Browsing by Author "Lambrechts, M. G."
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- ItemDivergent regulation of the evolutionarily closely related promoters of the Saccharomyces cerevisiae STA2 and MUC1 genes(1999) Gagiano, M.; Van Dyk, D.; Bauer, Florian; Lambrechts, M. G.; Pretorius, I. S.The 5' upstream regions of the Saccharomyces cerevisiae glucoamylase- encoding genes STA1 to -3 and of the MUC1 (or FLO11) gene, which is critical for pseudohyphal development, invasive growth, and flocculation, are almost identical, and the genes are coregulated to a large extent. Besides representing the largest yeast promoters identified to date, these regions are of particular interest from both a functional and an evolutionary point of view. Transcription of the genes indeed seems to be dependent on numerous transcription factors which integrate the information of a complex network of signaling pathways, while the very limited sequence differences between them should allow the study of promoter evolution on a molecular level. To investigate the transcriptional regulation, we compared the transcription levels conferred by the STA2 and MUC1 promoters under various growth conditions. Our data show that transcription of both genes responded similarly to most environmental signals but also indicated significant divergence in some aspects. We identified distinct areas within the promoters that show specific responses to the activating effect of Flo8p, Msn1p (or Mss10p, Fup1p, or Phd2p), and Mss11p as well as to carbon catabolite repression. We also identified the STA10 repressive effect as the absence of Flo8p, a transcriptional activator of flocculation genes in S. cerevisiae.
- ItemFlocculation, pseudohyphal development and invasive growth in commercial wine yeast strains(South African Society for Enology and Viticulture, 1998) Carstens, Elsa; Lambrechts, M. G.; Pretorius, I. S.Flocculation of Saccharomyces cerevisiae cells at the end of alcoholic fermentation is an important phenomenon in winemaking, especially in the production of bottle-fermented sparkling wine. Most wine yeast strains do not flocculate during the fermentation process and it is unknown whether they contain the necessary genes to flocculate and whether these genes are expressed adequately under wine-making conditions. These genes include the FLO1 flocculin gene which is one of the most important genes to confer the ability of yeast cells to flocculate and the MUC1 gene (subsequently also cloned as FLO11) encoding a mucin-Iike protein which was previously shown not only to play a key role in pseudohyphal development and invasive growth, but also to be involved in flocculation in S. cerevisiae. Together with MUC1, the involvement of FL08 (encoding a transcriptional activator of FLO1) and TUPI in flocculation, pseudohyphal development and invasive growth indicates that these processes might somehow be linked. Therefore, in order to construct wine yeast strains that are able to flocculate, 25 commercial wine yeast strains were investigated for their ability to flocculate, form pseudohyphae and invade solid media. Twenty-one of these strains were able to penetrate into agar media and different degrees of pseudohyphal and invasive growth were observed. The average length of cells and pseudohyphae and the efficiency of invasive growth varied among these strains. Two of the strains are known to flocculate in wine, while three other strains could be induced to aggregate to a limited degree in glycerol-ethanol medium. Southern blot analyses revealed the presence of homologous DNA sequences in all of the 25 strains using DNA fragments of FL08, MSS1O and MSS11 (encoding transcriptional activators of MUC1), FLO1 and MUC1 as probes. Using Northern blot analysis, FLO1 transcripts were detected in only one of the strains that showed constitutive flocculation in all the growth media tested. MUCJ transcripts of varying sizes could be detected in most of the strains. From these results it is clear that MUC1 does not primarily confer the phenotype of flocculation and that FLO1 (flocculation) and MUC1 (pseudohyphal differentiation, invasive growth and flocculation) are not co-regulated. We therefore suggest that MUC1, as opposed to FLO11, be retained as the most appropriate designation of this gene encoding the S. cerevisiae mucin-like protein.
