Magnetospirillum (Magnetospirillum magnetotacticum) is a Gram-negative, microaerophilic magnetotactic bacterium, first isolated from pond water by the microbiologist R. P. Blakemore in 1975. It is characterized by a spirillar, or helical, morphology. It is also a motile bacterium owing to the presence of flagella. It was originally classified as Aquaspirillum magnetotacticum (Maratea and Blakemore, 1981).

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 transition zone). 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.

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.