B739_RS00825-deleted strain of Riemerella anatipestifer CH-1: heme detoxication, oxidative stress resistance, and colonization

Abstract:

[Objective] The heme of host is an important iron source for pathogenic bacteria. However, excessive heme can cause damage to bacteria. Bacteria can reduce the heme toxicity through regulation, efflux, and chelation. Riemerella anatipestifer is a Gram-negative bacterium that infects ducks and other birds. The available studies have demonstrated that R. anatipestifer encodes a heme transport system to obtain heme from host hemoglobin. However, we are not clear whether this bacterium encodes heme detoxification protein or not. In this study, we analyzed the roles of B739_RS00825encoding nitric oxide synthase in heme detoxification, oxidative stress resistance, and host colonization. [Methods] We constructed the B739_RS00825-deleted strain and studied its roles in heme detoxification, oxidative stress resistance, and host colonization through establishing the growth curve and determining the survival rate under H₂O₂ stress, the lethality to ducklings, and the colonization ability in ducklings. [Results] Compared with that of R. anatipestifer CH-1, the growth of CH-1ΔB739_RS00825 in the medium supplemented with excessive heme was not affected. However, compared with CH-1Δfur, CH-1ΔfurΔB739_RS00825 showed significantly inhibited growth in the medium containing excess heme and weakened resistance to H₂O₂. The transcription of B739_RS00825 was significantly upregulated under oxidative stress and in CH-1Δfur. Compared with CH-1, CH-1ΔB739_RS00825 did not show attenuated lethality or colonization in ducklings. [Conclusion] Gene B739_RS00825 was involved in the heme detoxification and oxidative stress resistance of R. anatipestifer and it was regulated by ferric uptake regulator (Fur). However, the gene was not involved in the lethality or colonization of R. anatipestifer in ducklings.