Valuable Techniques in the Genetic Manipulation of Industrial Yeast Strains

Abstract

Techniques such as mutation, classical hybridization, spheroplast (protoplast) fusion, and liposome-mediated transformation are being employed to effect genetic changes in brewing yeast strains. Each technique offers advantages and disadvantages, and a combination is often necessary to achieve the desired objective. Treatment of polyploid brewing strains with the compound benomyl permitted the recovery of industrial strains harboring recessive auxotrophic markers indigenous to these strains. Hybridization was employed primarily to construct strains suitable for use as partners in spheroplast fusion with brewing strains. The method of “rare mating” involving karyogamy defective (Kar) strains was employed to produce hybrids between laboratory-constructed strains with killer activity and industrial polyploid strains. In yeast transformation experiments with DNA and RNA encapsulated in liposomes, the liposomes (synthetic microcapsules, prepared by reverse-phase evaporation) protected entrapped UNA from nuclease degradation and also interacted strongly with yeast spheroplasts under conditions favoring somatic fusion and transformation.