Atypical adaptive and cross-protective responses against peroxide killing in a bacterial plant pathogen, Agrobacterium tumefaciens

Physiological adaptive and cross-protection responses to oxidants were investigated in Agrobacterium tumefaciens. Exposure of A. tumefaciens to sublethal concentrations of H₂O₂ induced adaptive protection to lethal concentrations of H₂O₂. Similar treatments with organic peroxide and menadione did not produce adaptive protection to subsequent exposure to lethal concentrations of these oxidants. Pretreatment of A. tumefaciens with an inducing concentration of menadione conferred cross-protection against H₂O₂, but not to tert-butyl hydroperoxide (tBOOH), killing. The menadione induced cross-protection to H₂O₂ was due to the compound's ability to highly induce the peroxide scavenging enzyme, catalase. The levels of catalase directly correlated with the bacterium's ability to survive H ₂O₂ treatment. Some aspects of the oxidative stress response of A. tumefaciens differ from other bacteria, and these differences may be important in plant/microbe interactions.