CONSTRUCTION AND PHYSIOLOGICAL ANALYSIS OF A XANTHOMONAS MUTANT TO EXAMINE THE ROLE OF THE OXYR GENE IN OXIDANT-INDUCED PROTECTION AGAINST PEROXIDE KILLING

We constructed and characterized a Xanthomonas campestris pv. phaseoli oxyR mutant. The mutant was hypersensitive to H2O2 and menadione kill ing and had reduced aerobic plating efficiency. The oxidants' inductio n of the catalase and ahpC genes was also abolished in the mutant. Ana lysis of the adaptive responses showed that hydrogen peroxide-induced protection against hydrogen peroxide was lost, while menadione-induced protection against hydrogen peroxide was retained in the oxyR mutant. These results show that X campestris pv. phaseoli oxyR is essential t o peroxide adaptation and revealed the existence of a novel superoxide -inducible peroxide protection system that is independent of OxyR.