Showing papers on "Magnetotactic bacteria published in 2009"

Genomics, Genetics, and Cell Biology of Magnetosome Formation

Abstract: Magnetosomes are specialized organelles for magnetic navigation that comprise membrane-enveloped, nano-sized crystals of a magnetic iron mineral; they are formed by a diverse group of magnetotactic bacteria (MTB). The synthesis of magnetosomes involves strict genetic control over intracellular differentiation, biomineralization, and their assembly into highly ordered chains. Physicochemical control over biomineralization is achieved by compartmentalization within vesicles of the magnetosome membrane, which is a phospholipid bilayer associated with a specific set of proteins that have known or suspected functions in vesicle formation, iron transport, control of crystallization, and arrangement of magnetite particles. Magnetosome formation is genetically complex, and relevant genes are predominantly located in several operons within a conserved genomic magnetosome island that has been likely transferred horizontally and subsequently adapted between diverse MTB during evolution. This review summarizes the recent progress in our understanding of magnetobacterial cell biology, genomics, and the genetic control of magnetosome formation and magnetotaxis.

Critical superparamagnetic/single-domain grain sizes in interacting magnetite particles: implications for magnetosome crystals

Abstract: Magnetotactic bacteria contain chains of magnetically interacting crystals (magnetosome crystals), which they use for navigation (magnetotaxis). To improve magnetotaxis efficiency, the magnetosome crystals (usually magnetite or greigite in composition) should be magnetically stable single-domain (SSD) particles. Smaller single-domain particles become magnetically unstable owing to thermal fluctuations and are termed superparamagnetic (SP). Previous calculations for the SSD/SP threshold size or blocking volume did not include the contribution of magnetic interactions. In this study, the blocking volume has been calculated as a function of grain elongation and separation for chains of identical magnetite grains. The inclusion of magnetic interactions was found to decrease the blocking volume, thereby increasing the range of SSD behaviour. Combining the results with previously published calculations for the SSD to multidomain threshold size in chains of magnetite reveals that interactions significantly increase the SSD range. We argue that chains of interacting magnetosome crystals found in magnetotactic bacteria have used this effect to improve magnetotaxis.

Production, Modification and Bio-Applications of Magnetic Nanoparticles Gestated by Magnetotactic Bacteria.

Abstract: Magnetotactic bacteria (MTB) were first discovered by Richard P. Blakemore in 1975, and this led to the discovery of a wide collection of microorganisms with similar features i.e., the ability to internalize Fe and convert it into magnetic nanoparticles, in the form of either magnetite (Fe3O4) or greigite (Fe3S4). Studies showed that these particles are highly crystalline, monodisperse, bioengineerable and have high magnetism that is comparable to those made by advanced synthetic methods, making them candidate materials for a broad range of bio-applications. In this review article, the history of the discovery of MTB and subsequent efforts to elucidate the mechanisms behind the magnetosome formation are briefly covered. The focus is on how to utilize the knowledge gained from fundamental studies to fabricate functional MTB nanoparticles (MTB-NPs) that are capable of tackling real biomedical problems.

Isolation and characterization of a magnetotactic bacterial culture from the Mediterranean Sea

Abstract: The widespread magnetotactic bacteria have the peculiar capacity of navigation along the geomagnetic field. Despite their ubiquitous distribution, only few axenic cultures have been obtained worldwide. In this study, we reported the first axenic culture of magnetotactic bacteria isolated from the Mediterranean Sea. This magneto-ovoid strain MO-1 grew in chemically defined O(2) gradient minimal media at the oxic-anoxic transition zone. It is phylogenetically related to Magnetococcus sp. MC-1 but might represent a novel genus of Proteobacteria. Pulsed-field gel electrophoresis analysis indicated that the genome size of the MO-1 strain is 5 ± 0.5 Mb, with four rRNA operons. Each cell synthesizes about 17 magnetosomes within a single chain, two phosphorous-oxygen-rich globules and one to seven lipid storage granules. The magnetosomes chain seems to divide in the centre during cell division giving rise to two daughter cells with an approximately equal number of magnetosomes. The MO-1 cell possesses two bundles of seven individual flagella that were enveloped in a unique sheath. They swam towards the north pole with a velocity up to 300 μm per second with frequent change from right-hand to left-hand helical trajectory. Using a magneto-spectrophotometry assay we showed that MO-1 flagella were powered by both proton-motive force and sodium ion gradient, which is a rare feature among bacteria.

