Showing papers on "Magnetotactic bacteria published in 2010"
TL;DR: The results indicated that the C-terminal region of the Mms6 protein has significant control over the morphology of magnetite crystals in the chemical synthetic method, and this method can, therefore, be useful as an alternative method of controlling the size and morphology of magnetsite crystals under ambient conditions.
125 citations
TL;DR: Populations of a moderately thermophilic magnetotactic bacterium were discovered in Great Boiling Springs, Nevada, ranging from 32 to 63°C, and belonged to the phylum Nitrospirae.
Abstract: Populations of a moderately thermophilic magnetotactic bacterium were discovered in Great Boiling Springs, Nevada, ranging from 32 to 63°C. Cells were small, Gram-negative, vibrioid to helicoid in morphology, and biomineralized a chain of bullet-shaped magnetite magnetosomes. Phylogenetically, based on 16S rRNA gene sequencing, the organism belongs to the phylum Nitrospirae.
109 citations
TL;DR: In this paper, the authors 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.
97 citations
TL;DR: The marine QH-2 strain seems to be both phylogenetically and magnetotactically distinct from the freshwater Magnetospirillum spp.
90 citations
TL;DR: It is suggested that the iron-phosphorus granules constitute a distinct bacterial organelle in RS-1, the only reported species of cultured magnetotactic bacteria that is outside of the α-Proteobacteria and that forms bullet-shaped crystals.
Abstract: Intracellular magnetite crystal formation by magnetotactic bacteria has emerged as a powerful model for investigating the cellular and molecular mechanisms of biomineralization, a process common to all branches of life. Although magnetotactic bacteria are phylogenetically diverse and their crystals morphologically diverse, studies to date have focused on a few, closely related species with similar crystal habits. Here, we investigate the process of magnetite biomineralization in Desulfovibrio magneticus sp. RS-1, the only reported species of cultured magnetotactic bacteria that is outside of the alpha-Proteobacteria and that forms bullet-shaped crystals. Using a variety of high-resolution imaging and analytical tools, we show that RS-1 cells form amorphous, noncrystalline granules containing iron and phosphorus before forming magnetite crystals. Using NanoSIMS (dynamic secondary ion mass spectroscopy), we show that the iron-phosphorus granules and the magnetite crystals are likely formed through separate cellular processes. Analysis of the cellular ultrastructure of RS-1 using cryo-ultramicrotomy, cryo-electron tomography, and tomography of ultrathin sections reveals that the magnetite crystals are not surrounded by membranes but that the iron-phosphorus granules are surrounded by membranous compartments. The varied cellular paths for the formation of these two minerals lead us to suggest that the iron-phosphorus granules constitute a distinct bacterial organelle.
71 citations
TL;DR: Compared to previously reported methods, the chemostat culture technique with the MSR-1 strain significantly increased cell density, cell yield, and magnetosome yield in a shorter time window and thus reduced the cost of production.
Abstract: Magnetotactic bacteria have long intrigued researchers because they synthesize intracellular nano-scale (40-100 nm) magnetic particles composed of Fe3O4, termed magnetosomes. Current research focuses on the molecular mechanisms of bacterial magnetosome formation and its practical applications in biotechnology and medicine. Practical applications of magnetosomes are based on their ferrimagnetism, nanoscale size, narrow size distribution, dispersal ability, and membrane-bound structure. However, the applications of magnetosomes have not yet been developed commercially, mainly because magnetotactic bacteria are difficult to cultivate and consistent, high yields of magnetosomes have not yet been achieved. We report a chemostat culture technique based on pH-stat feeding that yields a high cell density of Magnetospirillum gryphiswaldense strain MSR-1 in an auto-fermentor. In a large-scale fermentor, the magnetosome yield was significantly increased by adjusting the stirring rate and airflow which regulates the level of dissolved oxygen (DO). Low concentration of sodium lactate (2.3 mmol l-1) in the culture medium resulted in more rapid cell growth and higher magnetosome yield than high concentration of lactate (20 mmol l-1). The optical density of M. gryphiswaldense cells reached 12 OD565 nm after 36 hr culture in a 42 L fermentor. Magnetosome yield and productivity were 83.23 ± 5.36 mg l-1 (dry weight) and 55.49 mg l-1 day-1, respectively, which were 1.99 and 3.32 times higher than the corresponding values in our previous study. Compared to previously reported methods, our culture technique with the MSR-1 strain significantly increased cell density, cell yield, and magnetosome yield in a shorter time window and thus reduced the cost of production. The cell density and magnetosome yield reported here are the highest so far achieved with a magnetotactic bacteria. Refinement of this technique will enable further increase of cell density and magnetosome yield.
