Use of chloramphenicol-inherent resistance in protoplast fusion of industrial yeast strains

Abstract

Thirty strains, consisting of industrial yeast strains, e. g. wine yeast Saccharomyces cerevisiae W3 etc., were screened for inherent resistance to 0.5% chloramphenicol (CM). Ten (33%) of the 30 strains showed inherent resistance to the inhibitory effect of 0.5% CM. The petites converted from the CM-inherent resistants by treating with acriflavine or ethidium bromide retained the CM-resistance ( ρ − CMR), and thus were fused by the Ca 2+PEG method with industrial strains ( ρ + CMS). The fusion products were selected in glycerol medium with 0.5% CM and isolated at frequencies ranging from 1.4 × 10 −6 to 3.3 × 10 −6 for used protoplasts. In this case, the reversion rates were less than 10 −9. The resulting fusion products were CM-resistant strains showing respiratory competence ( ρ + CMR). Thus it was demonstrated that the fusion products contained the traits ( ρ − and CMR) of both parents. The CM-inherent resistance of industrial yeast strains may be used as a suitable selection marker in the protoplast fusion of industrial strains, for which it is preferable to avoid mutagenesis.