FIG. 2.

Transcriptional activity of the alc operon promoter. Alcaligin siderophore-deficient alc::mini-Tn5 lacZ1 mutants BRM1, BRM6, and BRM9, each carrying the alcR⁺ plasmid pRK21 or the control plasmid vector pRK415, were cultured in iron-replete or iron-depleted SS medium with or without supplementation of the SS medium with 20 μg of purified alcaligin/ml. Transcriptional activities of the fusion genes were monitored using β-galactosidase assays, with results expressed in Miller units (means ± 1 standard deviation, n = 3). Solid bars, iron-replete cultures; hatched solid bars, iron-replete cultures supplemented with alcaligin; open bars, iron-depleted cultures; hatched open bars, iron-depleted cultures supplemented with alcaligin.