Divergence in wine characteristics produced by wild and domesticated strains of Saccharomyces cerevisiae

The budding yeast Saccharomyces cerevisiae is the primary species used by wine makers to convert sugar into alcohol during wine fermentation. Saccharomyces cerevisiae is found in vineyards, but is also found in association with oak trees and other natural sources. Although wild strains of S. cerevisiae as well as other Saccharomyces species are also capable of wine fermentation, a genetically distinct group of S. cerevisiae strains is primarily used to produce wine, consistent with the idea that wine making strains have been domesticated for wine production. In this study, we demonstrate that humans can distinguish between wines produced using wine strains and wild strains of S. cerevisiae as well as its sibling species, Saccharomyces paradoxus. Wine strains produced wine with fruity and floral characteristics, whereas wild strains produced wine with earthy and sulfurous characteristics. The differences that we observe between wine and wild strains provides further evidence that wine strains have evolved phenotypes that are distinct from their wild ancestors and relevant to their use in wine production.     

Niche-driven evolution of metabolic and life-history strategies in natural and domesticated populations of Saccharomyces cerevisiae

Background  

Variation of resource supply is one of the key factors that drive the evolution of life-history strategies, and hence the interactions between individuals. In the yeast Saccharomyces cerevisiae, two life-history strategies related to different resource utilization have been previously described in strains from different industrial origins. In this work, we analyzed metabolic traits and life-history strategies in a broader collection of yeast strains sampled in various ecological niches (forest, human body, fruits, laboratory and industrial environments).     

Evidence for autotetraploidy associated with reproductive isolation in Saccharomyces cerevisiae: towards a new domesticated species

Partial or whole‐genome duplications have played a major role in the evolution of new species. We have investigated the variation of ploidy level in a panel of domesticated strains of Saccharomyces cerevisiae coming from different geographical origins. Segregation studies and crosses with tester strains of different ploidy levels showed that part of the strains were well‐balanced autotetraploids displaying tetrasomic inheritance. The presence of up to four different alleles for various loci is consistent with a polyploidization mechanism relying on the fusion of two nonreduced meiospores coming from two S. cerevisiae strains. Autotetraploidy was also in accordance with karyotype and flow cytometry analyses. Interestingly, most bakery strains were tetraploids, suggesting a link between ploidy level and human use. The null or drastically reduced fertility of the hybrids between tetraploid and diploid strains indicated that domesticated S. cerevisiae strains are composed of two groups isolated by post‐zygotic reproductive barriers.     

Evidence for short-patch mismatch repair in Saccharomyces cerevisiae

Recombination events between non-identical sequences most often involve heteroduplex DNA intermediates that are subjected to mismatch repair. The well-characterized long-patch mismatch repair process, controlled in eukaryotes by bacterial MutS and MutL orthologs, is the major system involved in repair of mispaired bases. Here we present evidence for an alternative short-patch mismatch repair pathway that operates on a broad spectrum of mismatches. In msh2 mutants lacking the long-patch repair system, sequence analysis of recombination tracts resulting from exchanges between similar but non-identical (homeologous) parental DNAs showed the occurrence of short-patch repair events that can involve <12 nucleotides. Such events were detected both in mitotic and in meiotic recombinants. Confirming the existence of a distinct short-patch repair activity, we found in a recombination assay involving homologous alleles that closely spaced mismatches are repaired independently with high efficiency in cells lacking MSH2 or PMS1. We show that this activity does not depend on genes required for nucleotide excision repair and thus differs from the short-patch mismatch repair described in Schizosaccharomyces pombe.     

The age structure of populations of Saccharomyces cerevisiae

A discrete deterministic model is described for the growth of an age-structured population of yeast, Saccharomyces cerevisiae, incorporating recent information on the asymmetry of cell division and control of the cell cycle in this species. Solutions are obtained for the age structure of the population at equilibrium, and for the equilibrium distribution of relative frequency of cells through the cell cycle. The model is applied to experimental data on the changing age structure of nonequilibrium populations of yeast. The model predicts well both the transient behavior and the equilibrium structure of such populations. It is shown that the asymmetry of cell division explains (1) the excess of newly formed daughter cells in the population as compared to the frequency of older cells and (2) the damped oscillations in the frequencies of cells of different ages as demographic equilibrium is approached.     

Evidence for dual physiological formsof ergosterol in Saccharomyces cerevisiae

Data obtained from acid hydrolysis and extraction of yeast have demonstrated that routine saponification does not recover total sterol from the cells. This suggests the existence of a form of ergosterol resistant to saponification. Time course analyses of sterol synthesis by resting cell suspensions reveal an inverse relationship between the amounts of base labile and acid labile forms of sterol. These data give strong presumptive evidence for dual forms of ergosterol which are interconvertible according to the respiratory state of the cell.     

Evidence for a new chromosome in Saccharomyces cerevisiae.

