Showing papers on "Magnetotactic bacteria published in 2007"
TL;DR: Protein quantification analysis of Mms6 in the synthesised particles indicated tight association of this protein onto the crystal, suggesting that the protein acts as a template for the nucleus formation and/or acts as an growth regulator by recognising crystal faces.
243 citations
TL;DR: In MTB a number of magnetosome proteins with putative functions in the biomineralization of the nanoparticles have been identified by genetic and biochemical approaches, and initial results obtained indicate that some of these proteins have an impact on nanomagnetite properties in vitro.
Abstract: Magnetotactic bacteria (MTB) have the ability to navigate along the Earth's magnetic field. This so-called magnetotaxis is a result of the presence of magnetosomes, organelles which comprise nanometer-sized intracellular crystals of magnetite (Fe(3)O(4)) enveloped by a membrane. Because of their unique characteristics, magnetosomes have a high potential for nano- and biotechnological applications, which require a specifically designed particle surface. The functionalization of magnetosomes is possible either by chemical modification of purified particles or by genetic engineering of magnetosome membrane proteins. The second approach is potentially superior to chemical approaches as a large variety of biological functions such as protein tags, fluorophores, and enzymes may be directly incorporated in a site-specific manner during magnetosome biomineralization. An alternative to the bacterial production of magnetosomes are biomimetic approaches, which aim to mimic the bacterial biomineralization pathway in vitro. In MTB a number of magnetosome proteins with putative functions in the biomineralization of the nanoparticles have been identified by genetic and biochemical approaches. The initial results obtained by several groups indicate that some of these proteins have an impact on nanomagnetite properties in vitro. In this article the key features of magnetosomes are discussed, an overview of their potential applications are given, and different strategies are proposed for the functionalization of magnetosome particles and for the biomimetism of their biomineralization pathway.
178 citations
TL;DR: Magnetite nanocrystals are synthesized in the presence of a recombinant Mms6 protein thought to be involved in the biomineralization of bacterial magnetite magnetosomes, the mammalian iron-storage protein, ferritin, and two proteins not known to bind iron, lipocalin (Lcn2) and bovine serum albumin (BSA) as mentioned in this paper.
Abstract: Magnetite nanocrystals are synthesized in the presence of a recombinant Mms6 protein thought to be involved in the biomineralization of bacterial magnetite magnetosomes, the mammalian iron-storage protein, ferritin, and two proteins not known to bind iron, lipocalin (Lcn2) and bovine serum albumin (BSA). To mimic the conditions at which magnetite nanocrystals are formed in magnetotactic bacteria, magnetite synthesis is performed in a polymeric gel to slow down the diffusion rates of the reagents. Recombinant Mms6 facilitates formation of ca. 30 nm single-domain, uniform magnetite nanocrystals in solution, as verified by using transmission electron microscopy analysis and magnetization measurements. The nanocrystals formed in the presence of ferritin, Lcn2, and BSA, do not exhibit the uniform sizes and shapes observed for those produced in the presence of Mms6. Mms6-derived magnetite nanoparticles show the largest magnetization values above the blocking temperature, as well as the largest magnetic susceptibility compared to those of the nanomaterials synthesized with other proteins. The latter is indicative of a substantial effective magnetic moment per particle, which is consistent with the presence of magnetite with a well-defined crystalline structure. The combination of electron microscopy analysis and magnetic measurements confirms our hypothesis that Mms6 promotes the shape-selective formation of uniform superparamagnetic nanocrystals. This provides a unique bioinspired route for synthesis of uniform magnetite nanocrystals.
168 citations
TL;DR: Comparisons between four sequenced magnetotactic Alphaproteobacteria found a set of approximately 152 genus-specific genes shared by the three Magnetospirillum strains, and 28 genes as group specific, which represent less than 1% of the 4,268 open reading frames of the MSR-1 genome, are likely to be specifically involved in magnetotaxis.
