Sib1, Sib2, and Sib3 proteins are required for ferrichrome-mediated cross-feeding interaction between  Schizosaccharomyces pombe  and  Saccharomyces cerevisiae .
Although  Saccharomyces cerevisiae  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  S. cerevisiae  cells  via  Arn1. Unlike  S. cerevisiae ,  Schizosaccharomyces pombe  synthesizes and secretes Fc. The  sib1   +  and  sib2   +  genes encode, respectively, a Fc synthetase and an ornithine-N 5 -oxygenase, which are required for Fc production. When both genes were expressed in  S. pombe , cross-feeding experiments revealed that  S. cerevisiae fet3 Δ  arn1-4 Δ cells expressing Arn1 could grow in the vicinity of  S. pombe  under low-iron conditions. In contrast, deletion of  sib1   +  and  sib2   +  produced a defect in the ability of  S. pombe  to keep  S. cerevisiae  cells alive when Fc is used as the sole source of iron. Further analysis identified a gene designated  sib3   +  that encodes an N 5 -transacetylase required for Fc production in  S. pombe . The  sib3 Δ mutant strain exhibited a severe growth defect in iron-poor media, and it was unable to promote Fc-dependent growth of  S. cerevisiae  cells. Microscopic analyses of  S. pombe  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  S. pombe  providing Fc that enables  S. cerevisiae  to grow when Fc is used as the sole source of iron.
Brault A, Mbuya B, Labbé S