A relatively large number of different species of bacteria and yeasts contribute to the process of cider fermentation. Interspecies hybridization of the yeasts from the Saccharomyces genus has important biotechnological potential in alcoholic fermentations. The purpose of this research was to genetically and phenotypically characterize populations of Saccharomyces species and their hybrids that participate in spontaneous cider fermentations at the remote mountain farms of the Koroška region. Twenty-six strains of Saccharomyces species and their hybrids were identified by sequencing of their ribosomal DNA and with species-specific PCR primers. We identified the following species: S. cerevisiae, S. uvarum, S. paradoxus and hybrids S. eubayanus x S. cerevisiae, S. eubayanus x S. uvarum, S. cerevisiae x S. kudriavzevii and S. eubayanus x S. cerevisiae x S. uvarum. An intraspecies genetic diversity was evaluated by electrophoretic karyotyping and by determinination of the copy number variations in selected microsatellite loci. Based on the latter method, strains of S. uvarum and S. cerevisiae were divided into two groups, of which many strains were heterozygous. The strains were phenotyped by determining their relative growth rate on media with high glucose concentrations and with the addition of ethanol, acetic acid, ethylphenol and ethylguaiacol, and at 4 °C and 37 °C. Under these conditions which mimick those of cider fermentation, species of S. uvarum, S cerevisiae and hybrid S. eubayanus x S. cerevisiae x S. uvarum grew faster than other species and hybrids. The strains of S. cerevisiae and S. eubayanus x S. cerevisiae hybrid were best adapted to the conditions of fermentation.
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