Magnetotactic bacteria isolated from swamp water were grown in pure culture in the laboratory. This newly isolated species was cultured in the magnetic and the nonmagnetic state. Magnetic cells, which were rich in iron, also produced particles similar to those found previously in other magnetic bacteria of marshes and bogs. By contrast, their nonmagnetic counterparts had much lower iron levels and lacked the crystal structures. Mossbauer spectroscopic analyses of whole cells of magnetic bacteria indicated that they contained the mineral magnetite.