Toward Cloning of the Magnetotactic Metagenome: Identification of Magnetosome Island Gene Clusters in Uncultivated Magnetotactic Bacteria from Different Aquatic Sediments

Abstract: In this report, we describe the selective cloning of large DNA fragments from magnetotactic metagenomes from various aquatic habitats. This was achieved by a two-step magnetic enrichment which allowed the mass collection of environmental magnetotactic bacteria (MTB) virtually free of nonmagnetic contaminants. Four fosmid libraries were constructed and screened by end sequencing and hybridization analysis using heterologous magnetosome gene probes. A total of 14 fosmids were fully sequenced. We identified and characterized two fosmids, most likely originating from two different alphaproteobacterial strains of MTB that contain several putative operons with homology to the magnetosome island (MAI) of cultivated MTB. This is the first evidence that uncultivated MTB exhibit similar yet differing organizations of the MAI, which may account for the diversity in biomineralization and magnetotaxis observed in MTB from various environments.

Whole genome sequence of Desulfovibrio magneticus strain RS-1 revealed common gene clusters in magnetotactic bacteria

Abstract: Magnetotactic bacteria are ubiquitous microorganisms that synthesize intracellular magnetite particles (magnetosomes) by accumulating Fe ions from aquatic environments. Recent molecular studies, including comprehensive proteomic, transcriptomic, and genomic analyses, have considerably improved our hypotheses of the magnetosome-formation mechanism. However, most of these studies have been conducted using pure-cultured bacterial strains of α-proteobacteria. Here, we report the whole-genome sequence of Desulfovibrio magneticus strain RS-1, the only isolate of magnetotactic microorganisms classified under δ-proteobacteria. Comparative genomics of the RS-1 and four α-proteobacterial strains revealed the presence of three separate gene regions (nuo and mamAB-like gene clusters, and gene region of a cryptic plasmid) conserved in all magnetotactic bacteria. The nuo gene cluster, encoding NADH dehydrogenase (complex I), was also common to the genomes of three iron-reducing bacteria exhibiting uncontrolled extracellular and/or intracellular magnetite synthesis. A cryptic plasmid, pDMC1, encodes three homologous genes that exhibit high similarities with those of other magnetotactic bacterial strains. In addition, the mamAB-like gene cluster, encoding the key components for magnetosome formation such as iron transport and magnetosome alignment, was conserved only in the genomes of magnetotactic bacteria as a similar genomic island-like structure. Our findings suggest the presence of core genetic components for magnetosome biosynthesis; these genes may have been acquired into the magnetotactic bacterial genomes by multiple gene-transfer events during proteobacterial evolution.

Visualizing Implanted Tumors in Mice with Magnetic Resonance Imaging Using Magnetotactic Bacteria

Abstract: Purpose: To determine if magnetotactic bacteria can target tumors in mice and provide positive contrast for visualization using magnetic resonance imaging. Experimental Design: The ability of the magnetotactic bacterium, Magnetospirillum magneticum AMB-1 (referred to from here as AMB-1), to confer positive magnetic resonance imaging contrast was determined in vitro and in vivo . For the latter studies, AMB-1 were injected either i.t. or i.v. Bacterial growth conditions were manipulated to produce small (∼25-nm diameter) magnetite particles, which were observed using transmission electron microscopy. Tumor targeting was confirmed using 64 Cu-labeled bacteria and positron emission tomography and by determination of viable cell counts recovered from different organs and the tumor. Results: We show that AMB-1 bacteria with small magnetite particles generate T1-weighted positive contrast, enhancing in vivo visualization by magnetic resonance imaging. Following i.v. injection of 64 Cu-labeled AMB-1, positron emission tomography imaging revealed increasing colonization of tumors and decreasing infection of organs after 4 hours. Viable cell counts showed that, by day 6, the bacteria had colonized tumors but were cleared completely from other organs. Magnetic resonance imaging showed a 1.22-fold ( P = 0.003) increased positive contrast in tumors on day 2 and a 1.39-fold increase ( P = 0.0007) on day 6. Conclusion: Magnetotactic bacteria can produce positive magnetic resonance imaging contrast and colonize mouse tumor xenografts, providing a potential tool for improved magnetic resonance imaging visualization in preclinical and translational studies to track cancer. (Clin Cancer Res 2009;15(16):5170–7)

