Some Basic Characteristics of Bacterial Freezing Nuclei

Abstract

Freezing spectra of INA bacteria from different parts of the world were compared. A slight increase in efficiency of freezing nuclei produced by strains from warmer climates was observed. Whole cells of the most efficient strain produced nuclei active at temperatures ranging from 2 to 10°C, whereas fragments from these cells exhibited activity only at 8 to 10°C. In all cases, the frequency of active cells in a population proved low. Thus, activity at 8 to 10°C was evidenced by 1 cell in about 300, the corresponding ratio being 1 in 104 at 2 to 4°C. It was shown in several ways that the variety of `freezer' individuals was not due to a need for multicell aggregation or any other cooperative process. Also, the time at which a given individual in a cell population expressed its latent freezing potential was shown to vary with time and cell physiological state.