Antioxidant response of Xanthomonas axonopodis pv. citri to hydrogen peroxide

TONDO, M.; JORGELINA OTTADO; ORELLANO, ELENA

Pinamar

Congreso; 10th Congress Panamerican Association for Biochemistry and Molecular Biology; 2005

Xanthomonas axonopodis pv. citri (Xac) is the phytopathogen responsible for citrus canker. During invasion of host plant tissues, Xac is exposed to plant-produced hydrogen peroxide (H2O2), which is toxic to the pathogen. We studied the response of Xac to H2O2 and its possible participation in the interaction with plants. We evaluated the H2O2 resistance of early exponential Xac cultures and found that there is a decrease in viability with concentrations higher to 1 mM. Cultures pre-treated with sub-lethal concentrations of the oxidant showed an adaptive response that led to a higher resistance to lethal concentrations. These treatments produced an increase in the catalase activity. We also analysed this enzyme in different growth phases and observed that it was higher in stationary-phase compared to early-exponential phase. This was consistent with the capacity to resist H2O2. To investigate the possible participation of catalases in the interaction with host plants we determined the levels of this enzyme in Xac cultures grown in standard media and in XVM2, suspected to mimic the environment of plant intercellular spaces. We found that the catalase activity was higher in XVM2 compared to the other media, as well as the survival to H2O2. Our results indicate that catalase profile in Xac is different to that observed in other Xanthomonas, which show higher activity in early-exponential phase. In addition, catalase induction in XVM2 suggests a possible role of this enzyme in plant-pathogen interactions allowing the bacteria to overcome the oxidative stress associated to invasion.