A homozygous diploid subset of commercial wine yeast strains.
Heather Brown, Keith Richards, Soon Lee, John Bradbury, Rod Dunbar, Richard Gardner
School of Biological Sciences, University of Auckland, 5 Symonds Street, Auckland, New Zealand
Genetic analysis was performed on 45 commercial yeasts used in winemaking because of their superior fermentation properties. Forty strains had diploid genomes and 5 had a range of aneuploid sizes from 1.2-1.8 times larger. DNA sequencing of the internal transcribed spacer (ITS) region of nrDNA of a few strains suggested that the diploid strains are Saccharomyces cerevisiae. Four of the 5 aneuploid strains had sequences identical to S. kudriavzevii and likely correspond to interspecific hybrids with S. cerevisiae. An identification fingerprint was constructed for the commercial yeast strains using 17 molecular markers, including 7 new microsatellites. The markers provided unambiguous identification of all strains, except for five that appeared identical. The markers allowed us to identify a set of 10 commercial wine yeast strains that appear to be genetically homozygous. These strains are presumed to undergo regular inbreeding, a process referred to previously by Mortimer as 'genome renewal'. All the homozygous strains sporulated with good efficiency, provided >80% of tetrads with four viable spores and were homothallic. Two strains showed good transformation frequencies using standard yeast replicating vectors. Haploid strains derivable from such strains should represent laboratory-friendly, model wine yeasts suitable for genetic research, but possessing a high capacity for fermentation under commercial conditions.