Oxidative stress leads to Fur-mediated activation offtnAinEscherichia coliindependently 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 ofE. coli ftnAexpression in response to oxidative stress, P_ftnA-luxCDABEtranscriptional fusion in different strains was used. It has been shown that P_ftnAis induced after the addition of oxidative stress inducers. The maximum amplitude of this activation did not depend on the presence of functional genesoxyRandsoxRin the cell, but completely disappeared in the absence offur. The response is amplified in theftnAmutant and is diminished in the FtnA-overproducing strain, which indicates that iron sequestration blocks the response. Exposure of a cell to H₂O₂initially 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 offtnAexpression. Thus, oxidative stress leads to P_ftnAactivation, which is mediated by Fur and time-delayed in comparison with OxyR-response.