Magnetic properties of magnetite synthesized by Magnetospirillum magnetotacticum MS-1 cultured with different concentrations of ferric iron.

To clarify the effect of Fe(3+) concentration on magnetite formation, Magnetospirillum magnetotacticum MS-1 was cultured at various initial concentrations of Fe(3+) and the yield and magnetic properties of the cells were investigated. Although total cell yields (g/l) were not dependent on the initial concentration of Fe(3+) (0-68 µM) in the growth medium, the percentage of magnetic cells increased as the initial Fe(3+) concentration increased. The coercivity (H c) and saturation magnetization (M s) of dried MS-1 cells increased and the blocking temperature (T B) decreased as the initial Fe(3+) concentration increased. These values are similar to those reported previously. The Verwey transition temperature (T V) was almost identical for all initial Fe(3+) concentrations (95-97 K), except for medium without added Fe(3+) (0 µM; 88 K). Fe(3+) concentration strongly affects the magnetic properties of MS-1 cells, especially in the lower concentration range, suggesting that the Fe(3+) concentration should be considered when evaluating the magnetic properties of MS-1 cells.