FIGURE 4.

The uptake of extracellular putrescine depends on yeeF. Overnight precultures of SK591, SK595, and SK594 were inoculated in 100-ml LBG supplemented with (gray bars) or without (white bars) 400 μm putrescine in 500-ml Erlenmeyer flasks. The medium was supplemented with chloramphenicol (15 μg/ml) to maintain the plasmids. The initial optical density of the culture, measured at 600 nm, was adjusted to 0.001. The flasks were shaken at 150 rpm at 37 °C. Bacterial cells were harvested at A₆₀₀ = 1.1–1.3 and washed once with cold M9 glucose. The assays were performed three times with independent bacterial cultures. Values are expressed as the mean ± S.D. A, [¹⁴C]putrescine uptake by strains. The cells were incubated with 50 μm [¹⁴C]putrescine, and the reaction was terminated after 0, 1, 7, 13, or 20 min. The linearity between the uptake of [¹⁴C]putrescine and the incubation time was confirmed. B, concentration of intracellular putrescine in the different strains.