Showing papers on "Magnetotactic bacteria published in 2008"
731 citations
TL;DR: The magnetofossil record extends robustly to the Cretaceous and with lesser certainty to the late Archean, and the magnetotactic bacteria are recognized based on their narrow size and shape distributions, distinctive morphologies with blunt crystal edges, chain arrangement, chemical purity and crystallographic perfection as discussed by the authors.
305 citations
TL;DR: The genes and proteins identified from studies have allowed us to express functional proteins efficiently onto BacMPs, through genetic engineering, permitting the preservation of the protein activity, leading to a simple preparation of functional protein–magnetic particle complexes.
Abstract: Magnetic particles offer high technological potential since they can be conveniently collected with an external magnetic field. Magnetotactic bacteria synthesize bacterial magnetic particles (BacMPs) with well-controlled size and morphology. BacMPs are individually covered with thin organic membrane, which confers high and even dispersion in aqueous solutions compared with artificial magnetites, making them ideal biotechnological materials. Recent molecular studies including genome sequence, mutagenesis, gene expression and proteome analyses indicated a number of genes and proteins which play important roles for BacMP biomineralization. Some of the genes and proteins identified from these studies have allowed us to express functional proteins efficiently onto BacMPs, through genetic engineering, permitting the preservation of the protein activity, leading to a simple preparation of functional protein–magnetic particle complexes. They were applicable to high-sensitivity immunoassay, drug screening and cell separation. Furthermore, fully automated single nucleotide polymorphism discrimination and DNA recovery systems have been developed to use these functionalized BacMPs. The nano-sized fine magnetic particles offer vast potential in new nano-techniques.
224 citations
TL;DR: A total of 28 conserved genes present in various magnetic bacteria were identified to be specifically associated with the magnetotactic phenotype, most of which are located in the genomic magnetosome island.
Abstract: The ability of magnetotactic bacteria (MTB) to orient in magnetic fields is based on the synthesis of magnetosomes, which are unique prokaryotic organelles comprising membrane-enveloped, nano-sized crystals of a magnetic iron mineral that are aligned in well-ordered intracellular chains. Magnetosome crystals have species-specific morphologies, sizes, and arrangements. The magnetosome membrane, which originates from the cytoplasmic membrane by invagination, represents a distinct subcellular compartment and has a unique biochemical composition. The roughly 20 magnetosome-specific proteins have functions in vesicle formation, magnetosomal iron transport, and the control of crystallization and intracellular arrangement of magnetite particles. The assembly of magnetosome chains is under genetic control and involves the action of an acidic protein that links magnetosomes to a novel cytoskeletal structure, presumably formed by a specific actin-like protein. A total of 28 conserved genes present in various magnetic bacteria were identified to be specifically associated with the magnetotactic phenotype, most of which are located in the genomic magnetosome island. The unique properties of magnetosomes attracted broad interdisciplinary interest, and MTB have recently emerged as a model to study prokaryotic organelle formation and evolution.
204 citations
TL;DR: It is suggested that the MamGFDC proteins have partially redundant functions and, in a cumulative manner, control the growth of magnetite crystals by an as-yet-unknown mechanism.
