Siderophore uptake and use by the yeast Saccharomyces cerevisiae

The non-reductive uptake of several siderophores (ferrioxamine B. ferrichro me, triacetylfusarinine C and ferricrocin) by various strains of Saccharomy ces cerevisiae was studied, Several aspects of siderophore transport were e xamined, including specificity of transport, regulation of transport and in tracellular localization of the ferri-siderophores, Ferrioxamine B was take n up preferentially via the products of the SIT1 gene and triacetylfusarini ne C by the TAF1 gene product, but the specificity was not absolute, Ferric hrome and ferricrocin uptake was not dependent on a single major facilitato r superfamily (MFS) gene product, The apparent specificity of transport was strongly dependent on the genetic background of the cells, Non-reductive u ptake of siderophores was induced under more stringent conditions (of iron deprivation) than was the reductive uptake of ferric citrate. Regulation of transport depended on the transcriptional factors Aft1 and Tup1/Ssn6, Cell s disrupted for the TUP? or SSN6 genes were constitutively derepressed for the uptake of ferrichrome, ferricrocin or ferrioxamine B, but not for the u ptake of triacetylfusarinine C, Cells bearing the AFT1(up) mutation accumul ated large amounts of ferric siderophores, Intracellular decomplexation of the siderophores occurred when transcription of the AFT1(up) gene was repre ssed. Ferrioxamine B and ferrichrome seemed to accumulate in an endosomal c ompartment, as shown by biochemical studies and by confocal microscopy stud y of cells loaded with a fluorescent derivative of ferrichrome, Endocytosis was, however, not involved in the non-reductive uptake of siderophores.