The current yeast map has 16 chromosomes, each originally defined by a centromere-linked gene unlinked to previously defined centromere markers. We examined four genes, cly2, KRB1, AMY2, and tsm0115, each centromere linked, but previously thought to be not on chromosomes I to XVI. We found that AMY2 is linked to cly2, and both are on chromosome II. tsm0115 is on the left arm of chromosome XVI. We confirm the earlier evidence that KRB1 is not on chromosomes I through XVI. This gene thus defines a new chromosome XVII. We also report meiotic linkage of met4 and pet8 (on chromosome XIV), confirming the connection between the petx-kex2 fragment of XIV and the centromere of XIV.     

Flow cytometry analysis of recombinant Saccharomyces cerevisiae populations

A new fluorescent stain has been developed for detecting cloned beta-galactosidase activity in individual cells of Saccharomyces cerevisiae by flow cytometry. The staining reaction is based on enzymatic cleavage of alpha-naphthol-beta-D-galactopyranoside by intracellular beta-galactosidase and trapping of the liberated naphthol by hexazoniumpararosaniline yielding a fluorescent, insoluble end product. This stain, in connection with an appropriate host strain, has been applied for detecting plasmids encoding inducible beta-galactosidase in unstable recombinant cell populations carrying plasmids with different origins of replication. The method enables rapid determination of the fraction of plasmid-containing cells as well as quantitation of intracellular beta-galactosidase content by kinetic enzyme assay. Inducibility of the marker enzyme is important for maintaining correlation between enzyme and gene content.     

Evidence for the occurrence of nucleotide-activated oligosaccharides in Saccharomyces cerevisiae

Recently, nucleotide-activated oligosaccharides have been found to be involved in the biosynthesis of certain glycoconjugates in archaeal and bacterial procaryotes. This paper describes the isolation and partial chemical characterization of nucleotide-activated oligosaccharides from the eucaryotic microbe Saccharomyces cerevisiae. We purified four different nucleotide-activated oligosaccharides from cell extracts of Saccharomyces cerevisiae. Three of the oligosaccharides were UDP, and one was TDP-activated. D-Glucose was the only carbohydrate constituent, except for one oligosaccharide, which also contained glucosamine. The chain length varied between two and four sugar residues.     

Population subdivision and adaptation in asexual populations of Saccharomyces cerevisiae

Population subdivision limits competition between individuals, which can have a profound effect on adaptation. Subdivided populations maintain more genetic diversity at any given time compared to well-mixed populations, and thus "explore" larger parts of the genotype space. At the same time, beneficial mutations take longer to spread in such populations, and thus subdivided populations do not "exploit" discovered mutations as efficiently as well-mixed populations. Whether subdivision inhibits or promotes adaptation in a given environment depends on the relative importance of exploration versus exploitation, which in turn depends on the structure of epistasis among beneficial mutations. Here we investigate the relative importance of exploration versus exploitation for adaptation by evolving 976 independent asexual populations of budding yeast with several degrees of geographic subdivision. We find that subdivision systematically inhibits adaptation: even the luckiest demes in subdivided populations on average fail to discover genotypes that are fitter than those discovered by well-mixed populations. Thus, exploitation of discovered mutations is more important for adaptation in our system than a thorough exploration of the mutational neighborhood, and increasing subdivision slows adaptation.     

Evidence for a second function for Saccharomyces cerevisiae Rev1p

The function of the Saccharomyces cerevisiae REV1 gene is required for translesion replication and mutagenesis induced by a wide variety of DNA-damaging agents. We showed previously that Rev1p possesses a deoxycytidyl transferase activity, which incorporates dCMP opposite abasic sites in the DNA template, and that dCMP insertion is the major event during bypass of an abasic site in vivo. However, we now find that Rev1p function is needed for the bypass of a T-T (6-4) UV photoproduct, a process in which dCMP incorporation occurs only very rarely, indicating that Rev1p possesses a second function. In addition, we find that Rev1p function is, as expected, required for bypass of an abasic site. However, replication past this lesion was also much reduced in the G-193R rev1-1 mutant, which we find retains substantial levels of deoxycytidyl transferase activity. This mutant is, therefore, presumably deficient principally in the second, at present poorly defined, function. The bypass of an abasic site and T-T (6-4) lesion also depended on REV3 function, but neither it nor REV1 was required for replication past the T-T dimer; bypass of this lesion presumably depends on another enzyme.     

Evidence for contribution of neutral trehalase in barotolerance of Saccharomyces cerevisiae

In yeast, trehalose accumulation and its hydrolysis, which is catalyzed by neutral trehalase, are believed to be important for thermotolerance. We have shown that trehalose is one of the important factors for barotolerance (resistance to hydrostatic pressure); however, nothing is known about the role of neutral trehalase in barotolerance. To estimate the contribution of neutral trehalase in resisting high hydrostatic pressure, we measured the barotolerance of neutral trehalase I and/or neutral trehalase II deletion strains. Under 180 MPa of pressure for 2 h, the neutral trehalase I deletion strain showed higher barotolerance in logarithmic-phase cells and lower barotolerance in stationary-phase cells than the wild-type strain. Introduction of the neutral trehalase I gene (NTH1) into the deletion mutant restored barotolerance defects in stationary-phase cells. Furthermore, we assessed the contribution of neutral trehalase during pressure and recovery conditions by varying the expression of NTH1 or neutral trehalase activity with a galactose-inducible GAL1 promoter with either glucose or galactose. The low barotolerance observed with glucose repression of neutral trehalase from the GAL1 promoter was restored during recovery with galactose induction. Our results suggest that neutral trehalase contributes to barotolerance, especially during recovery.     

