Electron microscopic studies of magnetosomes in magnetotactic bacteria

Electron microscopic studies on magnetosomes in magnetotactic bacteria have revealed much information on their composition, structure, and even the formation of their mineral phase. The mineral phases of the magnetosomes are of two general types: iron oxides and iron sulfides. Iron oxide‐type magnetosomes contain particles of the ferrimagnetic mineral magnetite (Fe3O4) while the iron sulfide‐type contain ferrimagnetic greigite (Fe3S4), greigite and non‐magnetic pyrite (FeS2), or possibly ferrimagnetic pyrrhotite (Fe7S8). Regardless of their composition, the crystalline particles in magnetosomes have a narrow size range: approximately 35 to 120 nm. Magnetite crystals in this size range are single‐magnetic‐domains and confer a permanent magnetic dipole moment to the cell. The single‐domain size range for greigite is not known but is probably similar to that for magnetite.

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