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.