GROWTH IN IRON-ENRICHED MEDIUM PARTIALLY COMPENSATES ESCHERICHIA-COLIFOR THE LACK OF MANGANESE AND IRON SUPEROXIDE-DISMUTASE

Enrichment of the growth medium with iron partially relieves the pheno typic deficits imposed on Escherichia coli by lack of both manganese a nd iron superoxide dismutases. Thus iron supplementation increased the aerobic growth rate, decreased the leakage of sulfite, and diminished sensitivity toward paraquat. Iron supplementation increased the activ ities of several [4Fe-4S]-containing dehydratases, and this was seen e ven in the presence of 50 mu g/ml of rifampicin, an amount which compl etely inhibited growth. Assessing the O-2(radical anion) scavenging ac tivity by means of lucigenin luminescence indicated that the iron-enri ched sodAsodB cells had gained some means of eliminating O-2(radical a nion) which was not detectable as superoxide dismutase activity in cel l extracts. It is noteworthy that iron-enriched cells were not more se nsitive toward the lethality of H2O2 despite having the usual amount o f catalase activity. This indicates that iron taken into the cells fro m the medium is not available for Fenton chemistry, but is available f or reconstitution of iron-sulfur clusters.We suppose that oxidation of the [4Fe-4S] clusters of dehydratases by O-2(radical anion) and their subsequent reductive reconstitution provides a mechanism for scavengi ng O-2(radical anion), and that speeding this reductive reconstitution by iron enrichment both spared other targets from O-2(radical anion) attack and maintained adequate levels of these enzymes to meet the met abolic needs of the cells.