Identification of an Ice-nucleating Bacterium KUIN-1 as Pseudomonas fluorescens and Its Ice Nucleation Properties

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An ice-nucleating bacterium, strain KUIN-1, was isolated from the leaves of field beans (Phaseolus vulgaris L.). Strain KUIN-1 was identified as Pseudomonas fluorescens from its taxonomical characteristics. Ice-nucleating activity was obtained when strain KUIN-1 was cultured aerobically in a medium containing Koser citrate broth (pH 7.0) for 24 hr at 18°C. The icenucleating activity did not appear until the bacterial cell concentration reached 10⁷ to 10⁸/ml. Nucleation at - 3.0°C was detected in suspensions (1.8 × 10⁹ cells/ml) of cells that had been grown on the medium containing Koser citrate broth. Strain KUIN-1 produced a lower nucleation frequency (i.e. the number of ice nuclei/cell) than did ice-nucleating Pseudomonas syringae No. 31 suspensions, particularly at temperatures above - 5°C. The nucleation frequency of strain KUIN-suspensions was similar to that obtained for an ice-nucleating Erwinia herbicola No. 26 at - 5°C.