Studies on the ‘Osmophilic’ Yeast Saccharomyces rouxii and an Obligate Osmophilic Mutant

SUMMARY: An obligate osmophilic mutant (strain B1/4) of Saccharomyces rouxii has been isolated that fails to grow at osmotic pressures corresponding to 20% (w/v) sucrose or less. In 30% sucrose the yeast is filamentous and grows slowly. In 40% sucrose it is mainly filamentous and has over twice the normal diameter. In 60% sucrose it grows in the yeast form with a growth rate twice that of the culture in 40% sucrose. This mutant is lysed by a sudden drop in the osmotic pressure of the environment. Cell envelopes of the parent strain contained glucose and mannose in the ratio 1.2:1 and contained 3.8% (w/v) hexosamine, whereas the envelopes of the mutant contained 0.8% hexosamine. Cell envelopes of the mutant grown in 40% sucrose contained glucose and mannose in the ratio 1.9:1, whereas for envelopes of the yeast grown in 60% sucrose the ratio was 1.2:1. Neutral lipids from whole cells and those from the envelopes of the mutant strain generally contained more unsaturated fatty acids than the corresponding fractions from the parent strain.