Abstract: Magnetotactic bacteria (MTB) are a heterogeneous group of aquatic prokaryotes with a unique intracellular organelle, the magnetosome, which orients the cell along magnetic field lines. Magnetotaxis is a complex phenotype, which depends on the coordinate synthesis of magnetosomes and the ability to swim and orient along the direction caused by the interaction with the Earth's magnetic field. Although a number of putative magnetotaxis genes were recently identified within a conserved genomic magnetosome island (MAI) of several MTB, their functions have remained mostly unknown, and it was speculated that additional genes located outside the MAI might be involved in magnetosome formation and magnetotaxis. In order to identify genes specifically associated with the magnetotactic phenotype, we conducted comparisons between four sequenced magnetotactic Alphaproteobacteria including the nearly complete genome of Magnetospirillum gryphiswaldense strain MSR-1, the complete genome of Magnetospirillum magneticum strain AMB-1, the complete genome of the magnetic coccus MC-1, and the comparative-ready preliminary genome assembly of Magnetospirillum magnetotacticum strain MS-1 against an in-house database comprising 426 complete bacterial and archaeal genome sequences. A magnetobacterial core genome of about 891 genes was found shared by all four MTB. In addition to a set of approximately 152 genus-specific genes shared by the three Magnetospirillum strains, we identified 28 genes as group specific, i.e., which occur in all four analyzed MTB but exhibit no (MTB-specific genes) or only remote (MTB-related genes) similarity to any genes from nonmagnetotactic organisms and which besides various novel genes include nearly all mam and mms genes previously shown to control magnetosome formation. The MTB-specific and MTB-related genes to a large extent display synteny, partially encode previously unrecognized magnetosome membrane proteins, and are either located within (18 genes) or outside (10 genes) the MAI of M. gryphiswaldense. These genes, which represent less than 1% of the 4,268 open reading frames of the MSR-1 genome, as yet are mostly of unknown functions but are likely to be specifically involved in magnetotaxis and, thus, represent prime targets for future experimental analysis.
167 citations
TL;DR: This review focuses on recent advances in understanding the molecular mechanisms of magnetosome formation and magnetite biomineralization.
Abstract: Magnetotactic bacteria are a diverse group of microorganisms with the ability to use geomagnetic fields for direction sensing. This unique feat is accomplished with the help of magnetosomes, nanometer-sized magnetic crystals surrounded by a lipid bilayer membrane and organized into chains via a dedicated cytoskeleton within the cell. Because of the special properties of these magnetic crystals, magnetotactic bacteria have been exploited for a variety of applications in diverse disciplines from geobiology to biotechnology. In addition, magnetosomes have served as a powerful model system for the study of biomineralization and cell biology in bacteria. This review focuses on recent advances in understanding the molecular mechanisms of magnetosome formation and magnetite biomineralization.
154 citations
126 citations
01 Jan 2007
TL;DR: This work has shown Magnetite-Based Magnetoreception in Higher Organisms and Formation of Magnetic Minerals by Non-Magnetotactic Prokaryotes as well as mineralogical and Isotopic Properties of Biogenic Nanocrystalline Magnetites.
Abstract: Magneto-Aerotaxis.- Diversity and Taxonomy of Magnetotactic Bacteria.- Ecophysiology of Magnetotactic Bacteria.- Geobiology of Magnetotactic Bacteria.- Structure, Behavior, Ecology and Diversity of Multicellular Magnetotactic Prokaryotes.- Genetic Analysis of Magnetosome Biomineralization.- Cell Biology of Magnetosome Formation.- Mineralogical and Isotopic Properties of Biogenic Nanocrystalline Magnetites.- Characterization of Bacterial Magnetic Nanostructures Using High-Resolution Transmission Electron Microscopy and Off-Axis Electron Holography.- Molecular Bioengineering of Bacterial Magnetic Particles for Biotechnological Applications.- Paleomagnetism and Magnetic Bacteria.- Formation of Magnetic Minerals by Non-Magnetotactic Prokaryotes.- Magnetite-Based Magnetoreception in Higher Organisms.
122 citations
TL;DR: This review describes the recent advances in the fundamental analysis of bacterial magnetic particles and the development of surface-protein-modified magnetic particles for biotechnological applications.
