ISOLATION AND CHARACTERIZATION OF A NOVEL ICE-NUCLEATING BACTERIUM, PSEUDOMONAS SP, KUIN4, WHICH HAS STABLE ACTIVITY IN ACIDIC SOLUTION

A novel ice-nucleating bacterium, KUIN-4 was isolated from a cherry leaf, which was unsusceptible to frost injury, Strain KUIN-4 was identified as Pseudomonas sp, from its characteristics and taxonomics; the optimum temperature and pH for its growth were 18 degrees C and 4.5, respectively, When strain KUIN-4 was cultured aerobically in CYE medium (pH 4.5) for 48 h at 18 degrees C, the ice-nucleating activities of strain KUIN-4 cells and culture broth (extracellular ice-nucleating matter) after removal of the cell were obtained, The ice-nucleating temperature, T-50 (degrees C), was indicated to be -2.8 degrees C in cell suspensions (4.25 x 10(7) cell/ml) of strain KUIN-4 Also, it had become apparent that the ice-nucleating activity involved class A, B, and C structures as judged by its freezing difference spectrum in D2O versus H2O. The ice-nucleating activity of this strain as well as other ice-nucleating bacteria was significantly decreased by heat treatment (40 degrees C, 30 min), The ice-nucleating activity from this strain had unique features, which was stable under acidic conditions (pH 3.5-5.0) and was weakly inhibited by denaturants and protein-modifying reagents.