71 citations
TL;DR: It is demonstrated that mamK-like is transcribed in AMB-1 wild-type and ΔmamK mutant cells and that the actin-like filamentous structures observed in the ΔmAMK strain are probably MamK- like polymers, which is the first evidence of a functional mam gene encoded outside the magnetosome genomic island.
Abstract: Magnetotactic bacteria are able to swim navigating along geomagnetic field lines. They synthesize ferromagnetic nanocrystals that are embedded in cytoplasmic membrane invaginations forming magnetosomes. Regularly aligned in the cytoplasm along cytoskeleton filaments, the magnetosome chain effectively forms a compass needle bestowing on bacteria their magnetotactic behaviour. A large genomic island, conserved among magnetotactic bacteria, contains the genes potentially involved in magnetosome formation. One of the genes, mamK has been described as encoding a prokaryotic actin-like protein which when it polymerizes forms in the cytoplasm filamentous structures that provide the scaffold for magnetosome alignment. Here, we have identified a series of genes highly similar to the mam genes in the genome of Magnetospirillum magneticum AMB-1. The newly annotated genes are clustered in a genomic islet distinct and distant from the known magnetosome genomic island and most probably acquired by lateral gene transfer rather than duplication. We focused on a mamK-like gene whose product shares 54.5% identity with the actin-like MamK. Filament bundles of polymerized MamK-like protein were observed in vitro with electron microscopy and in vivo in E. coli cells expressing MamK-like-Venus fusions by fluorescence microscopy. In addition, we demonstrate that mamK-like is transcribed in AMB-1 wild-type and ΔmamK mutant cells and that the actin-like filamentous structures observed in the ΔmamK strain are probably MamK-like polymers. Thus MamK-like is a new member of the prokaryotic actin-like family. This is the first evidence of a functional mam gene encoded outside the magnetosome genomic island.
68 citations
TL;DR: In the last decade, additional criteria have been established (e.g., the Magnetite Assay for Biogenicity), and new tools and technologies have been developed to determine the origin of specific types of magnetite particles as mentioned in this paper.
Abstract: [1] Over the years, nanometer-sized magnetite (Fe3O4) crystals have been recovered from many modern and ancient environments including sediments and soils and even meteorites. In some cases these crystals have been used as “magnetofossils” for evidence of the past presence of specific microbes. Magnetite nanocrystals can be formed by a number of different biological and inorganic mechanisms resulting in crystals with different physical and magnetic characteristics. Prokaryotes (bacteria) biomineralize magnetite through two methods that differ mechanistically, including: biologically induced mineralization (BIM) and biologically controlled mineralization (BCM). Magnetite nanocrystals produced by BIM are known to be synthesized by the dissimilatory iron-reducing bacteria, are deposited external to the cell, and generally are physically indistinguishable from magnetite particles formed inorganically. BCM magnetites, in contrast, are synthesized by the magnetotactic bacteria and some higher organisms and are precipitated intracellularly as membrane-bounded structures called magnetosomes. These magnetites appear to have unique crystal morphologies and a narrow size range leading to their original use as magnetofossils. Because of the discovery of nanometer-sized crystals of magnetite in the Martian meteorite ALH84001, the use of these criteria for the determination of whether magnetite crystals could constitute a prokaryotic biomarker was questioned. Thus, there is currently great debate over what criteria to use in the determination of whether specific magnetite crystals are biogenic or not. In the last decade, additional criteria have been established (e.g., the Magnetite Assay for Biogenicity), and new tools and technologies have been developed to determine the origin of specific types of magnetite crystals.
67 citations
TL;DR: In this article, the authors measured the Fe L2, 3 X-ray magnetic circular dichroism (XMCD) signal from individual, 30 nm diameter magnetosomes in a magnetotactic bacterium, specifically the marine vibrio strain MV-1.
