Showing papers on "Magnetotactic bacteria published in 2006"

Magnetosomes Are Cell Membrane Invaginations Organized by the Actin-Like Protein MamK

Abstract: Magnetosomes are membranous bacterial organelles sharing many features of eukaryotic organelles. Using electron cryotomography, we found that magnetosomes are invaginations of the cell membrane flanked by a network of cytoskeletal filaments. The filaments appeared to be composed of MamK, a homolog of the bacterial actin-like protein MreB, which formed filaments in vivo. In a mamK deletion strain, the magnetosome-associated cytoskeleton was absent and individual magnetosomes were no longer organized into chains. Thus, it seems that prokaryotes can use cytoskeletal filaments to position organelles within the cell.

An acidic protein aligns magnetosomes along a filamentous structure in magnetotactic bacteria

Abstract: Aquatic magnetobacteria are able to navigate along Earth's magnetic field thanks to organelles called magnetosomes. In these, magnetite crystals are enclosed in a membrane and arranged in chains so as to act rather like compass needles. A gene cluster in the magnetobacterium Magnetospirillum gryphiswaldense was recently implicated in magnetosome formation. Now one of its genes, mamJ, is shown to code for a protein similar in structure to those controlling biomineralization in bones. In the absence of this protein, the magnetosomes collapse. MamJ protein seems to act by connecting empty vesicles to the filamentous structure, so that magnetite crystals then grow within the vesicles. Magnetotactic bacteria are widespread aquatic microorganisms that use unique intracellular organelles to navigate along the Earth's magnetic field. These organelles, called magnetosomes, consist of membrane-enclosed magnetite crystals that are thought to help to direct bacterial swimming towards growth-favouring microoxic zones at the bottom of natural waters1. Questions in the study of magnetosome formation include understanding the factors governing the size and redox-controlled synthesis of the nano-sized magnetosomes and their assembly into a regular chain in order to achieve the maximum possible magnetic moment, against the physical tendency of magnetosome agglomeration. A deeper understanding of these mechanisms is expected from studying the genes present in the identified chromosomal ‘magnetosome island’, for which the connection with magnetosome synthesis has become evident2. Here we use gene deletion in Magnetospirillum gryphiswaldense to show that magnetosome alignment is coupled to the presence of the mamJ gene product. MamJ is an acidic protein associated with a novel filamentous structure, as revealed by fluorescence microscopy and cryo-electron tomography. We suggest a mechanism in which MamJ interacts with the magnetosome surface as well as with a cytoskeleton-like structure. According to our hypothesis, magnetosome architecture represents one of the highest structural levels achieved in prokaryotic cells.

Extracellular biosynthesis of magnetite using fungi.

Abstract: The development of synthetic processes for oxide nanomaterials is an issue of considerable topical interest. While a number of chemical methods are available and are extensively used, the collaborations are often energy intensive and employ toxic chemicals. On the other hand, the synthesis of inorganic materials by biological systems is characterized by processes that occur at close to ambient temperatures and pressures, and at neutral pH (examples include magnetotactic bacteria, diatoms, and S-layer bacteria). Here we show that nanoparticulate magnetite may be produced at room temperature extracellularly by challenging the fungi, Fusarium oxysporum and Verticillium sp., with mixtures of ferric and ferrous salts. Extracellular hydrolysis of the anionic iron complexes by cationic proteins secreted by the fungi results in the room-temperature synthesis of crystalline magnetite particles that exhibit a signature of a ferrimagnetic transition with a negligible amount of spontaneous magnetization at low temperature.

Controlled manipulation and actuation of micro-objects with magnetotactic bacteria

Abstract: Bacterial actuation and manipulation are demonstrated where Magnetospirillum gryphiswaldense magnetotactic bacteria (MTB) are used to push 3 μ m beads at an average velocity of 7.5 μ m s − 1 along preplanned paths by modifying the torque on a chain of magnetosomes in the bacterium with a directional magnetic field of at least 0.5 G generated from a small programmed electrical current. But measured average thrusts of 0.5 and 4 pN of the flagellar motor of a single Magnetospirillum gryphiswaldense and MC-1 MTB suggest that average velocities greater than 16 and 128 μ m s − 1 , respectively could be achieved.

Origin of magnetosome membrane: proteomic analysis of magnetosome membrane and comparison with cytoplasmic membrane.

