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Dirk Schüler - One of the best experts on this subject based on the ideXlab platform.
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a compass to boost navigation cell biology of bacterial Magnetotaxis
2020Co-Authors: Frankdietrich Muller, Dirk Schüler, Daniel PfeifferAbstract:ABSTRACT Magnetotactic bacteria are aquatic or sediment-dwelling microorganisms able to take advantage of the Earth’s magnetic field for directed motility. The source of this amazing trait is magnetosomes, unique organelles used to synthesize single nanometer-sized crystals of magnetic iron minerals that are queued up to build an intracellular compass. Most of these microorganisms cannot be cultivated under controlled conditions, much less genetically engineered, with only few exceptions. However, two of the genetically amenable Magnetospirillum species have emerged as tractable model organisms to study magnetosome formation and Magnetotaxis. Recently, much has been revealed about the process of magnetosome biogenesis and dedicated structures for magnetosome dynamics and positioning, which suggest an unexpected cellular intricacy of these organisms. In this minireview, we summarize new insights and place the molecular mechanisms of magnetosome formation in the context of the complex cell biology of Magnetospirillum spp. First, we provide an overview on magnetosome vesicle synthesis and magnetite biomineralization, followed by a discussion of the perceptions of dynamic organelle positioning and its biological implications, which highlight that magnetotactic bacteria have evolved sophisticated mechanisms to construct, incorporate, and inherit a unique navigational device. Finally, we discuss the impact of Magnetotaxis on motility and its interconnection with chemotaxis, showing that magnetotactic bacteria are outstandingly adapted to lifestyle and habitat.
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Single-step transfer of biosynthetic operons endows a non-magnetotactic Magnetospirillum strain from wetland with magnetosome biosynthesis.
2020Co-Authors: Marina V. Dziuba, René Uebe, Theresa Zwiener, Dirk SchülerAbstract:The magnetotactic lifestyle represents one of the most complex traits found in many bacteria from aquatic environments and depends on magnetic organelles, the magnetosomes. Genetic transfer of magnetosome biosynthesis operons to a non-magnetotactic bacterium has only been reported once so far, but it is unclear whether this may also occur in other recipients. Besides magnetotactic species from freshwater, the genus Magnetospirillum of the Alphaproteobacteria also comprises a number of strains lacking magnetosomes, which are abundant in diverse microbial communities. Their close phylogenetic interrelationships raise the question whether the non-magnetotactic magnetospirilla may have the potential to (re)gain a magnetotactic lifestyle upon acquisition of magnetosome gene clusters. Here, we studied the transfer of magnetosome gene operons into several non-magnetotactic environmental magnetospirilla. Single-step transfer of a compact vector harbouring >30 major magnetosome genes from M. gryphiswaldense induced magnetosome biosynthesis in a Magnetospirillum strain from a constructed wetland. However, the resulting magnetic cellular alignment was insufficient for efficient Magnetotaxis under conditions mimicking the weak geomagnetic field. Our work provides insights into possible evolutionary scenarios and potential limitations for the dissemination of Magnetotaxis by horizontal gene transfer and expands the range of foreign recipients that can be genetically magnetized.
