Particulate iron phases in D. magneticus (RS-1). Insets: FFTs with indicated zone axis (normal to image plane). (a) Amorphous Fe-P granule (t = 120 h); (b) polycrystalline particle with spherical morphology similar to Fe-P granule, but partial magnetite crystal structure (t = 56 h), see the electronic supplementary material, figure S3, for further analysis; (c) small magnetite particle with surface-bound secondary phases (t = 56 h); (d) magnetite twin crystal with surface-bound secondary phases, see figure 7 and the electronic supplementary material, figure S4, for further analysis; (e,f) aggregate-like magnetite particles (t = 56 h) with similar to mature (g–i) elongated morphology (t = 120 h). (Online version in colour.)