Isolation and Characterization of a Mutant of Schwanniomyces Castellii with Altered Respiration

We have tried to isolate respiratory deficient mutants of the amylolytic yeast Schwanniomyces castellii CBS 2863 after mutagenesis with acriflavine. One of the mutants called DR 12 has been studied in more detail. Pasteur effect present in the wild-type is lost in the mutant, on the contrast an obvious Crabtree effect was observed: fermentation was almost as active in aerobiosis as in anaerobiosis. Moreover, the rate of anaerobic fermentation of the mutant was almost twice that of the wild type. This mutant was cytochrome b-deficient while the amount of the other cytochromes was larger than in the wild-type. Moreover, the level of these remaining cytochromes in the mutant was higher on non-repressive medium than on glucose medium. However, the fact that the mutant DR 12 retained a cyanide-sensitive respiration and that it was able to grow on ethanol as a non-fermentable substrate is noteworthy.