Classic techniques for improvement of industrial yeast strains. Part I? Construction of ethanol-resistant and osmophilic industrial strains of Saccharomyces cerevisiae by electrofusion
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The effective production of biomass or ethanol in industrial media of high osmolality requires new yeast strains. The present work focused on the development of such strains. Genetic engineering methods using cytoplasmatically-marked yeast (electrofusion of protoplasts of heterothallic haploids; electrotransformation of killer dsRNA or VLPs into haploids; generation of rho-) were used. The characteristics of the hybrids were evaluated by conventional analytical and instrumental methods, followed by statistical interpretation. After screening for a minimum 10% increase in industrially-relevant parameters, 3 osmophilic hybrids of baker's yeast, as well as 8 improved strains of distillery yeasts were selected. The baker?s yeasts showed optimum growth in a relatively concentrated molasses wort (1:5 ratio of molasses to final volume). The alcohol-resistant yeasts (including killer) produced up to 14.5% (w/w) ethanol in a medium containing 34% dissolved solids (a mixed mash of sucrose and potato). The characteristics of the alcohol-resistant and osmophilic yeasts were stable over several years of their industrial applications.The results show that electrical techniques (fusion to obtain hybrids, with interpretation by computer-aided image analysis, and transformation to give marked strains) can be used effectively enough for the construction of some industrially-productive yeasts.
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A.T. Salek, Milan-Science, Institut of Microbiology, Dr. Ernst-Derra Str. 4, 94036 Passau, Germany