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quantifying the benefit of a dedicated magnetoskeleton in bacterial Magnetotaxis by live cell motility tracking and soft agar swimming assay
2020Co-Authors: Daniel Pfeiffer, Dirk SchülerAbstract:The alphaproteobacterium Magnetospirillum gryphiswaldense has the intriguing ability to navigate within magnetic fields, a behavior named Magnetotaxis, governed by the formation of magnetosomes, intracellular membrane-enveloped crystals of magnetite. Magnetosomes are aligned in chains along the cell's motility axis by a dedicated multipart cytoskeleton ("magnetoskeleton"); however, precise estimates of its significance for Magnetotaxis have not been reported. Here, we estimated the alignment of strains deficient in various magnetoskeletal constituents by live-cell motility tracking within defined magnetic fields ranging from 50 μT (reflecting the geomagnetic field) up to 400 μT. Motility tracking revealed that ΔmamY and ΔmamK strains (which assemble mispositioned and fragmented chains, respectively) are partially impaired in Magnetotaxis, with approximately equal contributions of both proteins. This impairment was reflected by a required magnetic field strength of 200 μT to achieve a similar degree of alignment as for the wild-type strain in a 50-μT magnetic field. In contrast, the ΔmamJ strain, which predominantly forms clusters of magnetosomes, was only weakly aligned under any of the tested field conditions and could barely be distinguished from a nonmagnetic mutant. Most findings were corroborated by a soft agar swimming assay to analyze Magnetotaxis based on the degree of distortion of swim halos formed in magnetic fields. Motility tracking further revealed that swimming speeds of M. gryphiswaldense are highest within the field strength equaling the geomagnetic field. In conclusion, magnetic properties and intracellular positioning of magnetosomes by a dedicated magnetoskeleton are required and optimized for bacterial Magnetotaxis and most efficient locomotion within the geomagnetic field.IMPORTANCE In Magnetospirillum gryphiswaldense, magnetosomes are aligned in quasi-linear chains in a helical cell by a complex cytoskeletal network, including the actin-like MamK and adapter MamJ for magnetosome chain concatenation and segregation and MamY to position magnetosome chains along the shortest cellular axis of motility. Magnetosome chain positioning is assumed to be required for efficient magnetic navigation; however, the significance and contribution of all key constituents have not been quantified within defined and weak magnetic fields reflecting the geomagnetic field. Employing two different motility-based methods to consider the flagellum-mediated propulsion of cells, we depict individual benefits of all magnetoskeletal constituents for Magnetotaxis. Whereas lack of mamJ resulted almost in an inability to align cells in weak magnetic fields, an approximately 4-fold-increased magnetic field strength was required to compensate for the loss of mamK or mamY In summary, the magnetoskeleton and optimal positioning of magnetosome chains are required for efficient Magnetotaxis.
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crystal structure of the magnetobacterial protein mtxa c terminal domain reveals a new sequence structure relationship
2015Co-Authors: G Davidov, Dirk Schüler, Frankdietrich Muller, Jens Baumgartner, Ronit Bitton, Damien Faivre, Raz ZarivachAbstract:Magnetotactic bacteria (MTB) are a diverse group of aquatic bacteria that have the Magnetotaxis ability to align themselves along the geomagnetic field lines and to navigate to a microoxic zone at the bottom of chemically stratified natural water. This special navigation is the result of a unique linear assembly of a specialized organelle, the magnetosome, which contains a biomineralized magnetic nanocrystal enveloped by a cytoplasmic membrane. The Magnetospirillum gryphiswaldense MtxA protein (MGR_0208) was suggested to play a role in bacterial Magnetotaxis due to its gene location in an operon together with putative signal transduction genes. Since no homology is found for MtxA, and to better understand the role and function of MtxA in MTB’s Magnetotaxis, we initiated structural and functional studies of MtxA via X-ray crystallography and deletion mutagenesis. Here, we present the crystal structure of the MtxA C-terminal domain and provide new insights into its sequence-structure relationship.
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polarity of bacterial Magnetotaxis is controlled by aerotaxis through a common sensory pathway
2014Co-Authors: Felix Popp, Judith P Armitage, Dirk SchülerAbstract:Most motile bacteria navigate within gradients of external chemical stimuli by regulating the length of randomly oriented swimming episodes. Magnetotactic bacteria are characterized by chains of intracellular ferromagnetic nanoparticles and their ability to sense the geomagnetic field, which is believed to facilitate directed motion, but is not well understood at the behavioural and molecular level. Here, we show that cells of Magnetospirillum gryphiswaldense unexpectedly display swimming polarity that depends on aerotactic signal transduction through one of its four chemotaxis operons (cheOp1). Growth of cells in magnetic fields superimposed on oxygen gradients results in a gradual inherited bias of swimming runs with one of the cell poles leading, such that the resulting overall swimming direction of entire populations can be reversed by changes in oxygen concentration. These findings clearly show that there is a direct molecular link between aerotactic sensing and the determination of magnetotactic polarity, through the sensory pathway, CheOp1.
