The Aspergillus fumigatus siderophore biosynthetic gene sidA, encoding L-ornithine N5-oxygenase, is required for virulence

Aspergillus fumigatus is the leading cause of invasive mold infection and is a serious problem in immuno-compromised populations worldwide. We have previously shown that survival of A. fumigatus in serum may be related to secretion of siderophores. In this study, we identified and characterized the sidA gene of A. fumigatus, which encodes L-ornithine N-5-oxygenase, the first committed step in hydroxamate siderophore biosynthesis. A. fumigatus sidA codes for a protein of 501 amino acids with significant homology to other fungal L-ornithine N-5-oxygenases. A stable Delta sidA strain was created by deletion of A. fumigatus sidA. This strain was unable to synthesize the siderophores N',N",N'''-triacetylfusarinine C (TAF) and ferricrocin. Growth of the Delta sidA strain was the same as that of the wild type in rich media; however, the Delta sidA strain was unable to grow in low-iron defined media or media containing 10% human serum unless supplemented with TAF or ferricrocin. No significant differences in ferric reduction activities were observed between the parental strain and the Delta sidA strain, indicating that blocking siderophore secretion did not result in upregulation of this pathway. Unlike the parental strain, the Delta sidA strain was unable to remove iron from human transferrin. A rescued strain (Delta sidA + sidA) was constructed; it produced siderophores and had the same growth as the wild type on iron-limited media. Unlike the wild-type and rescued strains, the Delta sidA strain was avirulent in a mouse model of invasive aspergillosis, indicating that sidA is necessary for A. fumigatus virulence.