Mitotic recombination and genetic changes in Saccharomyces cerevisiae during wine fermentation

Natural strains of Saccharomyces cerevisiae are prototrophic homothallic ye asts that sporulate poorly, are often heterozygous, and may be aneuploid. T his genomic constitution may confer selective advantages in some environmen ts. Different mechanisms of recombination, such as meiosis or mitotic rearr angement of chromosomes, have been proposed for wine strains. We studied th e stability of the URA3 locus of a URA3/ura3 wine yeast in consecutive grap e must fermentations. ura3/ura3 homozygotes were detected at a rate of 1 x 10(-5) to 3 x 10(-5) per generation, and mitotic rearrangements for chromos omes VIII and XII appeared after 30 mitotic divisions. We used the karyotyp e as a meiotic marker and determined that sporulation was not involved in t his process. Thus, we propose a hypothesis for the genome changes in wine y easts during vinification. This putative mechanism involves mitotic recombi nation between homologous sequences and does not necessarily imply meiosis.