Iron-storage protein. 4 Fe(2+) + 6 H2O + O2 = 12 H(+) + 4 iron(III) oxide-hydroxide Induced by iron. Repressed by PerR. Negatively regulated by Fur. In addition, is regulated in a PerR-independent way under metal-depleted conditions. Belongs to the ferritin family. Prokaryotic subfamily.