Fig 4.

Chelation of iron with dipyridyl enhances the survival of S. meliloti in H₂O₂. (A) Survival of S. meliloti strains in 1 mM H₂O₂ without (dark shaded bars) or with (light shaded bars) the addition of the iron chelator dipyridyl. Survival is normalized to that of the wild-type strain not treated with dipyridyl. Error bars indicate standard deviations. Asterisks indicate significant differences from the wild type without dipyridyl (P, <0.05). (B) Absorbance of ferrozine reagent in response to amounts of Fe²⁺ (dark shaded bars) or Fe³⁺ and Fe²⁺ (light shaded bars) found in EPS-I or the exoY culture supernatant.