近日,，國(guó)際著名雜志Geomicrobiology Journal在線刊登了中科院地質(zhì)與地球物理所研究人員的最新研究成果“Environmental Factors Affect Magnetite Magnetosome Synthesis in Magnetospirillum magneticum AMB-1: Implications for Biologically Controlled Mineralization
”,，文章中，研究者發(fā)現(xiàn)環(huán)境因子影響趨磁細(xì)菌AMB-1磁鐵礦合成 ,。
趨磁細(xì)菌能在細(xì)胞內(nèi)合成有生物膜包被,、納米尺寸、單磁疇（SD）的磁鐵礦（Fe3O4）或膠黃鐵礦（Fe3S4）晶體顆粒—磁小體。磁小體合成條件和生物控制礦化機(jī)理是利用化石磁小體重建古環(huán)境和開(kāi)發(fā)新型磁性納米材料的重要前提,。過(guò)去,，磁小體一直被認(rèn)為是在基因嚴(yán)格調(diào)控下的產(chǎn)物，即晶形完美和化學(xué)純度高等,，是否也受到細(xì)菌生長(zhǎng)環(huán)境變化的影響并不清楚,。
中科院地質(zhì)與地球物理所地球深部結(jié)構(gòu)與過(guò)程研究室古地磁與年代學(xué)實(shí)驗(yàn)室、中-法生物礦化與納米結(jié)構(gòu)聯(lián)合實(shí)驗(yàn)室李金華博士和潘永信研究員,，綜合利用透射電子顯微鏡（TEM）,、X-射線衍射（XRD）和巖石磁學(xué)技術(shù)，系統(tǒng)研究了趨磁螺菌Magnetospirillum magneticum AMB-1磁小體的合成過(guò)程及其與環(huán)境因子（氧濃度）之間的關(guān)系,。研究結(jié)果顯示：（1）在厭氧靜止（ANS）,、有氧靜止（AS）、有氧振蕩80 rpm（A80）和有氧振蕩120 rpm（A120）四種生長(zhǎng)條件下,，隨著培養(yǎng)過(guò)程中供氧增強(qiáng)和振蕩加劇,，磁小體的數(shù)目和尺寸減小，顆粒由拉長(zhǎng)形和截角鈍圓趨向立方形和截角尖銳,，孿晶磁小體出現(xiàn)頻率由~20.2%升高到~51.6%,；（2）細(xì)胞的磁學(xué)性質(zhì)包括矯頑力（Bc）、剩磁矯頑力（Bcr）,、剩磁比（Mrs/Ms）和Verwey轉(zhuǎn)換溫度(Tv)逐漸降低,，分別由ANS培養(yǎng)的22.0 mT、31.3 mT,、0.45和108 K降低到A120培養(yǎng)的5.2 mT,、9.3 mT、0.31和98 K,；（3）四種生長(zhǎng)條件下,，AMB-1均合成截角八面體型（Truncated octahedron）磁鐵礦，表明磁小體的礦物相和晶型可能具有菌種或菌株特異性,，受細(xì)胞基因水平的嚴(yán)格調(diào)控,。環(huán)境因子（如氧氣）能顯著影響磁小體的形貌和尺寸等物理性質(zhì)、結(jié)晶度和化學(xué)計(jì)量純度等晶體化學(xué)性質(zhì),、以及細(xì)胞的磁學(xué)性質(zhì),；環(huán)境氧濃度增加導(dǎo)致趨磁細(xì)菌AMB-1合成“不純（非標(biāo)準(zhǔn)化學(xué)計(jì)量比）”的磁鐵礦。
該項(xiàng)研究揭示,，雖然趨磁細(xì)菌磁鐵礦是在生物控制下合成,，其礦化過(guò)程和產(chǎn)物受環(huán)境因子的影響；磁小體形成與環(huán)境氧濃度相關(guān),，化石磁小體可以作為古環(huán)境研究的替代指標(biāo),，用來(lái)重建古氧濃度,；此外，磁小體磁鐵礦的晶格缺陷和環(huán)境調(diào)控給磁小體的人工改造（如Co等其他過(guò)渡簇金屬元素的摻雜）帶來(lái)了機(jī)會(huì),，將提高其在高密度磁存儲(chǔ),、靶向藥物輸送和腫瘤細(xì)胞磁熱療等領(lǐng)域的應(yīng)用價(jià)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.
