ABSTRACT
This chapter describes the genetic improvement of industrial strains of Saccharomyces cerevisiae used for fermentation of alcoholic beverages (brewing strains), especially that of wine yeasts, through protoplast fusion technique. There are two types of targets for the improvement of brewing yeasts: One is the improvement of certain inborn characteristics in the parental strain, and the other is the introduction of foreign, novel characteristics into the parental strain. Recently, inactivation of a certain desired gene through recombination between introduced recombinant DNA sequence and the gene sequence, or insertion of the foreign DNA into the target gene has become possible in brewing yeast. For construction of wine yeasts through protoplast fusion, cytoduction of K2 killer plasmids into wine yeasts has been reported. More efficient techniques for protoplast fusion will promote application of protoplast fusion to genetic improvement of industrial yeast strains, which will lead to an increase of fusant strains that are employed for industrial fermentation of alcoholic beverages.
