Dependence of the putrescine content of Escherichia coli on the osmotic strength of the medium.

Putrescine is the polyamine present in highest concentration in Escherichia coli; however, few specific functions for it are known. We found that cells growing in nutrient broth supplemented with high concentrations of NaCl, KCl, MgCl*, or sucrose had greatly reduced levels of cellular putrescine. On the basis of osmotic strength, all four solutes produced similar decreases in putrescine content. In contrast, glycerol had little effect on the amount of cellular putrescine. Cellular spermidine content was not affected by any of the additives. When cells were grown in high NaCl, pools for most amino acids increased; a few remained the same or decreased slightly. A sudden increase in the osmolarity of the medium led to a rapid excretion of cellular putrescine while there was no decrease in spermidine or free amino acids. This loss of putrescine could be blocked by sodium azide or sodium arsenate. The mechanism of putrescine excretion has two components; one is dependent on high concentrations of potassium ion in the medium, and the other is not. Cells grown in the presence of 11 mM potassium and then put into high osmolarity medium lacking potassium failed to excrete [r4C]putrescine rapidly. Replacing the potassium greatly stimulated putrescine excretion within 1 min. The rate of [14C]putrescine excretion was half-maximal at a potassium concentration of 0.69 mM. E. coli which were grown in medium containing 0.1 mM potassium and resuspended in 11 mM potassium initially could excrete [i4C]putrescine only slowly but regained the ability to excrete putrescine maximally after 15 min. Sodium, magnesium, ammonium, and rubidium ions and pH from 6.4 to 7.3 did not affect the rate of [14C]putrescine excretion. A sudden increase in the osmolarity of the medium produces a rapid increase in the cellular potassium content. However, this rapid uptake of potassium was not dependent on excretion of large quantities of cellular putrescine. When cells growing in high salt medium were transferred to low salt medium, the putrescine content approached the low salt value only after 140 min. However, the ability of