The interplay between vacuolar and siderophore-mediated iron storage in Aspergillus fumigatus

Iron is an essential element for all eukaryotes but its excess has deleterious effects. Aspergillus fumigatus produces extracellular siderophores for iron uptake and the intracellular siderophore ferricrocin (FC) for distribution and storage of iron. Iron excess has previously been shown to increase the content of ferric FC and the expression of the putative vacuolar iron importer CccA (AFUA_4G12530), indicating a role of both the vacuole and FC in iron detoxification. In this study, we show that CccA-deficiency decreases iron resistance in particular in combination with derepressed iron uptake, while overproduction of CccA increases iron resistance. Green fluorescence protein-tagging confirmed localization of CccA in the vacuolar membrane. In contrast to CccA-deficiency, inactivation of FC biosynthesis did not affect iron resistance, which indicates that vacuolar rather than FC-mediated iron storage is the major iron detoxifying mechanism. After uptake, extracellular siderophore backbones are hydrolyzed and recycled. Lack of FC, CccA, and in particular lack of both increased the cellular content of iron chelated by siderophore breakdown products. These data indicate that the transfer of iron from extracellular siderophores to the metabolism, FC or the vacuole precedes recycling of siderophore breakdown products. Furthermore, this study indicates that CccA does not play an exclusive role in vacuolar iron storage for nutritional reuse.