Effect of NaN3 on Oxygen-Dependent Lethality of UV-A in Escherichia coli Mutants Lacking Active Oxygen-Defence and DNA-Repair Systems

Escherichia coli mutants which lack defence systems against such active oxygen forms as OxyR (ΔoxyR), superoxide dismutase (SOD) (sodA and sodB) and catalase (katE and katG) are sensitive to UV-A lethality under aerobic conditions, whereas OxyR- and SOD-mutants have resistance under anaerobic conditions and in the presence of sodium azide (NaN3) during irradiation. UV-A induces lipid peroxidation in the ΔoxyR mutant, which is suppressed by NaN3. These results suggest that UV-A generates ¹O2 or the hydroxyl radical to produce lipid peroxides intracellularly in the ΔoxyR mutant and that O2^- stress may be generated in the sodAB mutant after 8 hr of exposure to UV-A. The sensitivities of such DNA repair-deficient mutants as recA^ind- and uvrA to UV-A also were examined and compared. These mutants are sensitive to UV-A lethality under aerobic conditions but show only slight resistance under anaerobic conditions or in the presence of NaN3 during irradiation. We conclude that NaN3 protects these mutant cells from oxygen-dependent UV-A lethality.