Abstract: Magnetospirillum gryphiswaldense and related magnetotactic bacteria form magnetosomes, which are membrane-enclosed organelles containing crystals of magnetite (Fe3O4) that cause the cells to orient in magnetic fields. The characteristic sizes, morphologies, and patterns of alignment of magnetite crystals are controlled by vesicles formed of the magnetosome membrane (MM), which contains a number of specific proteins whose precise roles in magnetosome formation have remained largely elusive. Here, we report on a functional analysis of the small hydrophobic MamGFDC proteins, which altogether account for nearly 35% of all proteins associated with the MM. Although their high levels of abundance and conservation among magnetotactic bacteria had suggested a major role in magnetosome formation, we found that the MamGFDC proteins are not essential for biomineralization, as the deletion of neither mamC, encoding the most abundant magnetosome protein, nor the entire mamGFDC operon abolished the formation of magnetite crystals. However, cells lacking mamGFDC produced crystals that were only 75% of the wild-type size and were less regular than wild-type crystals with respect to morphology and chain-like organization. The inhibition of crystal formation could not be eliminated by increased iron concentrations. The growth of mutant crystals apparently was not spatially constrained by the sizes of MM vesicles, as cells lacking mamGFDC formed vesicles with sizes and shapes nearly identical to those formed by wild-type cells. However, the formation of wild-type-size magnetite crystals could be gradually restored by in-trans complementation with one, two, and three genes of the mamGFDC operon, regardless of the combination, whereas the expression of all four genes resulted in crystals exceeding the wild-type size. Our data suggest that the MamGFDC proteins have partially redundant functions and, in a cumulative manner, control the growth of magnetite crystals by an as-yet-unknown mechanism.
184 citations
TL;DR: MRI shows that these particles can be formed in vivo utilizing endogenous iron and can be used to visualize cells positive for magA, and demonstrates that magA alone is sufficient to produce magnetic nanoparticles.
Abstract: Magnetic resonance imaging (MRI) is routinely used to obtain anatomical images that have greatly advanced biomedical research and clinical health care today, but the full potential of MRI in providing functional, physiological, and molecular information is only beginning to emerge. In this work, we sought to provide a gene expression marker for MRI based on bacterial magnetosomes, tiny magnets produced by naturally occurring magnetotactic bacteria. Specifically, magA, a gene in magnetotactic bacteria known to be involved with iron transport, is expressed in a commonly used human cell line, 293FT, resulting in the production of magnetic, iron-oxide nanoparticles by these cells and leading to increased transverse relaxivity. MRI shows that these particles can be formed in vivo utilizing endogenous iron and can be used to visualize cells positive for magA. These results demonstrate that magA alone is sufficient to produce magnetic nanoparticles and that it is an appropriate candidate for an MRI reporter gene.
181 citations
TL;DR: The bacterium Actinobacter sp.
Abstract: The bacterium Actinobacter sp. has been shown to be capable of extracellularly synthesizing iron based magnetic nanoparticles, namely maghemite (γ-Fe2O3) and greigite (Fe3S4) under ambient conditions depending on the nature of precursors used. More precisely, the bacterium synthesized maghemite when reacted with ferric chloride and iron sulfide when exposed to the aqueous solution of ferric chloride-ferrous sulfate. Challenging the bacterium with different metal ions resulted in induction of different proteins, which bring about the specific biochemical transformations in each case leading to the observed products. Maghemite and iron sulfide nanoparticles show superparamagnetic characteristics as expected. Compared to the earlier reports of magnetite and greigite synthesis by magnetotactic bacteria and iron reducing bacteria, which take place strictly under anaerobic conditions, the present procedure offers significant advancement since the reaction occurs under aerobic condition. Moreover, reaction end p...
172 citations
TL;DR: In this paper, controlled in vivo cobalt doping of magnetosomes in three strains of the bacterium Magnetospirillum was reported, and the presence of cobalt increases the coercive field of the magnetosome by 36-45% depending on the strain and the cobalt content.
Abstract: Magnetotactic bacteria biomineralize iron into magnetite (Fe3O4) nanoparticles that are surrounded by lipid vesicles. These 'magnetosomes' have considerable potential for use in bio- and nanotechnological applications because of their narrow size and shape distribution and inherent biocompatibility. The ability to tailor the magnetic properties of magnetosomes by chemical doping would greatly expand these applications; however, the controlled doping of magnetosomes has so far not been achieved. Here, we report controlled in vivo cobalt doping of magnetosomes in three strains of the bacterium Magnetospirillum. The presence of cobalt increases the coercive field of the magnetosomes--that is, the field necessary to reverse their magnetization--by 36-45%, depending on the strain and the cobalt content. With elemental analysis, X-ray absorption and magnetic circular dichroism, we estimate the cobalt content to be between 0.2 and 1.4%. These findings provide an important advance in designing biologically synthesized nanoparticles with useful highly tuned magnetic properties.