Comparative analysis of magnetosome gene clusters in magnetotactic bacteria provides further evidence for horizontal gene transfer

Abstract: The organization of magnetosome genes was analysed in all available complete or partial genomic sequences of magnetotactic bacteria (MTB), including the magnetosome island (MAI) of the magnetotactic marine vibrio strain MV-1 determined in this study. The MAI was found to differ in gene content and organization between Magnetospirillum species and strains MV-1 or MC-1. Although a similar organization of magnetosome genes was found in all MTB, distinct variations in gene order and sequence similarity were uncovered that may account for the observed diversity of biomineralization, cell biology and magnetotaxis found in various MTB. While several magnetosome genes were present in all MTB, others were confined to Magnetospirillum species, indicating that the minimal set of genes required for magnetosome biomineralization might be smaller than previously suggested. A number of novel candidate genes were implicated in magnetosome formation by gene cluster comparison. Based on phylogenetic and compositional evidence we present a model for the evolution of magnetotaxis within the Alphaproteobacteria, which suggests the independent horizontal transfer of magnetosome genes from an unknown ancestor of magnetospirilla into strains MC-1 and MV-1.

Complete Genome Sequence of the Chemolithoautotrophic Marine Magnetotactic Coccus Strain MC-1

Abstract: The marine bacterium strain MC-1 is a member of the alpha subgroup of the proteobacteria that contains the magnetotactic cocci and was the first member of this group to be cultured axenically. The magnetotactic cocci are not closely related to any other known alphaproteobacteria and are only distantly related to other magnetotactic bacteria. The genome of MC-1 contains an extensive (102 kb) magnetosome island that includes numerous genes that are conserved among all known magnetotactic bacteria, as well as some genes that are unique. Interestingly, certain genes that encode proteins considered to be important in magnetosome assembly (mamJ and mamW) are absent from the genome of MC-1. Magnetotactic cocci exhibit polar magneto-aerotaxis, and the MC-1 genome contains a relatively large number of identified chemotaxis genes. Although MC-1 is capable of both autotrophic and heterotrophic growth, it does not appear to be metabolically versatile, with heterotrophic growth confined to the utilization of acetate. Central carbon metabolism is encoded by genes for the citric acid cycle (oxidative and reductive), glycolysis, and gluconeogenesis. The genome also reveals the presence or absence of specific genes involved in the nitrogen, sulfur, iron, and phosphate metabolism of MC-1, allowing us to infer the presence or absence of specific biochemical pathways in strain MC-1. The pathways inferred from the MC-1 genome provide important information regarding central metabolism in this strain that could provide insights useful for the isolation and cultivation of new magnetotactic bacterial strains, in particular strains of other magnetotactic cocci.

Assemblies of Aligned Magnetotactic Bacteria and Extracted Magnetosomes: What Is the Main Factor Responsible for the Magnetic Anisotropy?

Abstract: The origin of the magnetic anisotropy is explained in an assembly of aligned magnetic nanoparticles. For that, nanoparticles synthesized biologically by Magnetospirillum magneticum AMB-1 magnetotactic bacteria are used. For the first time, it is possible to differentiate between the two contributions arising from the alignment of the magnetosome easy axes and the strength of the magnetosome dipolar interactions. The magnetic anisotropy is shown to arise mainly from the dipolar interactions between the magnetosomes.

Magnetite magnetosome and fragmental chain formation of Magnetospirillum magneticum AMB‐1: transmission electron microscopy and magnetic observations

Abstract: SUMMARY 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 ∼445 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 (47–181 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 (eg δ FC/δ ZFC > 20), 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