- ItemGeographic distribution and evaluation of saccharomyces cerevisiae strains isolated from vineyards in the warmer, Inland Regions of the Western Cape in South Africa(South African Society for Enology and Viticulture, 2000) Khan, W.; Augustyn, O. P. H.; Van der Westhuizen, T. J.; Lambrechts, M. G.; Pretorius, I. S.The aim of this study was to examine the geographic distribution of Saccharomyces cerevisiae strains indigenous to 19 sites in the warmer, inland regions of the Western Cape in South Africa. These strains were compared to those isolated previously from the cooler, coastal regions of the same province by subjecting both sets of organisms to the same characterisation procedures. Thirty isolates per sampling site were isolated and the S. cerevisiae strains subjected to the following characterisation procedures; karyotyping using pulse field gel electrophoresis (CHEF), randomly amplified polymorphic DNA, the polymerase chain reaction technique (RAPD-PCR), sugar fermentation ability, flocculation ability, stress resistance/response and extracellular enzyme activity. When considering biodiversity per sampling site, CHEF karyotypes indicated the recovery of 30 S. cerevisiae strains. This number was reduced to 21 when comparing banding patterns over sites. Addition of RAPD-PCR data expanded the number of unique strains to 29. Subsequent consideration of sugar fermentation data indicated that one of the strians with exactly equivalent CHEF and RAPD-PCR patterns was in fact galactose positive while the other was galactose negative. These data clearly indicate that characterisation of yeast strains by application of a single technique is not a sound practice. None of the S. cerevisiae strains isolated in this study occurred in the coastal regions. In addition, each site sampled in this study had its own unique collection of wine yeast strains and no strain common to all sites in the study region was found. Survival mechanisms of S. cerevisiae are obscure. Although we found that many of the isolated strains could grow invasively/form pseudohyphae and that these abilities could therefore contribute to the organism's overwintering ability, other mechanisms must also be involved.
- ItemThe influences of different winemaking techniques on the mouthfeel of Shiraz grapes(South African Society for Enology and Viticulture, 2015) Nel, A. P.; Louw, L.; Lambrechts, M. G.; Van Rensburg, P.The objective of this study was to determine the effect of ripeness and of different tannin extraction methods on the sensory properties of wine, with a specific focus on mouthfeel properties. Quantitative descriptive analysis (QDA) was performed to evaluate the sensory properties of 20 young Shiraz wines in two phases. In Phase 1, wines from a cool area were evaluated and, in Phase 2, wines from a warm area were evaluated. Clear differences were found between the wines from the two regions. Wines from the cooler region were generally associated with higher levels of total non-flavonoids and total anthocyanins, and more intense numbing and puckering sensations. In contrast, the wines from the warmer region as a group were associated with a more drying and grippy mouthfeel, as well as less total anthocyanins and total non-flavonoids. In the set of wines from the cooler region, the effect of ripeness was more pronounced than in the set of wines from the warmer region. In both cases, riper grapes resulted in a coarser surface smoothness, a more numbing sensation, a bitter aftertaste and less adhesive mouthfeel. The wines from the cooler region that were harvested at a riper stage were associated with many of the anthocyanins/ anthocyanin derivatives and were negatively associated with hydroxycinnamate, procyanidin B1 and delphinidin-3-glucoside-p-coumaric acid. In the warmer area, the riper grapes were again associated with anthocyanins/anthocyanin derivatives, but this time were strongly associated with procyanidin B2, caffeic acid, p-coumaric acid, catechin, coutaric acid and total non-flavonoids. The effect of tannin extraction method on the sensory properties of the wines from the warmer region was more pronounced than in the wines from the cooler region. Unfortunately, the differentiation between treatments was not consistent from one ripeness level to the next. However, it appeared that the cold soak treatment differed the least from the control, regardless of region or ripeness, whereas the post-maceration treatment differed the most based on mouthfeel and phenolic composition. Although some mouthfeel attributes and phenolic compounds were consistently associated with region and ripeness, it is not clear if mouthfeel can be manipulated consistently by tannin extraction methods.
