IRON ACQUISITION BY CRYPTOCOCCUS-NEOFORMANS

Iron is an essential element for the growth and metabolism of microbia l cells. Most pathogenic microbes elaborate powerful iron chelating ag ents (siderophores) to mobilize iron from ferric ligands. The pathogen ic yeast, Cryptococcus neoformans has not been found to produce sidero phores and its mechanism of iron acquisition is unknown. This investig ation explored an alternative pathway for iron acquisition by examinin g the interactions of iron with the cell surface. Iron uptake experime nts were conducted utilizing radiolabelled ferrous iron and ferric iro n chelates, with evidence for the presence of iron(II) receptors and t he generation of ferrous iron by surface reduction. Hyperbolic kinetic s were found when Fe-59(II) was presented to the organism and uptake w as blocked with bathophenanthroline sulphonate, an Fe2+ chelator. The yeast also acquired iron as [Fe-59(3+)]-citrate and [Fe-59(3+)]-pyroph osphate while bathophenanthroline sulphonate reduced the acquisition o f these ferric ligands by 48% and 52% respectively. Pre-incubation wit h either ferric ligand also reduced iron acquisition by 50%. KCN inhib ited uptake of iron(II) by 90% and uptake of [Fe-59(3+)]-pyrophosphate and [Fe-59(3+)]-citrate by 46% and 56% respectively; dinitrophenol ha d no effect on these processes. The data suggest that C. neoformans ca n (i) generate ferrous iron at the cell surface via a reduction of fer ric chelates, with the subsequent acquisition of the ferrous iron, and (ii) acquire iron through the interaction of ferric chelates with a s urface component.