Application of Killer Toxins in Stepwise Selection of Hybrids and Cybrids Obtained by Induced Protoplast Fusion

The most current method for selecting hybrid yeast clones obtained by means of protoplast fusion or transformation procedures is based on the auxotrophy of manipulated strains. Unfortunately, preparation of auxotrophic mutants without damage to the rest of the genome is time consuming, and, sometimes, as in the case of polyploid strains, practically impossible. For these reasons, namely in connection with improvement of industrial strains, selection techniques in which mutagenesis of manipulated parental strain is not required are attractive. Elimination of the industrial parent strain can be based, for example, on its natural sensitivity to some antibiotic or toxic compound, if the donor parental cell confers on the hybrid the ability to grow in the presence of such an agent.