TonB-independent ferrioxamine B-mediated iron transport in Escherichia coli K12

The TonB protein of Escherichia coli K12 couples the energized state of the cytoplasmic membrane with energy-dependent receptors in the outer membrane. High affinity iron transport mediated by ferric dicitrate, ferrienterobactin, ferriaerobactin, ferrichrome, and coprogen all require a functional tonB protein. However, we have found no difference between the growth rates of tonB+ strains and tonB strains using ferrioxamine B as the sole iron source. This TonB-independence of FOB transport and earlier results with a photoactive FOB analog indicate a separate mechanism for iron acquisition from FOB in E. coli.