Genetic instability of heterozygous, hybrid, natural wine yeasts

We describe a genetic instability found in natural wine yeasts but not in the common laboratory strains of Saccharomyces cerevisiae. Spontaneous cyh2(R)/cyh2(R) mutants resistant to high levels of cycloheximide can be directly isolated from cyh2(S)/cyh2(S) wine yeasts. Heterozygous cyh2(R)/cyh2(S) hybrid clones vary in genetic instability as measured by loss of heterozygosity at cyh2. There were two main classes of hybrids. The lawn hybrids have high genetic instability and generally become cyh2(R)/cyh2(R) homozygotes and lose the killer phenotype under nonselective conditions. The papilla hybrids have a much lower rate of loss of heterozygosity and maintain the killer phenotype. The genetic instability in lawn hybrids is 3 to 5 orders of magnitude greater than the highest loss-of-heterozygosity rates previously reported. Molecular mechanisms such as DNA repair by break-induced replication might account for the asymmetrical loss of heterozygosity. This loss-of-heterozygosity phenomenon could be economically important if it causes sudden phenotype changes in industrial or pathogenic yeasts and of more basic importance to the degree that it influences the evolution of naturally occurring yeast populations.     

Genetic differentiation within New Zealand Onychophora and their relationships to the Australian fauna

Specimens of peripatopsid Onychophora from New Zealand (the viviparous Peripatoid.es novaezealandiae and P. suteri and the oviparous Ooperipatellus insignis) have been analysed by allozyme electrophoresis and compared with three species of viviparous peripatus and 0. insignis from Australia. The data indicate that at least two species of Peripatoides are present, in addition to those described. Populations collected from Dunedin, in the South Island, are not referable on morphological grounds to any described genus. Furthermore, specimens exhibit such a high level of genetic distinctiveness that we speculate they have diverged from the Peripatoides and Euperipatoides lineages prior to the separation of Australia and New Zealand some 95 Myr ago. Specimens referable to 0. insignis from New Zealand are genetically quite distinct from 0. insignis at its type locality in Australia and must be considered endemic.     

Flavour-active wine yeasts

The flavour of fermented beverages such as beer, cider, saké and wine owe much to the primary fermentation yeast used in their production, Saccharomyces cerevisiae. Where once the role of yeast in fermented beverage flavour was thought to be limited to a small number of volatile esters and higher alcohols, the discovery that wine yeast release highly potent sulfur compounds from non-volatile precursors found in grapes has driven researchers to look more closely at how choice of yeast can influence wine style. This review explores recent progress towards understanding the range of ??flavour phenotypes?? that wine yeast exhibit, and how this knowledge has been used to develop novel flavour-active yeasts. In addition, emerging opportunities to augment these phenotypes by engineering yeast to produce so-called grape varietal compounds, such as monoterpenoids, will be discussed.     

Genetic diversity of Dekkera bruxellensis yeasts isolated from Australian wineries

Yeasts of the genus Dekkera and its anamorph Brettanomyces represent a significant spoilage issue for the global wine industry. Despite this, there is limited knowledge of genetic diversity and strain distribution within wine and winery-related environments. In this study, amplified fragment length polymorphism (AFLP) analysis was conducted on 244 Dekkera bruxellensis isolates from red wine made in 31 winemaking regions of Australia. The results indicated there were eight genotypes among the isolates, and three of these were commonly found across multiple winemaking regions. Analysis of 26S rRNA gene sequences provided further evidence of three common, conserved groups, whereas a phylogeny based upon the AFLP data demonstrated that the most common D. bruxellensis genotype (I) in Australian red wine was highly divergent from the D. bruxellensis type strain (CBS 74).     

Homothallism in wine yeasts

In an attempt to improve by hybridisation strains of pure-culture wine yeasts it could be shown, that of the seven strains used five are homothallic. Evidence is presented suggesting that the remainder are also homothallic.This investigation was aided by New Zealand U.G.C. Grant No. 71/60.     

Flocculent phenotypes in wine yeasts

The floc-forming ability of highly flocculent wine yeasts isolated from musts and wines was tested for susceptibility to heat and proteinase treatments. Four phenotypes were discriminated by treatments with pronase, proteinase K, trypsin and chymotrypsin. The most common phenotype was irreversibly lost only upon treatment with pronase, whereas the floc-forming ability was resistant to the action of proteinase K, trypsin and chymotrypsin. Another flocculent phenotype, represented by only one strain 6789, was resistant to the action of all proteolytic enzymes. The effect of high temperature on floc-forming ability in the presence or absence of Ca²⁺ions resulted in all the possible combinations and did not aid further general discrimination of flocculent phenotypes in Saccharomyces cerevisiae strains from wine.     

