Nonlethal freezing injury to metabolism and motility of Pseudomonas fluorescens and Escherichia coli.

Some specific effects of the conditions of freezing on death and metabolic injury of a psychrophilic and a mesophilic species of bacteria were investigated, with particular respect to changes in motility. It was found that the extent of nonlethal metabolic freezing injury and the changes in motility are apparently correlated and are affected by the time and temperature of storage and the nature and pH of the suspending fluid. There were significant differences between the resistance to cold of the test organisms, the mesophilic being the more sensitive. The motility of the psychrophilic Pseudomonas fluorescens decreased considerably less after low-temperature exposure than did that of the mesophilic Escherichia coli. The percentage of restoration in motility of the subcultures was lower after freezing in water than in other suspending fluids.