Abstract
Flor yeast strains represent a specialized group of Saccharomyces cerevisiae yeasts used for biological wine aging. We have sequenced the genomes of three flor strains originated from different geographic regions and used for production of sherry-like wines in Russia. According to the obtained phylogeny of 118 yeast strains, flor strains form very tight cluster adjacent to the main wine clade. SNP analysis versus available genomes of wine and flor strains revealed 2,270 genetic variants in 1,337 loci specific to flor strains. Gene ontology analysis in combination with gene content evaluation revealed a complex landscape of possibly adaptive genetic changes in flor yeast, related to genes associated with cell morphology, mitotic cell cycle, ion homeostasis, DNA repair, carbohydrate metabolism, lipid metabolism, and cell wall biogenesis. Pangenomic analysis discovered the presence of several well-known “non-reference” loci of potential industrial importance. Events of gene loss included deletions of asparaginase genes, maltose utilization locus, and FRE-FIT locus involved in iron transport. The latter in combination with a flor-yeast-specific mutation in the Aft1 transcription factor gene is likely to be responsible for the discovered phenotype of increased iron sensitivity and improved iron uptake of analyzed strains. Expansion of the coding region of the FLO11 flocullin gene and alteration of the balance between members of the FLO gene family are likely to positively affect the well-known propensity of flor strains for velum formation. Our study provides new insights in the nature of genetic variation in flor yeast strains and demonstrates that different adaptive properties of flor yeast strains could have evolved through different mechanisms of genetic variation.
Highlights
Flor yeast strains represent a specialized group of yeasts used for centuries in various countries for biological wine aging (Alexandre, 2013; Legras et al, 2016)
Several yeast strains belonging to the group of flor yeast were either isolated from different wineries of the former Soviet Union and other countries or obtained from other collections (Kishkovskaia et al, 2017)
Flor yeast strains are highly specialized microbial agents used for production of biological aged wines through sophisticated winemaking process (Alexandre, 2013)
Summary
Flor yeast strains represent a specialized group of yeasts used for centuries in various countries for biological wine aging (Alexandre, 2013; Legras et al, 2016). The physiological and biochemical properties of flor yeast strains associated with their application in specific winemaking processes are quite distinct from wine starter yeast strains and are relevant to the technological peculiarities of sherry-type wine formation (reviewed in Alexandre, 2013; Eldarov et al, 2016). One of the key Genomics of Flor Yeast Strains prominent features of flor yeast is their capability to form a biofilm on the surface of fortified wine (Martínez et al, 1997). This ability to float is critical for flor yeast metabolic changes associated with conditions of biological wine aging and their resistance to harsh winemaking conditions. Velum formation by flor yeast is generally considered as an adaptive mechanism ensuring oxygen access and resistance to harsh environmental conditions
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