Osmotic Properties of Spheroplasts from Saccharomyces cerevisiae Grown at Different Temperatures

Spheroplasts were prepared from cells of Saccharomyces cerevisiae NCYC 366, grown at 30 or 15 C, by incubating cells with snail-gut juice after pretreatment with 2-mercaptoethanol. Walls of cells grown batchwise or in continuous culture at 15 C were more resistant to digestion with snail juice than walls on cells grown under the same conditions as 30 C. Spheroplasts lysed when suspended in hypotonic solutions of mannitol. The resistance of spheroplasts to osmotic lysis tended to increase when the test temperature was lowered below 30 C. The increased resistance was greater with spheroplasts from cells grown at 15 C. Cations, especially Ca²⁺, protected spheroplasts against osmotic lysis. In general, the protective effects, measured at 30 C, were smaller with spheroplasts from cells grown at 15 C compared with 30 C. Citrate and ethylenediaminetetraacetate (EDTA) decreased the resistance of spheroplasts to osmotic lysis. On the whole, the decrease was greater with spheroplasts from cells grown at 30 C rather than 15 C. In the presence of EDTA, spheroplasts from cells grown at 30 C were less resistant to osmotic lysis at 5 C than at 30 C; when spheroplasts from cells grown at 15 C were similarly examined, they were more resistant to lysis at 5 C than at 30 C. Spheroplast membranes from cells grown at 15 C had slightly but significantly greater contents of Mg²⁺, Ca²⁺, K⁺, and Na⁺ compared with spheroplast membranes from cells grown at 15 C. Mg²⁺ and Ca²⁺ were more easily extracted with EDTA from membranes of 30 C-grown cells than from 15 C-grown cells.