FIG. 2.

Growth and iron uptake in E. coli expressing different iron transporters. Dose response experiments (panel A) or iron uptake (panel B) for E. coli strain GR536 (ΔfecABCDE::kan ΔzupT::cat ΔmntH ΔentC ΔfeoABC) harboring plasmids pASK-IBA7 (□), pMNTH (•), pFEO (▴), pZUPT (▪), or pZUPT-low (♦) from at least triplicate experiments with standard deviations are shown. Overnight cultures of E. coli strain GR536 (ΔfecABCDE::kan ΔzupT::cat ΔmntH ΔentC ΔfeoABC) grown in Luria-Bertani broth were diluted 1:500 in Tris-buffered mineral salt medium and grown overnight. (A) Cells were diluted 1:500 in fresh medium, and after 2 h of growth at 37°C, cells were diluted 1:500 in fresh medium with iron or different concentrations of EDTA. Cell growth was monitored as the optical density at 600 nm after 16 h of incubation at 37°C with shaking, and the final growth yield is given, or (B) 30 Klett units of cultures were inoculated into fresh medium at 37°C and grown to 60 Klett units. Expression of genes under control of the tet promoter from plasmid pASK-IBA7 was induced with of 200 ng of AHT/ml for 35 min. Uptake was started by addition of a reaction mix of ⁵⁵Fe (1 μCi), FeSO₄ (final concentration, 5 μM), and 1 mM ascorbate.