Eisendle Martin, Oberegger Harald, Zadra Ivo, Haas Hubertus
Department of Molecular Biology, University of Innsbruck, Fritz-Pregl-Str. 3, A-6020 Innsbruck, Austria.
Mol Microbiol. 2003 Jul;49(2):359-75. doi: 10.1046/j.1365-2958.2003.03586.x.
The filamentous ascomycete A. nidulans produces two major siderophores: it excretes triacetylfusarinine C to capture iron and contains ferricrocin intracellularly. In this study we report the characterization of two siderophore biosynthetic genes, sidA encoding l-ornithine N(5)-monooxygenase and sidC encoding a non-ribosomal peptide synthetase respectively. Disruption of sidC eliminated synthesis of ferricrocin and deletion of sidA completely blocked siderophore biosynthesis. Siderophore-deficient strains were unable to grow, unless the growth medium was supplemented with siderophores, suggesting that the siderophore system is the major iron assimilatory system of A. nidulans during both iron depleted and iron-replete conditions. Partial restoration of the growth of siderophore-deficient mutants by high concentrations of Fe(2+) (but not Fe(3+)) indicates the presence of an additional ferrous transport system and the absence of an efficient reductive iron assmilatory system. Uptake studies demonstrated that TAFC-bound iron is transferred to cellular ferricrocin whereas ferricrocin is stored after uptake. The siderophore-deficient mutant was able to synthesize ferricrocin from triacetylfusarinine C. Ferricrocin-deficiency caused an increased intracellular labile iron pool, upregulation of antioxidative enzymes and elevated sensitivity to the redox cycler paraquat. This indicates that the lack of this cellular iron storage compound causes oxidative stress. Moreover, ferricrocin biosynthesis was found to be crucial for efficient conidiation.
它分泌三乙酰铁载体C来捕获铁，并在细胞内含有铁载体菌素。在本研究中，我们报道了两个铁载体生物合成基因的特性，分别是编码L-鸟氨酸N(5)-单加氧酶的sidA和编码非核糖体肽合成酶的sidC。sidC的破坏消除了铁载体菌素的合成，而sidA的缺失则完全阻断了铁载体的生物合成。缺乏铁载体的菌株无法生长，除非在生长培养基中添加铁载体，这表明铁载体系统是构巢曲霉在缺铁和铁充足条件下的主要铁同化系统。高浓度的Fe(2+)（而非Fe(3+)）使缺乏铁载体的突变体的生长得到部分恢复，这表明存在一个额外的亚铁转运系统，且缺乏有效的还原铁同化系统。摄取研究表明，与三乙酰铁载体C结合的铁会转移到细胞内的铁载体菌素中，而铁载体菌素在摄取后会被储存。缺乏铁载体的突变体能够从三乙酰铁载体C合成铁载体菌素。铁载体菌素缺乏导致细胞内不稳定铁池增加、抗氧化酶上调以及对氧化还原循环剂百草枯的敏感性升高。这表明缺乏这种细胞内铁储存化合物会导致氧化应激。此外，发现铁载体菌素的生物合成对于高效产孢至关重要。