Uncultivated Magnetotactic Cocci from Yuandadu Park in Beijing, China

Abstract: In the present study, we investigated a group of uncultivated magnetotactic cocci, which was magnetically isolated from a freshwater pond in Beijing, China. Light and transmission electron microscopy showed that these cocci ranged from 1.5 to 2.5 m and contained two to four chains of magnetite magnetosomes, which sometimes were partially disorganized. Overall, the size of the disorganized magnetosomes was significantly smaller than that arranged in chains. All characterized magnetosome crystals were elongated (shape factor 0.64) and fall into the single-domain size range (30 to 115 nm). Comparative 16S rRNA gene sequence analysis and fluorescence in situ hybridization showed that the enriched bacteria were a virtually homogeneous population and represented a novel lineage in the Alphaproteobacteria. The closest cultivated relative was magnetotactic coccoid strain MC-1 (88% sequence identity). First-order reversal curve diagrams revealed that these cocci had relatively strong magnetic interactions compared to the single-chain magnetotactic bacteria. Low-temperature magnetic measurements showed that the Verwey transition of them was 108 K, confirming magnetite magnetosomes, and the delta ratio FC/ZFC was >2. Based on the structure, phylogenetic position and magnetic properties, the enriched magnetotactic cocci of Alphaproteobacteria are provisionally named as “Candidatus Magnetococcus yuandaducum.”

Characterization of Bacterial Magnetotactic Behaviors by Using a Magnetospectrophotometry Assay

Abstract: Magnetotactic bacteria have the unique capacity of synthesizing intracellular single-domain magnetic particles called magnetosomes. The magnetosomes are usually organized in a chain that allows the bacteria to align and swim along geomagnetic field lines, a behavior called magnetotaxis. Two mechanisms of magnetotaxis have been described. Axial magnetotactic cells swim in both directions along magnetic field lines. In contrast, polar magnetotactic cells swim either parallel to the geomagnetic field lines toward the North Pole (north seeking) or antiparallel toward the South Pole (south seeking). In this study, we used a magnetospectrophotometry (MSP) assay to characterize both the axial magnetotaxis of “Magnetospirillum magneticum” strain AMB-1 and the polar magnetotaxis of magneto-ovoid strain MO-1. Two pairs of Helmholtz coils were mounted onto the cuvette holder of a common laboratory spectrophotometer to generate two mutually perpendicular homogeneous magnetic fields parallel or perpendicular to the light beam. The application of magnetic fields allowed measurements of the change in light scattering resulting from cell alignment in a magnetic field or in absorbance due to bacteria swimming across the light beam. Our results showed that MSP is a powerful tool for the determination of bacterial magnetism and the analysis of alignment and swimming of magnetotactic bacteria in magnetic fields. Moreover, this assay allowed us to characterize south-seeking derivatives and non-magnetosome-bearing strains obtained from north-seeking MO-1 cultures. Our results suggest that oxygen is a determinant factor that controls magnetotactic behavior.

Manganese in biogenic magnetite crystals from magnetotactic bacteria.

Abstract: Magnetotactic bacteria produce either magnetite (Fe(3)O(4)) or greigite (Fe(3)S(4)) crystals in cytoplasmic organelles called magnetosomes. Whereas greigite magnetosomes can contain up to 10 atom% copper, magnetite produced by magnetotactic bacteria was considered chemically pure for a long time and this characteristic was used to distinguish between biogenic and abiogenic crystals. Recently, it was shown that magnetosomes containing cobalt could be produced by three strains of Magnetospirillum. Here we show that magnetite crystals produced by uncultured magnetotactic bacteria can incorporate manganese up to 2.8 atom% of the total metal content (Fe+Mn) when manganese chloride is added to microcosms. Thus, chemical purity can no longer be taken as a strict prerequisite to consider magnetite crystals to be of biogenic origin.

