Role of the Dickeya dadantii Dps protein

During infection, the phytopathogenic enterobacterium Dickeya dadantii has to cope with iron-limiting conditions and the production of reactive oxygen species by plant cells. A tight control of the bacterial intracellular iron content is necessary for full virulence of D. dadantii: previous studies have shown that the ferritin FtnA and the bacterioferrtin Bfr, devoted to iron storage, contribute differentially to the virulence of this species. In this work, we investigated the role of the Dps miniferritin in iron homeostasis in D. dadantii. We constructed a Dps-deficient mutant by reverse genetics. This mutant grew like the wild-type stain under iron starvation and showed no decreased iron content. However, the dps mutant displayed an increased sensitivity to hydrogen peroxide in comparison to the wild-type strain. This hydrogen peroxide susceptibility only occurs when bacteria are in the stationary phase. Unlike the bfr and the ftnA mutants, the dps mutant is not affected in its pathogenicity on host plants. The dps gene expression is induced at the stationary phase of growth. The Sigma S transcriptional factor is necessary for this control. Furthermore, dps expression is positively regulated by the oxidative stress response regulator OxyR during the exponential growth phase, after hydrogen peroxide treatment. These results indicate that the Dps miniferritin from D. dadantii has a minor role in iron homeostasis, but is important in conferring tolerance to hydrogen peroxide and for survival of cells that enter the stationary phase of growth.