Summary: Cultures of continue to grow without a lag following a sudden increase in temperature from O ºC to 20 °C (shift-up) or a reciprocal decrease (shift-down); the growth rate changes gradually to that typical of cultures grown isothermally at the final temperature. After a shift-down the phospholipid acyl chain length begins to change immediately, whereas there is a delay following a shift-up. However, the final fatty acid composition is attained within the same number of cell division times after a shift-up or shift-down. The changes in chain length after a shift-up or shift-down can be partially prevented by adding streptomycin or erythromycin at the time of the temperature shift. There is little or no turnover of the head-group or acyl chains of phospholipids during isothermal growth, at O °C or 20 °C, nor after a shift-down. In contrast, after a shift-up approximately 40% of the phosp_holipid turns over during the first 12 h after the shift, but none during the subsequent 24 h; phosphatidylglycerol turns over slightly faster than phospholipids during isothermal growth at O °C or 20 °C, nor after a shift-down. In contrast, and acyl chains of each phospholipid. There is evidence for the conversion of phosphatidylglycerol to cardiolipin. It is argued that as a psychrophilic organism, well adapted to growth at low temperatures, is more stressed by sudden increases of growth temperature than by a sudden decrease.


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