A comparative study of magnetic properties between whole cells and isolated magnetosomes of Magnetospirillum magneticum AMB-1 (original) (raw)
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Geophysical Journal International, 2009
Stable single-domain (SD) magnetite formed intracellularly by magnetotactic bacteria is of fundamental interest in sedimentary and environmental magnetism. In this study, we studied the time course of magnetosome growth and magnetosome chain formation (0-96 hr) in Magnetospirillum magneticum AMB-1 by transmission electron microscopy (TEM) observation and rock magnetism. The initial non-magnetic cells were microaerobically batch cultured at 26 • C in a modified magnetic spirillum growth medium. TEM observations indicated that between 20 and 24 hr magnetosome crystals began to mineralize simultaneously at multiple sites within the cell body, followed by a phase of rapid growth lasting up to 48 hr cultivation. The synthesized magnetosomes were found to be assembled into 3-5 subchains, which were linearly aligned along the long axis of the cell, supporting the idea that magnetosome vesicles were linearly anchored to the inner membrane of cell. By 96 hr cultivation, 14 cubo-octahedral magnetosome crystals in average with a mean grain size of ∼44.5 nm were formed in a cell. Low-temperature (10-300 K) thermal demagnetization, room-temperature hysteresis loops and first-order reversal curves (FORCs) were conducted on whole cell samples. Both coercivity (4.7-18.1 mT) and Verwey transition temperature (100-106 K) increase with increasing cultivation time length, which can be explained by increasing grain size and decreasing nonstoichiometry of magnetite, respectively. Shapes of hysteresis loops and FORCs indicated each subchain behaving as an 'ideal' uniaxial SD particle and extremely weak magnetostatic interaction fields between subchains. Low-temperature thermal demagnetization of remanence demonstrated that the Moskowitz test is valid for such linear subchain configurations (e.g. δ FC /δ ZFC > 2.0), implying that the test is applicable to ancient sediments where magnetosome chains might have been broken up into short chains due to disintegration of the organic scaffold structures after cell death. These findings provide new insights into magnetosome biomineralization of magnetotactic bacteria and contribute to better understanding the magnetism of magnetofossils in natural environments.
Magnetic properties of bacterial magnetosomes and chemosynthesized magnetite nanoparticles
In this work, the magnetic properties of biologically produced magnetite (magnetosomes) by a mineralization process of magnetotactic bacteria {Magnetospirillum sp.} AMB-1 were compared to those of chemically synthesized magnetite nanoparticles and nanorods. X-ray diffraction data reveal that for all samples the peaks come from magnetite. A sharp magnetic transition (Verwey transition) is clearly observed in magnetosomes at 105 K (magnetite nanocrystals obtained by mineralization) and nanorodes at 112 K, in opposite, this transition is significantly smeared in Fe_{3}O_{4} powder, where the magnetic nanoparticles are separated and the magnetic fluctuations are strong to overcome magnetic anisotropy and randomize magnetic moment. The existence of coercivity of 71 Oe at room temperature is related to the fact that the mean diameter (34 nm) is larger than the critical size for the transition from superparamagnetic to ferromagnetic behaviour. Figs 6, Refs 14.
Earth and Planetary Science Letters, 2010
Magnetosomes produced by magnetotactic bacteria are of great interest for understanding bacterial biomineralization along with sedimentary magnetism and environmental magnetism. One of the most intriguing species, Magnetobacterium bavaricum can synthesize hundreds of bullet-shaped magnetite magnetosomes per cell, which contribute significantly to magnetic properties of sediments. However, the biomineralization mechanism and magnetic properties of such magnetosomes remain unknown. In this paper, we have conducted a comprehensive study of the crystallography and magnetic properties of bullet-shaped magnetosomes formed by uncultivated giant rod magnetotactic bacteria (referred to as MYR-1), recently discovered in Lake Miyun (Beijing, China). Transmission electron microscopy observations reveal that each MYR-1 cell contains hundreds of bullet-shaped magnetite magnetosomes, which are arranged into 3 - 5 braid-like bundles of chains. The formation of the bullet-shaped magnetosomes can be divided into two stages: initial isotropic growth (up to ∼ 20 nm) followed by elongation along the [100] direction, which is unusual compared with the expected [111] magnetic easy axis. Although the [100] orientation is the hard axis of the face-centered cubic magnetite, the shape anisotropy of bullet-shaped magnetosomes and intra-bundle magnetostatic interactions confine the magnetization direction of the chain along the long axis of the cell/bundle. Due to each bundle of magnetosome chains effectively behaving as an elongated single domain particle, the MYR-1 cells show high coercivity, weak intra-bundle magnetostatic interaction, and high δ-ratio. These results provide new insights into the biomineralization process and magnetic properties of bullet-shaped magnetite magnetosomes.