Magnetic Particles for Biomedical Applications

Abstract: This chapter discusses applications of magnetic materials in bioengineering and medicine [1–8]. Magnetism and magnetic materials have been used for many decades in many modern medical applications, and several new applications are being developed in part because of the availability of superior electromagnets, superconducting magnets and permanent magnets [9–12]. Advances in the synthesis and characterization of magnetic particles, especially nanomagnetic particles, have also aided in the use of magnetic biomaterials [6–12]. We begin with an introduction to magnetism and magnetic materials, followed by a discussion of the characterization, synthesis techniques and applications of magnetic biomaterials [8, 9]. Magnetic materials can be applied to cell separation, immunoassay, magnetic resonance imaging (MRI), drug and gene delivery, minimally invasive surgery, radionuclide therapy, hyperthermia and artificial muscle applications [1–5, 7]. Physical properties which make magnetic materials attractive for biomedical applications are, first, that they can be manipulated by an external magnetic field – this feature is useful for separation, immunoassay and drug targeting, and second, hysteresis and other losses occur in alternating magnetic fields – this is useful in hyperthermia applications. In biology, there has been much interest in the possible use by bees and pigeons of magnetic materials as biological compasses for navigation. Some magnetotactic bacteria are known to respond to a magnetic field, they contain chains of small magnetite particles and they can navigate to the surface or bottom of the pools that they live in using these particles. These particles can be obtained by disruption of the cell wall followed by magnetic separation; the presence of the lipid layer makes these particles biocompatible and they can be readily functionalized for a variety of biomedical applications. The earliest known biomedical use of naturally occurring magnetic materials involves magnetite (Fe3O4) or lodestone which was used by the Indian surgeon Sucruta around 2,600 years ago. He wrote in the book Ayurveda that magnetite can be used to extract an iron arrow tip. Current areas in medicine to which magnetic biomaterials can be applied include molecular and cell biology, cardiology, neurosurgery, oncology and radiology.

Proteomic analysis of irregular, bullet‐shaped magnetosomes in the sulphate‐reducing magnetotactic bacterium Desulfovibrio magneticus RS‐1

Abstract: Recent molecular studies on magnetotactic bacteria have identified a number of proteins associated with bacterial magnetites (magnetosomes) and elucidated their importance in magnetite biomineralisation. However, these analyses were limited to magnetotactic bacterial strains belonging to the alpha-subclass of Proteobacteria. We performed a proteomic analysis of magnetosome membrane proteins in Desulfovibrio magneticus strain RS-1, which is phylogenetically classified as a member of the delta-Proteobacteria. In the analysis, the identified proteins were classified based on their putative functions and compared with the proteins from the other magnetotactic bacteria, Magnetospirillum magneticum AMB-1 and M. gryphiswaldense MSR-1. Three magnetosome-specific proteins, MamA (Mms24), MamK, and MamM, were identified in strains RS-1, AMB-1, and MSR-1. Furthermore, genes encoding ten magnetosome membrane proteins, including novel proteins, were assigned to a putative magnetosome island that contains subsets of genes essential for magnetosome formation. The collagen-like protein and putative iron-binding proteins, which are considered to play key roles in magnetite crystal formation, were identified as specific proteins in strain RS-1. Furthermore, genes encoding two homologous proteins of Magnetococcus MC-1 were assigned to a cryptic plasmid of strain RS-1. The newly identified magnetosome membrane proteins might contribute to the formation of the unique irregular, bullet-shaped crystals in this microorganism.

Magnetosomes and magneto-aerotaxis.

Abstract: Magnetotactic bacteria orient and migrate along geomagnetic field lines Magneto-aerotaxis increases the efficiency of respiring microaerophilic cells to efficiently find and maintain a position at a preferred microaerobic oxygen concentration Magneto-aerotaxis could also facilitate access to regions of higher nutrient and electron acceptor concentration via periodic excursions above and below the preferred oxygen concentration level

Formation of magnetite in Magnetospirillum gryphiswaldense studied with FORC diagrams

Abstract: In order to study the formation of magnetite in magnetotactic bacteria, FORC diagrams were measured on a set of cultured Magnetospirillum gryphiswaldense, following an assay in which the iron uptake is used only for magnetite formation and not for cell growth. This enabled us to follow the magnetite formation independently of growth. The FORC diagrams showed a clear evolution from a size-distribution with a majority of superparamagnetic grains, to a distribution dominated by stable, single-domain grains, but still containing some superparamagnetic particles. TEM observations confirm this evolution. According to the saturation isothermal remanent magnetization cooling and warming curves, the Verwey transition can only be seen in the most mature samples, and slightly below 120 K. This suggests that the samples may have suffered from some partial oxidation.

In vivo display of a multisubunit enzyme complex on biogenic magnetic nanoparticles.

