The functional identification of Dps in oxidative stress resistance and virulence of Riemerella anatipestifer CH-1 using a new unmarked gene deletion strategy

Abstract Excessive iron in the bacterial cytoplasm can potentiate the production of harmful reactive oxygen species (ROS). Riemerella anatipestifer (R. anatipestifer), a Gram-negative bacterium, encodes iron uptake systems but the mechanism of iron detoxification is unknown. In this study, the dps of R. anatipestifer CH-1 was deleted using sacB as a counterselection marker. The dps mutant was more sensitive to H2O2 than the wild-type when cultured in iron-rich conditions, but not in iron-limited conditions, suggesting that Dps prevents H2O2-induced oxidative stress damage through iron-binding activity. However, the dps mutant and wild-type were identically sensitive to bactericidal antibiotics, antibiotic treatment did not enhanced R. anatipestifer ROS production. Furthermore, Dps also prevents the DNA damage by binding DNA. R. anatipestifer dps transcription was higher in the stationary phase than in the early and exponential phases and was activated by OxyR in the presence of H2O2. Finally, compared with the wild-type, the colonization levels of the dps mutant in duckling was similar at 48 h post-infection, but decreased significantly at 60 h post-infection, suggesting that R. anatipestifer Dps is not involved in host invasion but increases resistance to host clearance. Dps thus likely plays an important role in the physiology and pathogenesis of R. anatipestifer through protection against oxidative stress.