Oxidant-inducible resistance to hydrogen peroxide killing in Agrobacterium tumefaciens requires the global peroxide sensor-regulator OxyR and KatA

Abstract

Induced adaptive and cross-protective responses to peroxide stress are important strategies used by bacteria to survive stressful environments. We have shown that exposure to low levels of peroxide (adaptive) and superoxide anions (cross-protection) induced high levels of resistance to peroxide killing in Agrobacterium tumefaciens. The mechanisms and genes involved in these processes have not been identified. Here, the roles played by peroxide ( oxyR) and superoxide ( soxR) global regulators and a catalase gene ( katA) during these responses were investigated. H 2O 2-induced adaptive protection was completely abolished in both the oxyR and katA mutants. Superoxide generator (menadione)-induced cross-protection to H 2O 2 killing was observed in a soxR mutant, but not in either an oxyR or a katA mutant. In vivo analysis of the katA promoter, using a katA::lacZ transcriptional fusion, revealed that it could be induced by menadione in an oxyR-dependent manner. These results lead us to conclude that H 2O 2 and superoxide anions directly or indirectly oxidize OxyR and it is the resulting activation of katA expression that is responsible for the induced protection against lethal concentrations of H 2O 2.