Catalase has only a minor role in protection against near-ultraviolet radiation damage in bacteria

Summary In bacterial cells near-ultraviolet radiation (NUV) generates H₂O₂ which can be decomposed by endogenous catalase to H₂O and O₂. To assess the roles of H₂O₂ and catalase in NUV lethality, we manipulated the amount of intracellular catalase (a) by the use of mutant and plasmid strains with altered endogenous catalase, (b) physiologically, by the addition of glucose, and (c) by induction of catalase synthesis with oxidizing agents. Not only was there no direct correlation between NUV-resistance and catalase activity, but in some cases the correlation was inverse. Also, while there was correlation between NUV and H₂O₂ sensitivity for most strains tested, there were a number of exceptions which indicates that the modes of killing were different for the two agents.