TEM images of the MTB and corresponding magnetosome size distributions. (a) T0, before iron addition (no magnetite detectable); (b) T3, 110 min; (c) T6, 280 min; (d) T8, 330 min; (e) T10, 420 min; and (f) T12, 1320 min, after iron addition (scale bars = 1000 nm and 200 nm for T3). Arrows indicate small magnetite particles in T3.