Magnetite formation by a magnetic bacterium capable of growing aerobically

Summary A helically shaped magnetic bacterium was isolated from freshwater sediment and a pure culture was obtained. The growth medium contained succinate, nitrate and ferric malate as the carbon, nitrogen and iron sources, respectively. The magnetic bacterium, designated AMB-1, was able to grow in free gaseous exchange with an air atmosphere. When cells were grown aerobically on agar, oxidase activity was present, and white non-magnetic colonies, which did not show catalase activity, were formed. The stationary phase of growth was reached 4–5 days later at a cell concentration of 1.4×10⁹ cells/ml in liquid culture when an initial cell concentration of 10⁵ cells/ml was employed. After ultrasonic disruption of harvested cells, 2.6 mg bacterial magnetite was obtained from a 11 culture. Offprint requests to: T. Matsunaga