Showing papers on "Magnetotactic bacteria published in 1989"

Magnetofossils, the Magnetization of Sediments, and the Evolution of Magnetite Biomineralization

Abstract: Magnetite (Fe_3O_4) is one of the most stable carriers of natural remanent magnetization (NRM) in sedimentary rocks, and paleomagnetic studies of magnetite-bearing sediments, such as deep-sea cores and pelagic limestones, have provided a detailed calibration between the biostratigraphic and magnetic polarity time scales. Despite this important role, there is as yet a very poor understanding of how ultrafine-grained (< 0.1 µm) magnetite is formed, transported, and preserved in marine environments. A major conceptual advance in our understanding of these processes is the recent discovery that biogenic magnetite, formed by magnetotactic bacteria and/or other magnetite-precipitating organisms, is responsible for much of the stable magnetic remanence in many marine sediments and sedimentary rocks. Since these magnetite particles are of biogenic origin, they are termed properly magnetofossils (Kirschvink & Chang 1984).

Magnetite biomineralization and geomagnetic sensitivity in higher animals: An update and recommendations for future study

Abstract: Magnetite, the only known biogenic material with ferromagnetic properties, has been identified as a biochemical precipitate in three of the five kingdoms of living organisms, with a fossil record that now extends back nearly 2 billion years. In the magnetotactic bacteria, protoctists, and fish, single-domain crystals of magnetite are arranged in membrane-bound linear structures called magnetosomes, which function as biological bar magnets. Magnetosomes in all three of these groups bear an overall structural similarity to each other, which includes alignment of the individual crystallographic [111] directions parallel to the long axis. Although the magnetosomes represent only a small volume fraction in higher organisms, enough of these highly energetic structures are present to provide sensitivity to extremely small fluctuations and gradients in the background geomagnetic field. Previous experiments with elasmobranch fish are reexamined to test the hypothesis that gradients played a role in their successful geomagnetic conditioning, and a variety of four-turn coil designs are considered that could be used to test the various hypotheses proposed for them.

Magnetofossil dissolution in a palaeomagnetically unstable deep-sea sediment

Abstract: MAGNETOFOSSILS1, the fossil remains of bacterial magneto-somes2, are found in various deep-sea sediments, and have been linked to the preservation of stable natural remanent magnetization in many of them1,3–5. They have also been extracted and identified from lithified carbonates of Jurassic5 and Precambrian6 age, showing that magnetotactic bacteria have been a sedimentary source of fine-grained magnetite for much of geological time. Some clay-rich deep-sea sediments, however, do not record a stable remanent magnetization, for unknown reasons. Here we report results from a high-resolution transmission-electron-microscope study on samples of this type collected by the Deep Sea Drilling Project (DSDP); the material contains a complex mixture of single-domain magnetic minerals. Well-preserved magnetofossils show the same crystal structures as those found in magnetosomes from recent bacteria7–10, whereas others in these same preparations display a wide range of dissolution, corrosion and aggregation effects. Rock magnetic measurements are consistent with the presence of these alterations in many DSDP sediments, including those that preserve reliable palaeomagnetic directions. As we were unable to fina authigenic magnetic minerals in our sample, and as the magnetic fraction is dominated by well preserved magnetofossils, we suggest that the poor preservation of the magnetization is a result of diagenetic interactions between the magnetofossils and the clay minerals in the matrix.

Magnetite and magnetotaxis in microorganisms

Abstract: Magnetotactic bacteria from freshwater and marine sediments orient and navigate along geomagnetic field lines. Their magnetotactic response is based on intracellular, single magnetic domains of ferrimagnetic magnetite, which impart a permanent magnetic dipole moment to the cell.

Phagocytosis of bacterial magnetite by leucocytes

Abstract: Magnetotactic bacteria were introduced into granulocytes and monocytes by phagocytosis. The number of phagocytes containing bacterial magnetites (magneto-sensitive cells) became constant after 1.5 h incubation, and viable phagocytes contained about 20–40 cells of magnetotactic bacteria. Granulocytes and monocytes containing bacterial magnetites were separated by magnet a Samarium-cobalt from lymphocytes. After separation, 89% of lymphocytes were recovered and 95% of the cells were viable. The contamination of phagocytes in the recovered lymphocytes was below 0.8%. Magneto-sensitive granulocytes and monocytes were removed by applying a magnetic field. The nitro-blue tetrazolium-reducing, chemotactic and phagocytic abilities of phagocytes ingesting magnetotactic bacteria were 84%, 88% and 87% respectively after 1 h incubation.

