Magnetotactic bacteria

About: Magnetotactic bacteria is a research topic. Over the lifetime, 1118 publications have been published within this topic receiving 43741 citations.

The Identification and Interpretation of Microbial Biogeomagnetism

Abstract: Microbial activity plays a major role in the sedimentary iron cycle. Some microbes gain energy by reducing or oxidizing iron and thus induce changes in the sedimentary iron mineral assemblage. Magnetotactic bacteria engage in controlled, intracellular precipitation of magnetic iron minerals. These biological transformations are frequently a major influence on the magnetic properties of sediments. Understanding the biogeochemical iron cycle therefore facilitates the interpretation of sedimentary paleomagnetism; conversely, magnetic tools provide a non-destructive and rapid way of analyzing the biogeochemical iron cycle in modern and ancient environments. Ferromagnetic resonance (FMR) spectroscopy, a form of microwave spectroscopy, provides a rapid means of assessing internal fields generated in magnetic particles by interparticle interactions and particle anisotropy. It can therefore assess particle shape, arrangement, and heterogeneity. Because magnetotactic bacteria typically produce chains of crystals with narrow distributions of size and shape, FMR spectroscopy is well suited as a screening tool for identifying fossil magnetotactic bacteria (magnetofossils). Application of FMR and other techniques to modern carbonate sediments of the Triple Goose Creek region, Andros Island, Bahamas, reveals the contributions of magnetotactic bacteria, iron metabolizing bacteria, and sulfate reducing bacteria to the magnetization of carbonate sediments. In sediments above mean tide level, magnetofossils dominate sediment magnetism. Although stable remanent magnetization is preserved throughout the sediments, the quantity of biological magnetite diminishes by an order of magnitude in the iron reduction zone. Below this zone, the development of a sulfate reduction interval can lead to the authigenesis of magnetic iron sulfides. Supratidal portions of shallowing-upward parasequences in carbonate rocks therefore likely provide the most accurate record of syndepositional paleomagnetism. Anomalous magnetic properties of clay deposited in the Atlantic Coastal Plain, New Jersey, during the Paleocene/Eocene Thermal Maximum (PETM) led previous authors to speculate that an extraterrestrial impact triggered the PETM. Reexamination of the clay using FMR and transmission electron microscopy reveals instead that the clay hosts abundant magnetofossils. The first identification of ancient biogenic magnetite using FMR indicates that the anomalous magnetic properties of PETM sediments were not produced by an impact, but instead reflect paleoenvironmental changes along the western North Atlantic margin.

Effect of applied magnetic fields on motility and magnetotaxis in the uncultured magnetotactic multicellular prokaryote 'Candidatus Magnetoglobus multicellularis'.

Abstract: Magnetotactic bacteria are found in the chemocline of aquatic environments worldwide. They produce nanoparticles of magnetic minerals arranged in chains in the cytoplasm, which enable these microorganisms to align to magnetic fields while swimming propelled by flagella. Magnetotactic bacteria are diverse phylogenetically and morphologically, including cocci, rods, vibria, spirilla and also multicellular forms, known as magnetotactic multicellular prokaryotes (MMPs). We used video-microscopy to study the motility of the uncultured MMP 'Candidatus Magnetoglobus multicellularis' under applied magnetic fields ranging from 0.9 to 32 Oersted (Oe). The bidimensional projections of the tridimensional trajectories where interpreted as plane projections of cylindrical helices and fitted as sinusoidal curves. The results showed that 'Ca. M. multicellularis' do not orient efficiently to low magnetic fields, reaching an efficiency of about 0.65 at 0.9-1.5 Oe, which are four to six times the local magnetic field. Good efficiency (0.95) is accomplished for magnetic fields ≥10 Oe. For comparison, unicellular magnetotactic microorganisms reach such efficiency at the local magnetic field. Considering that the magnetic moment of 'Ca. M. multicellularis' is sufficient for efficient alignment at the Earth's magnetic field, we suggest that misalignments are due to flagella movements, which could be driven by photo-, chemo- and/or other types of taxis.

Biological Effects of Stationary Magnetic Fields

Abstract: An inherent sensitivity to the weak geomagnetic field ( ≃ 50 µT) has been demonstrated for a number of different organisms and animal species. It has been well documented experimentally that weak magnetic fields influence the migratory patterns of birds, 1–4 the kinetic movements of mollusks, 5 the waggle dance of bees, 6 the direction-finding of elasmobranch fishes, 7,8 and the orientation and swimming direction of magnetic bacteria. 9,10 The mechanisms underlying the magnetic sensitivity of elasmobranchs and magnetotactic bacteria have been described in the preceding chapter.11 A precise mechanism underlying the magnetic sensitivity of other organisms has not been elucidated, although small deposits of magnetite crystals have been discovered in the cranium of pigeons, 12,13 the tooth denticles of mollusks, 14,15 and the abdominal region of bees.16 Magnetite has also been reported to be localized in various anatomical sites in dolphins, 17 tuna, butterflies,18 turtles,19 mice20 and humans. 22,23 The possible role of magnetite in the geomagnetic direction-finding mechanism possessed by some of these species has not been established, nor is it clear that a sensitivity to the geomagnetic field direction exists for all of the mammalian species in which magnetite deposits have been reported to occur.24,25

Magnetotactic Bacteria, Magnetosomes, and Nanotechnology

Abstract: Magnetotactic bacteria are motile, mostly aquatic, ubiquitous prokaryotes whose direction of swimming is profoundly influenced by the Earth’s and other magnetic fields. These microorganisms biomineralize magnetosomes which are intracellular, tens of nanometer sized, membrane-bounded magnetic crystals of the minerals magnetite (Fe3O4) and greigite (Fe3S4). Magnetosomes are anchored within the cell and cause it to passively align along magnetic field lines while it swims. Construction of the magnetosome chain is an elaborate biomineralization process that is under strict genetic and environmental control. Because of their unique magnetic and physical properties, magnetotactic bacteria and their unique organelles are useful in numerous scientific, commercial, and medical applications.

Application of magnetosomes in magnetic hyperthermia

Abstract: Magnetosomes, i.e. nanoparticles synthesized in nature by magnetotactic bacteria, are very promising for use in magnetic hyperthermia for the cancer treatment. Using the solution of the stochastic Landau-Lifshitz equation we calculate the specific absorption rate in an alternating magnetic field of assemblies of magnetosome chains depending on the particle size, the distance between particles in a chain, and the angle of the applied magnetic field with respect to the chain axis. The dependence of specific absorption rate on the distance between the chain particles is shown to have a bell-shaped form with a pronounced maximum. The maximum specific absorption rate only weakly depends on the diameter of the nanoparticles and the length of the chain. However, a significant decrease in specific absorption rate occurs in a dense chain assembly due to the strong magneto-dipole interaction of nanoparticles of different chains.