63 citations
TL;DR: The identified and analyzed a homologue of the ferric uptake regulator Fur in Magnetospirillum gryphiswaldense, which was able to complement a fur mutant of Escherichia coli, and demonstrated that Fur is a regulator involved in global iron homeostasis, which also affects magnetite biomineralization.
Abstract: Magnetotactic bacteria synthesize specific organelles, the magnetosomes, which are membrane-enveloped crystals of the magnetic mineral magnetite (Fe3O4) The biomineralization of magnetite involves the uptake and intracellular accumulation of large amounts of iron However, it is not clear how iron uptake and biomineralization are regulated and balanced with the biochemical iron requirement and intracellular homeostasis In this study, we identified and analyzed a homologue of the ferric uptake regulator Fur in Magnetospirillum gryphiswaldense, which was able to complement a fur mutant of Escherichia coli A fur deletion mutant of M gryphiswaldense biomineralized fewer and slightly smaller magnetite crystals than did the wild type Although the total cellular iron accumulation of the mutant was decreased due to reduced magnetite biomineralization, it exhibited an increased level of free intracellular iron, which was bound mostly to a ferritin-like metabolite that was found significantly increased in Mossbauer spectra of the mutant Compared to that of the wild type, growth of the fur mutant was impaired in the presence of paraquat and under aerobic conditions Using a Fur titration assay and proteomic analysis, we identified constituents of the Fur regulon Whereas the expression of most known magnetosome genes was unaffected in the fur mutant, we identified 14 proteins whose expression was altered between the mutant and the wild type, including five proteins whose genes constitute putative iron uptake systems Our data demonstrate that Fur is a regulator involved in global iron homeostasis, which also affects magnetite biomineralization, probably by balancing the competing demands for biochemical iron supply and magnetite biomineralization
63 citations
TL;DR: It is suggested that the FtsZ-like protein is required for synthesis of SD particles and magnetosomes in M. gryphiswaldense.
Abstract: Magnetotactic bacteria (MTB) synthesize unique organelles termed “magnetosomes,” which are membraneenclosed structures containing crystals of magnetite or greigite. Magnetosomes form a chain around MamK cytoskeletal filaments and provide the basis for the ability of MTB to navigate along geomagnetic field lines in order to find optimal microaerobic habitats. Genomes of species of the MTB genus Magnetospirillum ,i n addition to a gene encoding the tubulin-like FtsZ protein (involved in cell division), contain a second gene termed “ftsZ-like,” whose function is unknown. In the present study, we found that the ftsZ-like gene of Magnetospirillum gryphiswaldense strain MSR-1 belongs to a 4.9-kb mamXY polycistronic transcription unit. We then purified the recombinant FtsZ-like protein to homogeneity. The FtsZ-like protein efficiently hydrolyzed ATP and GTP, with ATPase and GTPase activity levels of 2.17 and 5.56 mol phosphorus per mol protein per min, respectively. The FtsZ-like protein underwent GTP-dependent polymerization into long filamentous bundles in vitro. To determine the role of the ftsZ-like gene, we constructed a ftsZ-like mutant (ftsZ-like mutant) and its complementation strain (ftsZ-like_C strain). Growth of ftsZ-like cells was similar to that of the wild type, indicating that the ftsZ-like gene is not involved in cell division. Transmission electron microscopic observations indicated that the ftsZ-like cells, in comparison to wild-type cells, produced smaller magnetosomes, with poorly defined morphology and irregular alignment, including large gaps. Magnetic analyses showed that ftsZ-like produced mainly superparamagnetic (SP) magnetite particles, whereas wildtype and ftsZ-like_C cells produced mainly single-domain (SD) particles. Our findings suggest that the FtsZ-like protein is required for synthesis of SD particles and magnetosomes in M. gryphiswaldense.
TL;DR: Findings suggest that magnetosomes are covered with MamA oligomers in near-native environments and provide important clues to the supramolecular architecture of the bacterial organelle, the magnetosome, and insight into the function of the proteins localized in the organelle.