Christopher T. Lefèvre - One of the best experts on this subject based on the ideXlab platform.
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Repeated horizontal gene transfers triggered parallel evolution of Magnetotaxis in two evolutionary divergent lineages of magnetotactic bacteria
2020Co-Authors: Caroline L. Monteil, Denis S. Grouzdev, Guy Perrière, Béatrice Alonso, Zoé Rouy, Stéphane Cruveiller, Nicolas Ginet, David Pignol, Christopher T. LefèvreAbstract:Under the same selection pressures, two genetically divergent populations may evolve in parallel toward the same adaptive solutions. Here, we hypothesized that Magnetotaxis (i.e., magnetically guided chemotaxis) represents a key adaptation to micro-oxic habitats in aquatic sediments and that its parallel evolution homogenized the phenotypes of two evolutionary divergent clusters of freshwater spirilla. All magnetotactic bacteria affiliated to the Magnetospirillum genus (Alphaproteobacteria class) biomineralize the same magnetic particle chains and share highly similar physiological and ultrastructural features. We looked for the processes that could have contributed at shaping such an evolutionary pattern by reconciling species and gene trees using newly sequenced genomes of Magnetospirillum related bacteria. We showed that repeated horizontal gene transfers and homologous recombination of entire operons contributed to the parallel evolution of Magnetotaxis. We propose that such processes could represent a more parsimonious and rapid solution for adaptation compared with independent and repeated de novo mutations, especially in the case of traits as complex as Magnetotaxis involving tens of interacting proteins. Besides strengthening the idea about the importance of such a function in micro-oxic habitats, these results reinforce previous observations in experimental evolution suggesting that gene flow could alleviate clonal interference and speed up adaptation under some circumstances.
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Complete Genome Sequence of Strain BW-2, a Magnetotactic Gammaproteobacterium in the Family Ectothiorhodospiraceae, Isolated from a Brackish Spring in Death Valley, California.
2020Co-Authors: Corey Geurink, Fernanda Abreu, Christopher T. Lefèvre, Caroline L. Monteil, Viviana Morillo-lopez, Dennis A. Bazylinski, Denis TrubitsynAbstract:ABSTRACT We report the complete 4.1-Mb genome sequence of strain BW-2, a magnetotactic, sulfur-oxidizing rod, belonging to the family Ectothiorhodospiraceae of the class Gammaproteobacteria, that biomineralizes membrane-bounded magnetite nanocrystals in its magnetosomes. This genome sequence, in comparison with those of other magnetotactic bacteria, is essential for understanding the origin and evolution of Magnetotaxis and magnetosome biomineralization.
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Genomic study of a novel magnetotactic Alphaproteobacteria uncovers the multiple ancestry of Magnetotaxis
2018Co-Authors: Caroline L. Monteil, Guy Perrière, Béatrice Alonso, Stéphane Cruveiller, Nicolas Ginet, David Pignol, Nicolas Menguy, Nicolas Waisbord, Christopher T. LefèvreAbstract:Ecological and evolutionary processes involved in magnetotactic bacteria (MTB) adaptation to their environment have been a matter of debate for many years. Ongoing efforts for their characterization are progressively contributing to understand these processes, including the genetic and molecular mechanisms responsible for biomineralization. Despite numerous culture-independent MTB characterizations, essentially within the Proteobacteria phylum, only few species have been isolated in culture because of their complex growth conditions. Here, we report a newly cultivated magnetotactic, microaerophilic and chemoorganoheterotrophic bacterium isolated from the Mediterranean Sea in Marseille, France: Candidatus Terasakiella magnetica strain PR-1 that belongs to an Alphaproteobacteria genus with no magnetotactic relative. By comparing the morphology and the whole genome shotgun sequence of this MTB with those of closer relatives, we brought further evidence that the apparent vertical ancestry of magnetosome genes suggested by previous studies within Alphaproteobacteria hides a more complex evolutionary history involving horizontal gene transfers and/or duplication events before and after the emergence of Magnetospirillum, Magnetovibrio and Magnetospira genera. A genome-scale comparative genomics analysis identified several additional candidate functions and genes that could be specifically associated to MTB lifestyle in this class of bacteria.
