A Nonrespiratory Variant of Saccharomyces cerevisiae

Abstract

Ethylene oxide acting on S. cerevisiae produces mutant colonies. The mutant cells may fuse to become diploid. One fairly stable haploid mutant strain was examined in detail. Unlike the parent strain, resting suspensions of this variant showed no ability to oxidize either glucose or alcohol under aerobic conditions. The parent yeast showed absorption bands cor-resp.to reduced cytochromes A, B, and C at 605, 552, and 563 A. Variant suspensions showed a strong band at 563 A. (cytochrome C) but lacked the other 2 bands. The variant, unlike its parent, gave no test for indophenol oxidase with Nadi reagents according to the method of Keilin. The variant fermented the same sugars as the parent strain and used them as substrates for growth. Unlike the parent, it did not grow with alcohol as C source. Whereas the parent thallus occurred as single cells and pairs, that of the variant consisted of clusters of from 3 to 20 cells. The variant has lost the ability to form ascospores.