Polymorphism of the Iron Homeostasis Genes and Iron Sensitivity in Saccharomyces cerevisiae Flor and Wine Strains

Abstract

Iron is an essential micronutrient for all living organisms. The mechanisms of iron transport and homeostasis have been studied in detail in Saccharomyces cerevisiae yeasts, and iron metabolism in the strains isolated from different ecological niches was found to vary. In the present work, comparative analysis of iron homeostasis in the wine and flor yeast strains was carried out. Flor yeasts are characterized by their ability to grow as a biofilms on the surface of fortified wine materials, where they carry out oxidative metabolism. We have found that flor strains are more sensitive to elevated iron concentrations as compared to wine strains and accumulate iron more efficiently when grown in iron-limited media. These features correlate with the Q648X mutation in the Aft1p transcription factor, resulting in emergence of its truncated form and with the chromosomal rearrangement resulting in the deletion of the FRE-FIT cluster containing the Fre3p and Fre5p iron reductase genes and of the Fit2p and Fit3p membrane proteins responsible for accumulation of siderophore-bound iron in the cell wall. Our results indicate a significant adaptive role of these variations in the iron homeostasis genes for the physiology of flor yeasts, since selection of these organisms was accompanied by adaptation to growth on materials with low iron content, such as fortified fermented wort obtained from grapes grown in traditional areas of sherry wine-making, which is important for the preservation of specific properties of sherry wines.