Fungal siderophores ‐ membrane reactive ionophores

An increased excretion of desferri‐siderophores is observed during iron deficient growth conditions of fungi. On the other hand a small amount of siderophores could be detected in fungi, grown in an iron containing medium, indicating that a certain level of siderophores may be present during normal growth conditions. Fungal siderophores function in iron transport. After intracellular iron delivery the ligands are again excreted for another round of transport. The observed uptake rates confirmed the concept of a specificity of siderophore iron uptake and the existence of siderophore transport systems in fungal membranes, which recognize structure and conformation of the various siderophores. The chirality of siderophores plays a key role in iron transport in fungi. The interaction of siderophores with a receptor on the cytoplasma membrane of fungi is different from their interaction with bacterial membranes. Bacterial ferrichrome receptors are generally located within the outer membrane. Transport of siderophores is inhibited by respiratory poisons, uncouplers, and also by SH‐alkylating agents. Results indicate that the membrane potential plays a central role in siderophore iron transport in fungi.