Mitochondrial DNA duplication, recombination, and introgression during interspecific hybridization

AbstractmtDNA recombination events in yeasts are known, but altered mitochondrial genomes were not completed. Therefore, we analyzed recombined mtDNAs in six Saccharomyces cerevisiae × Saccharomyces paradoxus hybrids in detail. Assembled molecules contain mostly segments with variable length introgressed to other mtDNA. All recombination sites are in the vicinity of the mobile elements, introns in cox1, cob genes and free standing ORF1, ORF4. The transplaced regions involve co-converted proximal exon regions. Thus, these selfish elements are beneficial to the host if the mother molecule is challenged with another molecule for transmission to the progeny. They trigger mtDNA recombination ensuring the transfer of adjacent regions, into the progeny of recombinant molecules. The recombination of the large segments may result in mitotically stable duplication of several genes.

Heterogeneous mutation rates and spectra within and between species of yeast and their hybrids

Mutation rates and spectra vary between species and among populations. Hybridization can contribute to this variation but its role remains poorly understood. Estimating mutation rates requires controlled conditions where the effect of natural selection can be minimized. One way to achieve this is through mutation accumulation experiments coupled with genome sequencing. Here we investigate 400 mutation accumulation lines initiated from 11 genotypes spanning intra-lineage, inter-lineage and interspecific crosses of the yeasts Saccharomyces paradoxus and S. cerevisiae, and propagated for 770 generations. We find significant differences in mutation rates and spectra among crosses, which are not related to the level of divergence of parental strains, but are genotype specific. We find that departures from neutrality, differences in growth rate, ploidy and loss of heterozygosity only play a minor role as a source of variation and conclude that unique combinations of parental genotypes drive distinct rates and spectra in some crosses.

Wine Fermentation Performance of Indigenous Saccharomyces cerevisiae and Saccharomyces paradoxus Strains Isolated in a Piedmont Vineyard

The role of yeast in wine quality is very important. The use of selected autochthonous yeasts is becoming more and more frequent in enology, not only to obtain a diversification of wines, but also as a link between the wine and its territory of origin. The objectives of this work were to test two indigenous yeasts in a cellar on a pilot scale. The yeasts were a strain of Saccharomyces cerevisiae and a strain of Saccharomyces paradoxus previously isolated in a vineyard in Piedmont (Italy). Studying the oenological characteristics of S. paradoxus is of particular interest, as it is rarely found in the cellar–vineyard environment. Molecular biology methods confirmed the predominance of the strain inoculated in the various fermentation tests. Additionally, products of yeast metabolism, including volatile compounds, were quantified at the end of the alcoholic fermentation and sensory profile of wines was tested by a trained panel of tasters. Our results indicated that both strains have good characteristics to be used as starter in winemaking; S. paradoxus was characterized by a high production of glycerol and the ability to degrade malic acid, together with a lower production of ethanol and a low volatile acidity, while S. cerevisiae conferred to the wine a pleasant smell of rose, as highlighted in the sessions of sensory analysis.

Saccharomyces paradoxus Transcriptional Alterations in Cells of Distinct Phenotype and Viral dsRNA Content

Killer yeasts are attractive antifungal agents with great potential applications in the food industry. Natural Saccharomyces paradoxus isolates provide new dsRNA-based killer systems available for investigation. The presence of viral dsRNA may alter transcriptional profile of S. paradoxus. To test this possibility, a high-throughput RNA sequencing was employed to compare the transcriptomes of S. paradoxus AML 15-66 K66 killer strains after curing them of either M-66 alone or both M-66 and L-A-66 dsRNA viruses. The S. paradoxus cells cured of viral dsRNA(s) showed respiration deficient or altered sporulation patterns. We have identified numerous changes in the transcription profile of genes including those linked to ribosomes and amino acid biosynthesis, as well as mitochondrial function. Our work advance studies of transcriptional adaptations of Saccharomyces spp. induced by changes in phenotype and set of dsRNA viruses, reported for the first time.

Isolation, screening, identification and tolerance of yeast in cherry wine lees

In this study, yeast was isolated from cherry wine lees by rose Bengal medium, and its species was identified through three-stage screening, morphological observation and molecular biological identification. Moreover, the tolerance of screened strains was studied. The results showed that 30 strains of yeast were isolated from cherry wine lees, and five strains of yeast were selected, which were named YJN10, YJN16, YJN18, YJN19 and YJN28. After preliminary appraisal, strain YJN10 was Saccharomyces kudriavzevii, strain YJN16 was Saccharomyces paradoxus, and strains YJN18, YJN19, YJN28 were Saccharomyces cerevisiae. In the tolerance study, the tolerable sugar concentrations of the five strains were 650, 650, 550, 600 and 600 g/L. The tolerable alcohol volume fractions were 20, 20, 16, 18 and 18%. The tolerable molar concentration of potassium chloride was 1.8, 1.8, 1.5, 1.5 and 1.5 mol/L. Finally, strains YJN10, YJN16, YJN19 and YJN28 showed good tolerance, which laid a foundation for subsequent application in cherry wine fermentation.

