EFFECTS OF 1,10-PHENANTHROLINE AND HYDROGEN-PEROXIDE IN ESCHERICHIA-COLI - LETHAL INTERACTION

It has been observed that when Escherichia coli cells are treated simu ltaneously with phenanthroline and H2O2, there is a lethal interaction . In order to analyze the mechanism of this lethal interaction, wild-t ype and xthA mutant cells of E. coli were treated with 2.5 mM H2O2 and 1 mM phenanthroline. This treatment was preceded by treatments with d ifferent metal chelators (dipyridyl for Fe2+, desferal for Fe3+ and ne ocuproine for Cu2+) or conducted simultaneously to other treatments wi th chelators and radical scavengers (thiourea, ethanol and sodium benz oate). The lethal interaction was observed in both the E. coli wild-ty pe strain and xthA mutant strain, which is deficient in the exonucleas e III repair enzyme. Nevertheless, the mutant strain was much more sen sitive than the wild-type one. Dipyridyl pretreatment protected the ce lls against the lethal interaction, while desferal pretreatment was un able to do so. This suggests that the lethal interaction requires Fe2 and not Fe3+ ions. Ethanol and sodium benzoate were incapable of prot ecting bacterial cells against the lethal interaction. Even a 20-min p retreatment with benzoate did not confer protection. On the other hand , thiourea protected the cells completely. Based on our results, we pr opose that the lethal interaction may be caused not only by the reacti on kinetics of phenanthroline and Fe, but also by the ability of phena nthroline to intercalate in DNA. After forming the mono and bis comple xes, phenanthroline would serve as a shuttle and take the Fe2+ ions to the DNA. So, the Fenton reaction would take its course with the conse quent generation of OH. radicals near DNA. This proximity to the DNA w ould protect the OH. radicals against the scavengers' action, thus opt imizing the Fenton reaction. (C) 1997 Elsevier Science B.V.