Figure 1.

Fiu belongs to a distinct group of catecholate siderophore transporters. A, a phylogenetic tree of diverse, functionally characterized TBDTs, showing that Fiu forms a clade with PiuA/D that is distant from the catecholate siderophore transporters FepA and Cir. Catecholate-transporting TBDT subgroups are color coded: blue, enterobactin-transporting; green, nonenterobactin-transporting FepA-related; red, nonenterobactin-transporting Fiu-related. Circles represent TBDTs present in E. coli BW25113. B, a scheme showing the sequential deletion of TBDTs in E. coli BW25113 utilized in this study, colored as in A. C, strains from B grown on LB agar in the presence of 0–150 μm 2,2′-bipyridine (BP). Sequential loss of FepA and Fiu leads to defects in the ability of strains to grow under iron-limiting conditions.