ISOLATION AND CHARACTERIZATION OF A MULTIPLE PEROXIDE RESISTANT MUTANT FROM XANTHOMONAS-CAMPESTRIS PV PHASEOLI

We have isolated a spontaneous multiple peroxide resistant Xanthomonas campestris pv. phaseoli mutant (XpHr). In the presence of peroxides, the mutant had a higher growth rate than the parent. It also had a gre ater than 100-fold increase in resistance levels to H2O2 killing but o nly slightly more resistance to tert-butyl hydroperoxide killing. Incr eases in activity were detected for the peroxide scavenging enzymes ca talase (100-fold) and AhpC (over 30-fold). Also observed was cross-res istance to thermal killing; however, no cross-resistance to other oxid ants or chemicals was found. Analysis of protein profiles revealed tha t proteins with molecular masses of 22 and 58 kDa were accumulated whi le proteins of 29, 33 and 41 kDa were depressed in the mutant. These r esults indicate that the mutant may have defect(s) in peroxide regulat ion, which resulted in high constitutive expression of peroxide scaven ging enzymes. Nevertheless, the mutant retained growth phase dependent regulation of peroxide killing. The mutant should he useful in unrave lling the nature of a complex peroxide stress regulon.