FIG. 4.

Transcriptional activity of the alc operon varies with alcaligin inducer concentration. BRM13(pRK21) cells were cultured in iron-depleted SS medium supplemented with different concentrations (0, 1, 2, 5, 10, 20, 39, 79, 156, 313, and 625 ng/ml) of purified alcaligin, and transcriptional activity of the alcA::mini-Tn5 lacZ1 fusion gene was monitored by β-galactosidase assay. (Inset) Enlarged scale in the concentration range from 0 to 50 ng of alcaligin/ml. β-Galactosidase activities, expressed in Miller units, are shown as means ± 1 standard deviation (n = 3).