趋磁细菌概述及应用进展

趋磁细菌是一类具有趋磁行为的革兰氏阴性茵的统称,其趋磁特性是由于菌体内含有磁小体。磁小体是由膜包被的纳米尺寸单磁畴颗粒,在菌体内多呈链状排列。自被发现以来,趋磁细菌及磁小体已逐步成为新的生物资源被广泛研究于材料学、医学、生物学、物理学、地质学等多个学科领域,并在仿生学、生态学、医学、地质学、工业处理、卫生检验等多个领域得到应用。主要介绍了趋磁细菌的生物特征、研究发展进程,以及近年来在多个学科领域的研究与应用。     

趋磁细菌及其应用于生物导航的研究进展

趋磁性细菌是一种由于体内含有对磁场具有敏感性的磁小体,而能够沿着磁力线运动的特殊细菌,本文综述了趋磁细菌的分布、分类、特性、磁小体研究以及趋磁细菌在生物导航方面的研究进展.     

趋磁细菌多样性与应用研究进展 *

趋磁细菌是一类可以沿磁场方向进行运动的微生物统称,在细胞内合成由生物膜包被、链状排列、纳米级、单磁畴的磁铁矿 (Fe₃O₄) 或胶黄铁矿 (Fe₃S₄) 的磁小体颗粒。趋磁细菌在自然界分布广泛且多样性丰富,不仅在水环境和沉积环境的铁、硫、碳、氮、磷等元素生物地球化学循环中发挥重要作用,而且在污染治理、疾病诊断和治疗等方面有较好的应用。趋磁细菌磁小体由生物膜包被并在细胞调控下合成,是一类新型的生物源磁性纳米材料。相比常规化学合成的磁性纳米颗粒,磁小体具有大小均一、生物相容性高、兼具化学修饰和基因工程修饰功能等特点,在磁性分离、固定化酶、食品检测、环境监测、医学诊断、磁共振成像、磁热疗和靶向治疗等方面具有广阔的应用前景。在介绍趋磁细菌多样性研究的基础上,综述了趋磁细菌和磁小体的制备、修饰及其应用的最新进展,并对未来的研究进行了展望。     

趋磁细菌及其应用于生物导航的研究进展

趋磁性细菌是一种由于体内含有对磁场具有敏感性的磁小体,而能够沿着磁力线运动的特殊细菌,本文综述了趋磁细菌的分布、分类、特性、磁小体研究以及趋磁细菌在生物导航方面的研究进展。     

细菌纳米磁小体的合成机制及应用

综述了近年趋磁细菌纳米磁小体生物合成的分子机制及应用进展。磁小体的合成涉及磁小体膜的形成、铁的吸收和转运、磁小体晶体的矿化、成熟以及磁小体的链状排列等。其中Mam J和Mam K互作并丝状排列,固定磁小体使其链状排列及磁小体膜由细胞质膜内陷而形成是两个令人注目的成就。我们也提出了关于磁小体的生理意义及合成机制的假说:细胞在低氧浓度下由于氧胁迫大量吸收铁,Fe³⁺/Fe²⁺电子对可起到类似O₂/H₂O的作用,产生能量并作为电子受体;Fe3+得到电子还原成的Fe²⁺可引起Fenton反应,此反应产生的活性氧可影响到生物体的正常生理代谢,细胞为降低Fe²⁺浓度,将其与Fe³⁺一同转化为Fe₃O₄颗粒;磁小体的生理功能之一是降低胞内的活性氧。     

趋磁细菌磁小体研究进展

趋磁细菌能在细胞内形成由膜包裹的纳米级单畴磁性颗粒——磁小体。磁小体的形成是受生物严格控制的矿化过程,包括铁离子的吸收、转运和结晶成核等。磁小体膜在磁铁矿（Fe3O4）晶体的形成中起着重要的作用。主要介绍近年来关于磁小体形成过程和参与这一过程的蛋白质等方面的一些重要研究进展。     

