Abstract
The effect of different mutagens on brewing yeast is described together with the results of selection for strains possessing improved commercial properties. The mutagens n-methyl-n-nitroso nitroguanidine (NTG), ultraviolet light (UV), ethyl methane sulfonic acid ester (EMS), and nitrous acid were assessed by the rate of induction of genetically stable auxotrophic mutants. Commercial brewing strains of Saccharomyces cerevisiae and S. carlsbergensis were particularly sensitive to NTG and UV. Specific selective techniques were designed to isolate mutants with changed ability to synthesize diacetyl and hydrogen sulfide, and with altered degrees of flocculence. Mutants were isolated successfully for these parameters from three different strains of brewing yeast after NTG or UV treatment. The significance of these results is discussed in relation to the ploidy of the strains employed as determined by estimation of DNA content. The properties of some of these mutants compared with the parental strains show that induced mutation is an effective method for production of improved brewing yeast.
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