Abstract: The unique ability of magnetotactic bacteria to navigate along a geomagnetic field is accomplished with the help of prokaryotic organelles, magnetosomes. The magnetosomes have well-ordered chain-like structures, comprising membrane-enveloped, nano-sized magnetic crystals, and various types of specifically associated proteins. In this study, we applied atomic force microscopy (AFM) to investigate the spatial configuration of isolated magnetosomes from Magnetospirillum magneticum AMB-1 in near-native buffer conditions. AFM observation revealed organic material with a ∼7-nm thickness surrounding a magnetite crystal. Small globular proteins, identified as magnetosome-associated protein MamA, were distributed on the mica surface around the magnetosome. Immuno-labeling with AFM showed that MamA is located on the magnetosome surface. In vitro experiments showed that MamA proteins interact with each other and form a high molecular mass complex. These findings suggest that magnetosomes are covered with MamA oligomers in near-native environments. Furthermore, nanodissection revealed that magnetosomes are built with heterogeneous structures that comprise the organic layer. This study provides important clues to the supramolecular architecture of the bacterial organelle, the magnetosome, and insight into the function of the proteins localized in the organelle.
TL;DR: The mamY gene deletion mutant was found to have expanded magnetosome vesicles and a greater number of small magnetite crystals relative to the wild‐type strain, suggesting that the function of the MamY protein is to constrict the magnetosomes membrane during magnetosom vesicle formation, following which, the magnetites grow to maturity within them.
Abstract: Magnetotactic bacteria synthesize intracellular magnetosomes that are comprised of membrane-enveloped magnetic crystals. In this study, to identify the early stages of magnetosome formation, we isolated magnetosomes containing small magnetite crystals and those containing regular-sized magnetite crystals from Magnetospirillum magneticum AMB-1. This was achieved by using a novel size fractionation technique, resulting in the identification of a characteristic protein (Amb1018/MamY) from the small magnetite crystal fraction. The gene encoding MamY was located in the magnetosome island. Like the previously reported membrane deformation proteins, such as bin/amphiphysin/Rvs (BAR) and the dynamin family proteins, recombinant MamY protein bound directly to the liposomes, causing them to form long tubules. We established a mamY gene deletion mutant (DeltamamY) and analysed MamY protein localization in it for functional characterization of the protein in vivo. The DeltamamY mutant was found to have expanded magnetosome vesicles and a greater number of small magnetite crystals relative to the wild-type strain, suggesting that the function of the MamY protein is to constrict the magnetosome membrane during magnetosome vesicle formation, following which, the magnetite crystals grow to maturity within them.
TL;DR: In this paper, the authors present an overview of the magnetic effects on living cultures and their effects on yeast and bacteria in free-cell bioreactors with and without magnetically assisted working volumes.
Abstract: 3. Magnetically assisted free-cell bioreactors 3.1. Basic concept and overview of magnetic effects on living cultures 3.2. Reactors with entirely magnetically assisted working volumes 3.2.1. Magnetically assisted activated sludge processes 3.2.2. Magnetically assisted Saccharomyces cerevisiae growth 3.2.2.1. Proliferation of yeast in response to magnetic field application 3.2.2.2. Comments on the proliferation studies: microlevel dynamo concept 3.2.2.3. Fermentation processes 3.2.3. Spirulina behavior under magnetic fields 3.2.4. Magnetotactic bacteria (Magnetospirillum magneticum) 3.2.5. Escherichia coli behavior under magnetic field 3.2.5.1. Static and high-intensity field exposures 3.2.5.2. Low-intensity, time-varying field exposures 3.2.5.3. Brief comments on the magnetic field exposures of E. coli 3.2.6. Other processes exposed to magnetic fields 3.2.6.1. Static magnetic field effects on yeast and bacteria 3.2.6.2. Time-varying magnetic field effects on yeast and bacteria 3.2.6.3. Time-varying magnetic field effects on enzyme activity 3.3. Reactors with recirculation and external culture magnetization 3.3.1. Forced circulation loop of a batch submerged fermentation process 3.3.2. External-loop airlift with magnetization 3.3.3. Comments on the bioreactors with external loops and intermittent magnetizations 3.4. Comments on free-cell magnetically assisted bioreactors
TL;DR: It is postulate that docking is a key mechanism for building the functional cellular magnetic dipole, which in turn is required for magnetotaxis in bacteria.
TL;DR: The methyl-accepting chemotaxis protein Amb0994 of Magnetospirillum magneticum AMB-1 was found to be capable of carrying out magnetotaxis function, and the C-terminal domain of Amb0992, which interacts with MamK, is responsible for this phenotype, suggesting that the interaction between Amb 0994 and MamK plays a key role in magnetot axis.
