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Yeast cell walls have two major roles, to preserve physical integrity of the cell, and to ensure communication with surrounding molecules and cells. While the first function requires evolutionary conserved polysaccharide network synthesis, the second needs to be flexible and provide adaptability to different habitats and lifestyles. In this study, the comparative in silico analysis of proteins required for cell wall biosynthesis and functions containing 187 proteins of 92 different yeasts was performed in order to assess which proteins were broadly conserved among yeasts and which were more species specific. Proteins were divided into several groups according to their role and localization. As expected, many Saccharomyces cerevisiae proteins involved in protein glycosylation, glycosylphosphatidylinositol (GPI) synthesis and the synthesis of wall polysaccharides had orthologues in most other yeasts. Similarly, a group of GPI anchored proteins involved in cell wall biosynthesis (Gas proteins and Dfg5p/Dcw1p) and other non-GPI anchored cell wall proteins involved in the wall synthesis and remodeling were highly conserved. However, GPI anchored proteins involved in flocculation, aggregation, cell separation, and those of still unknown functions were not highly conserved. The proteins localized in the cell walls of various yeast species were also analyzed by protein biotinylation and blotting. Pronounced differences were found both in the patterns, as well as in the overall amounts of different groups of proteins. The amount of GPI-anchored proteins correlated with the mannan to glucan ratio of the wall. Changes of the wall proteome upon temperature shift to 42 °C were detected.

New double- and triple-hybrid Saccharomyces yeasts were characterized using PCR-restriction fragment length polymorphism of 35 nuclear genes, located on different chromosome arms, and the sequencing of one nuclear and one mitochondrial gene. Most of these new hybrids were originally isolated from fermentations; however, two of them correspond to clinical and dietary supplement isolates. This is the first time that the presence of double-hybrid S. cerevisiae×S. kudriavzevii in non-fermentative substrates has been reported and investigated. Phylogenetic analysis of the MET6 nuclear gene confirmed the double or triple parental origin of the new hybrids. Restriction analysis of gene regions in these hybrids revealed a high diversity of genome types. From these molecular characterizations, a reduction of the S. kudriavzevii fraction of the hybrid genomes is observed in most hybrids. Mitochondrial inheritance in hybrids was deduced from the analysis of mitochondrial COX2 gene sequences, which showed that most hybrids received the mitochondrial genome from the S. kudriavzevii parent. However, two strains inherited a S. cerevisiae COX2, being the first report of S. cerevisiae×S. kudriavzevii hybrids with S. cerevisiae mitochondrial genomes. These two strains are those showing a higher S. kudriavzevii nuclear genome reduction, especially in the wine hybrid AMH. This may be due to the release of selective pressures acting on the other hybrids to maintain kudriavzevii mitochondria-interacting genes., (Copyright © 2011 John Wiley & Sons, Ltd.)