FIG. 2.

Resistance to oxidant killing and levels of peroxide-scavenging enzymes in XpHR and its parental strain. (A) Qualitative determination of levels of resistance to killing concentrations of H₂O₂, menadione (MD), and tert-butyl hydroperoxide (t-BOOH) in X. campestris pv. phaseoli (Xp; □), X. campestris pv. phaseoli oxyR (Xp oxyR; ▒), XpHR (■), and XpHR oxyR ( ). Essentially, log-phase cells were mixed with Silva Buddenhagen (SB) top agar and poured onto SB plates. Six microliters of the indicated concentrations of oxidants were spotted on paper disks and placed on top of cell lawns. The zone of growth inhibition was measured after 30 h of incubation (16). Experiments were repeated at least three times, and representative data are shown. (B) Catalase levels of various Xanthomonas strains. (C) Western analysis of AhpC levels in various Xanthomonas strains. Forty micrograms of total protein was loaded into each lane. Western analysis and catalase assays were performed as previously described (17).