119 citations
TL;DR: The dynamics of the motile magnetotactic bacterium Magnetospirillum gryphiswaldense in a rotating magnetic field is investigated experimentally and analyzed by a theoretical model.
96 citations
TL;DR: It is concluded that the biomineralization of magnetite occurs rapidly in magnetotactic bacteria on a similar time scale to high-temperature chemical precipitation reactions, and it is suggested that this finding is caused by a biological catalysis of the process.
Abstract: Magnetosomes are magnetite nanoparticles formed by biomineralization within magnetotactic bacteria. Although there have been numerous genetic and proteomic studies of the magnetosome-formation process, there have been only limited and inconclusive studies of mineral-phase evolution during the formation process, and no real-time studies of such processes have yet been performed. Thus, suggested formation mechanisms still need substantiating with data. Here we report the examination of the magnetosome material throughout the formation process in a real-time in vivo study of Magnetospirillum gryphiswaldense, strain MSR-1. Transmission EM and x-ray absorption spectroscopy studies reveal that full-sized magnetosomes are seen 15 min after formation is initiated. These immature magnetosomes contain a surface layer of the nonmagnetic iron oxide-phase hematite. Mature magnetite is found after another 15 min, concurrent with a dramatic increase in magnetization. This rapid formation result is contrary to previously reported studies and discounts the previously proposed slow, multistep formation mechanisms. Thus, we conclude that the biomineralization of magnetite occurs rapidly in magnetotactic bacteria on a similar time scale to high-temperature chemical precipitation reactions, and we suggest that this finding is caused by a biological catalysis of the process.
96 citations
TL;DR: This new synthesis pathway enables facile room-temperature shape-specific synthesis of complex magnetic crystalline nanomaterials with particle sizes in the range of 40-100 nm that are difficult to produce using conventional techniques.
Abstract: Magnetotactic bacteria produce exquisitely ordered chains of uniform magnetite (Fe(3)O(4)) nanocrystals, and the use of the bacterial mms6 protein allows for the shape-selective synthesis of Fe(3)O(4) nanocrystals. Cobalt ferrite (CoFe(2)O(4)) nanoparticles, on the other hand, are not known to occur in living organisms. Here we report on the use of the recombinant mms6 protein in a templated synthesis of CoFe(2)O(4) nanocrystals in vitro. We have covalently attached the full-length mms6 protein and a synthetic C-terminal domain of mms6 protein to self-assembling polymers in order to template hierarchical CoFe(2)O(4) nanostructures. This new synthesis pathway enables facile room-temperature shape-specific synthesis of complex magnetic crystalline nanomaterials with particle sizes in the range of 40-100 nm that are difficult to produce using conventional techniques.
TL;DR: A morphologically, physiologically, and phylogenetically diverse assemblage of motile, mostly aquatic prokaryotes that passively align along geomagnetic field lines as they swim.
Abstract: Publisher Summary The magnetotactic bacteria represent a morphologically, physiologically, and phylogenetically diverse assemblage of motile, mostly aquatic prokaryotes that passively align along geomagnetic field lines as they swim. Magnetotactic bacteria are fastidious with regard to their growth requirements and are difficult to isolate in pure culture and cultivate in the laboratory. Because of this, research in this area has been painfully slow at times. Magnetosomes are defined as intracellular crystals of a magnetic mineral surrounded by a lipid bilayer membrane. Despite their differences, the magnetotactic bacteria share several features: (1) they are Gram-negative prokaryotes phylogenetically associated with the domain bacteria, (2) they are motile by means of flagella, (3) grow only microaerophilically with oxygen or anaerobically or both, (4) with one exception possess a solely respiratory form of metabolism, (5) display nitrogenase activity and so are able to fix atmospheric dinitrogen, (6) are mesophilic with respect to growth temperatures, and (7) all possess magnetosomes.
TL;DR: These findings show that morphology, ultrastructure, and behavior are the main characteristics of the MMPs, not the type of magnetic crystal biomineralized in the magnetosomes.
