Lower Brian H, Bazylinski Dennis A
School of Environment and Natural Resources, The Ohio State University, Columbus, Ohio, USA.
J Mol Microbiol Biotechnol. 2013;23(1-2):63-80. doi: 10.1159/000346543. Epub 2013 Apr 18.
The bacterial magnetosome is a unique prokaryotic organelle comprising magnetic mineral crystals surrounded by a phospholipid bilayer. These inclusions are biomineralized by the magnetotactic bacteria which are ubiquitous, aquatic, motile microorganisms. Magnetosomes cause cells of magnetotactic bacteria to passively align and swim along the Earth's magnetic field lines, as miniature motile compass needles. These specialized compartments consist of a phospholipid bilayer membrane surrounding magnetic crystals of magnetite (Fe3O4) or greigite (Fe3S4). The morphology of these membrane-bound crystals varies by species with a nominal magnetic domain size between 35 and 120 nm. Almost all magnetotactic bacteria arrange their magnetosomes in a chain within the cell there by maximizing the magnetic dipole moment of the cell. It is presumed that magnetotactic bacteria use magnetotaxis in conjunction with chemotaxis to locate and maintain an optimum position for growth and survival based on chemistry, redox and physiology in aquatic habitats with vertical chemical concentration and redox gradients. The biosynthesis of magnetosomes is a complex process that involves several distinct steps including cytoplasmic membrane modifications, iron uptake and transport, initiation of crystallization, crystal maturation and magnetosome chain formation. While many mechanistic details remain unresolved, magnetotactic bacteria appear to contain the genetic determinants for magnetosome biomineralization within their genomes in clusters of genes that make up what is referred to as the magnetosome gene island in some species. In addition, magnetosomes contain a unique set of proteins, not present in other cellular fractions, which control the biomineralization process. Through the development of genetic systems, proteomic and genomic work, and the use of molecular and biochemical tools, the functions of a number of magnetosome membrane proteins have been demonstrated and the molecular mechanism for the biomineralization of magnetosomes in these organisms is beginning to be revealed.
细菌磁小体是一种独特的原核细胞器，由被磷脂双分子层包围的磁性矿物晶体组成。这些内含物由趋磁细菌生物矿化形成，趋磁细菌是普遍存在的水生运动微生物。磁小体使趋磁细菌的细胞被动排列，并像微型运动指南针一样沿着地球磁场线游动。这些特殊的隔室由围绕磁铁矿（Fe3O4）或硫复铁矿（Fe3S4）磁性晶体的磷脂双分子层膜组成。这些膜结合晶体的形态因物种而异，其标称磁畴大小在35至120纳米之间。几乎所有趋磁细菌都将其磁小体排列在细胞内的一条链中，从而使细胞的磁偶极矩最大化。据推测，趋磁细菌利用趋磁作用与趋化作用相结合，在具有垂直化学浓度和氧化还原梯度的水生生境中，根据化学、氧化还原和生理学特性来定位并维持生长和生存的最佳位置。磁小体的生物合成是一个复杂的过程，涉及几个不同的步骤，包括细胞质膜修饰、铁的摄取和运输、结晶起始、晶体成熟和磁小体链形成。虽然许多机制细节仍未解决，但趋磁细菌似乎在其基因组中包含磁小体生物矿化的遗传决定因素，这些基因在某些物种中组成了所谓的磁小体基因岛。此外，磁小体含有一组独特的蛋白质，在其他细胞组分中不存在，这些蛋白质控制着生物矿化过程。通过遗传系统的开发、蛋白质组学和基因组学研究以及分子和生化工具的使用，已经证明了许多磁小体膜蛋白的功能，这些生物体中磁小体生物矿化的分子机制也开始被揭示。