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MamA as a Model Protein for Structure-Based Insight into the Evolutionary Origins of Magnetotactic Bacteria
2015Co-Authors: Natalie Zeytuni, Christopher T. Lefèvre, Samuel Cronin, Pascal Arnoux, Dror Baran, Zvi Shtein, Geula Davidov, Raz ZarivachAbstract:MamA is a highly conserved protein found in magnetotactic bacteria (MTB), a diverse group of prokaryotes capable of navigating according to magnetic fields - an ability known as Magnetotaxis. Questions surround the acquisition of this magnetic navigation ability; namely, whether it arose through horizontal or vertical gene transfer. Though its exact function is unknown, MamA surrounds the magnetosome, the magnetic organelle embedding a biomineralised nanoparticle and responsible for Magnetotaxis. Several structures for MamA from a variety of species have been determined and show a high degree of structural similarity. By determining the structure of MamA from Desulfovibrio magneticus RS-1 using X-ray crystallography, we have opened up the structure-sequence landscape. As such, this allows us to perform structural-and phylogenetic-based analyses using a variety of previously determined MamA from a diverse range of MTB species across various phylogenetic groups. We found that MamA has remained remarkably constant throughout evolution with minimal change between different taxa despite sequence variations. These findings, coupled with the generation of phylogenetic trees using both amino acid sequences and 16S rRNA, indicate that Magnetotaxis likely did not spread via horizontal gene transfer and instead has a significantly earlier, primordial origin.
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Phylogenetic significance of composition and crystal morphology of magnetosome minerals.
2013Co-Authors: Mihály Pósfai, Christopher T. Lefèvre, Dennis A. Bazylinski, Denis Trubitsyn, Richard B. FrankelAbstract:Magnetotactic bacteria (MTB) biomineralize magnetosomes, nano-scale crystals of magnetite or greigite in membrane enclosures, that comprise a permanent magnetic dipole in each cell. MTB control the mineral composition, habit, size, and crystallographic orientation of the magnetosomes, as well as their arrangement within the cell. Studies involving magnetosomes that contain mineral and biological phases require multidisciplinary efforts. Here we use crystallographic, genomic and phylogenetic perspectives to review the correlations between magnetosome mineral habits and the phylogenetic affiliations of MTB, and show that these correlations have important implications for the evolution of magnetosome synthesis, and thus Magnetotaxis.
Dennis A. Bazylinski - One of the best experts on this subject based on the ideXlab platform.
