Properties of putrescine uptake by PotFGHI and PuuP and their physiological significance in Escherichia coli.

Properties of putrescine uptake by PotFGHI and PuuP and their physiological significance were studied using a polyamine biosynthesis and uptake deficient Escherichia coli KK3131 transformed with pACYC184 containing potFGHI or puuP. Putrescine uptake activity of E. coli KK3131 transformed with pACYC184-PotFGHI was higher than that of E. coli 3131 transformed with pACYC-PuuP when cells were cultured in the absence of putrescine. Putrescine uptake by PotFGHI was both ATP and membrane potential dependent, while that by PuuP was membrane potential dependent. Feedback inhibition by polyamines occurred at the PotFGHI uptake system but not at the PuuP uptake system. Expression of PuuP was reduced in the presence of PuuR, a negative regulator for PuuP, and expression of PuuR was positively regulated by glucose, which reduces the level of cAMP. The complex of cAMP and CRP (cAMP receptor protein) inhibited the expression of PuuR in the absence of glucose. Thus, the growth rate of E. coli KK3131 in the presence of both 0.4% (22.2 mM) glucose and 10 mM putrescine was in the order of cells transformed with pACYC-PotFGHI > pACYC-PuuP > pACYC-PuuP + PuuR, which was parallel with the polyamine content in cells. The results indicate that PotFGHI is necessary for rapid cell growth in the presence of glucose as an energy source. When glucose in medium was depleted, however, PuuP was absolutely necessary for cell growth in the presence of putrescine, because accumulation of putrescine to a high level by PuuP was necessary for utilization of putrescine as an energy source.