FIG 5.

Iron deficiency is accountable for the phenotype of the ΔsspA strain. (A) Extracellular iron and intracellular iron in the WT, ΔsspA mutant, and the complemented version (ΔsspA^C) of the ΔsspA mutant. (B) Prodiginine biosynthesis of the ΔsspA strain in the presence of FeSO₄ and FeCl₃. (C) Effects of iron on the relative expression of the pigA gene in the ΔsspA strain. The transcription level of the WT was defined as 1.0. (D) Effects of iron on prodiginine production in the wild type. Cultures of the WT strain grown in Zobell 2216E were pelleted for prodiginine production without or with 0.4 and 0.8 mM FeCl₃. The optical density at 535 nm (OD₅₃₅) was read for the detection of prodiginine. Meanwhile, the number of CFU was determined for each culture. The relative prodiginine concentration was expressed as OD₅₃₅/log CFU. In panels A, C, and D, experiments were performed in biological triplicates, and error bars indicate the standard deviations. Asterisks indicate statistically significant differences compared to the WT: **, P < 0.01; ***, P < 0.001.