Role of Spermidine in the Ice-Nucleating Activity of the EIM from Erwinia uredovora KUIN-3

Abstract

Polyamines have been shown to be necessary for the activity of the extracellular ice-nucleating matter (EIM) from the ice-nucleating bacterium, Erwinia uredovora KUIN-3. When this bacterium was cultured in the presence of methylglyoxal bis(guanylhydrazone), MGBG (2 mM), the ice-nucleating activity of the EIM significantly decreased. Further, the thermal (25-40°C) and pH (alkaline region) stabilities of the activity were stimulated by the addition of spermidine. This phenomenon only occurred in the class A and B structures, and it showed that the hydrophobicities of the class A and B structures in the EIM increased with the addition of spermidine as judged by the freezing difference spectra. We then found by using fluorescent reagents that the physiological roles of spermidine in the EIM controlled the charge, free-amino groups, and hydrophobicities on the surface of the EIM. In conclusion, one could predict that spermidine took part in the charge of the surface, the control of hydrophobicity, and the stability of protein conformation in the class A and B structures in the EIM, and is a critical component in the class A and B nucleating structures.