144 citations
TL;DR: The data demonstrate the use of GFP as a reporter for protein localization under magnetite-forming conditions and the utility of MamC as an anchor for magnetosome-specific display of heterologous gene fusions.
Abstract: The magnetosomes of magnetotactic bacteria are prokaryotic organelles consisting of a magnetite crystal bounded by a phospholipid bilayer that contains a distinct set of proteins with various functions. Because of their unique magnetic and crystalline properties, magnetosome particles are potentially useful as magnetic nanoparticles in a number of applications, which in many cases requires the coupling of functional moieties to the magnetosome membrane. In this work, we studied the use of green fluorescent protein (GFP) as a reporter for the magnetosomal localization and expression of fusion proteins in the microaerophilic Magnetospirillum gryphiswaldense by flow cytometry, fluorescence microscopy, and biochemical analysis. Although optimum conditions for high fluorescence and magnetite synthesis were mutually exclusive, we established oxygen-limited growth conditions, which supported growth, magnetite biomineralization, and GFP fluorophore formation at reasonable rates. Under these optimized conditions, we studied the subcellular localization and expression of the GFP-tagged magnetosome proteins MamC, MamF, and MamG by fluorescence microscopy and immunoblotting. While all fusions specifically localized at the magnetosome membrane, MamC-GFP displayed the strongest expression and fluorescence. MamC-GFP-tagged magnetosomes purified from cells displayed strong fluorescence, which was sensitive to detergents but stable under a wide range of temperature and salt concentrations. In summary, our data demonstrate the use of GFP as a reporter for protein localization under magnetite-forming conditions and the utility of MamC as an anchor for magnetosome-specific display of heterologous gene fusions.
99 citations
TL;DR: In this paper, the authors studied the properties of magnetosomes at several steps of maturity and found that the morphology of mature magnetosome is not exclusively determined by vectorial regulation at the organic boundaries or by molecular interaction with the magnetosOME membrane, but also by the rates of Fe uptake, which suggests that the expression of different faces is favored for different growth conditions.
Abstract: Magnetotactic bacteria are known to mediate the formation of intracellular magnetic nanoparticles in organelles called magnetosomes. These magnetite crystals are formed through a process called biologically controlled mineralization, in which the microorganisms exert a strict control over the formation and development of the mineral phase. By inducing magnetite nucleation and growth in resting, Fe-starved cells of Magnetospirillum gryphiswaldense, we have followed the dynamics of magnetosome development. By studying the properties of the crystals at several steps of maturity, we observed that freshly induced particles lacked a well-defined morphology. More surprisingly, although the mean particle size of mature magnetosomes is similar to that of magnetosomes formed by constantly growing and Fe-supplemented bacteria, we found that other physical properties such as crystal-size distribution, aspect ratio, and morphology significantly differ. Correlating these results with measurements of Fe uptake rates, we suggest that the expression of different faces is favored for different growth conditions. These results imply that the biological control over magnetite biomineralization by magnetotactic bacteria can be disturbed by environmental parameters. Specifically, the morphology of magnetite crystals is not exclusively determined by biological intervention through vectorial regulation at the organic boundaries or by molecular interaction with the magnetosome membrane, but also by the rates of Fe uptake. This insight may contribute to better define biomarkers and to an improved understanding of biomineralizing systems.
98 citations
TL;DR: The magnetic properties of intact magnetosome chains in magnetospirillum gryphiswaldense bacteria were investigated by means of static and dynamic magnetic analyses and ferromagnetic resonance spectroscopy as mentioned in this paper.
TL;DR: In this article, the magnetism, geochemistry and geobiology of uncultured magnetite and greigite-producing magnetotactic bacteria (MB) and magnetically responsive protists (MRP) in Salt Pond (Falmouth, MA, USA), a small coastal, marine basin (∼5 m deep) that becomes chemically stratified during the summer months.