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Magnetotaxis in prokaryotes
2020Co-Authors: Fernanda Abreu, Denis Trubitsyn, Viviana Morillo, Dennis A. BazylinskiAbstract:Magnetotaxis refers to the behaviour of some motile, aquatic, bacteria that orient and swim along magnetic field lines. These microorganisms, called magnetotactic bacteria (MTB), contain intracellular structures known as magnetosomes, which are nano-sized, magnetic, iron-mineral crystals, each enveloped by a biological (phospholipid bilayer) membrane. Magnetosomes are usually arranged in chains within the cell, providing it with a permanent magnetic dipole moment that facilitates location and retention in the cell's preferred habitat at or below the oxic–anoxic interface in the water column or sediment. Although all MTB are motile by means of flagella and have a cell wall structure characteristic of Gram-negative bacteria, their diversity is reflected by the large number of different morphotypes found in environmental samples of water or sediment, and by phylogenetic analysis of both cultured and uncultured organisms. Key Concepts: Prokaryotes (bacteria), like eukaryotes, internally compartmentalise and contain organelles. The prokaryotic flagellum rotates clockwise and counter clockwise thereby propelling the cell during swimming. Magnetotaxis is bacterial motility directed by a magnetic field. Magnetotactic bacteria contain intracellular, nano-scale, membrane-enveloped, magnetic iron-mineral crystals called magnetosomes. Magnetosomes impart a permanent magnetic dipole moment to cells of magnetotactic bacteria causing them to behave as miniature, motile, compass needles. Magnetotaxis works in conjunction with aerotaxis to increase energy transduction in magnetotactic bacteria. Genes for magnetosome formation are clustered in a region of the genomes of magnetotactic bacteria known as a magnetosome gene or genomic island. Magnetotactic bacteria are important in the cycling of a number of important elements including carbon, iron, nitrogen and sulfur. Keywords: aerotaxis; biomineralisation; chemically stratified environments; flagellar motion; greigite; magnetite; magnetosome; magnetotactic bacteria; Magnetotaxis
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Complete Genome Sequence of Strain BW-2, a Magnetotactic Gammaproteobacterium in the Family Ectothiorhodospiraceae, Isolated from a Brackish Spring in Death Valley, California.
2020Co-Authors: Corey Geurink, Fernanda Abreu, Christopher T. Lefèvre, Caroline L. Monteil, Viviana Morillo-lopez, Dennis A. Bazylinski, Denis TrubitsynAbstract:ABSTRACT We report the complete 4.1-Mb genome sequence of strain BW-2, a magnetotactic, sulfur-oxidizing rod, belonging to the family Ectothiorhodospiraceae of the class Gammaproteobacteria, that biomineralizes membrane-bounded magnetite nanocrystals in its magnetosomes. This genome sequence, in comparison with those of other magnetotactic bacteria, is essential for understanding the origin and evolution of Magnetotaxis and magnetosome biomineralization.
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magnetosome gene duplication as an important driver in the evolution of Magnetotaxis in the alphaproteobacteria
2019Co-Authors: Wenyan Zhang, Dennis A. Bazylinski, Wensi Zhang, Weijia Zhang, Hongmiao Pan, Yongxin Pan, Tian Xiao, Wei LinAbstract:ABSTRACT The evolution of microbial magnetoreception (or Magnetotaxis) is of great interest in the fields of microbiology, evolutionary biology, biophysics, geomicrobiology, and geochemistry. Current genomic data from magnetotactic bacteria (MTB), the only prokaryotes known to be capable of sensing the Earth’s geomagnetic field, suggests an ancient origin of Magnetotaxis in the domain Bacteria. Vertical inheritance, followed by multiple independent magnetosome gene cluster loss, is considered to be one of the major forces that drove the evolution of Magnetotaxis at or above the class or phylum level, although the evolutionary trajectories at lower taxonomic ranks (e.g., within the class level) remain largely unstudied. Here we report the isolation, cultivation, and sequencing of a novel magnetotactic spirillum belonging to the genus Terasakiella (Terasakiella sp. strain SH-1) within the class Alphaproteobacteria. The complete genome sequence of Terasakiella sp. strain SH-1 revealed an unexpected duplication event of magnetosome genes within the mamAB operon, a group of genes essential for magnetosome biomineralization and Magnetotaxis. Intriguingly, further comparative genomic analysis suggests that the duplication of mamAB genes is a common feature in the genomes of alphaproteobacterial MTB. Taken together, with the additional finding that gene duplication appears to have also occurred in some magnetotactic members of the Deltaproteobacteria, our results indicate that gene duplication plays an important role in the evolution of Magnetotaxis in the Alphaproteobacteria and perhaps the domain Bacteria. IMPORTANCE A diversity of organisms can sense the geomagnetic field for the purpose of navigation. Magnetotactic bacteria are the most primitive magnetism-sensing organisms known thus far and represent an excellent model system for the study of the origin, evolution, and mechanism of microbial magnetoreception (or Magnetotaxis). The present study is the first report focused on magnetosome gene cluster duplication in the Alphaproteobacteria, which suggests the important role of gene duplication in the evolution of Magnetotaxis in the Alphaproteobacteria and perhaps the domain Bacteria. A novel scenario for the evolution of Magnetotaxis in the Alphaproteobacteria is proposed and may provide new insights into evolution of magnetoreception of higher species.
