ROLE OF ENTEROBACTIN AND INTRACELLULAR IRON IN CELL LETHALITY DURING NEAR-UV IRRADIATION IN ESCHERICHIA-COLI

In Escherichia coli, fur mutants that constitutively express their nat ive iron chelating agent, enterobactin, are significantly more sensiti ve to near-UV radiation (NUV) than wild type, An entA mutant, which is incapable of synthesizing enterobactin, is equal to wild type in resi stance to NUV irradiation, However, the addition of Fe+3 enterobactin but not Al+3 enterobactin to entA cell suspensions just prior to irrad iation results in an increased sensitivity to NUV irradiation, A fes m utant, which is unable to reduce and release iron from enterobactin, i s significantly more sensitive to NUV irradiation than wild type. The addition of nontoxic levels of H2O2 (5 mu M) just prior to irradiation significantly increases sensitivity of both fur and fes mutants, Thes e results suggest that one mechanism by which NUV irradiation leads to cell lethality is by creating a transient iron overload, producing ve ry favorable conditions for the production of highly deleterious free radicals through a variety of mechanisms that lead to oxidative stress and DNA damage including lethal and mutagenic lesions, These results are consistent with the hypothesis that enterobactin is an endogenous chromophore for NUV and contributes to cell lethality via the destruct ion of its ligand, releasing Fe+2 into the cytoplasm to catalyze the p roduction of highly reactive hydroxyl radicals and other toxic oxygen species via the Haber-Weiss reaction.