TL;DR: The first example of tellurium uptake and crystallization within a magnetotactic bacterial strain, Magnetospirillum magneticum AMB-1, is reported, which presents an ideal system for both bioremediation and magnetic recovery ofTellurite.
Abstract: Magnetotactic bacteria synthesize intracellular magnetosomes comprising membrane-enveloped magnetite crystals within the cell which can be manipulated by a magnetic field. Here, we report the first example of tellurium uptake and crystallization within a magnetotactic bacterial strain, Magnetospirillum magneticum AMB-1. These bacteria independently crystallize tellurium and magnetite within the cell. This is also highly significant as tellurite (TeO32−), an oxyanion of tellurium, is harmful to both prokaryotes and eukaryotes. Additionally, due to its increasing use in high-technology products, tellurium is very precious and commercially desirable. The use of microorganisms to recover such molecules from polluted water has been considered as a promising bioremediation technique. However, cell recovery is a bottleneck in the development of this approach. Recently, using the magnetic property of magnetotactic bacteria and a cell surface modification technology, the magnetic recovery of Cd2+ adsorbed onto the cell surface was reported. Crystallization within the cell enables approximately 70 times more bioaccumulation of the pollutant per cell than cell surface adsorption, while utilizing successful recovery with a magnetic field. This fascinating dual crystallization of magnetite and tellurium by magnetotactic bacteria presents an ideal system for both bioremediation and magnetic recovery of tellurite.
TL;DR: 16S rRNA gene sequences of nMMPs show that they form a separate phylogenetic branch within the MMP group in the Deltaproteobacteria class, probably representing a single species, which might support the hypothesis that acquisition of the magnetosome genes involves horizontal gene transfer.
Abstract: Magnetotactic multicellular prokaryotes (MMPs) are unique magnetotactic bacteria of the Deltaproteobacteria class and the first found to biomineralize the magnetic mineral greigite (Fe3S4). Thus far they have been reported only from marine habitats. We questioned whether MMPs exist in low-saline, nonmarine environments. MMPs were observed in samples from shallow springs in the Great Boiling Springs geothermal field and Pyramid Lake, both located in northwestern Nevada. The temperature at all sites was ambient, and salinities ranged from 5 to 11 ppt. These MMPs were not magnetotactic and did not contain magnetosomes (called nMMPs here). nMMPs ranged from 7 to 11 μm in diameter, were composed of about 40 to 60 Gram-negative cells, and were motile by numerous flagella that covered each cell on one side, characteristics similar to those of MMPs. 16S rRNA gene sequences of nMMPs show that they form a separate phylogenetic branch within the MMP group in the Deltaproteobacteria class, probably representing a single species. nMMPs exhibited a negative phototactic behavior to white light and to wavelengths of ≤480 nm (blue). We devised a “light racetrack” to exploit this behavior, which was used to photoconcentrate nMMPs for specific purposes (e.g., DNA extraction) even though their numbers were low in the sample. Our results show that the unique morphology of the MMP is not restricted to marine and magnetotactic prokaryotes. Discovery of nonmagnetotactic forms of the MMP might support the hypothesis that acquisition of the magnetosome genes involves horizontal gene transfer. To our knowledge, this is the first report of phototaxis in bacteria of the Deltaproteobacteria class.
TL;DR: A genome preparation method that involves magnetic separation of cells, flow cytometry, and multiple displacement amplification (MDA) using φ29 polymerase provides a new strategy to access individual genetic information from magnetotactic bacteria in environmental samples.