趋磁细菌的磁小体

趋磁细菌是一类对磁场有趋向性反应的细菌,其菌体能吸收外界环境中铁元素并在体内合成包裹有膜的纳米磁性颗粒Fe₃O₄或Fe₃O_{3S4晶体即磁小体。综述了趋磁细菌的磁小体生物矿化的条件,以及趋磁细菌的铁离子吸收、磁小体囊泡的形成、铁离子的转运到磁小体囊泡及囊泡中受控的Fe3O4生物矿化的分子生物学和生物化学等方面的研究进展,重点介绍了趋磁细菌磁小体合成机制的研究进展及未来研究磁小体的发展方向。}     

趋磁细菌蛋白参与磁铁矿生物矿化机制的研究进展

生物矿化是生命体系中的一种重要而又特殊的生理过程。生命体中存在着各种各样的生物矿化产物,从生物体骨骼与牙齿到纳米级的金属氧化物都是生物矿化的产物。生物矿化与普通矿化的最大不同就是其反应过程中有生物分子、生物代谢、细胞以及有机基质的参与。多种生物因素参与的矿化反应,不仅反应条件温和,而且反应产物具有更好的材料性能和生物兼容性,最为典型的是趋磁细菌可以通过生物矿化过程形成尺寸均一、单磁筹的生物膜包裹着的磁性纳米晶体——磁小体。本文主要介绍了趋磁细菌重要磁小体膜蛋白以及铁载体蛋白(铁蛋白)在磁铁矿生物矿化过程中的作用和功能,综述了该领域的最新研究概况。通过对趋磁细菌发生生物矿化过程的深入探讨可进一步揭示生物大分子调控无机矿物生长的分子机制,为仿生合成新型生物材料提供重要的理论依据。     

细菌纳米磁小体有望作为靶向药物载体

趋磁细菌细胞内合成的纳米磁小体具有颗粒均匀,晶型稳定的特点,每个磁小体有脂膜包被。提纯的磁小体毒性低,生物相容性好,可作为多种药物和大分子化合物的载体而应用于定向治疗肿瘤。本文介绍了细菌磁小体的结构特点,提出了采用细菌磁小体连接抗癌药物的策略,讨论了建立磁小体载药体系靶向治疗癌症的可能性。     

趋磁细菌及磁小体研究的回顾和展望

趋磁细菌及磁小体研究的回顾和展望陈明杰,卫扬保（武汉大学生命科学学院微生物学与免疫学系．武汉４３００７２）一趋磁细菌研究现状１趋磁细菌的发现１９７５年,美国人Ｂｌａｋｅｍｏｒｅ在显微镜下观察湖泊底部污泥的富集样品时,发现有一类细菌总是聚集在视野的靠北...     

A novel genus of multicellular magnetotactic prokaryotes from the Yellow Sea

Multicellular magnetotactic prokaryotes (MMPs) are a group of magnetotactic microorganisms composed of 10-40 Gram-negative cells. Currently, all the identified MMPs show a spherical morphology and synthesize mainly iron sulfide magnetosomes. In this study, we report a novel genus of MMPs with peculiar ellipsoidal morphology and iron oxide magnetosomes, which were discovered in intertidal sediment of the Yellow Sea in China. Optical and fluorescence microscopy revealed that this organism was ~10 × 8 μm in size and composed of ~40 cells enveloped by an outer layer. Scanning electron microscopy showed that the cells were arranged in 4-6 interlaced circles. Bullet-shaped magnetite magnetosomes were organized in chains roughly parallel to the long axis of the ellipsoidal MMPs when analysed by transmission electron microscopy. These MMPs displayed special escape motility, i.e. swimming rapidly from the edge to the centre of the droplet and then slowly back to the edge. In addition, they exhibited negative phototaxis. Light microscopy observations showed that the ellipsoidal MMPs reproduced by division along the body long axis. Both analysis of 16S rRNA gene sequence and fluorescence in situ hybridization revealed the ellipsoidal MMPs as a new genus of the Deltaproteobacteria. In summary, this novel genus of MMPs exhibit unique morphology, peculiar division process and distinct phylogenetic affiliation compared with the other MMPs.     