Abstract: Magnetotactic bacteria produce iron oxides, iron sulfides or both in organelles called magnetosomes. Most of these bacteria are unicellular and biomineralize magnetite (Fe3O4). In contrast, multicellular magnetotactic prokaryotes (MMPs) consisting of several gram-negative cells have only been known to crystallize the magnetic iron sulfide greigite (Fe3S4). In this work, we describe MMPs that mineralize magnetite in bullet-shaped crystals. Another unusual aspect is that magnetite occurs either as the only crystals or together with greigite crystals. MMPs containing only greigite in the magnetosomes occur in the same environment. These findings show that morphology, ultrastructure, and behavior are the main characteristics of the MMPs, not the type of magnetic crystal biomineralized in the magnetosomes.
TL;DR: Ribosomal RNA copy numbers obtained with quantitative polymerase chain reaction indicate that MTB comprise up to 10% of total Bacteria and that each organism has a characteristic distributional profile with respect to the chemocline.
Abstract: Magnetotactic bacteria (MTB) contain membrane-bound magnetic iron minerals and are globally abundant in the suboxic/anoxic portions of chemically stratified marine and freshwater environments. However, their population dynamics and potential quantitative contribution to the biogeochemical cycles that they influence (iron, sulfur, carbon) have not been previously considered. Here we report the first quantitative description of the distribution of individual species of magnetite- and greigite-producing MTB in a natural system. We developed a quantitative polymerase chain reaction assay targeting 16s rRNA genes to enumerate four major groups of marine MTB, and applied the assay to samples collected with respect to geochemical parameters during summer 2003 in seasonally stratified Salt Pond, MA. Using catalysed reporter deposition-fluorescent in situ hybridization, we also show that a large greigite-producing bacterium is distantly related to Thiomicrospira pelophila in the Gammaproteobacteria. Ribosomal RNA copy numbers obtained with quantitative polymerase chain reaction indicate that MTB comprise up to 10% of total Bacteria and that each organism has a characteristic distributional profile with respect to the chemocline.
TL;DR: In this article, the site occupancy of Fe cations in the ferrite spinels was determined using X-ray magnetic circular dichroism (XMCD), a synchrotron radiation-based technique able to determine the sites occupied by the cations.
Abstract: Ferrite spinels, especially magnetite (Fe3O4), can be formed either by geological, biological or chemical processes leading to chemically similar phases that show different physical characteristics. We compare, for the first time, magnetite produced by these three different methods using X-ray magnetic circular dichroism (XMCD), a synchrotron radiation based technique able to determine the site occupancy of Fe cations in the ferrite spinels. Extracellular nanoscale magnetite produced by different Fe(Ill)reducing bacteria was shown to have different degrees of stoichiometry depending on the bacteria and the method of formation, but all were oxygen deficient due to formation under anoxic conditions. Intracellular nano-magnetite synthesized in the magnetosomes of magnetotactic bacteria was found to have a Fe cation site occupancy ratio most similar to stoichiometric magnetite, possibly due to the tight physiological controls exerted by the magnetosome membrane. Chemically-synthesised nano-magnetite and bulk magnetite produced as a result of geological processes were both found to be cation deficient with a composition between magnetite and maghemite (oxidised magnetite).
TL;DR: In this article, a magnetotactic bacteria from the Seine River (France) has been studied using transmission electron microscopy using morphological criteria based on the number of magnetite crystals and their organization within cells, the size and shape of the cells and their statistical distribution.
Abstract: A freshwater population of magnetotactic bacteria has been extracted from the Seine River (France) and studied using transmission electron microscopy. Seventeen different morphotypes were recognized using morphological criteria, which rely on the number of magnetite crystals and their organization within cells, the size and shape of the cells and their statistical distribution. This study revealed new features in some magnetotactic bacteria that have not been described in the literature. In addition X-ray energy dispersive spectroscopy and electron diffraction analyses revealed cells containing Ba-rich and CaO inclusions. Two major modes of magnetite crystals growth were derived from the distributions of the crystal shapes in this population. Numerous cases of crystals elongations along axes different from the [111] axis are related to one singular process of crystal growth. Thus, this population of magnetites collected from cells extracted from the Seine River does not meet some of the criteria for biogenicity, which have been used so far for biomagnetites, particularly those concerning the [111] elongation axis.
