Magnetotactic bacteria (MTB) have long fascinated geologists and biologists because they biomineralize intracellular single domain (SD) magnetite crystals within magnetosomes that are generally organized into single or multiple chains. MTB remains in the geological record (magnetofossils) are ideal magnetic carriers and are used to reconstruct paleomagnetic and paleoenvironmental information. Here we studied the biomineralization and magnetic properties of magnetosomal magnetite produced by uncultured magnetotactic coccus strain THC‐1, isolated from the Tanghe River, China, by combining transmission electron microscope (TEM) and rock magnetic approaches. Our results reveal that THC‐1 produces hexagonal prismatic magnetite single crystals that are elongated along the [111] crystallographic direction. Most of the magnetite crystals within THC‐1 are dispersed without obvious chain assembly. A whole‐cell THC‐1 sample yields a normal SD hysteresis loop and a Verwey transition temperature of ~112 K. In contrast to MTB cells with magnetosome chain(s), THC‐1 cells have a teardrop first‐order reversal curve distribution that is indicative of moderate interparticle interactions. Due to the absence of a magnetosome chain, THC‐1 has relatively high values of the difference between the saturation isothermal remanent magnetization (SIRM) below and above the Verwey transition temperature for field‐cooled and zero field‐cooled SIRM curves (δ_FC, δ_ZFC) and a low δ_FC/δ_ZFC value. Together with previous studies, our results demonstrate that some MTB species/strains can form magnetosomal magnetite without linear chain configurations. Magnetite produced by MTB has diverse magnetic properties, which are distinctive but not necessarily unique compared to other magnetite types. Therefore, combining bulk magnetic measurements and TEM observations remains necessary for identifying magnetofossils in the geological record.

中文翻译：

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具有非链状磁体磁铁矿纳米颗粒的未培养趋磁球菌THC-1的生物矿化和磁性

趋磁细菌（MTB）使地质学家和生物学家着迷很久，因为它们生物矿化磁小体内的细胞内单域（SD）磁铁矿晶体，这些晶体通常组织成单链或多链。保留在地质记录中的MTB（磁化石）是理想的磁性载体，用于重建古磁和古环境信息。在这里，我们结合透射电子显微镜（TEM）和岩石磁学方法研究了从唐河中分离出来的未经培养的趋磁球菌THC-1产生的磁体磁铁矿的生物矿化和磁性。我们的结果表明，THC-1产生了沿[111]晶体学方向伸长的六方棱柱形磁铁矿单晶。THC-1中的大多数磁铁矿晶体分散而没有明显的链组装。全细胞THC-1样品产生正常的SD磁滞回线，Verwey转变温度约为112 K.与具有磁小体链的MTB细胞相比，THC-1细胞具有泪滴一阶逆转曲线分布表明适度的颗粒间相互作用。由于缺少磁小体链，THC-1在场冷和零场冷却的SIRM曲线的Verwey转变温度以下和以上的饱和等温剩磁磁化强度（SIRM）之间的差异值相对较高（THC-1细胞具有一滴泪一阶逆转曲线分布，表明中等粒子间相互作用。由于缺少磁小体链，THC-1在场冷和零场冷却的SIRM曲线的Verwey转变温度以下和以上的饱和等温剩磁磁化强度（SIRM）之间的差异值相对较高（THC-1细胞具有一滴泪一阶逆转曲线分布，表明中等粒子间相互作用。由于缺少磁小体链，THC-1在场冷和零场冷却的SIRM曲线的Verwey转变温度以下和以上的饱和等温剩磁磁化强度（SIRM）之间的差异值相对较高（δ _FC，δ _ZFC），和低的δ _FC / δ _ZFC值。与以前的研究一起，我们的结果表明，某些MTB物种/菌株可以形成磁链磁铁矿，而没有线性链构型。MTB生产的磁铁矿具有多种磁性，与其他磁铁矿类型相比具有独特但不一定独特的磁性。因此，将大磁测量和TEM观测结合起来对于识别地质记录中的磁化石仍然是必要的。