FIGURE 5.

The Fur loss activates OxyR. (A,B) Effects of the fur mutation on sensitivity of S. oneidensis to H₂O₂. pBsdpaAB, B. subtilis dpaAB gene under the control of Ptac within pHGE-Ptac. Disk diffusion assay (A): paper disks of 6 mm in diameter loaded with 10 μl of 5 M H₂O₂ were placed on bacterial lawns (pre-grown for 6 h). Results shown were 24 h after the disks were in place. Survival assay (B): H₂O₂ was added to the mid-exponential phase cultures adjusted to 0.4 of OD₆₀₀ to a final concentration of 5 mM and viable cells were counted by plating. (C,D) Physiological functions of OxyR and Fur appear non-overlapping as shown by the cell pellet color (C) and viability on LB plates (D). (E) Immunoblot analysis of OxyR. In the indicated strains, His₆-tagged protein expression was induced with IPTG. Mid-exponential phase cells either treated with H₂O₂ of indicated concentrations for 30 min or not were collected, processed, and analyzed with antibodies against the hexahistidine tag. R, reduced form; O, oxidized form. Experiments were performed at least three times, and representative results are shown. *Represents OxyR^C203S, a mutant that could not be activated. ΔoxyR-con, the ΔoxyR strain does not express a his6-tagged OxyR as the control.