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origin of microbial biomineralization and Magnetotaxis during the archean
2017Co-Authors: Wei Lin, Dennis A. Bazylinski, Greig A Paterson, Qiyun Zhu, Yinzhao Wang, Evguenia Kopylova, Rob Knight, Rixiang Zhu, Joseph L KirschvinkAbstract:Microbes that synthesize minerals, a process known as microbial biomineralization, contributed substantially to the evolution of current planetary environments through numerous important geochemical processes. Despite its geological significance, the origin and evolution of microbial biomineralization remain poorly understood. Through combined metagenomic and phylogenetic analyses of deep-branching magnetotactic bacteria from the Nitrospirae phylum, and using a Bayesian molecular clock-dating method, we show here that the gene cluster responsible for biomineralization of magnetosomes, and the arrangement of magnetosome chain(s) within cells, both originated before or near the Archean divergence between the Nitrospirae and Proteobacteria. This phylogenetic divergence occurred well before the Great Oxygenation Event. Magnetotaxis likely evolved due to environmental pressures conferring an evolutionary advantage to navigation via the geomagnetic field. Earth’s dynamo must therefore have been sufficiently strong to sustain microbial Magnetotaxis in the Archean, suggesting that Magnetotaxis coevolved with the geodynamo over geological time.
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north seeking magnetotactic gammaproteobacteria in the southern hemisphere
2016Co-Authors: Pedro Leão, Fernanda Abreu, Dennis A. Bazylinski, Lia C R S Teixeira, Jefferson Cypriano, Marcos Farina, Ulysses LinsAbstract:ABSTRACT Magnetotactic bacteria (MTB) comprise a phylogenetically diverse group of prokaryotes capable of orienting and navigating along magnetic field lines. Under oxic conditions, MTB in natural environments in the Northern Hemisphere generally display north-seeking (NS) polarity, swimming parallel to the Earth9s magnetic field lines, while those in the Southern Hemisphere generally swim antiparallel to magnetic field lines (south-seeking [SS] polarity). Here, we report a population of an uncultured, monotrichously flagellated, and vibrioid MTB collected from a brackish lagoon in Brazil in the Southern Hemisphere that consistently exhibits NS polarity. Cells of this organism were mainly located below the oxic-anoxic interface (OAI), suggesting it is capable of some type of anaerobic metabolism. Magnetosome crystalline habit and composition were consistent with elongated prismatic magnetite (Fe 3 O 4 ) particles. Phylogenetic analysis based on 16S rRNA gene sequencing indicated that this organism belongs to a distinct clade of the Gammaproteobacteria class. The presence of NS MTB in the Southern Hemisphere and the previously reported finding of SS MTB in the Northern Hemisphere reinforce the idea that Magnetotaxis is more complex than we currently understand and may be modulated by factors other than O 2 concentration and redox gradients in sediments and water columns. IMPORTANCE Magnetotaxis is a navigational mechanism used by magnetotactic bacteria to move along geomagnetic field lines and find an optimal position in chemically stratified sediments. For that, magnetotactic bacteria swim parallel to the geomagnetic field lines under oxic conditions in the Northern Hemisphere, whereas those in the Southern Hemisphere swim antiparallel to magnetic field lines. A population of uncultured vibrioid magnetotactic bacteria was discovered in a brackish lagoon in the Southern Hemisphere that consistently swim northward, i.e., the opposite of the overwhelming majority of other Southern Hemisphere magnetotactic bacteria. This finding supports the idea that Magnetotaxis is more complex than previously thought.