Abstract: SUMMARY Magnetic properties of suspended material in the water columns of freshwater and marine environments provide snapshots of magnetic biomineralization that have yet to be affected by the eventual time-integration and early diagenetic effects that occur after sediment deposition. Here, we report on the magnetism, geochemistry and geobiology of uncultured magnetite- and greigite-producing magnetotactic bacteria (MB) and magnetically responsive protists (MRP) in Salt Pond (Falmouth, MA, USA), a small coastal, marine basin (∼5 m deep) that becomes chemically stratified during the summer months. At this time, strong inverse O2 and H2S concentration gradients form in the water column and a well-defined oxic–anoxic interface (OAI) is established at a water depth of about 3.5 m. At least four morphological types of MB, both magnetite and greigite producers, and several species of magnetically responsive protists are found associated with the OAI and the lower sulphidic hypolimnion. Magnetic properties of filtered water were determined through the water column across the OAI and were consistent with the occurrence of magnetite- and greigite-producing MB at different depths. Sharp peaks in anhysteretic remanent magnetization (ARM) and saturation isothermal remanent magnetization (SIRM) and single-domain (SD) values of ARM/SIRM occur within the OAI corresponding to high concentrations of MB and MRP with magnetically derived cell densities of 10 4 –10 6 ml −1 . Low-temperature ( 1 per cent) is present within magnetite magnetosomes, produced either
TL;DR: It is suggested that the development of a thick suboxic zone with high iron bioavailability—a product of dramatic changes in weathering and sedimentation patterns driven by severe global warming—drove diversification of magnetite-forming organisms, likely including eukaryotes.
Abstract: We report the discovery of exceptionally large biogenic magnetite crystals in clay-rich sediments spanning the Paleocene–Eocene Thermal Maximum (PETM) in a borehole at Ancora, NJ. Aside from previously described abundant bacterial magnetofossils, electron microscopy reveals novel spearhead-like and spindle-like magnetite up to 4 μm long and hexaoctahedral prisms up to 1.4 μm long. Similar to magnetite produced by magnetotactic bacteria, these single-crystal particles exhibit chemical composition, lattice perfection, and oxygen isotopes consistent with an aquatic origin. Electron holography indicates single-domain magnetization despite their large crystal size. We suggest that the development of a thick suboxic zone with high iron bioavailability—a product of dramatic changes in weathering and sedimentation patterns driven by severe global warming—drove diversification of magnetite-forming organisms, likely including eukaryotes.
TL;DR: In this paper, structural characterization and magnetic properties of various assemblies of chains of magnetosomes are reported, and the same magnetic properties are observed for the magnetotactic bacteria and for the extracted chains, isolated in a polymer.
Abstract: We report structural characterization and magnetic properties of various assemblies of chains of magnetosomes. The same magnetic properties are observed for the magnetotactic bacteria and for the extracted chains of magnetosomes isolated in a polymer. When the extracted chains of magnetosomes form a denser structure than that observed in the bacteria, the magnetic properties change markedly. A decrease in the coercivity and reduced remanence is observed. This behavior is attributed to an enhancement of the dipolar interactions between the chains of magnetosomes in the limit of a weakly interacting system; that is, the magnetostatic energy is lower than the anisotropy energy. The effect of the dipolar interactions is more pronounced at 250 K than at 10 K. This behavior is attributed to the existence of a family of small magnetosomes, which undergo a transition from a ferromagnetic to a superparamagnetic state.
TL;DR: Preliminary phylogenetic analysis indicated that the Qingdao Huiquan low tide magnetotactic bacteria belong to a new genus affiliated with the alpha-subclass of Proteobacteria, suggesting the adaptation of the Magnetotactic bacterial population to the marine tide.
