Hissen Anna H T, Wan Adrian N C, Warwas Mark L, Pinto Linda J, Moore Margo M
Department of Biological Sciences, Simon Fraser University, 8888 University Drive, Burnaby, British Columbia V5A 1S6, Canada.
Infect Immun. 2005 Sep;73(9):5493-503. doi: 10.1128/IAI.73.9.5493-5503.2005.
Aspergillus fumigatus is the leading cause of invasive mold infection and is a serious problem in immunocompromised 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 DeltasidA 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 DeltasidA strain was the same as that of the wild type in rich media; however, the DeltasidA 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 DeltasidA strain, indicating that blocking siderophore secretion did not result in upregulation of this pathway. Unlike the parental strain, the DeltasidA strain was unable to remove iron from human transferrin. A rescued strain (DeltasidA + 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 DeltasidA strain was avirulent in a mouse model of invasive aspergillosis, indicating that sidA is necessary for A. fumigatus virulence.
烟曲霉是侵袭性霉菌感染的主要病因，在全球免疫功能低下人群中是一个严重问题。我们之前已经表明，烟曲霉在血清中的存活可能与铁载体的分泌有关。在本研究中，我们鉴定并表征了烟曲霉的sidA基因，该基因编码L-鸟氨酸N(5)-加氧酶，这是异羟肟酸铁载体生物合成的第一步关键反应。烟曲霉sidA编码一个由501个氨基酸组成的蛋白质，与其他真菌的L-鸟氨酸N(5)-加氧酶具有显著同源性。通过缺失烟曲霉sidA构建了一个稳定的ΔsidA菌株。该菌株无法合成铁载体N',N",N'''-三乙酰铁载体C（TAF）和铁色素。ΔsidA菌株在丰富培养基中的生长与野生型相同；然而，ΔsidA菌株在低铁限定培养基或含有10%人血清的培养基中无法生长，除非补充TAF或铁色素。亲本菌株和ΔsidA菌株之间未观察到铁还原活性的显著差异，表明阻断铁载体分泌不会导致该途径的上调。与亲本菌株不同，ΔsidA菌株无法从人转铁蛋白中去除铁。构建了一个拯救菌株（ΔsidA + sidA）；它产生铁载体，并且在铁限制培养基上的生长与野生型相同。与野生型和拯救菌株不同，ΔsidA菌株在侵袭性曲霉病小鼠模型中无致病性，表明sidA是烟曲霉致病所必需的。
