Magnetospirillum

Magnetospirillum magnetotacticum bacteria with black magnetosome chains visible

Magnetospirillum is a Gram-negative, microaerophilic genus of magnetotactic bacterium, first isolated from pond water by the microbiologist R. P. Blakemore in 1975.^[1] It is characterized by a spirillar, or helical, morphology. It is also a motile bacterium owing to the presence of a polar flagellum at each end. Four species have been described: Magnetospirillum magnetotacticum strain MS-1^[2] (originally classified as Aquaspirillum magnetotacticum;^[3]) Magnetospirillum magneticum strain AMB-1;^[4] Magnetospirillum gryphiswaldense;^[2] and Magnetospirillum bellicus.^[5]

The typical habitat of Magnetospirillum consists of shallow fresh water and sediments, characterized by low concentrations of oxygen for growth (microaerophilic) where it lives in the upper portion of the sediment (oxic/anoxic interface). It prefers an oxygen gradient of approximately 1-3%.

Probably the most peculiar characteristic of Magnetospirillum is its capacity to orient itself according to Earth's magnetic field, an ability which has been named magnetotaxis. This is achieved through the presence into the bacterium's cytoplasm of special organelles called magnetosomes. Magnetospirillum also resorts to aerotaxis, in order to remain in favourable O₂ concentration conditions. When the bacteria ingest iron, proteins inside their bodies interact with it to produce tiny crystals of the mineral magnetite, the most magnetic mineral on Earth.^[6]

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 there is also a commercial interest in the bacteria. The crystals are thought to have the potential to produce magnetic tapes and magnetic target drugs.^[7]

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