Abstract: Magnetotactic bacteria comprise a phylogenetically diverse group that is capable of synthesizing intracellular magnetic particles Although various morphotypes of magnetotactic bacteria have been observed in the environment, bacterial strains available in pure culture are currently limited to a few genera due to difficulties in their enrichment and cultivation In order to obtain genetic information from uncultured magnetotactic bacteria, a genome preparation method that involves magnetic separation of cells, flow cytometry, and multiple displacement amplification (MDA) using 29 polymerase was used in this study The conditions for the MDA reaction using samples containing 1 to 100 cells were evaluated using a pure-culture magnetotactic bacterium, “Magnetospirillum magneticum AMB-1,” whose complete genome sequence is available Uniform gene amplification was confirmed by quantitative PCR (Q-PCR) when 100 cells were used as a template This method was then applied for genome preparation of uncultured magnetotactic bacteria from complex bacterial communities in an aquatic environment A sample containing 100 cells of the uncultured magnetotactic coccus was prepared by magnetic cell separation and flow cytometry and used as an MDA template 16S rRNA sequence analysis of the MDA product from these 100 cells revealed that the amplified genomic DNA was from a single species of magnetotactic bacterium that was phylogenetically affiliated with magnetotactic cocci in the Alphaproteobacteria The combined use of magnetic separation, flow cytometry, and MDA provides a new strategy to access individual genetic information from magnetotactic bacteria in environmental samples
TL;DR: It is found that NS and SS cells could obviously coexist in hypomagnetic field and even, when the oxidation-reduction gradient configuration is suitable, in the geomagnetic Field.
Abstract: Summary
Magnetotactic bacteria are capable of aligning and swimming along the geomagnetic field lines; such a behaviour is called magnetotaxis. Previous studies reported that bacteria in the northern hemisphere migrate preferentially towards the North Pole of the Earth's magnetic field (north-seeking, NS), whereas those in the southern hemisphere swim towards the South Pole (south-seeking, SS). The orientated swimming is thought to guide bacteria migrating downward to the favourable microaerobic or anaerobic regions in stratified water column or sediments. Recent identification of SS populations in northern hemisphere challenged the model of the adaptive value of magnetotaxis. To seek explanation for the apparent discrepancy, we analysed magnetotaxis polarity of axenic cultures under simulated growth conditions in hypomagnetic, northern-hemisphere-like or southern-hemisphere-like magnetic fields. We found that NS and SS cells could obviously coexist in hypomagnetic field and even, when the oxidation-reduction gradient configuration is suitable, in the geomagnetic field. These results reveal the selectivity of the redox gradient configuration on magnetotactic polarity of the cells and reconcile the discrepancy of the early reports.
TL;DR: Direct Transmission Electron Microscopy evidence is reported that division occurs at a central point of the cell and the chain, cleaving the magnetosome chain in two, and the new magnetosomes chain relocates rapidly to the centre of the daughter cell.
Abstract: Cell division in magnetotactic bacteria has attracted much interest, speculation and hypothesis with respect to the biomineralised chains of magnetic iron-oxide particles known as magnetosomes. Here we report direct Transmission Electron Microscopy (TEM) evidence that division occurs at a central point of the cell and the chain, cleaving the magnetosome chain in two. Additionally, the new magnetosome chain relocates rapidly to the centre of the daughter cell and the number of magnetosomes is directly proportional to the cell length, even during the division part of the cell cycle. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Patent•
18 Nov 2010
TL;DR: In this article, the authors describe a method for the treatment of tumor(s) or tumor cell(s), or cancer (s) in a subject in need by the generation of heat.
Abstract: In this disclosure, we describe a method for the treatment of tumor(s) or tumor cell(s) or cancer(s) in a subject in need by the generation of heat. The latter is produced by chains of magnetosomes extracted from whole magnetotactic bacteria and subjected to an alternative magnetic field. These chains of magnetosomes yield efficient antitumoral activity whereas magnetosomes unbound from the chains or kept within the whole bacteria produce poor or no antitumoral activity. The introduction of various chemicals such as chelating agents and/or transition metals within the growth medium of the bacteria improves the heating properties of the chains of magnetosomes. Moreover, the insertion of the chains of magnetosomes within a lipid vesicle is also suggested in order to favor their rotation in vivo and hence to improve their heating capacity. The vesicle can contain an antitumoral agent together with the chains of magnetosomes. In this case, the agent is released within the tumors by heating the vesicle.
TL;DR: In this paper, the coupling field between the aligned magnetite particles of 55 mT was determined by the strong influence of the anisotropy properties of the studied magnetic composite.
11 Nov 2010
TL;DR: In vitro experiments were performed to assess the capability of MC-1 magnetotactic bacteria to penetrate tumor tissue for the delivery of therapeutic agents and show the ability of these MTB when submitted to a directional magnetic field to penetrate inside a 3D multicellular tumor spheroid through openings present in the tissue.
