Ferric alcaligin utilization assays. Bars indicate mean diameters in millimeters (n = 3) (±1 standard deviation) of growth stimulation zones surrounding wells filled with iron source solutions. Relevant genotypes of B. pertussis indicator strains used are as follows: UT25Sm1, fauA+; PM11, ΔfauA2; PM11(pRK415), ΔfauA2 (plasmid vector control); and PM11(pRK18), ΔfauA2/fauA+ (fauA+ in trans). The dashed line corresponds to the 6-mm diameter of the sample well containing the iron source solution. Filled bars, alcaligin (125 μM); open bars, hemin chloride (100 μM) (positive control iron source).