SUMMARY: The temperature limits of growth of three psychrophilic yeasts, and , were examined. All species grew well at subzero temperatures (— 1 °C). The maximum temperature of growth was significantly higher with glucose as substrate (18 to 20 °C) than with ethanol (17 to 18 °C). There was a positive correlation between the growth temperature and the degree of fatty-acid unsaturation of the cell lipids; the lower the temperature, the greater the degree of fatty-acid unsaturation. At subzero temperatures (— 1 °C) with ethanol as substrate, 90% of the total fatty acid was unsaturated with linolenic (35 to 50%) and linoleic (25 to 30%) acids predominating. At temperatures close to the maximum for growth, linolenic acid accounted for less than 20% of the total fatty acid and oleic (20 to 40%) and linoleic (30 to 50%) acids were the major components. Difference spectra of intact cells showed marked changes in the ratios and amounts of individual cytochromes as a function of growth temperature. In with glucose as substrate, the ratios of cytochromes : at 8 and 19 °C were 1:1·1:2·9 and 1:2·3:16·7 respectively. Similar changes in cytochrome ratios were noted for , but changes were much less marked for The temperature effects were interpreted as supporting the view that membrane structure and composition are fundamental to temperature adaptation in psychrophilic yeasts.


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