Some Basic Characteristics of Bacterial Freezing Nuclei

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.