Changes in chemical structure and function in Escherichia coli cell membranes caused by freeze-thawing. I. Change of lipid state in bilayer vesicles and in the original membrane fragments depending on rate of freezing.

The effect of different rates of freezing on the character of lipids in unilamellar lipid bilayer vesicles and in the original membrane fragments of Escherichia coli B cells was investigated by measuring the temperature-dependent fluorescence polarization ratio changes of cis- and trans-parinaric acids. In lipid bilayer vesicles, both slow and rapid freezing brought about significant alterations in fluorescence polarization ratios in the specimens derived from both logarithmic and stationary-phase cells. In the original membrane fragments derived from logarithmic-phase cells, slow freezing gave rise to a similar alteration in fluorescence polarization ratio change, but no such alteration was found in the case of rapid freezing. Logarithmic-phase cells suffered from a membrane permeability change during slow freezing, which subsequently resulted in low cell viability. The cells suffered only slight impairment in membrane function during rapid freezing, and maintained higher viability. These results suggest that the primary site of damage due to freezing of the cells is the cellular membranes, and this destruction is due to a lipid state change in the membranes brought about by freezing.