TL;DR: A simple apparatus for measuring the magnetism of magnetotactic bacteria was developed with a common laboratory spectrophotometer, and a novel magnetism parameter, R(mag), exhibited a better linearity than C(mag) with respect to the percentage of magnetosome-containing bacteria.
TL;DR: In this article, the authors compared properties of magnetites prepared by co-precipitation with those of magnetosomes isolated from MSR-1 in detail, such as crystalline, morphology, crystal-size distributions, vitro cytotoxicity, and magnetic properties and quantified primary amino groups on the magnetosome membrane surface by fluorescamine assay for the first time.
TL;DR: The ultrastructure of the flagellar apparatus in many‐celled magnetotactic prokaryotes (MMP) that consist of several Gram‐negative cells arranged radially around an acellular compartment is studied.
Abstract: Magnetotactic bacteria orient and migrate along geomagnetic field lines. Each cell contains membrane-enclosed, nano-scale, iron-mineral particles called magnetosomes that cause alignment of the cell in the geomagnetic field as the bacteria swim propelled by flagella. In this work we studied the ultrastructure of the flagellar apparatus in many-celled magnetotactic prokaryotes (MMP) that consist of several Gram-negative cells arranged radially around an acellular compartment. Flagella covered the organism surface, and were observed exclusively at the portion of each cell that faced the environment. The flagella were helical tubes never as long as a complete turn of the helix. Flagellar filaments varied in length from 0.9 to 3.8 micro m (average 2.4 +/- 0.5 micro m, n = 150) and in width from 12.0 to 19.5 nm (average 15.9 +/- 1.4 nm, n = 52), which is different from previous reports for similar microorganisms. At the base of the flagella, a curved hook structure slightly thicker than the flagellar filaments was observed. In freeze-fractured samples, macromolecular complexes about 50 nm in diameter, which possibly corresponded to part of the flagella basal body, were observed in both the P-face of the cytoplasmic membrane and the E-face of the outer membrane. Transmission electron microscopy showed that magnetosomes occurred in planar groups in the cytoplasm close and parallel to the organism surface. A striated structure, which could be involved in maintaining magnetosomes fixed in the cell, was usually observed running along magnetosome chains. The coordinated movement of the MMP depends on the interaction between the flagella of each cell with the flagella of adjacent cells of the microorganism.
TL;DR: This is the first report of Mediterranean magnetotactic bacteria, which should be useful for studies of biogeochemical cycling and geohistory of the Mediterranean Sea.
Abstract: Magnetotactic bacteria are a diverse group of motile prokaryotes that are ubiquitous in aquatic habitats and cosmopolitan in distribution. In this study, we collected magnetotactic bacteria from the Mediterranean Sea. A remarkable diversity of morphotypes was observed, including multicellular types that seemed to differ from those previously found in North and South America. Another interesting organism was one with magnetosomes arranged in a six-stranded bundle which occupied one third of the cell width. The magnetosome bundle was evident even under optic microscopy. These cells were connected together and swam as a linear entire unit. Magnetosomes did not always align up to form a straight linear chain. A chain composed of rectangle magnetosomes bent at a position with an oval crystal. High resolution transmission electron microscopy analysis of the crystal at the pivotal position suggested uncompleted formation of the crystal. This is the first report of Mediterranean magnetotactic bacteria, which should be useful for studies of biogeochemical cycling and geohistory of the Mediterranean Sea.
TL;DR: Transmission electron microscopy and X-ray microanalysis of thin-sectioned ciliates showed the presence of M. multicellularis and magnetosomes inside vacuoles in different degrees of degradation, which indicates that iron from the magnetosome may be recycled to the environment in a more soluble form.
