Functional characterization of Fur in iron metabolism, oxidative stress resistance and virulence of Riemerella anatipestifer

Iron is essential for most bacteria to survive, but excessive iron leads to damage by the Fenton reaction. Therefore, the concentration of intracellular free iron must be strictly controlled in bacteria. Riemerella anatipestifer (R. anatipestifer), a Gram-negative bacterium, encodes the iron uptake system. However, the iron homeostasis mechanism remains largely unknown. In this study, it was shown that compared with the wild type R. anatipestifer CH-1, R. anatipestifer CH-1 Delta fur was more sensitive to streptonigrin, and this effect was alleviated when the bacteria were cultured in iron-depleted medium, suggesting that the fur mutant led to excess iron accumulation inside cells. Similarly, compared with R. anatipestifer CH-1 increment recA, R. anatipestifer CH-1 increment recA Delta fur was more sensitive to H2O2-induced oxidative stress when the bacteria were grown in iron-rich medium rather than iron-depleted medium. Accordingly, it was shown that R. anatipestifer CH-1 increment recA Delta fur produced more intracellular ROS than R. anatipestifer CH-1 increment recA in iron-rich medium. Electrophoretic mobility shift assays showed that R. anatipestifer CH-1 Fur suppressed the transcription of putative iron uptake genes through binding to their promoter regions. Finally, it was shown that compared with the wild type, R. anatipestifer CH-1 Delta fur was significantly attenuated in ducklings and that the colonization ability of R. anatipestifer CH-1 Delta fur in various tissues or organs was decreased. All these results suggested that Fur is important for iron homeostasis in R. anatipestifer and its pathogenic mechanism.

Automated summary

Iron is crucial for the survival of most bacteria, but excessive iron can lead to damage. The study showed that the Fur protein plays a vital role in iron homeostasis and pathogenic mechanism of R. anatipestifer bacterium. Mutations in the Fur gene may result in excess intracellular iron accumulation.