水稻土嗜中性微好氧亚铁氧化菌多样性及微生物成矿研究

摘要

微生物驱动亚铁氧化过程在水稻土中十分普遍，该过程被认为是水稻土中联接各生物地球化学过程的中心枢纽。嗜中性微好氧亚铁氧化菌能够利用氧气作为电子受体将亚铁氧化成三价铁，获得生长所需能量。然而，对水稻土中微好氧亚铁氧化菌的多样性与分布及其微生物成矿类型仍然未知。采用铁氧反向浓度梯度管法富集培养并分离水稻土中微好氧亚铁氧化菌，利用16S rRNA基因测序手段分析培养过程中微好氧亚铁氧化菌群落多样性与分布，并初步研究分离得到的亚铁氧化菌的亚铁氧化能力与生物成矿类型。结果表明，在富集培养和传代培养过程中，Azospira、Magnetospirillum、Clostridium 和Rhodoplanes等属在群落中占优势。在分离最后阶段，得到几种细菌的混合菌团，可能是由于这几种亚铁氧化菌存在互养关系而难以纯化分离，其中占优势的为Azospira（63.9%）。Azospira是一类已知硝酸盐依赖型FeOB，可以利用硝酸盐、氯酸盐和高氯酸盐为电子受体进行厌氧亚铁氧化。混合菌团具有活跃的亚铁氧化能力，反应第15天生成6.9 mmol·L-1HCl-Fe。XRD结果表明菌团氧化亚铁形成的三价铁矿物类型为无定形铁氧化物。TEM结果显示微好氧FeOB菌体呈杆状，细菌表面和周围散布着颗粒状的物质，可能是由无定形铁氧化物组成。综上所述，认为反硝化细菌可能在水稻土有氧-无氧界面进行微好氧亚铁氧化，其氧化亚铁的产物为无定形铁氧化物。%Microbially mediated iron oxidation is prevalent and thought to be central to many biogeochemical processes in paddy soils. Neutrophilic, microaerophilic Fe(Ⅱ)-oxidizing bacteria (FeOB) can oxidize Fe(Ⅱ) using O2 as electron acceptor to gain energy for growth, yet little is known about the diversity and distribution of FeOB and the formation of Fe(Ⅲ)-minerals by microaerophilic FeOB in paddy soil. In this study, gradient tubes with opposing gradient Fe(Ⅱ) and O2 were used to enrich and isolate microaerophilic FeOB from paddy soil, where 16S rRNA gene sequencing methods were used to profile the microbial diversity and distribution of FeOB in continuous cultivation and then the ability of Fe(Ⅱ) oxidation by the isolated FeOB and the Fe(Ⅲ) products were tested as well. The results showed thatAzospira,Magnetospirillum,ClostridiumandRhodoplaneswere abundant in the cultured communities. A mixture of several species remained together till the last stage of isolation, which might due to the syntrophic associations among the FeOBs. Among them, Azospira was the dominant FeOB with a relative abundance of 63.9%. Azospira is a well-known nitrate-reducing FeOB, which is capable of utilizing nitrate, chlorate or perchlorate as alternative electron acceptors. The isolated FeOB mixture actively oxidized Fe(Ⅱ), the concentration of HCl-Fe was 6.9 mmol·L-1on day 15.XRD results revealed that amorphous iron oxides were formed as the products of microbial iron oxidation. TEM results showed that cells of microaerophilic FeOB were rod-shaped with globular shaped particles sparsely deposited on the surface or around the cell, which might consist of amorphous Fe(Ⅲ) oxides. Overall, our results revealed that denitrifying bacteria might be capable of microaerophilic Fe(Ⅱ) oxidation which could be stimulated in the oxic-anoxic interface in paddy soil, and amorphous iron oxides were formed as microbial Fe(Ⅱ) oxidation by such bacteria.