Sib1, Sib2, and Sib3 proteins are required for ferrichrome-mediated cross-feeding interaction between and .

Although is unable to produce siderophores, this fungal organism can assimilate iron bound to the hydroxamate-type siderophore ferrichrome (Fc) produced and secreted by other microbes. Fc can enter cells Arn1. Unlike , synthesizes and secretes Fc. The and genes encode, respectively, a Fc synthetase and an ornithine-N-oxygenase, which are required for Fc production. When both genes were expressed in , cross-feeding experiments revealed that Δ Δ cells expressing Arn1 could grow in the vicinity of under low-iron conditions. In contrast, deletion of and produced a defect in the ability of to keep cells alive when Fc is used as the sole source of iron. Further analysis identified a gene designated that encodes an N-transacetylase required for Fc production in . The Δ mutant strain exhibited a severe growth defect in iron-poor media, and it was unable to promote Fc-dependent growth of cells. Microscopic analyses of cells expressing a functional Sib3-GFP protein revealed that Sib3 was localized throughout the cells, with a proportion of Sib3 being colocalized with Sib1 and Sib2 within the cytosol. Collectively, these results describe the first example of a one-way cross-feeding interaction, with providing Fc that enables to grow when Fc is used as the sole source of iron.