Growth of Escherichia coli in Iron-enriched Medium Increases HPI Catalase Activity

induced during logarithmic growth in response to low concentrations of hydrogen peroxide. This induction is OxyR-dependent. On the other hand, HPII is not peroxide-inducible but is induced in entry to the stationary phase. We demonstrate here that E. coli displayed higher HPI catalase activity when compared to the cultures that were grown in a normal medium, if grown in a medium supplemented with iron-citrate. Iron supplementation had no effect on HPII catalase. This increase of HPI activity was OxyR-independent and not observed in a ∆fur mutant. The physiological significance of the increase of HPI activity is unclear, but it appears that the katG gene that codes for HPI catalase is among the genes that are regulated by Fur