Abstract: Prokaryotes are known to have evolved one or more unique organelles. Although several hypotheses have been proposed concerning the biogenesis of these intracellular components, the majority of these proposals remains unclear. Magnetotactic bacteria synthesize intracellular magnetosomes that are enclosed by lipid bilayer membranes. From the identification and characterization of several surface and transmembrane magnetosome proteins, we have postulated that magnetosomes are derived from the cytoplasmic membrane (CM). To confirm this hypothesis, a comparative proteomic analysis of the magnetosome membrane (MM) and CM of the magnetotactic bacterium, Magnetospirillum magneticum AMB-1, was undertaken. Based on the whole genome sequence of M. magneticum AMB-1, 78 identified MM proteins were also found to be prevalent in the CM, several of which are related to magnetosome biosynthesis, such as Mms13, which is tightly bound on the magnetite surface. Fatty acid analysis was also conducted, and showed a striking similarity between the CM and MM profiles. These results suggest that the MM is derived from the CM.

Biogenic nanoparticles: production, characterization, and application of bacterial magnetosomes

Abstract: The ability of magnetotactic bacteria (MTB) to navigate along magnetic field lines is based on unique nanosized organelles (magnetosomes), which are membrane-enclosed intracellular crystals of a magnetic iron mineral that assemble into highly ordered chain-like structures The biomineralization of magnetosomes is a process with genetic control over the accumulation of iron, the deposition of the magnetic crystal within a specific compartment, as well as the assembly, alignment and intracellular organization of particle chains Magnetite crystals produced by MTB have uniform species-specific morphologies and sizes, which are mostly unknown from inorganic systems The unusual characteristics of magnetosome particles have attracted a great interdisciplinary interest and inspired numerous ideas for their biotechnological application In this article, we summarize the current knowledge of magnetosome biomineralization in bacteria In addition, we will present results on the mass production, as well as the biochemical and physico-chemical analysis and functionalization of bacterial magnetosomes, with emphasis on their characterization as a novel class of magnetic nanoparticles Finally, we describe the potential of magnetosomes in various biomedical and technological applications

South-seeking magnetotactic bacteria in the Northern Hemisphere.

Abstract: Magnetotactic bacteria contain membrane-bound intracellular iron crystals (magnetosomes) and respond to magnetic fields. Polar magnetotactic bacteria in vertical chemical gradients are thought to respond to high oxygen levels by swimming downward into areas with low or no oxygen (toward geomagnetic north in the Northern Hemisphere and geomagnetic south in the Southern Hemisphere). We identified populations of polar magnetotactic bacteria in the Northern Hemisphere that respond to high oxygen levels by swimming toward geomagnetic south, the opposite of all previously reported magnetotactic behavior. The percentage of magnetotactic bacteria with south polarity in the environment is positively correlated with higher redox potential. The coexistence of magnetotactic bacteria with opposing polarities in the same redox environment conflicts with current models of the adaptive value of magnetotaxis.

Complex intracellular structures in prokaryotes

Abstract: Complex Intracellular Structures in Prokaryotes.- Prokaryote Complex Intracellular Structures: Descriptions and Discoveries.- Proteasomes and Other Nanocompartmentalized Proteases of Archaea.- Assembly and Disassembly of Phycobilisomes.- Chlorosomes: Antenna Organelles in Photosynthetic Green Bacteria.- Gas Vesicles of Archaea and Bacteria.- Carboxysomes and Carboxysome-like Inclusions.- Magnetosomes in Magnetotactic Bacteria.- Structure, Function and Formation of Bacterial Intracytoplasmic Membranes.- Membrane-bounded Nucleoids and Pirellulosomes of Planctomycetes.- Anammoxosomes of Anaerobic Ammonium-oxidizing Planctomycetes.- The Enigmatic Cytoarchitecture of Epulopiscium spp..- Additional Complex Intracellular Structures.- Cytoskeletal Elements in Prokaryotes.- Cryo-electron Tomography Reveals the Architecture of a Bacterial Cytoskeleton.- Organization and Assembly of the Mycoplasma pneumoniae Attachment Organelle.- The Junctional Pore Complex: Molecular Motor of Microbial Motility.- Type III Secretion Systems: Bacterial Injection Devices for Microbe-Host Interactions.- Gas Vesicles in Actinomycetes: Not Simply a Case of Flotation in Water-Logged Soil.- Bacterial Endosymbionts in Prokaryotes.