Abstract: Preliminary experiments showed that MC-1 magnetotactic bacteria (MTB) could be used for the delivery of therapeutic agents to tumoral lesions. Each bacterium can provide a significant thrust propulsion force generated by two flagella bundles exceeding 4pN. Furthermore, a chain of single-domain magnetosomes embedded in the cell allows computer directional control and tracking using a magnetic resonance imaging (MRI) system. Although these embedded functionalities suggest that MTB when under the influence of an external computer could be considered as biological microrobots with the potential of targeting tumors, little is known about their level of penetration in tumoral tissues. In this paper, in vitro experiments were performed to assess the capability of these bacteria to penetrate tumor tissue for the delivery of therapeutic agents. Multicellular tumor spheroids were used since they reproduce many properties of solid tumors. The results show the ability of these MTB when submitted to a directional magnetic field to penetrate inside a 3D multicellular tumor spheroid through openings present in the tissue.
TL;DR: By taking advantage of the magnetotactic bacterial system, the first experimental evidence for the presumed energy consumption during assembly of naturally occurring sub-100 nm intra-cellular organelles is presented.
Abstract: Magnetotactic bacteria are unique prokaryotes possessing the feature of cellular organelles called magnetosomes (membrane bound 40-50 nm vesicles entrapping a magnetic nano-crystal of magnetite or greigite). The obvious energetic impact of sophisticated eukaryotic-like membrane-bound organelle assembly on a presumably simpler prokaryotic system is not addressed in literature. In this work, while presenting evidence of direct coupling of carbon source consumption to synthesis of magnetosomes, we provide the first experimentally derived estimate of energy for organelle synthesis by Magnetospirillum gryphiswaldense as approximately 5 nJoules per magnetosome. Considering our estimate of approximately 0.2 microJoules per bacterial cell as the energy required for growth, we show that the energetic load of organelle synthesis results in stunting of cell growth. We also show that removal of soluble iron or sequestration by exogenous compounds in the bacterial cell cultures reverses the impact of the excess metabolic load exerted during magnetosomal synthesis. Thus, by taking advantage of the magnetotactic bacterial system we present the first experimental evidence for the presumed energy consumption during assembly of naturally occurring sub-100 nm intra-cellular organelles.
TL;DR: An additional level of organization of the magnetosome chains in uncultured magnetotactic cocci found in marine and freshwater sediments is described and it is suggested that genetic determinants that are not present or active in bacteria with magnetosomes randomly rotated within a chain must be present in bacteria that organize magnetosites so precisely.
Abstract: Magnetotactic bacteria produce magnetosomes, which are magnetic particles enveloped by biological membranes, in a highly controlled mineralization process. Magnetosomes are used to navigate in magnetic fields by a phenomenon called magnetotaxis. Two levels of organization and control are recognized in magnetosomes. First, magnetotactic bacteria create a spatially distinct environment within vesicles defined by their membranes. In the vesicles, the bacteria control the size, composition and purity of the mineral content of the magnetic particles. Unique crystal morphologies are produced in magnetosomes as a consequence of this bacterial control. Second, magnetotactic bacteria organize the magnetosomes in chains within the cell body. It has been shown in a particular case that the chains are positioned within the cell body in specific locations defined by filamentous cytoskeleton elements. Here, we describe an additional level of organization of the magnetosome chains in uncultured magnetotactic cocci found in marine and freshwater sediments. Electron microscopy analysis of the magnetosome chains using a goniometer showed that the magnetic crystals in both types of bacteria are not oriented at random along the crystal chain. Instead, the magnetosomes have specific orientations relative to the other magnetosomes in the chain. Each crystal is rotated either 60°, 180° or 300° relative to their neighbors along the chain axis, causing the overlapping of the (1 1 1) and [Formula in text] capping faces of neighboring crystals. We suggest that genetic determinants that are not present or active in bacteria with magnetosomes randomly rotated within a chain must be present in bacteria that organize magnetosomes so precisely. This particular organization may also be used as an indicative biosignature of magnetosomes in the study of magnetofossils in the cases where this symmetry is observed.
Journal Article•
TL;DR: Transmission electron and scanning electron microscopy were used for morphological study of MTB and energy dispersive analysis of X-rays and vibrating sample magnetometer techniques were used to elucidate the phase and magnetization in the bacterially synthesized magnetosomes.