Abstract: Magnetosomes are unique bacterial organelles comprising membrane-enveloped magnetic crystals produced by magnetotactic bacteria. Because of several desirable chemical and physical properties, magnetosomes would be ideal scaffolds on which to display highly complicated biological complexes artificially. As a model experiment for the functional expression of a multisubunit complex on magnetosomes, we examined the display of a chimeric bacterial RNase P enzyme composed of the protein subunit (C5) of Escherichia coli RNase P and the endogenous RNA subunit by expressing a translational fusion of C5 with MamC, a known magnetosome protein, in the magnetotactic bacterium Magnetospirillum gryphiswaldense. As intended, the purified C5 fusion magnetosomes, but not wild-type magnetosomes, showed apparent RNase P activity and the association of a typical bacterial RNase P RNA. Our results demonstrate for the first time that magnetosomes can be employed as scaffolds for the display of multisubunit complexes.

Effects of static magnetic field on magnetosome formation and expression of mamA, mms13, mms6 and magA in Magnetospirillum magneticum AMB-1

Abstract: Magnetotactic bacteria produce nanometer-size intracellular magnetic crystals. The superior crystalline and magnetic properties of magnetosomes have been attracting much interest in medical applications. To investigate effects of intense static magnetic field on magnetosome formation in Magnetospirillum magneticum AMB-1, cultures inoculated with either magnetic or non-magnetic pre-cultures were incubated under 0.2 T static magnetic field or geomagnetic field. The results showed that static magnetic field could impair the cellular growth and raise C(mag) values of the cultures, which means that the percentage of magnetosome-containing bacteria was increased. Static magnetic field exposure also caused an increased number of magnetic particles per cell, which could contribute to the increased cellular magnetism. The iron depletion in medium was slightly increased after static magnetic field exposure. The linearity of magnetosome chain was also affected by static magnetic field. Moreover, the applied intense magnetic field up-regulated mamA, mms13, magA expression when cultures were inoculated with magnetic cells, and mms13 expression in cultures inoculated with non-magnetic cells. The results implied that the interaction of the magnetic field created by magnetosomes in AMB-1 was affected by the imposed magnetic field. The applied static magnetic field could affect the formation of magnetic crystals and the arrangement of the neighboring magnetosome.

Combined Approaches for Characterization of an Uncultivated Magnetotactic coccus from Lake Miyun near Beijing

Abstract: This paper reports the features of an as yet uncultivated magnetotactic coccus, named MYC-1, recently found from surface sediments of Lake Miyun near Beijing. Light microscope and Bacteriodrome analyses demonstrate that MYC-1 is north-seeking in the Earth's magnetic field. Transmission electron microscope (TEM) attached with energy-dispersive X-ray analyses reveal that this coccus contains a single chain of magnetosomes, containing approximately 10 large iron-oxide crystals. Morphology of these crystals is featured by prism with a mean length and width of 117 nm and 95 nm (statistics from 281 crystals), respectively; it yields an aspect factor of 1.24. A linear relationship (r2 = 0.83) clearly exists between the length and width of crystals. In agreement with previous results, we observed that the size distribution of the MYC-1 is distinctly asymmetric with cut off toward larger sizes, which is the opposite of non-biogenic crystals. Low-temperature magnetic measurements on bulk bacteria samples show a dis...

Iron oxide crystal formation on a substrate modified with the Mms6 protein from magnetotactic bacteria

Abstract: Mms6 is a small acidic protein which is tightly bound to magnetite in the bacterium Magnetospirillum magneticum AMB-1. Mms6 has been previously shown to promote iron-binding capacity as well as modulate the size and morphology of magnetic iron oxide crystals in vitro . In this study, we synthesized iron oxide crystals by using a monolayer-modified substrate. A self-assembled monolayer of octadecyltrimethoxysilane was modified on a silicon substrate. Recombinant Mms6 protein was attached to the substrate through the hydrophobic interactions between the protein molecules and the monolayer. The immobilization of protein molecules on the substrate surface was confirmed by fluorescent labeling of these molecules and subsequent fluorescence microscopy. This protein-modified substrate was then used as a template for iron oxide crystal formation in a ferrous solution. Scanning electron microscopy revealed site-specific formation of iron oxide crystals in substrate regions with immobilized proteins. This use of proteins might provide an alternative method for the bottom-up fabrication of nano-sized magnetic particles.

