THE WATER RELATIONS OF GROWTH AND POLYHYDROXY ALCOHOL PRODUCTION BY ASCOMYCETOUS YEASTS

The response of 31 ascomycetous yeasts to a reduction in water activit y (a(w)) adjusted with D-glucose or NaCl was investigated. The growth of most yeasts was more tolerant to glucose than to NaCl at equivalent a(w). Zygosaccharomyces rouxii was the most osmotolerant yeast examin ed. Natural abundance C-13-NMR spectroscopy and HPLC analyses of eight yeasts indicated that glycerol and arabitol or mannitol were accumula ted intracellularly in response to a(w) reduction. Pichia sorbitophila , Candida cacaoi, Candida magnoliae and Zygosaccharomyces bisporus res ponded to reduced a(w) by a decrease in specific growth rate and cell volume, and an accumulation of glycerol. The other polyol accumulated did not increase in concentration with a(w) reduction to the same degr ee as glycerol. A polyol concentration ratio (intra/extracellular) as high as 800-fold was attained across the membrane. Greater amounts of polyols were produced at equivalent a(w). values when adjusted with gl ucose than with NaCl. The ability to accumulate high concentrations of polyols appears to be the most important criterion in determining osm otolerance.