BIFUNCTIONAL CATALASE KatG OF Xanthomonas citri subsp. citri RESPONDS TO HYDROGEN PEROXIDE AND CONTRIBUTES TO UV RESISTANCE AND EPIPHYTIC SURVIVAL ON CITRUS LEAVES

TONDO M. L.; DELPRATO M. L.; KRAISELBURD I.; FERNÁNDEZ ZENOFF M. V.; FARIAS M. E.; ORELLANO A. G.

Córdoba

Congreso; Congreso Argentino de Microbiología General; 2015

SAMIGE

Xanthomonas citri subsp. citri (Xcc) is a Gram-negative obligate aerobic bacterium that infects citrus plants. During its life cycle Xcc is constantly exposed to hydrogen peroxide produced either by normal aerobic metabolism or as a part of the plant defense response against microbial invasion. In order to survive and colonize plant tissues Xcc must overcome hydrogen peroxide toxicity, and catalases are enzymes employed for its detoxification. We have previously shown that three catalase genes are effectively expressed in Xcc growing cells, being one of them the bifunctional catalase-peroxidase KatG. In this study we evaluated the physiological role of KatG and its relevance for Xcc virulence by the construction and characterization of a katG deficient mutant strain. We found that the Xcc katG mutant exhibit basal levels of catalase activity considerably lower than wild-type cells, and does not induce this activity when exposed to sub-lethal levels of hydrogen peroxide. In addition, the katG mutant was found to be extremely sensitive to hydrogen peroxide and does not increase its resistance after pre-adaptation with low doses of the oxidant. The extreme sensitivity of Xcc katG to oxidative stress was also evidenced by a significant build-up in cellular peroxides levels after treatment with low concentrations of hydrogen peroxide. The mutant strain also displayed reduced resistance to UV-A and UV-B radiation than wild type cells, and an impaired ability to develop biofilms on glass surfaces. In the interaction with orange plants, the katG mutant produced typical canker lesions when infiltrated directly in the apoplast space and was able to multiply inside plant tissues with similar kinetics of growth and to the same extent as wild-type cells. However, the mutant strain exhibited reduced epiphytic survival on host leaves, indicating that KatG may be important for the epiphytic state of Xcc prior to entry into the apoplast and colonization, which in term would determine the probability of diseaseoccurrence.