Magnetotactic bacteria from Lonar lake

Abstract: Magnetotactic bacteria (MTB) are motile, aquatic prokaryotes that swim along geomagnetic field lines. These bacteria display a myriad of cellular morphologies, including coccoid, rod, vibrioid, spirilloid etc. with their unique 'magnetosomes' within the cells. The Lonar lake in Maharashtra, formed due to a meteorite impact crater, is a closed basin lake characterized by high alkalinity and salinity. The MTB isolated by the 'magnetic collection' and 'capillary racetrack' methods showed a typical response in the form of movement towards the magnet and precise alignment at the edge of the hanging drop. Intracellular iron accumulation studies on these bacteria showed up to 11.5 times more iron than non-magnetic bacteria.

Laser Raman Spectroscopic Study on Magnetite Formation in Magnetotactic Bacteria

Abstract: Magnetotactic bacteria have one or more chains of magnetosome, consisting of nano-sized magnetic crystal covered with a phospholipid bilayer and use it to sense the geomagnetic fields. In order to elucidate the molecular process to make magnetosome from the iron compounds found in the bacteria, laser Raman spectroscopic measurements were performed with the magnetotactic bacterium, Magnetospirillum magnetotacticum MS-1 and the fractions separated from it. The clear Raman signals were observed at 662 cm-1 and 740 cm-1. The former was observed in whole cell and magnetosome fraction, but not in membrane and cytoplasmic fraction and assigned to the Raman signal of magnetite. The Raman signal of the latter was observed not only in the magnetosome fraction, but also in the cytoplasmic fraction and membrane fraction. This signal was assumed to ferrihydrite. Based on the results, the pathway of the magnetosome synthesis and possible roles of ferrihydrite in the magnetotactic bacteria were discussed.

Effects of pulsed magnetic field on the formation of magnetosomes in the Magnetospirillum sp. strain AMB-1.

Abstract: Magnetotactic bacteria are a diverse group of microorganisms which possess one or more chains of magnetosomes and are endowed with the ability to use geomagnetic fields for direction sensing, thus providing a simple and excellent model for the study of magnetite-based magnetoreception. In this study, a 50 Hz, 2 mT pulsed magnetic field (PMF) was applied to study the effects on the formation of magnetosomes in Magnetospirillum sp. strain AMB-1. The results showed that the cellular magnetism (Rmag) of AMB-1 culture significantly increased while the growth of cells remained unaffected after exposure. The number of magnetic particles per cell was enhanced by about 15% and slightly increased ratios of magnetic particles of superparamagnetic property (size 50 nm) were observed after exposure to PMF. In addition, the intracellular iron accumulation slightly increased after PMF exposure. Therefore, it was concluded that 50 Hz, 2 mT PMF enhances the formation of magnetosomes in Magnetospirillum sp. strain AMB-1. Our results suggested that lower strength of PMF has no significant effects on the bacterial cell morphologies but could affect crystallization process of magnetosomes to some extent. Bioelectromagnetics 31:246–251, 2010. © 2009 Wiley-Liss, Inc.

Gold Biorecovery from Plating Waste by Magnetotactic Bacterium, Magnetospirillum magneticum AMB-1

Abstract: Magnetotactic bacteria are a unique species of bacteria, commonly recognized by the presence of magnetic particles within them. These intracellular, nanosized magnetic particles enable the bacteria to migrate and be manipulated by magnetic force. To date, magnetotactic bacteria have been widely researched and implemented in various biotechnology based applications. In this study, as an extension to its applications, the magnetotactic bacterium, Magnetospirillum magneticum AMB-1, was applied in the microbial recovery of gold from plating waste. M. magneticum AMB-1 successfully precipitated approximately 42% and 100% of gold from growth medium containing 10 µM gold and from a mixture of plating waste/growth medium containing 0.4 µM gold, respectively. These observations and results strongly suggests that an important advancement in biorecovery of rare metals and bioremediation of toxic metals was achieved in which the application of whole cell bacteria, and direct precipitation of metals from plating waste using magnetotactic bacteria was performed for the first time.

Magnetic Properties of Bacterial Nanoparticles

Abstract: The objective of this study is to prepare and study magnetic properties of biological magnetic nanoparticles (magnetosomes) as a product of biomineralization process of magnetotactic bacteria Magnetospirillum sp. AMB-1. From temperature dependence of remanent magnetization and coercive field the Verwey transition is clearly seen at 105 K as a consequence of the large anisotropy along the chains of magnetosomes.