近日，国际著名杂志Geomicrobiology Journal在线刊登了中科院地质与地球物理所研究人员的最新研究成果“Environmental Factors Affect Magnetite Magnetosome Synthesis in Magnetospirillum magneticum AMB-1: Implications for Biologically Controlled Mineralization
”，文章中，研究者发现环境因子影响趋磁细菌AMB-1磁铁矿合成 。
趋磁细菌能在细胞内合成有生物膜包被、纳米尺寸、单磁畴（SD）的磁铁矿（Fe3O4）或胶黄铁矿（Fe3S4）晶体颗粒—磁小体。磁小体合成条件和生物控制矿化机理是利用化石磁小体重建古环境和开发新型磁性纳米材料的重要前提。过去，磁小体一直被认为是在基因严格调控下的产物，即晶形完美和化学纯度高等，是否也受到细菌生长环境变化的影响并不清楚。
中科院地质与地球物理所地球深部结构与过程研究室古地磁与年代学实验室、中-法生物矿化与纳米结构联合实验室李金华博士和潘永信研究员，综合利用透射电子显微镜（TEM）、X-射线衍射（XRD）和岩石磁学技术，系统研究了趋磁螺菌Magnetospirillum magneticum AMB-1磁小体的合成过程及其与环境因子（氧浓度）之间的关系。研究结果显示：（1）在厌氧静止（ANS）、有氧静止（AS）、有氧振荡80 rpm（A80）和有氧振荡120 rpm（A120）四种生长条件下，随着培养过程中供氧增强和振荡加剧，磁小体的数目和尺寸减小，颗粒由拉长形和截角钝圆趋向立方形和截角尖锐，孪晶磁小体出现频率由~20.2%升高到~51.6%；（2）细胞的磁学性质包括矫顽力（Bc）、剩磁矫顽力（Bcr）、剩磁比（Mrs/Ms）和Verwey转换温度(Tv)逐渐降低，分别由ANS培养的22.0 mT、31.3 mT、0.45和108 K降低到A120培养的5.2 mT、9.3 mT、0.31和98 K；（3）四种生长条件下，AMB-1均合成截角八面体型（Truncated octahedron）磁铁矿，表明磁小体的矿物相和晶型可能具有菌种或菌株特异性，受细胞基因水平的严格调控。环境因子（如氧气）能显著影响磁小体的形貌和尺寸等物理性质、结晶度和化学计量纯度等晶体化学性质、以及细胞的磁学性质；环境氧浓度增加导致趋磁细菌AMB-1合成“不纯（非标准化学计量比）”的磁铁矿。
该项研究揭示，虽然趋磁细菌磁铁矿是在生物控制下合成，其矿化过程和产物受环境因子的影响；磁小体形成与环境氧浓度相关，化石磁小体可以作为古环境研究的替代指标，用来重建古氧浓度；此外，磁小体磁铁矿的晶格缺陷和环境调控给磁小体的人工改造（如Co等其他过渡簇金属元素的掺杂）带来了机会，将提高其在高密度磁存储、靶向药物输送和肿瘤细胞磁热疗等领域的应用价值。
（生物谷Bioon.com）
doi:10.1080/01490451.2011.565401
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PMID:
Environmental Factors Affect Magnetite Magnetosome Synthesis in Magnetospirillum magneticum AMB-1: Implications for Biologically Controlled Mineralization
Jinhua Liab & Yongxin Panab
It is widely believed that magnetotactic bacteria (MTB) form membrane-enveloped magnetite crystals (magnetosomes) under strict genetic control. In this study, the Magnetospirillum magneticum strain AMB-1 was cultured in the same growth medium, but under four different growth conditions: Anaerobic static, aerobic static, aerobic 80-rpm rotating, and aerobic 120-rpm rotating to investigate possible environmental influences on magnetite magnetosome formation. Integrated analyses, using transmission electron microscopy, X-ray diffraction and rock magnetism, indicate that, from the anaerobic static to aerobic 120-rpm rotating culture, the formed magnetite magnetosomes became more equidimensional, smaller in grain size, and higher in crystal twinning frequency. Magnetic properties of magnetite magnetosomes such as coercivity, remanence coercivity, remanence ratio and Verwey transition temperature systematically decreased from 22.0 mT to 5.2 mT, 31.3 mT to 9.3 mT, 0.45 to 0.31, and 108 K to 98 K, respectively. Comparison of additional anaerobic 120-rpm rotating cultures with anaerobic static cultures showed that the effect of rotating, at least up to 120 rpm, on the cell growth and magnetite magnetosome formation is weak and negligible. Given that all samples were prepared and measured in the same way, the changes in physical and magnetic properties indicate that environmental factors (oxygen) affected the biomineralization of magnetite magnetosomes in magnetotactic bacteria, which supports the previous findings. In all experiments, only magnetite with the geometry of truncated octahedron was formed within magnetosomes, which suggests that the mineral phase and crystal habit remain to be genetically controlled. These results also imply the physical and magnetic properties of magnetite magnetosomes may, to some extent, reflect the external growth environments.
