趋磁细菌磁小体磁铁矿超精细和微磁结构研究

Magnetotactic bacteria (MTB) have the ability of navigating along the Earth’s magnetic field and synthesizing intracellular magnetosomes, which are single-domain magnetite (Fe3O4) crystals and usually organized into chain structures. Biomineralization and magnetism of magnetosomes are of great interest to a wide variety of disciplines ranging from biologically controlled mineralization and magnetoreception in higher organisms to paleomagnetic studies and nanomagnetic materials. The present project will rely on a dynamic effort to bring together several key disciplines: geomicrobiology, biomineralization and nanomagnetism. Combination of rock magnetism, electron microscopy and synchrotron approaches will be used to study: (1) superfine structure of magnetosome magnetites formed by four strains of cultured MTB and uncultured strain MYR-1; (2) Cobalt-doping-induced synthesis of magnetite crystals by Magnetospirillum magneticum AMB-1; and (3) micromagnetic structure of bullet-shaped magnetite formed by MYR-1. The main goals of this project are to clarify three following scientific issues: (1) whether magnetotactic bacteria magnetites are stoichiometric or not? (2) whether and how cobalt can be doped into MTB magnetite crystals? If doped, where is it and how do the magnetic properties change? (3) how does the micromagnetic structure of bullet-shaped magnetosome magnetite look like in MYR-1? We believe that this project will give new insights into better understanding the mechanism of biomineralization and magnetotaxis of MTB, amd provide some useful clues to identify magnetofossils from geological materials and decode the paleomagnetic information carried by them, as well as pave the way to produce novel biogenic nanomagnetic materials.

趋磁细菌是一类独具特色的地质微生物，能在细胞内合成单磁畴磁铁矿链（磁小体）和沿地磁场游弋。磁小体的生物矿化和磁学是趋磁细菌的研究核心，对认识生物控制矿化和生物响应地磁场机理、识别化石磁小体、及开发新型磁性纳米材料均具有重要科学意义。本项目拟综合应用微生物学、岩石磁学、电子显微学和同步辐射技术，以实验室可培养趋磁细菌和密云水库未培养细菌MYR-1为材料，重点研究：（1）磁小体磁铁矿的超精细结构；（2）磁小体磁铁矿的晶格修饰和钴（Co）替代；和（3）MYR-1子弹头形磁小体微磁结构。本项目的实施，将有助于从根本上澄清“趋磁细菌磁铁矿到底纯不纯”、“Co能否被掺入磁小体磁铁矿晶格中而实现其功能化改造”和“子弹头形磁小体磁畴结构及磁力线分布”三个基础科学问题和难题，有望在趋磁细菌生物控制矿化和趋磁性机理研究方面提出新认识，为化石磁小体识别提供新依据，也为新型生物源磁性纳米材料的开发提供新途径。

趋磁细菌生物矿化和磁小体磁性研究对认识生物控制矿化和生物响应地磁场机制、识别化石磁小体，及开发新型磁性纳米材料具有重要科学意义。解析趋磁细菌磁小体磁铁矿超精细和微磁结构有助于从本质上认识趋磁细菌生物矿化机理和磁小体链复杂磁性机制。本项目综合微生物学、岩石磁学、透射电子显微学和同步辐射等多种手段，系统地研究了趋磁大杆菌MYR-1细胞的结构与化学组成特征，揭示了子弹头形磁小体的多阶段晶体生长过程机制，提出子弹头形磁铁矿的[001]拉长是更可靠化石磁小体判据的新观点；研究了可培养趋磁螺菌AMB-1在不同浓度[Co2+]培养条件下细胞生长、磁小体合成过程及磁小体晶体化学组成，首次提供新证据证实了Co2+通过替代八面体位点上的Fe2+而掺入磁小体磁铁矿晶格中并显著改变其磁学性质；实验模拟和电子全息直接观测研究了磁小体链(束)的微磁结构及其磁化行为，证实了磁小体的链状结构是趋磁细菌高效利用地磁场定向游弋的物理基础，揭示了磁小体链在自然界可能的坍塌、聚集和排列等成化石过程及其对宏观磁性的影响，并提出一个新参数δ图，可以用于化石磁小体的识别；研发了“荧光-电子显微镜联用”技术，首次在单细胞水平上实现了微生物种类鉴定和磁小体生物矿化研究；利用该技术，鉴定并系统研究了两株新型趋磁细菌SHHR-1和SHHC-1的生物矿化过程。本项目研究成果为全面认识现代趋磁细菌种类及其磁小体生物矿化多样性提供了重要数据，揭示了磁小体链复杂磁性机制及趋磁细菌高效响应地磁场的物理基础，为化石磁小体识别提供了新参数，还为磁小体的磁性改良及开展其在纳米生物医学中的应用奠定了基础。项目执行顺利，完成预设目标，共发表SCI论文11篇，中文核心文章1篇，申请国内发明专利1项。项目执行期间，项目负责人获得了国家基金委优青资助和傅承义青年科技奖，项目负责人破格晋升研究员，项目组成员2人获得博士学位，1人获得硕士学位。