Cell viability in magnetotactic multicellular prokaryotes.

A magnetotactic multicellular prokaryote (MMP) is an assembly of bacterial cells organized side by side in a hollow sphere in which each cell faces both the external environment and an internal acellular compartment in the center of the multicellular organism. MMPs swim as a unit propelled by the coordinated beating of the many flagella on the external surface of each cell. At every stage of its life cycle, MMPs are multicellular. Initially, a spherical MMP grows by enlarging the size of each of its cells, which then divide. Later, the cells separate into two identical spheres. Swimming individual cells of MMPs have never been observed. Here we have used fluorescent dyes and electron microscopy to study the viability of individual MMP cells. When separated from the MMP, the cells cease to move and they no longer respond to magnetic fields. Viability tests indicated that, although several cells could separate from a MMP before completely losing their motility and viability, all of the separated cells were dead. Our data show that the high level of cellular organization in MMPs is essential for their motility, magnetotactic behavior, and viability.     

Juxtaposed membranes underpin cellular adhesion and display unilateral cell division of multicellular magnetotactic prokaryotes

Multicellular magnetotactic prokaryotes (MMPs) exhibit peculiar coordination of swimming along geomagnetic field lines. Approximately 40–80 cells assemble, with a helical geometry or axisymmetry, into spherical or ellipsoidal MMPs respectively. To contribute to a comprehensive understanding of bacterial multicellularity here we took multiple microscopic approaches to study the diversity, assembly, reproduction and motility of ellipsoidal MMPs. Using correlative fluorescence in situ hybridization and scanning electron microscopy analysis, we found an unexpected diversity in populations of ellipsoidal MMPs in the Mediterranean Sea. The high-pressure freezing/freeze substitution fixation technique allowed us to show, for the first time, that cells adhere via juxtaposed membranes and are held together by a rimming lattice. Fluorescence confocal microscopy and ultrathin section images revealed not only the one-layer hollow three-dimensional architecture, but also periphery–core unilateral constriction of constituent cells and unidirectional binary fission of the ellipsoidal MMPs. This finding suggests the evolution toward MMPs multicellularity via the mechanism of incomplete separation of offspring. Remarkably, thousands of flagellar at the periphery surface of cells underpin the coordinated swimming of MMPs in response to mechanical, chemical, magnetic and optical stimuli, including a magnetotactic photokinesis behaviour. Together these results unveil the unique structure and function property of ellipsoidal MMPs.     

Magnetic optimization in a multicellular magnetotactic organism

Unicellular magnetotactic prokaryotes, which typically carry a natural remanent magnetic moment equal to the saturation magnetic moment, are the prime example of magnetically optimized organisms. We here report magnetic measurements on a multicellular magnetotactic prokaryote (MMP) consisting of 17 undifferentiated cells (mean from 148 MMPs) with chains of ferrimagnetic particles in each cell. To test if the chain polarities of each cell contribute coherently to the total magnetic moment of the MMP, we used a highly sensitive magnetization measurement technique (1 fAm(2)) that enabled us to determine the degree of magnetic optimization (DMO) of individual MMPs in vivo. We obtained DMO values consistently above 80%. Numerical modeling shows that the probability of reaching a DMO > 80% would be as low as 0.017 for 17 randomly oriented magnetic dipoles. We simulated different scenarios to test whether high DMOs are attainable by aggregation or self-organization of individual magnetic cells. None of the scenarios investigated is likely to yield consistently high DMOs in each generation of MMPs. The observed high DMO values require strong Darwinian selection and a sophisticated reproduction mechanism. We suggest a multicellular life cycle as the most plausible scenario for transmitting the high DMO from one generation to the next.     

