The Improvement and Expansion of the Microbial Culture Collection


Project Number
IWBT 05-01

Project title
The improvement and expansion of the microbial culture collection

Project leader
Van Rensburg, P

Institution
University of Stellenbosch. Faculty of AgriSciences. Institute for Wine Biotechnology

Team members
Mocke, B
Muller-Patterton, H E
Volschenk, H

Project description
With the importance of Saccharomyces cerevisiae in winemaking now firmly established, there is a growing demand for new and improved wine yeast strains. New hybrid yeast strains were obtained through different breeding programs. The first type of hybrid was obtained by mating the spores of WE14 and VIN13. Forty-four confirmed hybrids have been obtained. Ten of these hybrids have been partially characterised and all of the hybrids have been used for small-scale vinifications using both white and red musts. Additionally, further hybrids were sought by mating the spores isolated from the VIN7 and WE372 wine yeast strains. No hybrids could be isolated from this mating experiment. Five further confirmed hybrids were obtained by mating the spores isolated from VIN13 and Saccharomyces paradoxes. These five hybrids have been partially characterised and small-scale vinification experiments have been completed. A further fifty-five unconfirmed hybrids are in the process of being characterised.

A random mating technique of wine yeast strains was used to develop further novel hybrids. This technique relies on the chance combination of optimal genotypes to achieve improvements in particular phenotypes. The screening of large numbers of mating type strains is however laborious and expensive, and therefore to circumvent this problem, we have used a re-iterative approach of random mass-mating coupled with rounds of selection and enrichment for hybrids with desired phenotypes. Various wine yeast strains currently used by industry as well as Saccharomyces paradoxes were used to obtain a mixed population of yeast presumably containing a wide variety of hybrids. Currently, stringent selection pressure during batch-culturing is being used to reduce the hybrid population and select those hybrids with the desired phenotypes. The stringent selection conditions include, during the first round of selection, synthetic must with low nitrogen content and high sugar concentrations. During the second round of selection, synthetic must containing only fructose as a carbon source was used. Additional rounds of selection will be performed in the coming months to reduce the hybrid population even further.

Presentation(s)
Mocke, B, Bauer, F F and Van Rensburg, P. 2004. A novel approach for novel yeast strain production. Paper presented at the 13th South African Society for Microbiology Conference. April 2004, Stellenbosch, South Africa.

Mocke, B, Bauer, F F and Van Rensburg, P. 2004. A novel approach for novel yeast strain production. Paper presented at the 19th International ICFMA Symposium, FoodMicro, Bled, Slovenia.

Wilding, M, Bauer F F and Van Rensburg, P. 2006. Strategies for improving wine yeast. Paper presented at the 3rd International Congress of the South African Society for Enology and Viticulture. 7-8 November, Somerset West, South Africa.

Article
Van Rensburg, P. 2005. Hybrid wine yeasts offering the winemaker a unique fermentation tool, Australian and New Zealand Grapegrower and Winemaker, Mnth Feb (493) (p. 56-60)

Van Rensburg, P. 2005. Hybrid wine yeasts, offering the wine maker a unique fermentation tool. (www.newworldwinemaker.com) New World Winemaker,

Van Rensburg, P. 2005. Les levures hybrides, un outil exceptionnel pour les fermentations, Revue Francaise d’Oenologie, (213) (p. 15-17)

Thesis
Mocke, B A. 2005. The breeding of yeast strains for novel enological outcomes. MSc. University of Stellenbosch, Stellenbosch.

FinalReport.pdf

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