Showing papers on "Magnetotactic bacteria published in 1999"

Bacterial magnetosomes: microbiology, biomineralization and biotechnological applications.

Abstract: Magnetotactic bacteria orient and migrate along geomagnetic field lines. This ability is based on intracellular magnetic structures, the magnetosomes, which comprise nanometer-sized, membrane-bound crystals of the magnetic iron minerals magnetite (Fe3O4) or greigite (Fe3S4). Magnetosome formation is achieved by a mineralization process with biological control over the accumulation of iron and the deposition of the mineral particle with specific size and orientation within a membrane vesicle at specific locations in the cell. This review focuses on the current knowledge about magnetotactic bacteria and will outline aspects of the physiology and molecular biology of the biomineralization process. Potential biotechnological applications of magnetotactic bacteria and their magnetosomes as well as perspectives for further research are discussed.

Biomimetics: Materials fabrication through biology

Abstract: Many multicellular organisms produce hard tissues such as bones, teeth, shells, skeletal units, and spicules (1). These hard tissues are biocomposites and incorporate both structural macromolecules (lipids, proteins, and polysaccharides) and minerals of, perhaps, 60 different kinds, including hydroxyapatite, calcium carbonate, and silica. A number of single-celled organisms (bacteria and algae) also produce inorganic materials either intracellularly or extracellularly (2). Examples include magnetotactic bacteria, which synthesize magnetite (3); chrysophytes (4), diatoms, and actinopoda (radiolarians; ref. 5), which synthesize siliceous materials; and S layer bacteria that have gypsum and calcium carbonate surface layers (6). Normally, hard tissues are mechanical devices (e.g., skeletal, cutting, grinding), or they serve a physical function (e.g., magnetic, optical, piezoelectric). Bioinorganics are also ion sources that are vital for physiological activities and, therefore, integral parts of the organisms (1, 2).

Formation of Magnetosomes in Magnetotactic Bacteria

Abstract: The ability of magnetotactic bacteria to orient and migrate along geomagnetic field lines is based on intracellular magnetic structures, the magnetosomes, which comprise nano-sized, membrane bound crystals of magnetic iron minerals. The formation of magnetosomes is achieved by a biological mechanism that controls the accumulation of iron and the biomineralization of magnetic crystals with a characteristic size and morphology within membrane vesicles. This paper focuses on the current knowledge about magnetotactic bacteria and will outline aspects of the physiology and molecular biology of magnetosome formation. The biotechnological potential of the biomineralization process is discussed.

Oxygen and iron isotope studies of magnetite produced by magnetotactic bacteria

Abstract: A series of carefully controlled laboratory studies was carried out to investigate oxygen and iron isotope fractionation during the intracellular production of magnetite (Fe 3 O 4 ) by two different species of magnetotactic bacteria at temperatures between 4° and 35°C under microaerobic and anaerobic conditions. No detectable fractionation of iron isotopes in the bacterial magnetites was observed. However, oxygen isotope measurements indicated a temperature-dependent fractionation for Fe 3 O 4 and water that is consistent with that observed for Fe 3 O 4 produced extracellularly by thermophilic Fe 3+ -reducing bacteria. These results contrast with established fractionation curves estimated from either high-temperature experiments or theoretical calculations. With the fractionation curve established in this report, oxygen-18 isotope values of bacterial Fe 3 O 4 may be useful in paleoenvironmental studies for determining the oxygen-18 isotope values of formation waters and for inferring paleotemperatures.

Synthesis of the bacterial magnetosome: the making of a magnetic personality

Abstract: Magnetotactic bacteria synthesize intracellular, enveloped, single magnetic domain crystals of magnetite (Fe3O4, Fe2+Fe2(3+)O4) and/or greigite (Fe3S4) called magnetosomes. The magnetosomes contain well-ordered crystals that have narrow size distributions and consistent species- and/or strain-specific morphologies. These characteristics are features of a process called biologically-controlled mineralization in which an organism exerts a great degree of crystallochemical control over the nucleation and growth of the mineral particle. Because of these features, the mineral particles have been used as biomarkers although not without controversy. These unique structures impart a permanent magnetic dipole moment to the cell causing it to align and swim along geomagnetic field lines, a behavior known as magnetotaxis. The apparent biological advantage of magnetotaxis is that it aids cells in more efficiently locating and maintaining position in vertical chemical gradients common in many natural aquatic environments.

Phosphorus‐rich granules in uncultured magnetotactic bacteria

Abstract: Amorphous intracellular minerals present in uncultured magnetotactic bacteria were studied with transmission electron microscopy, electron spectroscopic imaging and X-ray microanalysis Amorphous minerals were present as intracellular granules that contained phosphorus, calcium and oxygen, and could also incorporate iron, aluminum and zinc Granules showed evaporation typical of polyphosphate during exposure to high intensity electron beam Morphologically different bacteria presented granules of variable size and number This indicates that precipitation of amorphous minerals as phosphate granules is a characteristic feature of many uncultured magnetotactic bacteria The structure and composition of granules and magnetosomes (known to contain the iron oxide magnetite) differ

The significance of magnetotactic bacteria for the palaeomagnetic and rock magnetic record of Quaternary sediments and soils

Abstract: Magnetotactic bacteria are micro-organisms that form crystals of ferrimagnetic minerals intracellularly (Blakemore 1975). Many species of magnetotactic bacteria produce crystals of magnetite, which may ‘age’ and oxidize towards maghemite; some species, however, have been found to precipitate the ferrimagnetic iron sulphide greigite (Bazylinski et al. 1995). The ferrimagnetic particles are precipitated within an organic envelope and thus their size and shape are determined by this biological structure. The crystals dominantly fall within the singledomain (SD) grain size range (c. 0.03–0.05 μm for magnetite), are euhedral, often adopting unique and distinctive morphologies (including cubes, octahedra, ‘bullet’ and ‘boot’ shapes), and are aligned in chains. Some of these distinctive crystal morphologies are illustrated in the electron micrographs (Figs 1–3). The close linear arrangement of the magnetic particles results in positive interactions between them, which align the individual moments parallel to each other along the chain direction. Thus, the entire chain acts as an SD magnetic dipole. Microscopic investigation of Magnetobacterium bavaricum, a species found in fresh-water lakes of Bavaria, and some magnetic cocci shows that they possess as many as five discrete magnetosome chains (Hanzlik et al. 1996). The spatial arrangement of the chains is such that they are separated by the maximum possible distance, forcing them to be in direct contact with the cell envelope. As a result, the magnetic torque acting on the chains from the Earth’s magnetic field is transferred very effectively to the whole bacterial cell. Magnetotatic bacteria are highly motile correlate strongly with interglacial and interstadial climate