A novel species of ellipsoidal multicellular magnetotactic prokaryotes from Lake Yuehu in China

Two morphotypes of multicellular magnetotactic prokaryotes (MMPs) have been identified: spherical (several species) and ellipsoidal (previously one species). Here, we report novel ellipsoidal MMPs that are ～ 10 × 8 μm in size, and composed of about 86 cells arranged in six to eight interlaced circles. Each MMP was composed of cells that synthesized either bullet‐shaped magnetite magnetosomes alone, or both bullet‐shaped magnetite and rectangular greigite magnetosomes. They showed north‐seeking magnetotaxis, ping‐pong motility and negative phototaxis at a velocity up to 300 μm s^?1. During reproduction, they divided along either their long‐ or short‐body axes. For genetic analysis, we sorted the ellipsoidal MMPs with micromanipulation and amplified their genomes using multiple displacement amplification. We sequenced the 16S rRNA gene and found 6.9% sequence divergence from that of ellipsoidal MMPs, Candidatus Magnetananas tsingtaoensis and > 8.3% divergence from those of spherical MMPs. Therefore, the novel MMPs belong to different species and genus compared with the currently known ellipsoidal and spherical MMPs respectively. The novel MMPs display a morphological cell differentiation, implying a potential division of labour. These findings provide new insights into the diversity of MMPs in general, and contribute to our understanding of the evolution of multicellularity among prokaryotes.     

Effect of light wavelength on motility and magnetic sensibility of the magnetotactic multicellular prokaryote ‘Candidatus Magnetoglobus multicellularis’

‘Candidatus Magnetoglobus multicellularis’ is a magnetotactic microorganism composed of several bacterial cells. Presently, it is the best known multicellular magnetotactic prokaryote (MMP). Recently, it has been observed that MMPs present a negative photoresponse to high intensity ultraviolet and violet-blue light. In this work, we studied the movement of ‘Candidatus Magnetoglobus multicellularis’ under low intensity light of different wavelengths, measuring the average velocity and the time to reorient its trajectory when the external magnetic field changes its direction (U-turn time). Our results show that the mean average velocity is higher for red light (628 nm) and lower for green light (517 nm) as compared to yellow (596 nm) and blue (469 nm) light, and the U-turn time decreased for green light illumination. The light wavelength velocity dependence can be understood as variation in flagella rotation speed, being increased by the red light and decreased by the green light relative to yellow and blue light. It is suggested that the dependence of the U-turn time on light wavelength can be considered a form of light-dependent magnetotaxis, because this time represents the magnetic sensibility of the magnetotactic microorganisms. The cellular and molecular mechanisms for this light-dependent velocity and magnetotaxis are unknown and deserve further studies to understand the biochemical interactions and the ecological roles of the different mechanisms of taxis in MMPs.     

X-ray Absorption Spectroscopy and Magnetism of Synthetic Greigite and Greigite Magnetosomes in Magnetotactic Bacteria

Scanning transmission X-ray microscopy at the Fe 2p (L_2,3), O1s, C1s, and S2p edges was used to study greigite magnetosomes and other cellular content of a magnetotactic bacterium known as a multicellular magnetotactic prokaryote (MMP). X-ray absorption spectrum (XAS) and X-ray magnetic circular dichroism (XMCD) spectra of greigite (Fe₃S₄) nanoparticles, synthesized via a hydrothermal method, were measured. Although XAS of the synthetic greigite nanoparticles and biotic magnetosome crystals in MMPs are slightly different due to partial oxidation of the MMP greigite, the XMCD spectra of the two materials are in good agreement. The Fe 2p XAS and XMCD spectra of Fe₃S₄ are quite different from those of its oxygen analog, magnetite (Fe₃O₄), suggesting Fe₃S₄ has a different electronic and magnetic structure than Fe₃O₄ despite having the same crystal structure. Sulfate and sulfide species were also identified in MMPs, both of which are likely involved in sulfur metabolism.     