Mihály Pósfai - One of the best experts on this subject based on the ideXlab platform.
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critical single domain grain sizes in chains of interacting greigite particles implications for magnetosome crystals
2013Co-Authors: Adrian R. Muxworthy, Andrew P. Roberts, Liao Chang, Michael Winklhofer, Wyn Williams, Mihály PósfaiAbstract:Magnetotactic bacteria contain chains of magnetically interacting crystals (magnetosomes), which aid navigation (Magnetotaxis). To improve the efficiency of Magnetotaxis, magnetosome crystals (which can consist of magnetite or greigite) should be magnetically stable single domain (SD) particles. Larger particles subdivide into nonuniform multidomain (MD) magnetic structures that produce weaker magnetic signals, while small SD particles become magnetically unstable due to thermal fluctuations and exhibit superparamagnetic (SP) behavior. In this study, we determined the stable SD range as a function of grain elongation and interparticle separation for chains of identical greigite grains using fundamental parameters recently determined for greigite. Interactions significantly increase the stable SD range. For example, for cube-shaped greigite grains the upper stable SD threshold size is increased from 107 nm for isolated grains to 204 nm for touching grains arranged in chains. The larger critical SD grain size for greigite means that, compared to magnetite magnetosomes, greigite magnetosomes can produce larger magnetic signals without the need for intergrain interactions.
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Phylogenetic significance of composition and crystal morphology of magnetosome minerals.
2013Co-Authors: Mihály Pósfai, Christopher T. Lefèvre, Dennis A. Bazylinski, Denis Trubitsyn, Richard B. FrankelAbstract:Magnetotactic bacteria (MTB) biomineralize magnetosomes, nano-scale crystals of magnetite or greigite in membrane enclosures, that comprise a permanent magnetic dipole in each cell. MTB control the mineral composition, habit, size, and crystallographic orientation of the magnetosomes, as well as their arrangement within the cell. Studies involving magnetosomes that contain mineral and biological phases require multidisciplinary efforts. Here we use crystallographic, genomic and phylogenetic perspectives to review the correlations between magnetosome mineral habits and the phylogenetic affiliations of MTB, and show that these correlations have important implications for the evolution of magnetosome synthesis, and thus Magnetotaxis.
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Magnetic properties, microstructure, composition, and morphology of greigite nanocrystals in magnetotactic bacteria from electron holography and tomography
2006Co-Authors: Takeshi Kasama, Peter R. Buseck, Richard B. Frankel, Mihály Pósfai, R.k.k. Chong, Anna P. Finlayson, R. E. Dunin-borkowskiAbstract:Magnetotactic bacteria comprise several aquatic species that orient and migrate along geomagnetic Þ eld lines. This behavior is based on the presence of intracellular ferrimagnetic grains of the minerals magnetite (Fe3O4) or greigite (Fe3S4). Whereas the structural and magnetic properties of magnetite magnetosomes have been studied extensively, the properties of greigite magnetosomes are less well known. Here we present a study of the magnetic microstructures, chemical compositions, and threedimensional morphologies and positions of Fe-sulÞ de crystals in air-dried cells of magnetotactic bacteria. Data were obtained using several transmission electron microscopy techniques that include electron holography, energy-Þ ltered imaging, electron tomography, selected-area electron diffraction, and high-resolution imaging. The studied rod-shaped cells typically contain multiple chains of greigite magnetosomes that have random shapes and orientations. Many of the greigite crystals appear to be only weakly magnetic, because the direction of their magnetic induction is almost parallel to the electron beam. Nevertheless, the magnetosomes collectively comprise a permanent magnetic dipole moment that is sufÞ cient for Magnetotaxis. One of the cells, which is imaged at the point of dividing, contains multiple chains of both equidimensional Fe-sulÞ de and elongated Fe-oxide crystals. The equidimensional and elongated crystals have magnetic properties that are consistent with those of greigite and magnetite, respectively. These results can be useful for obtaining a better understanding of the function of Magnetotaxis in sulÞ de-producing cells, and they have implications for the interpretation of the paleomagnetic signals of greigite-bearing sedimentary rocks.
