Applications and Production of an Extracelllular Ice-Nucleating Substance by the Ice-Nucleating Bacteria

点击翻译按钮获取中文摘要

When Erwinia uredovora (KUIN-3) was cultured aerobically in a medium consisting of Simmons-citric acid broth (pH 6.1) for 24 hr at 18 ^ﾟC, the ice-nucleating activity of strain KUIN-3 cells was obtained. The ice-nucleating temperature, T_<50>(^ﾟC) was detected at -2.8 ^ﾟC in cell suspensions (1.1 x 10^8 cells/ml) of KUIN-3.The production of an extracellular ice-nucleating substance by KUIN-3 was examined. In an ice-nucleating medium containing yeast extract, 30 g ; sucrose, 10 g ; DL-serine, 2 g ; DL-alanine, 2 g ; K_2SO_4, 8.6 g and MgSO_4・7H_2O, 1.4 g, in one liter of distilled water, maximum growth was obtained with 1.1 mg/ml of the extracellular ice-nucleating substance at 18 ^ﾟC after 48 hr of shaking.Cell-free ice nuclei were shed from Pseudomonas viridiflave (KUIN-2) cells with 2 % Triton X-100 in the presence of 10 mM EDTA-2Na. KUIN-2 shed cell-free ice nuclei (0.22 mg protein/ml) active at -4.9 to -5.8 ^ﾟC. The ice-nucleating activity was greatly decreased by treating the cell-free ice nuclei for 30 min at 40 ^ﾟC, and was completely lost by heating at 90 ^ﾟC. The ice-nucleating activity of the cell-free ice nuclei was inhibited by the addition of proteases, protein-modifying reagents and denaturants. It is suggested that the ice-nucleating activity sites of cell-free ice nuclei contain proteins. The ice-nucleating activity of cell-free ice nuclei containing Mg^<2+> occurred within the temperature range -3.3 to -3.6 ^ﾟC.