FIG 4.

Fitness of the ΔentF mutant versus the wild type depends on initial cell density. The E. coli BW25113 arsB::cat strain was grown together with the E. coli BW25113 arsB::kan strain or the ΔentF mutant (E. coli ΔentF arsB::kan) in low-iron medium with or without supplements as indicated. Starting ratios were 1:1, and initial cell densities are shown. Blue bars represent the two Ent wild-type strains in unsupplemented low-iron medium. The CI was about 1 regardless of inoculum size. Black bars represent the ΔentF mutant and the wild type in unsupplemented medium. The ΔentF mutant is competitive only at initial cell densities of 10³ to 10⁴ or greater. Green bars represent the ΔentF mutant and wild type in medium supplemented with Ent (5 μg/ml). The mutant is competitive regardless of inoculum size. Cell numbers and frequencies were determined immediately after inoculation and at 14 h. The bars represent results from two independent experiments, and error bars show ranges.