The effects ofpolyamines on the ice*nucleating activity of an ice"nucleating bacterium, Erwinia uredovora KUIN-3, were investigated. The activity in the outer membrane derived from this bacterium was increased by the addition of spermidine (lOmM). Also, the activity was stabilized in alkaline pH buffer with the addition of polyamine. Further, the addition of methylglyoxal bis(guanylhydrazone) which inhibited the activity of S-adenosylmethionine decarboxylase, inhibited the ice-nucleating activity of the cells of this bacterium. The amount of polyamine in this bacterium was examined using HPLC. The components of the polyamines were three species, putrescine, cadaverine, and spermidine. The amounts of polyamines in the cells and outer membranes after MGBG treatment decreased. The results suggested that polyamine was the most important component of the ice-nucleating material in this bacterium. Much effort has been put into the study of the ability of

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