In iron-limited conditions, activates expression of the feuABCybbA operon, which encodes the bacillibactin uptake system. Acts by binding directly to a conserved direct repeat element upstream of the feuA promoter. Activity is increased in the presence of bacillibactin. Binds with high affinity to both apo-bacillibactin and iron-bacillibactin. Repressed by Fur in the presence of iron.