Abstract: Magnetotactic bacteria (MTB), Magnetospirillum magnetotacticum (MS-1) were successfully grown in modified magnetic spirillum growth medium (MSGM) at normal laboratory environment. About five-time increase in the bacterial yield was achieved in the modified MSGM medium without compromising their magnetosomes properties. Transmission electron and scanning electron microscopy (TEM & SEM) were used for morphological study of MTB. Energy dispersive analysis of X-rays (EDAX) and vibrating sample magnetometer (VSM) techniques, respectively, were used to elucidate the phase and magnetization in the bacterially synthesized magnetosomes. These studies were important to cross-check the morphology of magnetosomes, as the formation of magnetosomes was highly sensitive to environmental conditions.
TL;DR: In this paper, a new magnetite nanocrystal, called magnetosome, has been found in magnetotactic bacteria and the signal decay in the Magnetic Resonance images is found to change proportionally to the nanoparticles concentration.
Abstract: Iron oxide nanoparticle, named synthetic magnetite, as contrast agent has been widely used in clinical MRI. Recently, a new magnetite nanocrystal, called magnetosome, has been found in magnetotactic bacteria. Physicochemical and magnetorelaxo-metric characterization of bacteria magnetosomes and iron oxide nanoparticles are investigated. Bacterial magnetosomes have the larger mean aggregate size, better dispersion and obviously stronger ferromagnetism compared to synthetic magnetites. The samples of several concentrations of magnetic nanoparticles were analyzed using a clinical 3.0 T MR-scanner. The signal decay in the Magnetic Resonance images is found to change proportionally to the nanoparticles concentration. Two kinds of nanoparticles can be though as a negative contrast agent and show slight effects on T1, but strong effects on T2 weighted images. Notice that at the same concentration the signal attenuation of bacterial magnetite samples is more obvious than that of synthetic magnetite samples.
11 Nov 2010
TL;DR: It is found that nanoparticles synthesized by MC-1 MTB are the predominant source of contrast in MRI over motion and the cell body.
Abstract: This paper investigates the influence of the magnetosome's chain, the motility, and the bacterial cell of MC-1 magnetotactic bacteria (MTB) on the Magnetic Resonance imaging (MRI) contrast. Because of its embedded magnetic nanoparticles, that allow magnetic guidance and imaging contrast generation under MRI, magnetotactic bacteria are being considered for therapeutic drug delivery to tumors. In order to separately investigate the different potential sources of contrast in MRI, we used three samples of MC-1 MTB. The first sample was constituted of magnetic bacteria that successfully synthesize magnetic nanoparticles. MC-1 bacteria that do not synthesize magnetosomes form the second sample while the third sample is constituted from dead MC-1 magnetic bacteria containing magnetic nanoparticle. T2-weighted magnetic resonance images were obtained for multiple echo times. T 2 was then estimated by fitting the signal intensity data for different echo time values to a monoexponential decay curve. It is found that nanoparticles synthesized by MC-1 MTB are the predominant source of contrast in MRI over motion and the cell body.
TL;DR: In this study, a modified capillary magnetic separation system was designed to recover a deteriorating strain of Magnetospirillum magneticum AMB-1 that long-term cold-stored in a refrigerator and results show that all cells obtained after a 3-cycle treatment were vigorous and had the ability to produce magnetosomes.
Abstract: Cultivable magnetotactic bacteria (MTB) in laboratory can provide sufficient samples for molecular microbiological and magnetic studies. However, a cold-stored MTB strain, such as Magnetospirillum magneticum AMB-1, often loses its ability to synthesize magnetosomes and consequently fails to sense the external magnetic field. It is therefore important to quickly recover vigorous bacteria cells that highly capable of magnetosome producing. In this study, a modified capillary magnetic separation system was designed to recover a deteriorating strain of Magnetospirillum magneticum AMB-1 that long-term cold-stored in a refrigerator. The results show that all cells obtained after a 3-cycle treatment were vigorous and had the ability to produce magnetosomes. Moreover, the 3rd-cycle recovered cells were able to form more magnetosome crystals. Compared with the colony formation method, this new method is time-saving, easily operated, and more efficient for recovering vigorous MTB cells.