Abstract
Escherichia coli B cytoplasmic and outer membrane from cells in different growth phases showed different chemical compositions. In freezing, logarithmic phase cells showed a marked permeability increase in the outer as well as the cytoplasmic membrane. Whereas, in the stationary phase cells no such change in membrane permeability was observed. Cooling of phospholipids and lipopolysaccharides with trans-parinaric acid showed a distinct fluorescence increase from room temperature to far below 0°C. In the outer membrane the fluorescence similar to that of lipopolysaccharides was shown. The outer membranes of cells in different growth phases showed similar temperature-dependent fluorescence changes. The cytoplasmic membrane exhibited a temperature-dependent fluorescence similar to that of the phospholipids. The onset temperature of the increase in fluorescence differed with the cells at different growth phases. The presence of EDTA and MgCl 2 modified the fluorescence changes in the membranes from cells in logarithmic phase. Whereas, in the membranes from cells in stationary phase no such effect was observed. These results suggest that the organizational stability of the membranes from cells in stationary phase is a fundamental basis of the membrane's resistance to the freezing damage.
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