Fourteen strains of the yeastSaccharomyces cerevisiae were isolated from three wineries in the Salnés wine region (N.W. Spain) at the three different periods of the natural fermentation. Each wild yeast was screened for production of acetaldehyde, ethyl acetate, isobutanol,n-propanol, amylic alcohol and other important enological compounds during laboratory scale fermentations of grape juice. After 25 days at 20°C, the analytical results evidenced variations in the production of acetaldehyde (from 13.1 to 24.3 mg/l), isobutanol (from 27.7 to 51.1 mg/l), amyl alcohols (from 111 to 183 mg/l) and ethyl acetate (from 19.3 to 43.7 mg/l). Although isolated from the same wine region, differences in the wine composition were observed depending on the particular yeast strain used for the vinification experiments.

Electrophoretic karyotypes of two strains of Saccharomyces cerevisiae, a haploid laboratory strain and a wild strain known to be at least diploid, have been checked during vegetative growth. The karyotype of the haploid strain was very stable; however, the diploid strain underwent frequent modifications. In most cases the number of bands was reduced, but occasionally we observed one band splitting into two. In one case, chromosomal rearrangements took place between differently sized copies of chromosomes I and VI. We concluded that the chromosome length polymorphism observed among wild strains of S. cerevisiae could be explained partly by chromosomal structure reorganization occurring during mitosis. Chromosome length polymorphism among strains of Saccharomyces cerevisiae has been demonstrated by pulsedfield gel electrophoresis. The phenomenon was observed among baker's yeast strains (3, 12) and even more among enological strains (15, 16). The last case is interesting as the yeast strains used in wine making have recently been isolated from wild flora and may therefore indicate features of wild S. cerevisiae. The evolutionary mechanisms which result in polymorphism of chromosomal structures have not been elucidated. Pedersen (10), Nillson-Tillgren et al. (9), and Petersen et al. (11), studying brewer's yeast, have hypothesized interspecies hybridization, while Rank et al. (12), working with baker's yeast, concluded that intraspecific cryptic mechanisms were responsible. This work aims to contribute to the understanding of the origin of chromosomal polymorphism among wild strains of S. cerevisiae. As natural strains multiply by vegetative growth (mitotic cell cycle), we tested the hypothesis that asexual reproduction allows chromosomal rearrangements.

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Astaxanthin and other carotenoids from 29 mutant strains of the yeast Phafia rhodozyma obtained by means of benomyl andor ethyl-methanesulfonate treatment and extracted with dimethyl sulfoxide (DMSO) were separated by high-performance liquid chromatography. Detection a t 474 nm revealed variations in the pigment content of the different mutant strains. Hypopigmented mutants showed higher p-carotene contents than the wild type, whereas hyperpigmented mutants exhibited considerable increases (up to 232%) in astaxanthin contents. Furthermore, and contrary to the wild type, the pigments in some of the mutants could be directly extracted with ethanol, and although the yield of pigment decreased in relation to DMSO, the content of astaxanthin increased up to 80%.

Ethanol proved to be a strong mutagenic agent of Saccharomyces mitochondrial DNA. Other active membrane solvents, such as tert-butanol, isopropanol, and sodium dodecyl sulfate, also turned out to be powerful petite mutation [rho-] inducers. Mutants defective in ergosterol synthesis (erg mutants) showed an extremely high frequency of spontaneous petite cells, suggesting that mitochondrial membrane alterations that were caused either by changes in its composition, as in the erg mutants, or by the effects of organic solvents resulted in an increase in the proportion of petite mutants. Wine yeast strains were generally more tolerant to the mutagenic effects of alcohols on mitochondrial DNA and more sensitive to the effect of sodium dodecyl sulfate than laboratory strains. However, resistance to petite mutation formation in laboratory strains was increased by mitochondrial transfer from alcohol-tolerant wine yeasts. Hence, the stability of the [rho'] mitochondrial DNA in either the presence or absence of solvents depends in part on the nature of the mitochondrial DNA itself. The low frequency of petite mutants found in wine yeast-laboratory yeast hybrids and the fact that the high frequency of petite mutants of a particular wine spore segregated meiotically indicated that many nuclear genes also play an important role in the mitochondrial genome in both the presence and absence of membrane solvents.