Growth capacity and siderophore production by wild-type MR-1 and Δ so2426 strains in the presence of 2,2'-dipyridyl. (A) Aerobic growth of wild-type MR-1 (closed triangles) and the Δso2426 mutant (open circles) in LB supplemented with 80 μM of the Fe chelator 2,2'-dipyridyl. Cell growth was assessed for triplicate cultures and plotted as the mean OD600 ± SEM. (B) Absorbance at 630 nm of CAS-treated samples in the absence (open symbols) and presence (closed symbols) of 2,2'-dipyridyl. Results are shown for wild-type MR-1 (squares), the Δso2426 mutant (circles), and LB only (triangles). (C) Relative production of CAS-reactive siderophores by wild-type MR-1 (closed symbols) and the Δso2426 mutant (open symbols) under aerobic growth conditions. 2,2'-dipyridyl (80 μM) was added to mid-log-phase (OD600, 0.6) MR-1 and Δso2426 mutant cultures cultivated in LB broth, and relative siderophore synthesis was monitored over time using the CAS-based siderophore detection assay. The relative siderophore production was calculated by subtracting the supernatant A630 (absorbance at 630 nm) for the wild type or mutant from the control (uninoculated LB medium) and then determining the ratio of corrected supernatant A630 to control A630. Error bars represent the standard error of the mean for three replicate CAS measurements. Circles represent unamended LB cultures; squares represent iron-depleted cultures.