Abstract: Summary
Magnetotactic bacteria show an ability to navigate along magnetic field lines because of magnetic particles called magnetosomes. All magnetotactic bacteria are unicellular except for the multicellular prokaryote (recently named ‘Candidatus Magnetoglobus multicellularis’), which is formed by an orderly assemblage of 17–40 prokaryotic cells that swim as a unit. A ciliate was used in grazing experiments with the M. multicellularis to study the fate of the magnetosomes after ingestion by the protozoa. Ciliates ingested M. multicellularis, which were located in acid vacuoles as demonstrated by confocal laser scanning microscopy. Transmission electron microscopy and X-ray microanalysis of thin-sectioned ciliates showed the presence of M. multicellularis and magnetosomes inside vacuoles in different degrees of degradation. The magnetosomes are dissolved within the acidic vacuoles of the ciliate. Depending on the rate of M. multicellularis consumption by the ciliates the iron from the magnetosomes may be recycled to the environment in a more soluble form.
22 Oct 2007
TL;DR: It is shown that the magnetosomes embedded in each MTB can be used to track the displacement of these bacteria using an MRI system and MTB affect much more the T2-relaxation than T1- Relaxation rate and can be though as a negative contrast agent.
Abstract: MC-1 Magnetotactic Bacteria (MTB) are studied for their potential use as bio-carriers for drug delivery. The exploitation of the flagella combined with nanoparticles magnetite or magnetosomes chain embedded in each bacterium and used to change the swimming direction of each MTB through magnetotaxis provide both propulsion and steering in small diameters blood vessels. But for guiding these MTB towards a target, being capable to image these living bacteria in vivo using an existing medical imaging modality is essential. Here, it is shown that the magnetosomes embedded in each MTB can be used to track the displacement of these bacteria using an MRI system. In fact, these magnetosomes disturb the local magnetic field affecting T1 and T2-relaxation times during MRI. MR T1- weighted and T2-weighted images as well as T2-relaxivity of MTB are studied in order to validate the possibility of monitoring MTB drug delivery operations using a clinical MR scanner. This study proves that MTB affect much more the T2-relaxation than T1-relaxation rate and can be though as a negative contrast agent. The signal decay in the T2-weighted images is found to change proportionally to the bacterial concentration. These results show that a bacterial concentration of 2.2times107 cells/mL can be detected using a T2-weighted image, which is very encouraging to further investigate the application of MTB for in vivo applications.
TL;DR: A helical shaped bacterium capable of producing magnetosomes, designated WM-1, was isolated from freshwater sediment through an improved isolated method that combined magnetic separation and the “race track” method.
Abstract: A helical shaped bacterium capable of producing magnetosomes, designated WM-1, was isolated from freshwater sediment through an improved isolated method that combined magnetic separation and the “race track” method. The strain WM-1 was Gram-negative, 0.2–0.4 μm in diameter and 3–4 μm in length. The strain WM-1 was identified as genus Magnetospirillum in the α-Proteobacteria according to the sequence analysis of the 16S rDNA, the morphology and physiological characteristics. The shape of the magnetosomes in WM-1was cuboidal by electron microscopy. Statistical analysis of WM-1 magnetosome crystals showed that the average number of magnetosomes in a WM-1 bacterium was 8 ± 3.4, and the average length was 54 ± 12.3 nm, and the average width was 43 ± 10.9 nm.
TL;DR: It is reported reliable, reversible trapping of live magnetotactic bacteria, Magnetospirillum magneticum AMB-1, using a commercial magnetic recording head modified to generate spatially localized magnetic fields of high magnitude and gradient.
Abstract: We report reliable, reversible trapping of live magnetotactic bacteria, Magnetospirillum magneticum AMB-1, using a commercial magnetic recording head. The magnetic recording head was modified to generate spatially localized magnetic fields of high magnitude and gradient, and effectively trapped AMB-1, which have a magnetic moment per cell one order of magnitude smaller than cells previously trapped using Amperian fields. We also describe selective trapping of magnetic wild-type AMB-1 with discrimination against a nonmagnetic mutant strain of the same bacteria. Finally, we discuss the prospects of using the built-in spin valve sensor on a recording head for integrated detection of trapped bacteria. Using the chip-based methods we describe, it may be possible to capture, sort, and count magnetic bacteria quickly from samples taken directly from their natural aquatic habitat. More generally, the method may be applicable to the manipulation, spatial control, and integrated detection of magnetically labeled ce...
