FIG. 1.

Growth (A) and production of siderophores Pch (B) and Pvd (C) by P. aeruginosa strain PAO1 and its allelic exchange mutants in SMMCA supplemented with 1 μM FeCl₃. A bacterial growth assay was performed in a 96-well plate (0.1 ml of culture/well), and the growth was measured as OD₅₉₀ in a SPECTRAmax (Molecular Devices, Sunnyvale, Calif.), which is a microplate spectrophotometer with incubation and mixing functions, after bacterial inoculations at approximately 10⁶ CFU/ml. ○, strain PAO1; ▵, the pchD-inactivated mutant, PAD02; □, the pvdA-inactivated mutant, PAD06; +, the pchD- and pvdA-inactivated mutant, PAD07; ×, no inoculum (medium control). Pch (B) and Pvd (C) secreted into the culture supernatant were fluorometrically or photometrically measured as described in Materials and Methods; the values for Pch and Pvd amounts (fluorometric measurement with excitation at 350 nm and emission at 440 nm and OD₄₀₅, respectively) were corrected by dividing by the values for bacterial growth (OD₅₉₀).