- ItemMUC1, a mucin-like protein that is regulated by MSS10, is critical for pseudohyphal differentiation in yeast(1996) Lambrechts, M. G.; Bauer, Florian; Marmur, J.; Pretorius, I. S.Pseudohyphal differentiation in Saccharomyces cerevisiae was first described as a response of diploid cells to nitrogen limitation. Here we report that haploid and diploid starch-degrading S. cerevisiae strains were able to switch from a yeast form to a filamentous pseudohyphal form in response to carbon limitation in the presence of an ample supply of nitrogen. Two genes, MSS10 and MUC1, were cloned and shown to be involved in pseudohyphal differentiation and invasive growth. The deletion of MSS10 resulted in extremely reduced amounts of pseudohyphal differentiation and invasive growth, whereas the deletion of MUC1 abolished pseudohyphal differentiation and invasive growth completely. Mss10 appears to be a transcriptional activator that responds to nutrient limitation and coregulates the expression of MUC1 and the STAI-3 glucoamylase genes, which are involved in starch degradation. MUC1 encodes a 1367-amino acid protein, containing several serine/threonine-rich repeats. Muc1 is a putative integral membrane-bound protein, similar to mammalian mucin-like membrane proteins that have been implicated to play a role in the ability of cancer cells to invade other tissues.
- ItemThe effect of increased branched-chain amino acid transaminase activity in yeast on the production of higher alcohols and on the flavour profiles of wine and distillates(2006) Lilly, M.; Bauer, Florian; Styger, G.; Lambrechts, M. G.; Pretorius, I. S.In Saccharomyces cerevisiae, branched-chain amino acid transaminases (BCAAT ases) are encoded by the BAT1 and BAT2 genes. BCAATases catalyse the transfer of amino groups between those amino acids and α-keto-acids, α-Keto-acids are precursors for the biosynthesis of higher alcohols, which significantly influence the aroma and flavour of yeast-derived fermentation products. The objective of this study was to investigate the influence of BAT-gene expression on general yeast physiology, on aroma and flavour compound formation and on the sensory characteristics of wines and distillates. For this purpose, the genes were overexpressed and deleted in a laboratory strain, BY4742, and overexpressed in an industrial wine yeast strain, VIN13. The data show that, with the exception of a slow growth phenotype observed for the BAT1 deletion strain, the fermentation behaviour of the strains was unaffected by the modifications. The chemical and sensory analysis of fermentation products revealed a strong correction between BAT gene expression and the formation of many aroma compounds. The data suggest that the adjustment of BAT gene expression could play an important role in assisting winemakers in their endeavour to produce wines with specific flavour profiles. © 2006 Federation of European Microbiological Societies Published by Blackwell Publishing Ltd. All rights reserved.
- ItemThe effect of increased yeast alchohol acetyltransferase and esterase activity on the flavour profiles of wine and distillates(2006) Lilly, M.; Bauer, Florian; Lambrechts, M. G.; Swiegers, J. H.; Cozzolino, D.; Pretorius, I. S.The fruity odours of wine are largely derived from the synthesis of esters and higher alcohols during yeast fermentation. The ATF1- and ATF2-encoded alcohol acetyltransferases of S. cerevisiae are responsible for the synthesis of ethyl acetate and isoamyl acetate esters, while the EHT1-encoded ethanol hexanoyl transferase is responsible for synthesizing ethyl caproate. However, esters such as these might be degraded by the IAH1-encoded esterase. The objectives of this study were: (a) to overexpress the genes encoding ester-synthesizing and ester-degrading enzymes in wine yeast; (b) to prepare Colombard table wines and base wines for distillation using these modified strains; and (c) to analyse and compare the ester concentrations and aroma profiles of these wines and distillates. The overexpression of ATF1 significantly increased the concentrations of ethyl acetate, isoamyl acetate, 2-phenylethyl acetate and ethyl caproate, while the overexpression of ATF2 affected the concentrations of ethyl acetate and isoamyl acetate to a lesser degree. The overexpression of IAH1 resulted in a significant decrease in ethyl acetate, isoamyl acetate, hexyl acetate and 2-phenylethyl acetate. The overexpression of EHT1 resulted in a marked increase in ethyl caproate, ethyl caprylate and ethyl caprate. The flavour profile of the wines and distillates prepared using the modified strains were also significantly altered as indicated by formal sensory analysis. This study offers prospects for the development of wine yeast starter strains with optimized ester-producing capability that could assist winemakers in their effort to consistently produce wine and distillates such as brandy to definable flavour specifications and styles. Copyright © 2006 John Wiley & Sons, Ltd.
