Magnetotactic bacteria are a diverse group of procaryotes whose direction of motility is influenced by magnetic fields. These organisms are ubiquitous in aquatic habitats and contain unique intracellular iron-rich membrane-bounded inclusions called magnetosomes that are responsible for the cells’ magnetic behavior. The composition, size (40-100 nm), morphology, position, and orientation of the particles appear to be highly controlled by these bacteria. Ferrimagnetic magnetite (Fe3O4), greigite (Fe3S4), and pyrrhotite (Fe7S8) and nonmagnetic pyrite (FeS2) have been identified as the mineral phases of the magnetosomes in different bacteria. These organisms also contain other intracellular structures that reflect aspects of their physiology, metabolism, and ecology. In order to determine the external structural features of cells and the composition and structure of their intracellular inclusions, transmission electron microscopy (TEM), scanning-transmission electron microscopy (STEM), energy-dispersive x-ray detection (EDXA), and selected area electron diffraction (SAED) techniques were employed.
The results of a typical electron microscope (EM) and microanalytical study of a Fe3O4-producing magnetotactic bacterium is shown in Figures 1-4. This unidentified organism, designated strain MV-4, was isolated from sulfide-rich water and sediment collected from a salt marsh.