Magnetospirillum

Magnetospirillum is a Gram-negative, microaerophilic genus of magnetotactic bacterium, first isolated from pond water by the microbiologist R. P. Blakemore in 1975. They have a spiral (helical) shape and are propelled by a polar flagellum at each end of their cells. Four species have been described: "M. magnetotacticum" strain MS-1 (originally classified as "Aquaspirillum magnetotacticum"; "M. magneticum" strain AMB-1; "M. gryphiswaldense" and "M. bellicus".
Habitat.
The typical habitat of "Magnetospirillum" species consists of shallow fresh water and sediments, characterized by low concentrations of oxygen for growth (microaerophilic) where they live in the upper portion of the sediment (oxic/anoxic interface) and prefer an oxygen gradient of around 1–3%.
Magnetotaxis.
Probably the most peculiar characteristic of "Magnetospirillum" species is their capacity to orient themselves according to Earth's magnetic field, magnetotaxis. This is achieved through the presence in the bacterium's cytoplasm of special organelles called magnetosomes. "Magnetospirillum" species also resort to aerotaxis, to remain in favorable O2 concentration conditions. When the bacteria ingest iron, proteins inside their cells interact with it to produce tiny crystals of the mineral magnetite, the most magnetic mineral on Earth.
Purification of magnetosomes is accomplished by use of a magnetic separation column after disruption of the cell membrane. If a detergent is used on purified magnetosomes, they tend to agglomerate rather than staying in chain form. Due to the high quality of the single-domain magnetic crystals, a commercial interest has developed in the bacteria. The crystals are thought to have the potential to produce magnetic tapes and magnetic target drugs.