Abstract: Magnetotactic bacteria are a heterologous group of motile prokaryotes, ubiquitous in aquatic habitats and cosmopolitan in distribution. Here, we studied the diversity of magnetotactic bacteria in a seawater pond within an intertidal zone at Huiquan Bay in the China Sea. The pond is composed of a permanently submerged part and a low tide subregion. The magnetotactic bacteria collected from the permanently submerged part display diversity in morphology and taxonomy. In contrast, we found a virtually homogenous population of ovoid-coccoid magnetotactic bacteria in the low tide subregion of the pond. They were bilophotrichously flagellated and exhibited polar magnetotactic behaviour. Almost all cells contained two chains of magnetosomes composed of magnetite crystals. Intriguingly, the combination of restriction fragment length polymorphism analysis (RFLP) and sequencing of cloned 16S rDNA genes from the low tide subregion samples as well as fluorescence in situ hybridization (FISH) revealed the presence of a homogenous population. Moreover, phylogenetic analysis indicated that the Qingdao Huiquan low tide magnetotactic bacteria belong to a new genus affiliated with the alpha-subclass of Proteobacteria. This finding suggests the adaptation of the magnetotactic bacterial population to the marine tide.
TL;DR: P phylogenetic diversity studies of MTB enriched from the Miyun lake near Beijing showed that the result of capillary racetrack-based enrichment might have been biased by the magnetotaxis of magnetotactic bacteria, and it appears that the metagenome-based PCR approach better reflects the original diversity ofMTB in the environmental sample.
Abstract: The racetrack-based PCR approach is widely used in phylogenetic analysis of magnetotactic bacteria (MTB), which are isolated from environmental samples using the capillary racetrack method. To evaluate whether the capillary racetrack-based enrichment can truly reflect the diversity of MTB in the targeted environmental sample, phylogenetic diversity studies of MTB enriched from the Miyun lake near Beijing were carried out, using both the capillary racetrack-based PCR and a modified metagenome-based PCR approach. Magnetotactic cocci were identified in the studied sample using both approaches. Comparative studies showed that three clusters of magnetotactic cocci were revealed by the modified metagenome-based PCR approach, while only one of them (e.g. MYG-22 sequence) was detected by the racetrack-based PCR approach from the studied sample. This suggests that the result of capillary racetrack-based enrichment might have been biased by the magnetotaxis of magnetotactic bacteria. It appears that the metagenome-based PCR approach better reflects the original diversity of MTB in the environmental sample.
TL;DR: A large number of studies on less-well ordered minerals have focused on Fe-, As-, Mn-, Au-, Se- and Cd-precipitates that occur intracellularly, but the biological and environmental function of these particles remains a matter of debate.
Abstract: Thanks to the work of Terrance J. Beveridge and other pioneers in the field of metal–microbe interactions, prokaryotes are well known to sequester metals and other ions intracellularly in various forms. These forms range from poorly ordered deposits of metals to well-ordered mineral crystals. Studies on well-ordered crystalline structures have generally focused on intracellular organelles produced by magnetotactic bacteria that are ubiquitous in terrestrial and marine environments that precipitate Fe3O4 or Fe3S4, Fe-bearing minerals that have magnetic properties and are enclosed in intracellular membranes. In contrast, studies on less-well ordered minerals have focused on Fe-, As-, Mn-, Au-, Se- and Cd-precipitates that occur intracellularly. The biological and environmental function of these particles remains a matter of debate.
TL;DR: Observations of cell membrane invaginations, the trilaminar membrane structure of immature magnetosomes, and empty vesicles together suggested that greigite magnetosome formation begins by invagination of the cell membrane, as has been proposed for magnetite magnetOSomes.
Abstract: The ultrastructure of the greigite magnetosome membrane in the multicellular magnetotactic bacteria "Candidatus Magnetoglobus multicellularis" was studied. Each cell contains 80 membrane-enclosed iron-sulfide magnetosomes.
Cytochemistry methods showed that the magnetosomes are enveloped by a structure whose staining pattern and
dimensions are similar to those of the cytoplasmic membrane, indicating that the magnetosome membrane likely originates from the cytoplasmic membrane. Freeze-fracture showed intramembrane particles in the vesicles surrounding each magnetosome. Observations of cell membrane invaginations, the trilaminar membrane structure of immature magnetosomes, and empty vesicles together suggested that greigite magnetosome formation begins by invagination of the cell membrane, as has been proposed for magnetite magnetosomes.
