Unusual Gene-Controlled Combinations of Carbohydrate Fermentations in Yeast Hybrids

Abstract

The ability of Saccharomvces to ferment various sugars is gene-controlled. Many combinations have been produced by hybridization. The yeasts described, all ferment glucose and fructose and any hydrolysis which splits off one of the hexoses results in a positive test. In galactose-melibiose combinations the fermentation of the former and hydrolysis of the latter are controlled by 2 independent segregating genes. Melibiose is a disaccharide of glucose and galactose, yet there is a gene which ferments melibiose but not galactose. Tests for residual galactose suggest that the ME gene controls the production of a hydrolytic enzyme which breaks down melibiose. Other tests were made on raffinose, a trisaccharide with fructose, glucose and galactose (the fructose and glucose being united by a sucrose linkage). The ME gene will not ferment raffinose in the absence of the sucrose gene (SU). This suggests that hydrolysis of raffinose depends on sucrase and that complete hydrolysis of raffinose requires also subsequent action of meli-biase. In other expts. independent genes are shown to control the hydrolysis of alpha methyl glucoside and maltose; this was unexpected as alpha glucosidase is supposedly capable fo hydro-lyzing both in vitro.