥重要作用，特别是在水稻土元素循环中起到关键的作用。本项目以我国典型水稻土为主要研究对象，1) 我们描绘了我国水稻土中典型胞外呼吸菌Geobacteraceae的丰度和分布，明确了地理距离和无定型铁是影响我国水稻土中典型胞外呼吸菌Geobacteraceae的丰度和分布的主要因子；2）我们利用土壤微生物燃料电池（Soil microbial fuel cells, SMFCs）富集胞外呼吸菌，同时结合Illumina HiSeq高通量测序研究土壤理化性质和地理距离对SMFCs阳极细菌群落组成的影响，实验证明地理距离和土壤理化性质均显著影响不同稻田土壤的SMFCs 阳极细菌群落组成和多样性。3）我们研究了电子穿梭体（AQDS和biochar）对铁还原的影响，发现两种电子穿梭体都可以加速铁还原；我们进一步研究了电子穿梭体对厌氧铁氨氧化（Feammox）的影响，发现AQDS和生物炭的添加能够促进异化铁还原系统中Feammox过程；4）我们从水稻土中分离纯化得到了几株硝酸盐依赖的铁氧化菌，并对其中一株细菌的铁氧化特性进行了研究，发现发现了硝酸盐依赖的铁氧化菌的代谢活性；5）针对蚯蚓肠道微生物生态学功能过程中的作用方面也取得了新的进展，与原位土壤环境相比，蚯蚓肠道内容物被检测到了更高的Fe(Ⅲ)还原率，证明蚯蚓肠道微生物对土壤中Fe循环的巨大潜能；6) 最后我们综述了厌氧微生物氧化还原反应热力学能量耦合元素地球化学循环。