Fig. 2.

Characterization of metabolically partially active, dormant cells. a, b We starved cells of glucose for different periods of time and monitored ~1500 cells in two biological replicates. We observed dormant cells exhibiting partial metabolic activities; see text for detail. The number of these cells varied depending on the duration of starvation and was always lower than 5% of a population (b; the error bars indicate one standard deviation from two biological replicates). In all of these cells, 2NBDG signals decreased immediately upon nutrient upshift. In a, we plotted exemplary changes in 2NBDG signals for wild-type (WT) cells starved for 3 days (triangles) and ΔsodAΔsodB cells starved for 8 h (other symbols); the data showed a typical, rapid decrease in 2NBDG signals upon nutrient upshift. c, d We subjected a 3-day-starved culture to nutrient upshift. Dormant cells did not produce fluorescent proteins for several hours or a day; see the initial plateau in the fluorescence intensity c. Fluorescence intensity increased suddenly at later times c, indicating the spontaneous recovery of protein anabolism. This recovery was associated with growth resumption d. Note that we used ampicillin to avoid unrestricted growth of metabolically active cells (see text). With ampicillin, cells elongate without division until they eventually lyse [54], which is why cells appear unusually long in the plot. Out of ~4500 cells monitored, we observed 24 cells exhibiting such late recoveries. We observed similar fractions in two biological repeats