Oxidative stress leads to Fur-mediated activation of ftnA in Escherichia coli independently of OxyR/SoxRS regulators
Ferritin FtnA is the main scavenger of Fe2+ and storage of Fe3+ in bacterial cells, together with Dps and Bfr preventing the Fenton reaction and thus protecting the cell from iron-induced oxidative stress. However, until now, it was not known how its expression is regulated under conditions of oxidative stress, and the available evidence was contradictory. To study the regulation of E. coli ftnA expression in response to oxidative stress, PftnA-luxCDABE transcriptional fusion in different strains was used. It has been shown that PftnA is induced after the addition of oxidative stress inducers. The maximum amplitude of this activation did not depend on the presence of functional genes oxyR and soxR in the cell, but completely disappeared in the absence of fur. The response is amplified in the ftnA mutant and is diminished in the FtnA-overproducing strain, which indicates that iron sequestration blocks the response. Exposure of a cell to H2O2 initially inactivates Fur and a number of iron-utilizing proteins, and derepresses iron uptake. This results in an increase in the cellular iron content with the consequent Fur reactivation, which leads to the induction of ftnA expression. Thus, oxidative stress leads to PftnA activation, which is mediated by Fur and time-delayed in comparison with OxyR-response.