Magnetotactic bacteria are bacteria that use the magnetic field of Earth to orient themselves. This phenomenon is known as magnetotaxis. Magnetotaxis is another means by which bacteria can actively respond to their environment. Response to light (phototaxis) and chemical concentration (chemotaxis) exist in other species of bacteria.

The first magnetotactic bacterium, Aquasprilla magnetotactum was discovered in 1975 by Richard Blakemore. This organism, which is now called Magnetospirillum magnetotacticum, inhabits swampy water, where because of the decomposition of organic matter, the oxygen content in the water drops off sharply with increasing depth. The bacteria were shown to use the magnetic field to align themselves. By this behavior, they were able to position themselves at the region in the water where oxygen was almost depleted, the environment in which they grow best. For example, if the bacteria stray too far above or below the preferred zone of habitation, they...