Diversity and Taxonomy of Magnetotactic Bacteria

Abstract: Studies of the diversity of magnetotactic bacteria (MTB) benefit from the unique advantage that MTB can be readily separated from sediment particles and other bacteria based on their magnetotaxis This is the reason why current knowledge on MTB diversity relies to a lesser extent on the isolation and characterization of pure cultures, the classical tool of microbiology, than in other groups of microorganisms Microscopy of magnetotactic enrichments retrieved from various environmental samples has consistently revealed significant morphological and ultrastructural diversity of MTB However, of the many morphotypes detected, including spirilla, cocci, vibrios, ovoid, rod-shaped and even multicellular bacteria, only few bacteria could so far be brought into pure culture The taxonomy of MTB is therefore heavily based on comparative sequence analysis of their 16S rRNA genes which can be investigated without prior cultivation Based on 16S rRNA sequence similarity MTB are polyphyletic Most of the MTB pure cultures and many of the so far uncultured phylotypes cluster within the Alphaproteobacteria, but MTB have also been affiliated to Deltaproteobacteria, to the phylum Nitrospira, and, tentatively, also to Gammaproteobacteria

Critical single-domain/multidomain grain sizes in noninteracting and interacting elongated magnetite particles: Implications for magnetosomes

Abstract: [1] The critical size for stable single-domain (SD) behavior has been calculated as a function of grain elongation for magnetite grains using a numerical micromagnetic algorithm. Importantly, for the first time, we consider the contribution of intergrain magnetostatic interactions on the SD/multidomain (MD) critical size (d0). For individual grains our numerical estimates for d0 for elongated grains are lower than that determined by previous analytical and numerical calculations. Nevertheless, the inclusion of magnetostatic interactions into the model was found to increase d0 to values significantly higher than any previously published estimates of d0 for individual grains. Therefore the model calculations show that there is a relatively wide range of grain sizes within which depending on the degree of magnetostatic interactions and elongation, a grain can be either SD or MD. The model results are compared to observations of magnetosomes found in magnetotactic bacteria. The newly calculated upper d0 limit for the interacting grains now accommodates the largest magnetosomes reported in the literature. These large magnetosomes were previously thought to be MD, suggesting that evolutionary processes are highly efficient at optimizing magnetosome grain size and spatial distribution.

Ecophysiology of Magnetotactic Bacteria

Abstract: Magnetotactic bacteria are a physiologically diverse group of prokaryotes whose main common features are the biomineralization of magnetosomes and magnetotaxis, the passive alignment and active motility along geomagnetic field lines. Magnetotactic bacteria exist in their highest numbers at or near the oxic–anoxic interfaces (OAI) of chemically stratified aquatic habitats that contain inverse concentration gradients of oxidants and reductants. Few species are in axenic culture and many have yet to be well described. The physiology of those that have been described appears to dictate their local ecology. Known Fe 3 O 4-producing strains are microaerophiles that fix atmospheric nitrogen, a process mediated by the oxygen-sensitive enzyme nitrogenase. Marine Fe3O4-producing strains oxidize reduced sulfur species to support autotrophy through the Calvin–Benson–Bassham or the reverse tricarboxylic acid cycle. These organisms must compete for reduced sulfur species with oxygen, which chemically oxidizes these compounds, and yet the organism still requires some oxygen to respire with to catalyze these geochemical reactions. Most Fe3O4-producing strains utilize nitrogen oxides as alternate electron acceptors, the reductions of which are catalyzed by oxygen-sensitive enzymes. Fe3O4-producing magnetotactic bacteria must solve several problems. They must find a location where both oxidant (oxygen) and reductants (e.g., reduced sulfur species) are available to the cell and therefore in close proximity. They must also mediate oxygen-sensitive, ancillary biochemical reactions (e.g., nitrogen fixation) important for survival. Thus, the OAI appears to be a perfect habitat for magnetotactic bacteria to thrive since microaerobic conditions are maintained and oxidant and reductant often overlap.

Ferromagnetic resonance spectroscopy for assessment of magnetic anisotropy and magnetostatic interactions: A case study of mutant magnetotactic bacteria

Abstract: Ferromagnetic resonance spectroscopy (FMR) can be used to measure the effective magnetic field within a sample, including the contributions of both magnetic anisotropy and magnetostatic interactions. One particular use is in the detection of magnetite produced by magnetotactic bacteria. These bacteria produce single-domain particles with narrow size and shape distributions that are often elongated and generally arranged in chains. All of these features are detectable through FMR. Here, we examine their effects on the FMR spectra of magnetotactic bacteria strains MV-1 (which produces chains of elongate magnetite crystals), AMB-1 (which produces chains of nearly equidimensional magnetite crystals), and two novel mutants of AMB-1: mnm13 (which produces isolated, elongate crystals), and mnm18 (which produces nearly equidimensional crystals that are usually isolated). Comparison of their FMR spectra indicates that the positive magnetic anisotropy indicated by the spectra of almost all magnetotactic bacteria is a product of chain alignment and particle elongation. We also find correlations between FMR properties and magnetic measurements of coercivity and magnetostatic interactions. FMR thus provides a rapid method for assessing the magnetic properties of assemblages of particles, with applications including screening for samples likely to contain bacterial magnetofossils.