TL;DR: From the results, it was clear that magnetosomes have more potential in the biomedical applications than synthetic magnetite.
Abstract: Magnetite nanocrystals have been widely used in many fields. Recently, a new magnetite nanocrystals, called magnetosome, has been found in magnetotactic bacteria. In this article, we researched on the properties of magnetosomes in detail, such as crystalline, morphology, crystal-size distributions, vitro cytotoxicity, and magnetic properties and quantified primary amino groups on the magnetosomes membrane surface by fluorescamine assay for the first time. From the results, it was clear that magnetosomes have more potential in the biomedical applications than synthetic magnetite.
TL;DR: A cell surface display system has been developed by expressing hexahistidine residues within the outer coiled loop of the membrane-specific protein (Msp1) of the “Magnetospirillum magneticum” (proposed name) AMB-1 bacterium.
Abstract: Bacterial cell surface display is a widely used technology for bioadsorption and for the development of a variety of screening systems. Magnetotactic bacteria are unique species of bacteria due to the presence of magnetic nanoparticles within them. These intracellular, nanosized (50 to 100 nm) magnetic nanoparticles enable the cells to migrate and be manipulated by magnetic force. In this work, using this unique characteristic and based on whole-genomic and comprehensive proteomic analyses of these bacteria, a cell surface display system has been developed by expressing hexahistidine residues within the outer coiled loop of the membrane-specific protein (Msp1) of the “Magnetospirillum magneticum” (proposed name) AMB-1 bacterium. The optimal display site of the hexahistidine residues was successfully identified via secondary structure prediction, immunofluorescence microscopy, and heavy metal binding assay. The established AMB-1 transformant showed high immunofluorescence response, high Cd2+ binding, and high recovery efficiency in comparison to those of the negative control when manipulated by magnetic force.
TL;DR: Based on the formation process of chains in this reaction system, it is suggested that the localized environments favor the growth of SD nanoparticles, and the strong magnetic dipolar-dipolar interactions lead to the self-assembly ofSD nanoparticles.
Abstract: Magnetite chains with a number of magnetite particles arranged in a line parallel to the outer amorphous carbon coating have been prepared. The sizes of the nanoparticles range from 40 to 120 nm, with nearly identical gaps between every two adjacent particles. The synthesized chains display ferromagnetic properties with several single-magnetic-domain (SD) nanoparticles assembled in an orderly fashion. Based on the formation process of chains in our reaction system, it is suggested that the localized environments favor the growth of SD nanoparticles, and the strong magnetic dipolar–dipolar interactions lead to the self-assembly of SD nanoparticles. This research could offer some useful information in studying the formation mechanism of magnetosome chains and the origin of the special chain-like nanostructures in magnetotactic bacteria.
TL;DR: The results suggested that the geomagnetic field plays an important role in the biomineralization of magnetosomes.
Abstract: Magnetotactic bacteria synthesize intracellular magnetic particles, magnetosomes, which arrange in chain(s) and confer on cell a magnetic dipolar moment. To explore the function of geomagnetic field to magnetotactic bacteria, the effects of hypomagnetic field on magnetosome formation in Magnetospirillum magneticum AMB-1 were studied. Cells were cultivated in a specially designed device where geomagnetic field was reduced by about 100-fold to less than 500nT. AMB-1 cultures were incubated in hypomagnetic field or geomagnetic field. Results showed that hypomagnetic field had no significant effects on the average number of magnetic particles per bacterium and bacterial iron depletion. However, the growth (OD) of cell at stationary-phase was lower and cellular magnetism (Rmag) at exponential growth phase was higher than that of bacteria cultivated in geomagnetic field. Statistic results on transmission electron microscopy (TEM) micrographs showed that the average size of magnetic particles in AMB-1 cells in hypomagnetic field group was larger than that of in geomagnetic field group and more ratio of larger-size magnetic particles (>50 nm) was observed when cultivated 16 h under hypomagnetic field. Furthermore, the influences of hypomagnetic field on gene expression were studied in AMB-1 cells. Quantitative RT-PCR results showed that hypomagnetic field up-regulated mms13 ,d own-regulated mms6 and had no effect on magA .T ogether, the results showed that hypomagnetic field could affect the growth of AMB-1 at the stationaryphase, the crystallization process of magnetosomes, and mms13, mms6 expressions. In addition, our results suggested that the geomagnetic field plays an important role in the biomineralization of magnetosomes.
