GENOME RENEWAL - A NEW PHENOMENON REVEALED FROM A GENETIC-STUDY OF 43STRAINS OF SACCHAROMYCES-CEREVISIAE DERIVED FROM NATURAL FERMENTATIONOF GRAPE MUSTS

We have analyzed by genetic means 43 strains of Saccharomyces that had been isolated from fermenting grape musts in Italy. Twenty eight of t hese strains were isolated from 28 cellars in the Region of Emilia Rom agna. The other 15 strains came from 5 fermentations at four cellars n ear the city of Arpino, which is located south and east of Rome. We fo und that 20 of the 28 strains from Emilia Romagna were heterozygous at from one to seven loci. The balance were, within the limits of our de tection, completely homozygous. All these strains appeared to be diplo id and most were homozygous for the homothallism gene (HO/HO). Spore v iability varied greatly between the different strains and showed an in verse relation with the degree of heterozygosity. Several of the strai ns, and in particular those from Arpino, yielded asci that came from g enetically different cells. These different cells could be interpreted to have arisen from a heterozygote that had sporulated and, because o f the HO gene, yielded homozygous diploid spore clones. We propose tha t natural wine yeast strains can undergo such changes and thereby chan ge a multiple heterozygote into completely homozygous diploids, some o f which may replace the original heterozygous diploid. We call this pr ocess 'genome renewal'.