Functional Characterization of FeoAB in Iron Acquisition and Pathogenicity in Riemerella anatipestifer

The bacterium Riemerella anatipestifer requires iron for growth, but the mechanism of iron uptake is not fully understood. In this study, we disrupted the Feo system and characterized its function in iron import in R. anatipestifer ATCC 11845. Compared to the parent strain, the growth of the ΔfeoA, ΔfeoB, and ΔfeoAB strains was affected under Fe3+-limited conditions, since the absence of the feo system led to less intracellular iron than in the parent strain. In parallel, the ΔfeoAB strain was shown to be less sensitive to streptonigrin, an antibiotic that requires free iron to function. The sensitivity of the ΔfeoAB strain to hydrogen peroxide was also observed to be diminished compared with that of the parent strain, which could be related to the reduced intracellular iron content in the ΔfeoAB strain. Further research revealed that feoA and feoB were directly regulated by iron through the Fur regulator and that the transcript levels of feoA and feoB were significantly increased in medium supplemented with 1 mM MnCl2, 400 μM ZnSO4, and 200 μM CuCl2. Finally, it was shown that the ΔfeoAB strain of R. anatipestifer ATCC 11845 was significantly impaired in its ability to colonize the blood, liver, and brain of ducklings. Taken together, these results demonstrated that FeoAB supports ferrous iron acquisition in R. anatipestifer and plays an important role in R. anatipestifer colonization. IMPORTANCE In Gram-negative bacteria, the Feo system is an important ferrous iron transport system. R. anatipestifer encodes an Feo system, but its function unknown. As iron uptake may be required for oxidative stress protection and virulence, understanding the contribution of iron transporters to these processes is crucial. This study showed that the ΔfeoAB strain is debilitated in its ability to import iron and that its intracellular iron content was constitutively low, which enhanced the resistance of the deficient strain to H2O2. We were surprised to find that, in addition to responding to iron, the Feo system may play an important role in sensing manganese, zinc, and copper stress. The reduced colonization ability of the ΔfeoAB strain also sheds light on the role of iron transporters in host-pathogen interactions. This study is important for understanding the cross talk between iron and other metal transport pathways, as well as the pathogenic mechanism in R. anatipestifer.