PVD gene activities in response to constitutively-expressed putative regulators. The activities of pvdL-'lacZ (A), fpvA-'lacZ (B), and fpvR-'lacZ (C) (fusion strains: TR107.2.1, TR135.1.1, and TR107.5.1, respectively), in response to constitutively-expressed regulator genes pvdS, fpvI, and fpvR (in expression constructs pTR130.1, pTR130.2 and pTR130.3, respectively). β-galactosidase activity (fmol 4 MU/min/cell) was assayed for cells growing in CAA media supplemented with 100 μM 2,2'-dipyridyl (black bars), or 450 μM FeSO4 (white bars). Data are the means ± the standard errors of four independent experiments. Asterisks indicate that under the given iron regime, the reporter strain activity with expression construct significantly differs from the background activity of the reporter strain containing the pBroadgate-D (vector) using Dunnett's method at the P = 0.05 level of significance.