Effects of Fur, Fnr and iron chelation on transcription of ftnB. Transcriptional ftnB-lacZ activity was determined in 14028s (squares), Δfur (circles), and Δfnr (triangles) under (A) anaerobic, and (B) aerobic conditions in LB-MOPS-X media without (open symbols) and with (closed symbols) 200 μM of 2, 2' dipyridyl. β-galactosidase assay was conducted throughout the growth of the culture and activity is presented in the form of differential plots with representative data shown in (A) and (B). Best-fit lines, calculated as described in the Methods, are shown in (A) and (B). For (A) and (B), representative data are shown with the differential rate of synthesis (U/OD600) ± standard deviations from three independent experiments listed.