The use of mitochondrial mutants in hybridization of industrial yeast strains

Summary

The contributions of each of the parental strains to the genomes of the sporulating and non-sporulating hybrids, Saccharomyces diastaticus (S. cerevisiae) × Hansenula capsulata, S. diastaticus × Hansenula wingei, S. diastaticus × Torulopsis glabrata, S. diastaticus × Candida pseudo tropicalis (Kluyveromyces marxianus) S. diastaticus × Saccharomyces rouxii, S. diastaticus × Saccharomyces kluyveri, and Saccharomyces diastaticus × Saccharomyces bayanus, obtained by protoplast fusion, were determined by the methods of whole nuclear DNA-DNA reassociation. Petite mutants of S. diastaticus NCYC625, and respiratory-competent strains of the other species, were used. In all of the hybrids but one, the DNA from the S. diastaticus parent showed 93.3 to 109.3% homology with the DNA from the hybrids, and the other parents, from −7.7% (S. kluyveri) to 20.0% (S. bayanus). Reassociation between the DNA from S. diastaticus and the DNA from the other parental strains ranges from 4.7 to 19.4%. Reassociation between DNAs from S. diastaticus and that of the S. diastaticus × T. glabrata fusion hybrids were 15.2 and 18.9% respectively. Further investigation of this hybrid is desirable. The fusion products were relatively stable as compared to some fusion hybrids selected by use of nuclear markers, and could be maintained on normal media, with little or no selection pressure, but use of an appropriate carbon source. In most of the hybrids, except for S. diastaticus × T. glabrata, the S. diastaticus parent contributed most of the genome, and only a single chromosome, or a fragment of a chromosome, appeared to be transferred to the Saccharomyces nucleus, to form the genome of the fusion product.