The catalase-peroxidase KatG is required for virulence of Xanthomonas campestris pv. campestris in a host plant by providing protection against low levels of H2O2

Xanthomonas campestris pv. campestris katG encodes a catalase-peroxidase that has a role in protecting the bacterium against micromolar concentrations of H2O2. A knockout mutation in katG that causes loss of catalase-peroxidase activity correlates with increased susceptibility to H2O2 and a superoxide generator and is avirulent in a plant model system. katG expression is induced by oxidants in an OxyR-dependent manner. Catalase-peroxidases (KatGs) are heme-containing enzymes that possess catalatic and substantial peroxidatic activities. KatGs belong to class I of the superfamily of bacterial, fungal, and plant peroxidases, and they are present in a variety of prokaryotes and some ascomycete fungi (21). These enzymes function as H2O2 scavengers, protecting cells from H2O2 tox-icity. In addition, in Mycobacterium tuberculosis, KatG is also involved in the activation of the frontline antituberculosis drug isoniazid (32). A number of isoniazid-resistant strains are the consequence of mutations within katG (32). katG also has roles in bacterial pathogenicity (31)