Magnetotaxis

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Magnetotaxis is the ability of certain motile, aquatic bacteria to sense a magnetic field and coordinate their movement in response (similar to a tropism in plants). It was first described in 1975 by R. P. Blakemore.

Magnetotactic bacteria (e.g. Magnetospirillum magnetotacticum) contain internal structures known as magnetosomes. They appear as a chain of dark, membrane-bound crystals - often magnetite ( $Fe 3 O 4$ ). Some extremophile bacteria from sulforous environments have been isolated with 'greigite' (an iron-sulfide compound $Fe 3 S 4$ ).

It has been suggested that by orienting themselves toward the Earths poles, marine bacteria are able to direct their movement downwards, towards the sediment. Furthermore, bacteria that are able to metabolise metal compounds may also use magnetosomes to detect deposits of ferrous compounds.

Other organisms also have this ability, such as the flatworm (platyhelminthes)^{[citation needed]}.