Magnetic properties, microstructure, composition, and morphology of greigite nanocrystals in magnetotactic bacteria from electron holography and tomography

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 (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

Preliminary investigation of bio-carriers using magnetotactic bacteria.

Abstract: This paper proposes a novel micro-carrier based on magnetotactic bacteria (MTB). To confirm the feasibility of such carriers, the thrust force of the bacteria is evaluated. By measuring the swimming speed of MC-1 bacteria in an unbounded medium, a thrust of 4 pN generated by a single MC-1 bacterium is found. The effects on the MTB's swimming speed under the control of micro-electromagnets and influenced by the wall effects when each MTB is attached to a microbead are investigated.

Depth Distribution of Magnetofossils in Near-Surface Sediments From the Blake/Bahama Outer Ridge, Western North Atlantic Ocean, Determined by Low-Temperature Magnetism

Abstract: [1] Fe-oxide and Fe-sulfide trace minerals in sediments and sedimentary rocks provide proxy records of biogeochemical processes, record past variations in the geomagnetic field, and can serve as proxies for climatic variations. An important class of these Fe-oxides is produced by bacteria. Magnetic particles produced by magnetotactic bacteria have been proposed as a primary recorder of the geomagnetic field in many terrestrial marine sediments, and have also been suggested to represent fossil evidence of life on the planet Mars. To better understand their distribution and preservation in the sediment column, and their relationship to other biochemical processes, we present rock-magnetic data that document the occurrence and abundance of fossil biogenic magnetite (magnetofossils) in marine sediments from the Blake/Bahama Outer Ridge. Magnetic hysteresis and low-temperature magnetism both indicate that the occurrence of magnetofossils is closely linked to the depth of the modern Fe-redox boundary within the sediment column, and that a fraction of the magnetic minerals in the sediment column above the Fe-redox boundary are in the form of intact and relatively unaltered chains of nanophase magnetite crystals. Below the Fe-redox boundary the abundance of these magnetofossils is markedly decreased. The important conclusions of this work are to demonstrate that nondestructive rock-magnetic methods can be used to successfully document the occurrence and relative abundance of magnetofossils in geologic materials.

Molecular Bioengineering of Bacterial Magnetic Particles for Biotechnological Applications

Abstract: Magnetic particles are currently one of the most significant materials in the industrial sector, where they have been widely used for biotechnological and biomedical applications. Much effort has been devoted to the preparation of nanosized magnetite particles, and there is great interest with reference to their well-controlled size and shape. Magnetotactic bacteria synthesize uniform nanosized magnetite particles, the magnetosomes (also referred to as “bacterial magnetic particles”, BMPs), which are enveloped by organic lipid membrane. BMPs offer high technological potential since they can be conveniently manipulated with magnetic force. The thin organic membrane enveloping the individual BMPs confers high and even dispersion in aqueous solutions compared to artificial magnetites, making them ideal biotechnological materials. Based on the molecular studies of BMP biomineralization from genome analysis, proteomics, and transcriptomics of Magnetospirillum magneticum AMB-1, methods for the construction of functional BMPs were established through genetic engineering. They are applicable to high-sensitivity immunoassay, DNA detection, drug screening, and cell separation. Furthermore, high-throughput immunoassay, single-nucleotide polymorphism discrimination, and DNA recovery systems have been developed to use these functionalized BMPs. The nanosized fine magnetic particles offer vast potential in new nanotechniques.

Genetic Analysis of Magnetosome Biomineralization

Abstract: Magnetite crystals produced by magnetotactic bacteria (MTB) have uniform species–specific morphologies and sizes, which are mostly unknown from inorganic systems. This indicates that biomineralization in magnetosomes is a process with genetic control over the accumulation of iron, the deposition of the magnetic crystal within a specific compartment, as well as their intracellular assembly and alignment into chain-like structures. Our understanding of the molecular and genetic basis of magnetosome formation has substantially improved during the last few years due to the progress in genome analysis and the development of advanced genetic techniques to study MTB.