01 Jan 2008
TL;DR: The mutant phenotypes of the five mutants include the complete absence of magnetosomes, elongate crystals, reduced numbers of crystals and incomplete mineralization, which extends the environmental range of MB to astro- and paleobiologically relevant environments.
Abstract: Magnetotactic bacteria (MB) contain intracellular magnetic crystals of iron oxides and/or iron sulfides. These crystals and the membranes which enclose them are together known as magnetosomes. The crystals formed by MB fall into a narrow size range and have species-specific crystal morphologies. Magnetosomes are physically connected to the rest of the cell by actin-like filaments that are thought to allow the MB to take advantage of their passive orientation in the Earth’s magnetic field to navigate more efficiently across chemical gradients. The large excess of crystals in most strains suggests that magnetosomes may also function as an iron reservoir or as a redox battery. This thesis describes a number of investigations of the MB. First, a set of genes was identified as being conserved uniquely among the MB by comparative genomics. This method was validated by finding many of the genes already known to be involved in magnetotaxis. Many additional genes were identified and some of these genes were found to cluster together. Three of these clusters were genetically interrupted to determine their role in magnetite biomineralization. Second, a transposon mutagenesis was undertaken to identify genes necessary for the magnetic phenotype of MB. Out of 5809 mutants screened, nineteen were found to be non- or partially magnetic. Fourteen of these have insertion sites in genes known to be involved in magnetotaxis. Five more were found to have insertions in previously unsuspected genes. The mutant phenotypes of the five mutants include the complete absence of magnetosomes, elongate crystals, reduced numbers of crystals and incomplete mineralization. These mutant strains were used to develop ferromagnetic resonance theory of isolated single-domain particles and biogenic particle identification. Third, MB were discovered in hot springs and in hyper-saline, hyper-alkaline Mono Lake, CA. This extends the environmental range of MB to astro- and paleobiologically relevant environments. Magnetotactic Archaea were tentatively identified from Mono Lake, CA and are the first magnetotactic representatives of that domain.
TL;DR: The number of magnetosomes in ATCC 23270 and the magnetotaxis of cells were significantly related to the expression level of these three genes, suggesting that these genes were related with the iron transport during the process of magnetOSome formation in A. ferrooxidans.
TL;DR: In this article, the role of ferrihydrite in magnetosome synthesis in magnetotactic bacteria was discussed based on the results of laser Raman spectroscopic measurements.
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 major Raman signals at 662 cm � 1 and 740 cm � 1 were observed. The former was assigned to the Raman signal of magnetite and the latter, to that of ferrihydrite. The Raman signal of ferrihydrite was observed not only in the membrane fraction, but also in the cytoplasmic fraction. Based on the results, the role of ferrihydrite in magnetosome synthesis in the magnetotactic bacteria was discussed. [doi:10.2320/matertrans.MER2007333]
01 Jan 2008
TL;DR: A bold “Functional Control by Codon Bias” (FCCB) hypothesis suggesting that protein function is controlled by codons responsible for its primary sequence in addition to the primary sequence itself is proposed.
