Induced adaptive and cross-protection responses against oxidative stress killing in a bacterial phytopathogen, Xanthomonas oryzae pv. oryzae

Abstract

In Xanthomonas oryzae pv. oryzae, exposure to a sub-lethal concentration of H2O2conferred protection to subsequent challenges with a killing concentration of H2O2(30 mM, adaptive response). No adaptive response to tert-butylhydroperoxides (tBOOH) or the superoxide generator menadione was observed. However, exposure to sub-lethal concentrations of tBOOH or N-ethylmaleimide (a thiol reagent) induced cross-protection to low 30 mM lethal levels of H2O2but not to organic peroxides. Pre-treatment with a superoxide generator conferred cross-protection against a high lethal concentration (150 mM) of H2O2and an organic hydroperoxide (tBOOH). The levels of protection against H2O2killing caused by various inducers were correlated with their ability to induce catalase. There was no cross-regulation between oxidative stress and heat shock. Both adaptive and cross-protection responses required de novo protein synthesis. Many aspects of these responses in X. oryzae pv. oryzae are unlike responses previously observed in other microbes and they may have important physiological roles.