|
School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, UK
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
...
This 250-word extract was created in the absence of an abstract.