Abstract: Directed and controlled motion of small (micron sized and smaller) objects in fluid systems is an active area of research in biomedical nanotechnology. Magnetotactic bacteria undergo a kind of directed and control motion called magneto-aerotaxis by utilizing nanopropellers (flagella) and nanomagnets. While studying the role of nanomagnets in magnetic-bacterial motility to investigate nano-scale control of motion, we have serendipitously discovered a major protein specific codon bias residing in the Magnetospirillum magnetotacticum genome. While primary sequences of flagellar, iron uptake and the house-keeping RNA polymerase proteins are identical in magnetic bacteria compared to E. coli and mammalian cells, there is no genetic similarity for flagellar and iron uptake proteins. In contrast, the house-keeping RNA polymerase in magnetic bacteria shows complete genetic similarity also. Surprisingly, the lack of any genetic homology in flagellar and iron uptake proteins, in spite of identical primary amino acid sequences in different organisms, is a consequence of a protein specific codon bias, thereby resulting in non-identical gene sequences. This codon bias is directly correlated with differences in protein functions specific to magnetic bacteria. Based on our findings, we propose a bold “Functional Control by Codon Bias” (FCCB) hypothesis suggesting that protein function is controlled by codons responsible for its primary sequence in addition to the primary sequence itself. The remarkable feature of our proposal is that even if primary sequences of two proteins are identical, utilization of different codons to express those sequences directly affects the function of the proteins.
20 Mar 2008
TL;DR: In this article, the authors adapted an experimental technique for characterizing the magnetotactic bacteria and simplified it by transferring the burden to literal and numerical computation, which is an advantageous tradeoff.
Abstract: We adapted an experimental technique for characterizing the magnetotactic bacteria and simplified it by transferring the burden to literal and numerical computation, which is an advantageous tradeoff. In a magnetic field the bacteria tend to orient their magnetic axes along the direction of the magnetic field, resulting in an anisotropic distribution of the orientation and, consequently, a significant change of the directional distribution of the scattering efficiency of light. We made a simple experimental arrangement for measuring the scattering efficiency of light by the bacteria in certain directions for various values of an external magnetic field applied to the bacteria. We inferred from the fitting of the experimental to the theoretical data the most probable values for the magnetic moment and the dimensions of the magnetotactic bacteria. In the experiments a wild-type Magnetospirillum gryphiswaldense strain was used.
01 Jan 2008
TL;DR: The bacteria isolated from the sediments along the littoral zone of the Lonar Lake were found to be predominantly rods with some coccoidal forms, and showed a typical response in the form of movement towards the South Pole of the magnet and precise alignment at the edge of the hanging drop.
Abstract: Magnetotactic bacteria (MTB) are known to be major constituents of natural microbial communities in sediments and chemically stratified water columns such as those found in lakes and oceans and typically, such bacteria in the northern hemisphere are known to move to the magnetic South. Because of their potential to accumulate and precipitate iron minerals, these bacteria are assumed to have a great impact on biogeochemical cycling in natural sediments. A broad diversity of morphological forms of these bacteria with their unique character ofmagnetosomes' are today known and they have generated tremendous interest among microbiologists and biotechnologists as well as other interdisciplinary researchers. The Lonar Lake, formed in a meteorite impact crater in the Buldhana District of Maharashtra is a closed basin lake and is a unique environment characterized by high alkalinity (pH 9.5 - 10.0, CaCO3 alkalinity - 3.6 g/L) and salinity. Evidences of magnetic activity in the surrounding rocks and soil are also found. Several studies on the microbial biodiversity of this environment have been carried out previously but there are no reports of magnetotactic bacteria. This study reports the isolation and characterization of such magnetotactic bacteria from the sediments along the littoral zone of the Lonar Lake. The bacteria isolated bymagnetic collection' and thecapillary racetrack' methods were found to be predominantly rods with some coccoidal forms. Their response to a magnetic field was observed employing thehanging drop' technique under a microscope and the use of a semisolid medium. The bacteria showed a typical response in the form of movement towards the South Pole of the magnet and precise alignment at the edge of the hanging drop. Further studies on their characters and confirmation of the accumulation of intracellular magnetosomes are in progress.