厌氧水稻土中地杆菌和厌氧粘细菌的群落结构特征及其对异化铁还原的贡献

Microbial Fe(III) reduction plays a fundamental role in diverse processes in submerged rice fields, such as degradation of organic contaminants, suppression of methane emissions, and mobilization of toxic metals. Geobacter and anaeromyxobacter are typical representatives of obligate Fe(III) reducing microorganism in paddy soils. In this project, the dynamics of the community structure, abundance and transcription activity of geobacter and anaeromyxobacter in submerged unplanted paddy soils from geographically distinct regions in China will be investigated by reliance on Real-time PCR, denaturing gradient gel electrophoresis (DGGE) and high-throughput sequencing (HTS) to elucidate the relatedness between succession of geobacter and anaeromyxobacter and Fe(III) reduction. Furthermore, how temperature, pH, carbon source concentrations, iron oxides species and oxygen levels influence dynamics of the community structure, abundance and transcription activity of geobacter and anaeromyxobacter will also be covered in this project to clarify the effect environmental factors on succession of geobacter and anaeromyxobacter and their contribution to Fe(III) reduction in paddy soil. In addition, a rhizobox with three compartments and subsequent soil-slicing will be conducted to determine the effect of rhizosphere oxygen secretion on distribution of geobacter and anaeromyxobacter community in different profiles of paddy soil and their ecological function on Fe(III) reduction. This project will provide a theoretical basis of the characteristics of community structures and phylogenetic classification of Fe(III) reducing bacteria and aid in the interpretation of Fe dynamics in flooded paddy fields.

异化铁还原微生物不仅控制稻田铁循环过程，而且对有机物降解和变价重金属的转化具有重要作用。地杆菌和厌氧粘细菌是水稻土中两类主要的异化铁还原菌。本项目采用PCR-DGGE、高通量测序和Real-time PCR技术，研究淹水过程对不同水稻土中地杆菌和厌氧粘细菌的群落结构、丰度和转录活性的影响，以期阐明不同水稻土中地杆菌和厌氧粘细菌群落结构的动态变化特征及与铁还原的相关性；比较温度、pH值、碳源浓度、铁矿物种类及泥浆氧气浓度等环境因素对地杆菌和厌氧粘细菌群落结构特及丰度/转录活性的调控能力；利用根箱培养实验，探究根系泌氧过程对根区剖面微土层（0-12 mm）中地杆菌和厌氧粘细菌群落结构特及丰度/转录活性的影响及其与水稻土不同剖面铁还原作用的关系。

铁的氧化还原循环是稻田土壤中最重要的化学变化过程，与微生物参与的生物化学过程密切相关。异化铁还原微生物不仅控制稻田铁循环过程，而且对有机物降解和变价重金属的转化具有重要作用。本研究采用非种植厌氧恒温培养方法，探究了不同碳源、初始pH调节、培养温度、添加电子受体等环境条件变化下，土壤中地杆菌和厌氧粘细菌的群落结构对淹水时间的响应特征。采用根箱种植方法，探讨了不同水稻生长期的土壤分层中地杆菌、厌氧粘细菌及梭菌的丰度及转录活性，针对高通量测序结果，比较了铁还原微生物的相对丰度及其群落结构的演替特征，及根际与非根际土壤铁还原微生物数量及群落结构的差异。主要结果如下：1、淹水水稻土中，专性和兼性铁还原菌对于环境变化的响应敏感性差异较大。兼性铁还原菌较之专性铁还原菌对于环境变化的适应性强，添加碳源明显提升了兼性铁还原菌的贡献。调节水稻土初始pH使细菌群落丰富度和多样性明显降低。调低碱性水稻土初始pH显著降低了淹水前期专性及兼性铁还原菌的比值，使兼性铁环菌的作用明显增加。2、Fe(II)浓度变化随距根表距离的减小呈现出逐渐降低的趋势，植株生物量越大对Fe(II)浓度的影响也越强。根系泌氧引起的微生物的群落结构变化与Fe(III)还原过程密切相关。不同生长期根际土壤的地杆菌和厌氧粘细菌的活性均高于非根际，根际土壤的拷贝数变化随种植时间增加较非根际更为剧烈。根系泌氧过程增加了地杆菌微生物群落的多样性。3、添加水铁矿和针铁矿能显著增加培养前期地杆菌的相对丰度，而针铁矿使培养后期厌氧粘细菌相对丰度增加。添加水铁矿使培养前期地杆菌群落结构变化较大，而培养后期对于厌氧粘细菌群落结构有较大影响。不同水稻土中地杆菌和厌氧粘细菌对针铁矿和水铁矿的利用度存在差异。4、不同地杆菌科物种的丰度对氧气的耐受性不同，高氧浓度下地杆菌群落的演替方式发生变化。厌氧粘细菌表现出兼性厌氧特点，氧气促进厌氧粘细菌生长，且其丰度随培养时间而逐渐升高。.