Brewing potential of the wild yeast species Saccharomyces paradoxus

Saccharomyces paradoxus is commonly isolated from environmental samples in Northern Europe and North America, but is rarely found associated with fermentation. However, as novelty has become a selling point in beer markets, interest toward non-conventional and local yeasts is increasing. Here, we report the first comprehensive investigation of the brewing potential of the species. Eight wild strains of S. paradoxus were isolated from oak trees growing naturally in Finland, screened in a series of fermentation trials and the most promising strain was selected for lager beer brewing at pilot scale (40 l). Yeasts were evaluated according to their ability to utilize wort sugars, their production of flavour-active aroma volatiles, diacetyl and organic acids, and sensorial quality of beers produced. All strains could assimilate maltose but this occurred after a considerable lag phase. Once adapted, most wild strains reached attenuation rates close to 70%. Adaptation to maltose could be maintained by re-pitching and with appropriate handling of the adapted yeast. Fermentation at 15 °C with the best performing strain was completed in 17 days. Maltose was consumed as efficiently as with a reference lager yeast, but no maltotriose use was observed. Bottled beers were evaluated by a trained sensory panel, and were generally rated as good as, or better than, reference beers. S. paradoxus beers were considered full-bodied and had a relatively clean flavour profile despite the presence of the clove-like 4-vinyl guaiacol. In conclusion, S. paradoxus exhibits a number of traits relevant to brewing, and with appropriate handling could be applied industrially.

Population Size, Sex and Purifying Selection: Comparative Genomics of Two Sister Taxa of the Wild Yeast Saccharomyces paradoxus

This study uses population genomic data to estimate demographic and selection parameters in two sister lineages of the wild yeast Saccharomyces paradoxus and compare their evolution. We first estimate nucleotide and recombinational diversities in each of the two lineages to infer their population size and frequency of sex and then analyze the rate of mutation accumulation since divergence from their inferred common ancestor to estimate the generation time and efficacy of selection. We find that one of the lineages has significantly higher silent nucleotide diversity and lower linkage disequilibrium, indicating a larger population with more frequent sexual generations. The same lineage also shows shorter generation time and higher efficacy of purifying selection, the latter consistent with the finding of larger population size and more frequent sex. Similar analyses are also performed on the ancestries of individual strains within lineages and we find significant differences between strains implying variation in rates of mitotic cell divisions. Our sample includes some strains originating in the Chernobyl nuclear-accident exclusion zone, which has been subjected to high levels of radiation for nearly 30 years now. We find no evidence, however, for increased rates of mutation. Finally, there is a positive correlation between rates of mutation accumulation and length of growing period, as measured by latitude of the place of origin of strains. Our study illustrates the power of genomic analyses in estimating population and life history parameters and testing predictions based on population genetic theory.

Utjecaj različitih fungicidnih pripravaka na rast kvasaca skupine Saccharomyces sensu stricto

Cilj ovog istraživanja bio je utvrditi djelovanje četiri različita fungicidna pripravka na bazi djelatnih tvari mankozeb, kaptan, iprodion i zoksamid na kvasce iz skupine Saccharomyces sensu stricto u laboratorijskim uvjetima. Kvasci iz ove skupine, posebice vrste Saccharomyces cerevisiae i Saccharomyces paradoxus od iznimne su važnosti za proizvodnju vina jer svojim metabolizmom utječu na sam proces fermentacije kao i na stvaranje brojnih spojeva važnih za aromu vina. Filter-disk metodom ispitivan je utjecaj fungicidnih pripravaka koji se primjenjuju za suzbijanje bolesti vinove loze u koncentracijama preporučenima od strane proizvođača kao i u nekim umanjenim i uvećanim koncentracijama. Dokazan je utjecaj pripravaka Cadillac 80WP®, Electis WG® i Stoper® na rast ispitivanih sojeva S. cerevisiae i S. paradoxus dok Kidan® nije imao utjecaj na rast kvasaca ni pri jednoj od ispitivanih koncentracija. Najveći negativan utjecaj imao je Cadillac 80WP® koji je inhibirao rast ispitivanih sojeva čak i pri upola nižim koncentracijama od propisanih. Nije utvrđena razlika u osjetljivosti između vrsta S. cerevisiae i S. paradoxus, dok se istovremeno može zaključiti da su referentni sojevi bili osjetljiviji na Cadillac 80WP®, Electis WG® i Stoper® u usporedbi s autohtonim izolatima.