TL;DR: In this article, the morphology of two magnetic bacterial strains, magnetotacticum and magnetospirillum gryphiswaldense, was analyzed in two dimensions as length and width (in microns) under different magnetic fields using bar magnets.
Abstract: Nanomagnets manufactured by magnetotactic bacteria hold immense promise in magnetically directed drug delivery. In spite of discovery of these bacteria nearly three decades ago, it is not known how the bacteria are able to keep the nanomagnets trapped inside biological membranes (vesicles called magnetosomes). Understanding the physical nature of interactions, which these nanomagnets are capable of, is essential for envisaging any directed drug delivery application. We analyzed the morphology of two magnetic bacterial strains, Magnetospirillum magnetotacticum and Magnetospirillum gryphiswaldense, by defining the features of individual bacteria in two dimensions as length and width (in microns) under different magnetic fields using bar magnets. The control morphologies were taken to be the features of bacteria not under the influence of any magnetic field other than the earth’s own. Using analysis of variance (ANOVA), we found statistically significant morphological changes in the M. magnetotacticum under different conditions. In contrast, there were no morphological differences observed for M. gryphiswaldense under any conditions. The width of M. magnetotacticum was found to be significantly higher for the control conditions compared to any magnetic condition. The length of M. magnetotacticum was found to be significantly lower when only south poles of the bar magnets (single or couple) were towards the bacteria. These results reflect a possible difference in packaging of magnetosomes inside two different strains of magnetic bacteria and imply that it may be important to select the right microbial source of nanomagnets (in contrast to using just any strain), trapped inside biological membranes, for potential targeted drug delivery applications, whereby enhanced sensitivity to external magnetic fields would be preferred.
01 Jan 2007
TL;DR: Ferromagnetic resonance (FMR) spectroscopy has been used to identify fossil magnetotactic bacteria (magnetofossils) in carbonate sediments.
Abstract: Microbial activity plays a major role in the sedimentary iron cycle. Some microbes gain energy by reducing or oxidizing iron and thus induce changes in the sedimentary iron mineral assemblage. Magnetotactic bacteria engage in controlled, intracellular precipitation of magnetic iron minerals. These biological transformations are frequently a major influence on the magnetic properties of sediments. Understanding the biogeochemical iron cycle therefore facilitates the interpretation of sedimentary paleomagnetism; conversely, magnetic tools provide a non-destructive and rapid way of analyzing the biogeochemical iron cycle in modern and ancient environments. Ferromagnetic resonance (FMR) spectroscopy, a form of microwave spectroscopy, provides a rapid means of assessing internal fields generated in magnetic particles by interparticle interactions and particle anisotropy. It can therefore assess particle shape, arrangement, and heterogeneity. Because magnetotactic bacteria typically produce chains of crystals with narrow distributions of size and shape, FMR spectroscopy is well suited as a screening tool for identifying fossil magnetotactic bacteria (magnetofossils). Application of FMR and other techniques to modern carbonate sediments of the Triple Goose Creek region, Andros Island, Bahamas, reveals the contributions of magnetotactic bacteria, iron metabolizing bacteria, and sulfate reducing bacteria to the magnetization of carbonate sediments. In sediments above mean tide level, magnetofossils dominate sediment magnetism. Although stable remanent magnetization is preserved throughout the sediments, the quantity of biological magnetite diminishes by an order of magnitude in the iron reduction zone. Below this zone, the development of a sulfate reduction interval can lead to the authigenesis of magnetic iron sulfides. Supratidal portions of shallowing-upward parasequences in carbonate rocks therefore likely provide the most accurate record of syndepositional paleomagnetism. Anomalous magnetic properties of clay deposited in the Atlantic Coastal Plain, New Jersey, during the Paleocene/Eocene Thermal Maximum (PETM) led previous authors to speculate that an extraterrestrial impact triggered the PETM. Reexamination of the clay using FMR and transmission electron microscopy reveals instead that the clay hosts abundant magnetofossils. The first identification of ancient biogenic magnetite using FMR indicates that the anomalous magnetic properties of PETM sediments were not produced by an impact, but instead reflect paleoenvironmental changes along the western North Atlantic margin.