Sulfite formation by wine yeasts

Four strains of wine yeasts of two different species (Saccharomyces cerevisiae var. ellipsoideus and S. bayanus) were investigated with respect to regulation of NADPH- and benzyl viologen-dependent sulfite reductases by various sulfur sources. The enzyme activity was followed over a growth period of 96 h. The low sulfite-producing strains showed an increased biosynthesis of NADPH-dependent sulfite reductase during the exponential growth phase in the presence of sulfate, sulfite and djencolic-acid. This increase was not observed in the high sulfite-producing strains. Methionine and cysteine prevented this derepression. At the end of the exponential growth phase, enzyme biosynthesis was repressed again, presumably by sulfur-containing amino acids which were produced during growth. The regulatory influence of the various sulfur sources on benzyl viologen dependent sulfitereductase activity is obviously much weaker.Abbreviation BV benzyl viologen     

Sulfite formation by wine yeasts

Four strains of wine yeasts of two different species (Saccharomyces cerevisiae var. ellipsoideus and Saccharomyces bayanus) were investigated with respect to the influence of various sulfur compounds on the formation of O-acetylserine sulfhydrylase, O-acetylhomoserine sulfhydrylase and serine sulfhydrase. The specific enzyme activities were followed over a growth period of 96 h.In the presence of sulfate, sulfite and djencolic acid during exponential growth, a moderate increase of O-acetylserine sulfhydrylase and O-acetylhomoserine sulfhydrylase activities was recognized. In three strains cysteine and methionine prevented this derepression. At the end of the exponential growth phase, biosynthesis of these two enzymes was suppressed again. Serine sulfhydrase showed a modified regulation which indicates that its synthesis and the synthesis of O-acetylserine and O-acetylhomoserine sulfhydrylases are not coordinated.Abbreviations OAS O-acetylserine - OAHS O-acetylhomoserine     

Sulfite formation by wine yeasts

Eight different strains of wine yeasts were investigated phenomenologically with respect to their fermentation characteristics and sulfite production. It was established that the amount of produced sulfite is specific for each strain and proceeds parallel to the fermentation of sugar. A reduced production of biomass observed in the strongly sulfite-forming strains might be a result of an intracellular inhibition by the produced sulfite.     

Sulfite formation by wine yeasts

Five different strains of wine yeasts were investigated with respect to active uptake of [³⁵S] sulfate and its regulation by methionine. Considerable differences exist between low and high sulfite-producing strains in the initial velocity of sulfate uptake. Further differences were established in repression of sulfate permease by l-methionine, most evident in a total lack of repression in one of the high sulfite producers. These findings explain in part variable sulfite and sulfide formation.List of Abbreviations CCMP carbonylcyanide-p-trifluormethoxyphenylhydrazone     

Sulfite formation by wine yeasts

The enzyme catalyzing the reduction of sulfite by reduced benzyl viologen (BVH) was partially purified and characterized from two strains of wine yeasts, a sulfite-producing strain and a non-producing strain.Both enzymes showed corresponding features in pH-optima, optima of buffer and benzyl viologen concentrations.The enzymes did not catalyze the reduction of nitrite by reduced viologen dyes, but the reduction of sulfite was uncompetitively inhibited by nitrite. Compounds of sulfur metabolism such as sulfate, thiosulfate, cysteine, serine and methionine did not influence the activity of either of the enzymes. The main differences between the two enzymes exist in the specific activities in crude extracts, the K _m -values for sulfite, substrate inhibition rates, and localization in different fractions during (NH₄)₂SO₄ precipitation. The specific activity in crude extracts of the sulfite-producing strain (0.052 moles S^2- x min^-1 x mg^-1) was about three fold higher than that of the non-producing strain (0.0179 moles S^2- x min^-1 x mg^-1). On the other hand the sulfite-producing strain had a higher K _m -value for sulfite (2×10^-3 M) and was more strongly inhibited by the substrate than the non-producing strain (6×10^-3 M).     

The wine yeasts of the Cape

Summary The claims made byCusters in connection with the disproportionate yields of ethanol and carbon dioxide from the fermentative dissimilation of glucose in yeast water byBrett. claussenii were investigated forBrett. intermedius. All results obtained showed thatBrett. intermedius produced the normal equimolar amounts of ethanol and carbon dioxide, irrespective of whether the studies were conducted in yeast water or in dilute yeast water supplemented with a suitable nitrogen source. Re-investigation of the fermentative dissimilation of glucose in yeast water byBrett. claussenii gave the same results as withBrett. intermedius. Part I and II: Antonie van Leeuwenhoek24, 239, 1958;25, 145, 1959.     

The wine yeasts of the Cape

Summary Ascospore formation has been observed in three species of the genusBrettanomyces, viz. Brett. bruxellensis. Brett, intermedius andBrett. schanderlii. On media of adequate vitamin content these species form 1–4 hat-shaped ascospores. The spores are liberated rather soon after maturation. Heat treatment of ascogenous cultures indicated that these species are homothallic. In view of the fact that ascospore formation has been observed in the type species,Brett. bruxellensis, the transfer of the genus to theEndomycetaceae should be considered. Part I, II and III: Antonie van Leeuwenhoek 24, 239, 1958;25, 145, 1959;25, 449, 1959.     

Web-invasion and araneophagy by New Zealand and Australian pholcid spiders

Abstract

Pholcus phalangioides, Pholcus ancoralis, and Psilochorus sphaeroides were observed in the field in New Zealand (first species only) and Australia (all three species) to invade the webs of other species. P. phalangioides was observed to feed on spiders in alien webs. Webs of each species were frequently contiguous with webs of other spiders and P. sphaeroides sometimes invaded neighbouring webs in pursuit of insects.