The filamentous ascomycete A. nidulans produces three major siderophores: it excretes fusigen and triacetylfusarinine C to capture iron, and uses ferricrocin as a cellular iron storage compound. Here we report the characterization of two siderophore biosynthetic genes, sidA and sidC,encoding L-ornithine N5-monooxygenase and a nonribosomal peptide synthetase, respectively. Deletion of sidA resulted in a complete lack of siderophore biosynthesis. Such strains were unable to germinate and grow unless the growth medium was supplemented with siderophores. These results suggests that the siderophore system is the major iron assimilatory system of A. nidulans. Growth-stimulation of the siderophore-deficient mutant by a high concentration of ferrous salts suggested the presence of an additional ferrous transport system. Disruption of sidCresulted in the loss of the cellular siderophore ferricrocin and decreased conidiation. The intracellular labile iron pool, monitored with calcein, was significantly increased in ferricrocin-lacking mutants. Consistently, these mutants showed increased expression of genes encoding antioxidative enzymes (sodA, catB,and cycA) and elevated sensitivity to the redox cycler paraquat demonstrating that the lack of ferricrocin causes oxidative stress. Remarkably, the SidA-deficient mutant synthesized ferricrocin when feeded with triacetylfusarinine C proving that A. nidulans possesses the enzymatic machinery to regenerate L-hydroxyornithine from this siderophore. This work was supported by Austrian Science Foundation grant FWF-P13202-MOB (to H.H.) and Austrian National Bank (OENB) grant 8750 (to H.H.).
Fungal Genet. Newsl. 50 (Supl):abstract
Full conference title:
22nd Fungal Genetics Conference
- Fungal Genetics Conference 22nd (2001)