Genetic and phenotypic diversity of Saccharomyces sensu stricto strains isolated from Amarone wine

Individual yeast strains belonging to the Saccharomyces sensu stricto complex were isolated from Amarone wine produced in four cellars of the Valpolicella area (Italy) and characterized by conventional physiological tests and by RAPD-PCR and mtDNA restriction assays. Thirteen out of 20 strains were classified as Saccharomyces cerevisiae (ex S. cerevisiae p.r. cerevisiae and p.r. bayanus) and the remaining as Saccharomyces bayanus (ex S. cerevisiae p.r. uvarum). RAPD-PCR method proved to be a fast and reliable tool for identification of Saccharomyces sensu stricto strains and also gave intraspecific differentiation. Restriction analysis of mtDNA permitted to distinguish S. cerevisiae and S. bayanus species and to discern polymorphism among S. cerevisiae isolates. The assessment of the phenotypic diversity within the isolates by gas-chromatographic analysis of secondary fermentation products was explored. Small quantities of isobutanol were produced by most of the strains and higher amounts by some S. cerevisiae strains with phenotypes Gal- and Mel-; all S. bayanus strains produced low amounts of amilyc alcohols. From this study it appears that each winery owns particular strains, with different genetic and biochemical characteristics, selected by specific environmental pressures during the Amarone winemaking process carried out at low temperature in presence of high sugar content.