We report structural characterization and magnetic properties of various assemblies of chains of magnetosomes. The same magnetic properties are observed for the magnetotactic bacteria and for the extracted chains of magnetosomes isolated in a polymer. When the extracted chains of magnetosomes form a denser structure than that observed in the bacteria, the magnetic properties change markedly. A decrease in the coercivity and reduced remanence is observed. This behavior is attributed to an enhancement of the dipolar interactions between the chains of magnetosomes in the limit of a weakly interacting system; that is, the magnetostatic energy is lower than the anisotropy energy. The effect of the dipolar interactions is more pronounced at 250 K than at 10 K. This behavior is attributed to the existence of a family of small magnetosomes, which undergo a transition from a ferromagnetic to a superparamagnetic state.
Magnetosomes are bacterial magnetic nanoparticles. Magnetosome formation is achieved by a mineralization process with biological control over the accumulation of iron and the deposition of the mineral particle with orientation within a membrane vesicle at specific intracellular locations in the body of magnetotactic bacteria. These are small in size (50–100 nm) disperse very well because they are covered with a stable lipid membrane. Magnetosomes provide numerous attractive possibilities in various applications especially bioapplication and in the field of drug delivery, due to their unique magnetic and biochemical characteristics. In this work different type of cultivation process, techniques for the isolation and purification of magnetosomes from Magnetospirillum Magnetotacticum sp AMB-1 are described.
Magnetotactic Bacteria and Magnetosomes: Basic Properties and Applications
Magnetochemistry, 2021
Magnetotactic bacteria (MTB) belong to several phyla. This class of microorganisms exhibits the ability of magneto-aerotaxis. MTB synthesize biominerals in organelle-like structures called magnetosomes, which contain single-domain crystals of magnetite (Fe3O4) or greigite (Fe3S4) characterized by a high degree of structural and compositional perfection. Magnetosomes from dead MTB could be preserved in sediments (called fossil magnetosomes or magnetofossils). Under certain conditions, magnetofossils are capable of retaining their remanence for millions of years. This accounts for the growing interest in MTB and magnetofossils in paleo- and rock magnetism and in a wider field of biogeoscience. At the same time, high biocompatibility of magnetosomes makes possible their potential use in biomedical applications, including magnetic resonance imaging, hyperthermia, magnetically guided drug delivery, and immunomagnetic analysis. In this review, we attempt to summarize the current state of ...
Magnetic-field induced rotation of magnetosome chains in silicified magnetotactic bacteria
Scientific reports, 2018
Understanding the biological processes enabling magnetotactic bacteria to maintain oriented chains of magnetic iron-bearing nanoparticles called magnetosomes is a major challenge. The study aimed to constrain the role of an external applied magnetic field on the alignment of magnetosome chains in Magnetospirillum magneticum AMB-1 magnetotactic bacteria immobilized within a hydrated silica matrix. A deviation of the chain orientation was evidenced, without significant impact on cell viability, which was preserved after the field was turned-off. Transmission electron microscopy showed that the crystallographic orientation of the nanoparticles within the chains were preserved. Off-axis electron holography evidenced that the change in magnetosome orientation was accompanied by a shift from parallel to anti-parallel interactions between individual nanocrystals. The field-induced destructuration of the chain occurs according to two possible mechanisms: (i) each magnetosome responds indivi...
Molecules (Basel, Switzerland), 2018
Magnetotactic bacteria (MTB) biomineralize magnetosomes, which are defined as intracellular nanocrystals of the magnetic minerals magnetite (Fe₃O₄) or greigite (Fe₃S₄) enveloped by a phospholipid bilayer membrane. The synthesis of magnetosomes is controlled by a specific set of genes that encode proteins, some of which are exclusively found in the magnetosome membrane in the cell. Over the past several decades, interest in nanoscale technology (nanotechnology) and biotechnology has increased significantly due to the development and establishment of new commercial, medical and scientific processes and applications that utilize nanomaterials, some of which are biologically derived. One excellent example of a biological nanomaterial that is showing great promise for use in a large number of commercial and medical applications are bacterial magnetite magnetosomes. Unlike chemically-synthesized magnetite nanoparticles, magnetosome magnetite crystals are stable single-magnetic domains and...
From Bacterial to Biomimetic magnetosomes
Passive Orientation or Angle-Sensing in Magnetotaxis-R. Frankel Analysis and functional expression of gene clusters controlling magnetosome biosynthesis in magnetotactic bacteria-D. Schuler Genetic tool to study magnetosome membrane formation in Magnetospirillum magneticum AMB-1-E.