Biochemical and proteomic analysis of the magnetosome membrane in Magnetospirillum gryphiswaldense

We analyzed the biochemical composition of the magnetosome membrane (MM) in Magnetospirillum gryphiswaldense. Isolated magnetosomes were associated with phospholipids and fatty acids which were similar to phospholipids and fatty acids from other subcellular compartments (i.e., outer and cytoplasmic membranes) but were present in different proportions. The binding characteristics of MM-associated proteins were studied by selective solubilization and limited proteolysis. The MM-associated proteins were further analyzed by various proteomic approaches, including one- and two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by Edman and mass spectrometric (electrospray ionization-mass spectrometry-mass spectrometry) sequencing, as well as capillary liquid chromatography-mass spectrometry-mass spectrometry of total tryptic digests of the MM. At least 18 proteins were found to constitute the magnetosome subproteome, and most of these proteins are novel for M. gryphiswaldense. Except for MM22 and Mms16, all bona fide MM proteins (MMPs) were encoded by open reading frames in the mamAB, mamDC, and mms6 clusters in the previously identified putative magnetosome island. Eight of the MMPs display homology to known families, and some of them occur in the MM in multiple homologues. Ten of the MMPs have no known homologues in nonmagnetic organisms and thus represent novel, magnetotactic bacterium-specific protein families. Several MMPs display repetitive or highly acidic sequence patterns, which are known from other biomineralizing systems and thus may have relevance for magnetite formation.     

Molecular analysis of a subcellular compartment: the magnetosome membrane in<Emphasis Type="Italic"> Magnetospirillum gryphiswaldense</Emphasis>

The ability of magnetotactic bacteria (MTB) to orient and migrate along magnetic field lines is based on magnetosomes, which are membrane-enclosed intracellular crystals of a magnetic iron mineral. Magnetosome biomineralization is achieved by a process involving control over the accumulation of iron and deposition of the magnetic particle, which has a specific morphology, within a vesicle provided by the magnetosome membrane. In Magnetospirillum gryphiswaldense, the magnetosome membrane has a distinct biochemical composition and comprises a complex and specific subset of magnetosome membrane proteins (MMPs). Classes of MMPs include those with presumed function in magnetosome-directed uptake and binding of iron, nucleation of crystal growth, and the assembly of magnetosome membrane multiprotein complexes. Other MMPs comprise protein families of so far unknown function, which apparently are conserved between all other MTB. The mam and mms genes encode most of the MMPs and are clustered within several operons, which are part of a large, unstable genomic region constituting a putative magnetosome island. Current research is directed towards the biochemical and genetic analysis of MMP functions in magnetite biomineralization as well as their expression and localization during growth.Abbreviations MM Magnetosome membrane - MMP Magnetosome membrane protein - MTB Magnetotactic bacteria     

Biochemical and Proteomic Analysis of the Magnetosome Membrane in Magnetospirillum gryphiswaldense

We analyzed the biochemical composition of the magnetosome membrane (MM) in Magnetospirillum gryphiswaldense. Isolated magnetosomes were associated with phospholipids and fatty acids which were similar to phospholipids and fatty acids from other subcellular compartments (i.e., outer and cytoplasmic membranes) but were present in different proportions. The binding characteristics of MM-associated proteins were studied by selective solubilization and limited proteolysis. The MM-associated proteins were further analyzed by various proteomic approaches, including one- and two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by Edman and mass spectrometric (electrospray ionization-mass spectrometry-mass spectrometry) sequencing, as well as capillary liquid chromatography-mass spectrometry-mass spectrometry of total tryptic digests of the MM. At least 18 proteins were found to constitute the magnetosome subproteome, and most of these proteins are novel for M. gryphiswaldense. Except for MM22 and Mms16, all bona fide MM proteins (MMPs) were encoded by open reading frames in the mamAB, mamDC, and mms6 clusters in the previously identified putative magnetosome island. Eight of the MMPs display homology to known families, and some of them occur in the MM in multiple homologues. Ten of the MMPs have no known homologues in nonmagnetic organisms and thus represent novel, magnetotactic bacterium-specific protein families. Several MMPs display repetitive or highly acidic sequence patterns, which are known from other biomineralizing systems and thus may have relevance for magnetite formation.