The Ralstonia solanacearum catalase-peroxidase KatG is crucial to survive environmental stresses and also plays a role in plant infection

Throughout their life cycle, pathogens are challenged by Reactive Oxygen Species (ROS) and must deploy defence mechanisms against oxidative damage. Environmental stressors such as ultraviolet radiation and desiccation induce intracellular ROS production. Moreover, during pathogen colonisation, plant hosts initiate an oxidative burst, leading to the accumulation of hydrogen peroxide (H₂O₂). Catalases mitigate ROS toxicity by catalysing the breakdown of H₂O₂ into water and oxygen. In this study, we explored the roles of the monofunctional catalase (KatE) and the bifunctional catalase-peroxidase (KatG) in the phytopathogen Ralstonia solanacearum during both environmental stress conditions and in planta colonisation stages. Our results demonstrate that both catalases are critical for surviving ROS, with KatG having a more preponderant role. Plant pathogenicity assays show that catalases are not required for virulence although they are important for bacterial fitness in the apoplast. In contrast, we prove that both catalases are vital for R. solanacearum response to oxidative stress in the external environment. KatG was indispensable for survival in soil, as well as for enduring ultraviolet radiation and desiccation exposure. Our findings reveal that the primary function of R. solanacearum catalases is to counteract ROS generated by environmental stressors rather than host-derived oxidative defences. This research identifies specific environmental stressors that these catalases combat during pathogen survival. These insights pave the way for future strategies targeting catalase activity to control bacterial wilt disease.