Siderophore-mediated iron (III) transport in the mycelia of the cultivated fungus, Agaricus bisporus.

Three structurally diverse iron (III) sequestering compounds (siderophores) were isolated from the supernatants of early stationary phase iron-deficient cultures of vegetative mycelia of the cultivated mushroom, Agaricus bisporus (ATCC 36416). The compounds were purified as their ferric chelates to homogeneity by gel permeation, cation exchange, and low-pressure reversed phase C18 chromatographies, and characterized as trihydroxamic acids. The chelates were identified as ferrichrome, ferric fusarinine C, and an unusual compound, des (diserylglycyl) ferrirhodin (DDF) by HPTLC cochromatography and electrophoresis against authentic samples, hydrolysis and amino acid analysis, and FAB-MS and 1H NMR spectroscopy. The iron transport activities of the three compounds (and of some structurally similar exogenous compounds) in young mycelial cells were determined by time- and concentration-dependent kinetic assays and inhibition experiments (CN-, N3-) using 55Fe(3+)-labeled chelates. 55Iron (III) uptake mediated by all three compounds was found to be via high affinity, energy-dependent processes; transport effectiveness was in the order: ferrichrome > DDF >> ferric fusarinine C. The relative uptake of iron by lambda-cis ferrichromes was: ferrichrome > ferrirhodin >> ferrichrome A; transport activity by the delta-cis fusarinines was: ferric fusarinine C > tris cis-(and trans-) fusarinine iron (III) >> ferric N1-triacetylfusarinine C.