Browsing by Author "Khan, W."

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    Geographic 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.
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    Seasonal variation of indigenous saccharomyces cerevisiae strains isolated from vineyards of the Western Cape in South Africa
    (South African Society for Enology and Viticulture, 2000) Van der Westhuizen, T. J.; Augustyn, O. P. H.; Khan, W.; Pretorius, I. S.
    There is strong support for the use of naturally-occurring Saccharomyces cerevisiae strains that improve the sensory quality of wines and reflect the characteristics of a given region. Contrary to popular belief, S. cerevisiae is found at very low numbers on healthy, undamaged grapes and is rarely isolated from intact berries. The majority of studies on the population kinetics and geographic distribution of indigenous S. cerevisiae strains have not adequately focused on the variation in their numbers over a longer period of time. This paper discusses the results obtained in the first phase of a comprehensive research programme aimed at assessing how the natural population dynamics of S. cerevisiae are affected over the long term by abiotic factors. Indigenous strains of S. cerevisiae were aseptically isolated from eight sites in four areas in the coastal regions of the Western Cape, South Africa, during 1995 through 1998. Thirty colonies per site were isolated and the S. cerevisiae strains were characterised by electrophoretic karyotyping. Strain numbers per site varied over the four-year study period. Weather conditions resulting in severe fungal infestations and heavy applications of chemical sprays dramatically reduced the numbers of S. cerevisiae strains recovered during 1997. A return to normal weather patterns in 1998 resulted in a gradual recovery of the indigenous population. Indications are that some of the strains isolated are widespread in the study area and may represent yeasts typical of the area. Commercial wine yeast strains were recovered in only a few instances and the likelihood that commercial yeasts will eventually replace the natural yeast microflora in vineyards seems remote.