01 Jan 2007
TL;DR: The hypothesis for the existence of structures that transfer the torque from the magnetosome chains to the whole cell during the orientation of magnetotactic bacteria to a magnetic field lines is strengthened.
Abstract: Magnetospirillum magnetotacticum are magnetotactic bacteria that form a single chain of magnetite magnetosomes within its cytoplasm. Here, we studied the ultrastructure of M. magnetotacticum by freeze-fracture and deep-etching to understand the spatial correlation between the magnetosome chain and the cell envelope and its possible implications for magnetotaxis. Magnetosomes were found mainly near the cell envelope, forming chains that were closely associated with the granular cytoplasmic material. The membrane surrounding the magnetosomes could be visualized in deep-etching preparations. Thin connections between magnetosome chains and the cell envelope were observed in deep-etching images. These results strengthen the hypothesis for the existence of structures that transfer the torque from the magnetosome chains to the whole cell during the orientation of magnetotactic bacteria to a magnetic field lines.
TL;DR: The magnetotactic bacterium isolated from freshwater sediment from North Lake of Wuhan was Gram-negative, helical shaped, and studied by means of electron microscopy, indicating that the magnetosomes were composed of magnetite.
Abstract: The magnetotactic bacterium was isolated from freshwater sediment from North Lake of Wuhan. The isolate, designated WM-1, was Gram-negative, helical shaped, and studied by means of electron microscopy. The strain WM-1 was 0.2-0.4 μm in diameter and 3–4 μm in length. The DNA G + C content was found to be 65.7 mol%. Phylogenetic analysis of the 16S rDNA gene (Accession number DQ899734 in GeneBank) revealed that this isolate was a member ofαsubdivision of the Proteobacteria. Strain WM-1 was closely related (97.7%) to Magnetospirillum sp. AMB-1. Randomly amplified polymorphic DNA analysis showed that these two strains were in fact different strains. Electron diffraction patterns of WM-1 magnetosomes indicated that the magnetosomes were composed of magnetite. The magnetosomes from WM-1 were cuboidal in shape as observed by electron microscopy. Statistical analysis of magnetite crystals from WM-1 showed narrow asymmetric size distribution. The average number of magnetosomes in each WM-1 bacterium was 8 ± 3.4. The average length of magnetosomes in WM-1 was 54 ± 12.3 nm and the average width is 43 ± 10.9 nm. These data showed that the grains in WM-1 were single-domain crystals.
TL;DR: The research indicated that the combined approach of harvesting MTB by home-made apparatus and the method of plate colony isolation could purify and isolate magnetotactic bacteria effectively.
Abstract: A simple apparatus was designed to effectively isolate magnetotactic bacteria from soils or sediments based on their magnetotaxis. Through a series of processes including sample incubation, MTB harvesting, isolation, purification and identification, several strains of bacteria were isolated from the samples successfully. By Transmission Electron Microscopy (TEM) and Energy-Dispersive X-ray Analysis (EDXA), these bacteria were certificated to be magnetotactic bacteria. The phylogenetic relationship between the isolated magnetic strains and some known magnetotactic bacteria was inferred by the construction of phylogenetic tree based on 16SrDNA sequences. This apparatus has been proven to have the advantages of being inexpensive, simple to assemble, easy to perform and highly efficient to isolate novel magnetotactic bacteria. The research indicated that the combined approach of harvesting MTB by home-made apparatus and the method of plate colony isolation could purify and isolate magnetotactic bacteria effectively.