Identification of the Magnetic Poles on Strong Magnetic Grains from Meteorites Using Magnetotactic Bacteria

Abstract: Magnetotactic bacteria (north seeking bacteria) have been used to identify the magnetic S pole of iron-nickel grains selected from St. Severin LL6 chondrite. The results indicate that the bacteria are sensitive magnetic sensors which can be used to detect not only the S pole in the grains but also the directions of lines of magnetic force radiated from the grains. The magnetic coercive force and the stability of natural remanent magnetization can also be measured with the bacteria by applying a steady magnetic field. These methods can in principle be applied to terrestrial rocks having relatively strong natural remanent magnetization. Thus, the magnetotactic bacteria can give useful information for rock magnetism and paleomagnetism as a bio-magnetometer.Combining the method of south seeking bacteria and Bitter pattern analyses using colloidal magnetite particles, complex magnetization structures on the surface of Fe-Ni grains from the St. Severin meteorite have been revealed, which is important for an understanding the chondrite magnetism.

Why not use magnetotactic bacteria for domain analyses

Abstract: For nondestructive domain analyses of transformer sheets with stress coating, high voltage SEM techniques as well as special colloid techniques have been developed. In the present study, a medium containing magnetotactic bacteria was applied to the sample surface. It was found that the bacteria orient themselves in the stray fields originating from the domain structure, and swim in the field direction. This allows visualization of domains whose stray field is directed into the sheet. Comparisons between the bacteria technique, colloid technique and computer controlled field scanning method are discussed for different kinds of materials.

The Effect of Magnetotactic Bacteria on the Magnetic Properties of Marine Sediments

Abstract: Magnetotactic bacteria have been studied in three distinct sedimentary marine environments: a hypersaline lagoon, an intertidal CO3 marsh, and an open ocean basin. The bacteria and the ultra-fine grained, single domain magnetite (Fe3O4) they produce were extracted from the sediments and studied with transmission electron microscopy. Magnetic properties of the sediments were measured by rock magnetic techniques using a SQUID magnetometer. Our results show that magnetotactic bacteria contribute a significant fraction of the natural remanent magnetization to their sedimentary environment and in some cases may be the sole source of the stable remanence carrying mineral. The occurrence and abundance of these bacteria in a diversity of marine environments implies that they may also play a role in the microbial iron cycle.

Biochemical Magnetite Formation and its Application

Abstract: Magnetic particles have important applications in biochemistry and in medicine, for example in magnetoliposomes for cell sorting1 and for magnetic separation techniques2. Particles from magnetotactic bacteria are most suitable for such applications by virtue of their size3, but cannot be recovered in sufficient quantities for commercial purpose, because the growth of magnetotactic bacteria in culture is limited. This study was designed to gain an understanding of the mechanisms of magnetite formation in living organisms, and to synthesize magnetite particles for industrial applications.

Immunosensor Using Bacterial Magnetites

Abstract: Magnetotactic bacteria contain magnetic particles which consist of magnetite (Fe3O4). They are 500–1000 A in size, covered with organic thin films, and do not aggregate. It is therefore possible to immobilize larger quantities of bioactive substances. Moreover, such immobilized bioactive substances can be moved by a magnetic field. Recently, the author’s group has succeeded in culturing magnetotactic bacteria in a large amount. Bacterial magnetites were separated from these cells using several methods such as ultrasonication, lysozyme treatment, etc.. Separated bacterial magnetites have been employed for enzyme immobilization1. Glucose oxidase and uricase were immobilized on bacterial magnetites. Enzyme immobilized on bacterial magnetites showed higher activities than those immobilized on artificial magnetic particles and retained initial activities when they were reused. Furthermore, bacterial magnetites were also introduced into erythrocytes and leucocytes. Blood cells containing bacterial magnetites were separated with a magnet2,3. This article describes the immobilization of antibody on bacterial magnetites.