- ItemValidation of two Napping techniques as rapid sensory screening tools for high alcohol products.(ELSEVIER SCI LTD, THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD, ENGLAND,OXON, OX5 1GB, 2013) Louw, L.; Malherbe, S.; Naes, T.; Lambrechts, M. G.; Van Rensburg, P.; Nieuwoudt, Helene
- ItemWine and health : research in action(Academy of Science of South Africa, 2001) Armstrong, G. O.; Lambrechts, M. G.; Mansvelt, E. P. G.; Van Velden, D. P.; Pretorius, I. S.Is it possible that wine may indeed be the world's oldest medicine? Until the 18th century, wine played an integral role in medical practice. Not only was it safer to drink than most available water but its alcohol, antioxidant and acid content inhibited the growth of many spoilage and pathogenic organisms. The paradigm shifted in the second half of the 20th century, when alcohol consumption, including wine drinking, had become the target of health campaigners who, with some success, demanded warning labels on wine bottles. Substantial medical evidence, summarized in this article, was accumulated during the 1990s and indicated that the moderate consumption of especially red wine can reduce the incidence of coronary heart disease. Today it is perceived, and generally accepted, that moderate wine drinking can be socially beneficial, and can also be effective in the management of stress and reducing coronary heart disease. The prudent wine drinkers, however, continue to monitor their drinking habits so as to ensure that the benefits exceed the risks.
- ItemYeast and its importance to wine aroma(South African Journal of Enology and Viticulture, 2000) Lambrechts, M. G.; Pretorius, I. S.The most mysterious aspect of wine is the endless variety of flavours that stem from a complex, completely non-linear system of interactions among many hundreds of compounds. In its widest sense, wine flavour refers to the overall impression of both aroma and taste components. Aroma is usually associated with odorous, volatile compounds; the bouquet of wine refers to the more complex flavour compounds which evolve as a result of fermentation, elevage and ageing. With the exception of terpenes in the aromatic grape varieties and alkoxypyrazines in the herbaceous cultivars, perceived flavour is the result of absolute amounts and specific ratios of many of these interactive compounds, rather than being attributable to a single "impact" compound. Without underestimating the complexity of these interactive effects or negating the definitive role played by the accumulated secondary grape metabolites in the varietal character of wine, this review will focus mainly on the contribution of yeast fermentation to the sensorial quality of the final product. Yeast and fermentation conditions are claimed to be the most important factors influencing the flavours in wine. Both spontaneous and inoculated wine fermentations are affected by the diversity of yeasts associated with the vineyard and winery. During the primary alcoholic fermentation of sugar, the wine yeast, Saccharomyces cerevisiae, together with other indigenous non-Saccharomyces species, produce ethanol, carbon dioxide and a number of by-products. Of these yeast-derived metabolites, the alcohols, acetates and C4-C8 1tfatty acid ethyl esters are found in the highest concentration in wine. While the volatile metabolites contribute to the fermentation bouquet ubiquitous to all young wines, the production levels of these by-products are variable and yeast strain specific. Therefore, this article also highlights the importance of untapping the hidden wealth of indigenous yeast species present on grapes, and the selection and genetic development of yeast starter culture strains with improved flavour profiles. In the future, some winemakers may prefer to use mixtures of indigenous yeast species and tailored S. cerevisiae strains as starter cultures to reflect the biodiversity and stylistic distinctiveness of a given region. This will help winemakers to fullfil the consumer's demand for individual wines with intact local character and to ensure the survival of wine's most enthralling aspect - its endless variety.