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2006Co-Authors: Takeshi Kasama, Peter R. Buseck, Richard B. Frankel, Mihály Pósfai, R.k.k. Chong, Anna P. Finlayson, R. E. Dunin-borkowskiAbstract:ABSTRACT Magnetotactic bacteria comprise several aquatic species that orient and migrate along geomagnetic Þ eld lines. This behavior is based on the presence of intracellular ferrimagnetic grains of the minerals magnetite (Fe 3 O 4 ) or greigite (Fe 3 S 4 ). Whereas the structural and magnetic properties of magnetite magnetosomes have been studied extensively, the properties of greigite magnetosomes are less well known. Here we present a study of the magnetic microstructures, chemical compositions, and threedimensional morphologies and positions of Fe-sulÞ de crystals in air-dried cells of magnetotactic bacteria. Data were obtained using several transmission electron microscopy techniques that include electron holography, energy-Þ ltered imaging, electron tomography, selected-area electron diffraction, and high-resolution imaging. The studied rod-shaped cells typically contain multiple chains of greigite magnetosomes that have random shapes and orientations. Many of the greigite crystals appear to be only weakly magnetic, because the direction of their magnetic induction is almost parallel to the electron beam. Nevertheless, the magnetosomes collectively comprise a permanent magnetic dipole moment that is sufÞ cient for Magnetotaxis. One of the cells, which is imaged at the point of dividing, contains multiple chains of both equidimensional Fe-sulÞ de and elongated Fe-oxide crystals. The equidimensional and elongated crystals have magnetic properties that are consistent with those of greigite and magnetite, respectively. These results can be useful for obtaining a better understanding of the function of Magnetotaxis in sulÞ de-producing cells, and they have implications for the interpretation of the paleomagnetic signals of greigite-bearing sedimentary rocks
Wyn Williams - One of the best experts on this subject based on the ideXlab platform.
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critical single domain grain sizes in chains of interacting greigite particles implications for magnetosome crystals
2013Co-Authors: Adrian R. Muxworthy, Andrew P. Roberts, Liao Chang, Michael Winklhofer, Wyn Williams, Mihály PósfaiAbstract:Magnetotactic bacteria contain chains of magnetically interacting crystals (magnetosomes), which aid navigation (Magnetotaxis). To improve the efficiency of Magnetotaxis, magnetosome crystals (which can consist of magnetite or greigite) should be magnetically stable single domain (SD) particles. Larger particles subdivide into nonuniform multidomain (MD) magnetic structures that produce weaker magnetic signals, while small SD particles become magnetically unstable due to thermal fluctuations and exhibit superparamagnetic (SP) behavior. In this study, we determined the stable SD range as a function of grain elongation and interparticle separation for chains of identical greigite grains using fundamental parameters recently determined for greigite. Interactions significantly increase the stable SD range. For example, for cube-shaped greigite grains the upper stable SD threshold size is increased from 107 nm for isolated grains to 204 nm for touching grains arranged in chains. The larger critical SD grain size for greigite means that, compared to magnetite magnetosomes, greigite magnetosomes can produce larger magnetic signals without the need for intergrain interactions.
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critical superparamagnetic single domain grain sizes in interacting magnetite particles implications for magnetosome crystals
2009Co-Authors: Adrian R. Muxworthy, Wyn WilliamsAbstract: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.