Nonlinear dynamics of semiflexible magnetic filaments in an ac magnetic field.

Abstract: Flexible spontaneously magnetized filaments exist in the living world (magnetotactic bacteria) and arise in magnetic colloids with large magnetodipolar interaction parameter. We demonstrate that these filaments possess variety of novel nonlinear phenomena in an ac magnetic field: orientation of the filament in the direction perpendicular to the field and the development of the oscillating U-like shapes, which presumably can lead to the formation of rings of magnetic filaments. It is found that these phenomena are determined by the development of the localized boundary modes of the filament deformation. We have illustrated by qualitative estimates that the phenomena found may be useful for insight into the complex pattern formation phenomena in ensembles of magnetic particles under the action of an ac magnetic field.

Cell Biology of Magnetosome Formation

Abstract: Magnetosome chains are the intracellular structures that allow magnetotactic bacteria to align in and navigate along geomagnetic fields (Bazylinski and Frankel 2004). These organelles are typically defined as a unit consisting of a magnetite or greigite crystal surrounded by a lipid bilayer membrane (Balkwill et al. 1980). Although these magnetic minerals are the usual targets of most studies of magnetotactic bacteria it is the magnetosome membrane that fascinates cell biologists. One of the cornerstones of cell biology has been that membrane-bound organelles are unique to eukaryotes. However, it is now known that membranous organelles exist in many prokaryotes raising the possibility that the endo-membrane system of eukaryotic cells might have originated in prokaryotes (Jetten et al. 2003; Seufferheld et al. 2003; Fuerst 2005). Magnetosomes are one of the best-studied examples of these prokaryotic organelles with the potential to be an ideal system for the study of organelle development in prokaryotes. This work provides a review of the current knowledge of magnetosomes from a cell biological perspective focusing on the composition and formation of the magnetosome membrane and the cytoskeletal framework organizing individual magnetosomes into chains.

Characterization of Bacterial Magnetic Nanostructures Using High-Resolution Transmission Electron Microscopy and Off-Axis Electron Holography

Abstract: Magnetotactic bacteria can be regarded as model systems for studying the structural, chemical, and magnetic properties of arrangements of ferrimagnetic iron oxide and sulfide nanocrystals. The aim of the present chapter is to show how the size, shape, crystal structure, crystallographic orientation, and spatial arrangement of bacterial magnetite (Fe 3 O 4) and greigite (Fe3S4) crystals affect their magnetic properties. We present recent results obtained using transmission electron microscopy (TEM) techniques, including high-resolution TEM imaging and off-axis electron holography.

Crystal habits and magnetic microstructures of magnetosomes in coccoid magnetotactic bacteria

Abstract: We report on the application of off-axis electron holography and high-resolution TEM to study the crystal habits of magnetosomes and magnetic microstructure in two coccoid morphotypes of magnetotactic bacteria collected from a brackish lagoon at Itaipu, Brazil. Itaipu-1, the larger coccoid organism, contains two separated chains of unusually large magnetosomes; the magnetosome crystals have roughly square projections, lengths up to 250 nm and are slightly elongated along [111] (width/length ratio of about 0.9). Itaipu-3 magnetosome crystals have lengths up to 120 nm, greater elongation along [111] (width/length ∼ 0.6), and prominent corner facets. The results show that Itaipu-1 and Itaipu-3 magnetosome crystal habits are related, differing only in the relative sizes of their crystal facets. In both cases, the crystals are aligned with their [111] elongation axes parallel to the chain direction. In Itaipu-1, but not Itaipu-3, crystallographic positioning perpendicular to [111] of successive crystals in the magnetosome chain appears to be under biological control. Whereas the large magnetosomes in Itaipu-1 are metastable, single-magnetic domains, magnetosomes in Itaipu-3 are permanent, single-magnetic domains, as in most magnetotactic bacteria.

Magnetic microstructure of iron sulfide crystals in magnetotactic bacteria from off-axis electron holography

Abstract: Transmission electron microscopy, off-axis electron holography and energy-selected imaging were used to study the crystallography, morphology, and magnetic microstructure of nanoscale greigite (Fe3S4) magnetosomes in magnetotactic bacteria from a sulfidic habitat. The greigite magnetosomes were organized in chains, but were less ordered than magnetite magnetosomes in other bacteria. Nevertheless, the magnetosomes comprise a permanent magnetic dipole, sufficient for magnetotaxis.