Isolation and characterization of a multiple peroxide resistant mutant from Xanthomonas campestris pv. phaseoli

We have isolated a spontaneous multiple peroxide resistant Xanthamonas campestris pv. phaseoli mutant (XpHr). In the presence of peroxides, the mutant had a higher growth rate than the parent. It also had a greater than 100-fold increase in resistance levels to H2O2 killing but only slightly more resistance to tert-butyl hydroperoxide killing. Increases in activity were detected for the peroxide scavenging enzymes catalase (100-fold) and AhpC (over 30-fold). Also observed was cross-resistance to thermal killing; however, no cross-resistance to other oxidants or chemicals was found. Analysis of protein profiles revealed that proteins with molecular masses of 22 and 58 kDa were accumulated while proteins of 29, 33 and 41 kDa were depressed in the mutant. These results indicate that the mutant may have defect(s) in peroxide regulation, which resulted in high constitutive expression of peroxide scavenging enzymes. Nevertheless, the mutant retained growth phase dependent regulation of peroxide killing. The mutant should be useful in unravelling the nature of a complex peroxide stress regulon.