Evidence for Related Functions of the RNA Genes of Saccharomyces cerevisiae

The yeast genes RNA2-RNA11 are necessary for splicing of nuclear intron-containing pre-mRNAs. We investigated the relationships among these genes by asking whether increased expression of one RNA gene leads to suppression of the temperature-sensitive lethality of a mutation in any other RNA gene. The presence of extra plasmid-borne copies of the RNA3 gene relieves the lethality of temperature-sensitive rna4 mutations. A region of the yeast genome (SRN2) is described that suppresses temperature-sensitive rna2 mutations when it is present on either medium or high-copy number plasmids. Neither suppression occurs via a bypass of RNA gene function since null alleles of rna2 and rna4 are not suppressed by elevated dosage of SRN2 and RNA3, respectively. These results suggest that the SRN2 and RNA2 gene products have related functions, as do the RNA3 and RNA4 gene products.     

Electrochemical detection of wild type Saccharomyces cerevisiae responses to estrogens

The presence of an estrogen binding protein (EBP) and an endogenous ligand in three yeast species was first reported in 1982/1983. The ligand was shown to be 17beta-estradiol and the binding affinities of EBP were demonstrated to be similar to those of rat estrogen receptors. This report describes detection of the behaviour of a putative estrogen binding protein in Saccharomyces cerevisiae using a double mediator electrochemical detection system. The response to estrogen is shown to be quantitative with signals detectable from 10(-8) to 10(-14)M. An incubation period of 5h is established and a method to block electrochemical signals produced by the catabolism of exogenous substrates is demonstrated to be effective. The system provides a method that permits the use of wild type S. cerevisiae to quantify estrogens.     

Evidence for Contribution of Neutral Trehalase in Barotolerance of Saccharomyces cerevisiae

In yeast, trehalose accumulation and its hydrolysis, which is catalyzed by neutral trehalase, are believed to be important for thermotolerance. We have shown that trehalose is one of the important factors for barotolerance (resistance to hydrostatic pressure); however, nothing is known about the role of neutral trehalase in barotolerance. To estimate the contribution of neutral trehalase in resisting high hydrostatic pressure, we measured the barotolerance of neutral trehalase I and/or neutral trehalase II deletion strains. Under 180 MPa of pressure for 2 h, the neutral trehalase I deletion strain showed higher barotolerance in logarithmic-phase cells and lower barotolerance in stationary-phase cells than the wild-type strain. Introduction of the neutral trehalase I gene (NTH1) into the deletion mutant restored barotolerance defects in stationary-phase cells. Furthermore, we assessed the contribution of neutral trehalase during pressure and recovery conditions by varying the expression of NTH1 or neutral trehalase activity with a galactose-inducible GAL1 promoter with either glucose or galactose. The low barotolerance observed with glucose repression of neutral trehalase from the GAL1 promoter was restored during recovery with galactose induction. Our results suggest that neutral trehalase contributes to barotolerance, especially during recovery.     

Evidence of melanoma in wild marine fish populations

The increase in reports of novel diseases in a wide range of ecosystems, both terrestrial and marine, has been linked to many factors including exposure to novel pathogens and changes in the global climate. Prevalence of skin cancer in particular has been found to be increasing in humans, but has not been reported in wild fish before. Here we report extensive melanosis and melanoma (skin cancer) in wild populations of an iconic, commercially-important marine fish, the coral trout Plectropomus leopardus. The syndrome reported here has strong similarities to previous studies associated with UV induced melanomas in the well-established laboratory fish model Xiphophorus. Relatively high prevalence rates of this syndrome (15%) were recorded at two offshore sites in the Great Barrier Reef Marine Park (GBRMP). In the absence of microbial pathogens and given the strong similarities to the UV-induced melanomas, we conclude that the likely cause was environmental exposure to UV radiation. Further studies are needed to establish the large scale distribution of the syndrome and confirm that the lesions reported here are the same as the melanoma in Xiphophorus, by assessing mutation of the EGFR gene, Xmrk. Furthermore, research on the potential links of this syndrome to increases in UV radiation from stratospheric ozone depletion needs to be completed.     

Ozone response in wild type and radiation-sensitive mutants of Saccharomyces cerevisiae.

Summary The effect of ozone exposure on Saccharomyces cerevisiae was studied. Factors such as ozone concentration, treatment time, media, initial cell concentration and growth phase were shown to influence ozone response in this organism. Logarithmic phase cells were much more sensitive than stationary phase cells to the lethal effect of ozone.The radiation-sensitive mutants rad3, rad6, rad51 and rad52 of S. cerevisiae were exposed, in water, to 50 ppm of ozone for 30 min. On comparing their survival curves, the rad51 and the rad52 mutants showed a greater sensitivity to ozone exposure than the wild type.