Abstract
Ice-nucleation activity was measured with the bacteria isolated from gemmisphere of tea trees. The highest activity was obtained with a dominant bacterium which was coded as TGB-2 tentatively and characterized by yellow colonys on nutrient agar plate. The maximum and mean freezing temperatures of the bacterium by micropipette method were -2 and -2.7C, respectively. Population of the bacterium showed seasonal changes on gemmisphere of tea trees from the first frost season through the last frost season. The maximum population reached 106 cells/g of fresh buds from late April to early May. Because the highest activity of the bacterium maintained even at the dilution rate of 106 cells/ml, it was suggested that dew on tea buds could possibly be frozen at higher temperature in late April to early May when gemmisphere population of the bacterium increased over 106 cells/g of fresh buds. The freezing activity at cooler temperature (-8 to -12C) did not necessarily required the presence of intact cells. Ice-nucleation activity greatly decreased by treating bacterial suspension at 40C for 5min and was completely lost by heating it at 80C. Hydrogen peroxide showed no effect on ice-nucleation activity but calcium hypochlorite completely destroyed it. Methylene blue, safranin and tween 80 also reduce ice-nucleation activity.
