The Aspergillus fumigatus Siderophore Biosynthetic Gene sidA , Encoding l -Ornithine N ⁵ -Oxygenase, Is Required for Virulence

Abstract

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 ⌬sidA strain was created by deletion of A. fumigatus sidA. This strain was unable to synthesize the siderophores N,N؆,Nٟ-triacetylfusarinine C (TAF) and ferricrocin. Growth of the ⌬sidA strain was the same as that of the wild type in rich media; however, the ⌬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 ⌬sidA strain, indicating that blocking siderophore secretion did not result in upregulation of this pathway. Unlike the parental strain, the ⌬sidA strain was unable to remove iron from human transferrin. A rescued strain (⌬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 ⌬sidA strain was avirulent in a mouse model of invasive aspergillosis, indicating that sidA is necessary for A. fumigatus virulence.

Siderophores for molecular imaging applications

“…(1) siderophore biosynthesis and uptake are transcriptionally upregulated during iron starvation in vitro as well as in vivo in a murine model for pulmonary infection with the mold Aspergillus fumigatus (A. f.) [10,11], and (2) genetic inactivation of siderophore biosynthesis attenuates virulence of A. f. in a murine infection model, which demonstrates that siderophoremediated iron assimilation plays the major role for virulence [12,13]. Moreover, the siderophore of A. f., triacetylfusarinine C (TAFC) was shown to be able to extract iron from host transferrin [14]. A scheme of TAFC-mediated iron uptake is shown in Fig.…”

Role of Ser-257 in the Sliding Mechanism of NADP(H) in the Reaction Catalyzed by the Aspergillus fumigatus Flavin-dependent Ornithine N5-Monooxygenase SidA

“…Briefly, 25 mg of NADP ϩ (5.6 mM final concentration), 480 l of 2-propanol d 8 (1 M final concentration), and 50 units of alcohol dehydrogenase (Thermoanaerobium brockii) were added to 6 ml of 25 mM Tris-Cl (pH 9.0). The reaction was allowed to proceed for 30 min at 40°C with light agitation until the A 260 /A 340 ratio reached a value of ϳ2.5.…”

“…This reaction is essential for the production of functional hydroxamate-containing siderophores in Aspergillus spp. Deletion of the sidA gene in A. fumigatus leads to a mutant strain that is avirulent in mouse models (7,8). The absence of a SidA homolog in humans and the essential role of this enzyme in virulence suggest that SidA is an ideal drug target.…”

Aspergillosis and stem cell transplantation: An overview of experimental pathogenesis studies

“…Not surprisingly, siderophore biosynthesis has also been implicated in virulence in both neutropenic and non-neutropenic mouse models. [70][71][72][73] The A. fumigatus DsidA mutant, which is completely deficient in iron siderophore synthesis, grows poorly in low iron conditions and within alveolar macrophages and is completely avirulent. 73 Attenuated virulence has also been reported in other strains of A. fumigatus with mutations in the siderophore synthesis pathway and with other mutations affecting iron metabolism, including HapX, AcuM, and AcuK.…”