Variations in Cellular Polyamine Compositions and Contents of Vibrio Species during Growth in Media with Various NaCl Concentrations

In order to obtain insight into the possible physiological significance of norspermidine [NH₂(CH2)₃NH(CH₂)₃NH₂], which is characteristically present in the genus Vibrio, we have determined the cellular polyamine contents of Vibrio alginolyticus and V. parahaemolyticus during growth in media with various NaCl concentrations. Regardless of the medium NaCl concentration, the norspermidine content, on a per mg of protein basis, was highest in the early exponential phase and then declined with prolonged cultivation, whereas there was only a slight change in spermidine, the content of which was much lower than that of norspermidine throughout growth. Moreover, at higher NaCl concentrations, norspermidine was the major polyamine throughout growth. When the cells were suddenly exposed to media with various NaCl concentrations, the content of norspermidine increased immediately or after an initial precipitous drop with the onset of growth, but that of spermidine did not change markedly. The putrescine content of these vibrios was substantially elevated only when the cells were grown in or transferred to media with lower NaCl concentration. This pattern of polyamines suggests that, instead of spermidine, norspermidine might play some important role(s) in supporting growth, whereas putrescine may be mainly involved in maintaining cellular ionic or osmotic balance against a lower NaCl environment.