Hysteresis observed at population and colony levels. (a) Population distributions of relative fluorescence intensity. The cells initially showing only green (IPTG 0 μM) or red (IPTG 30 μM) fluorescence (illustrated as green or red distributions, resp.) were cultured under amino acid-supplied conditions and in the presence of various concentrations of IPTG (from 0 to 30 μM in 5-μM increments). Distributions of the newly formed populations are shown in green and red in accordance with the initial expression status. (b) Trajectories of averaged expression level. The relative concentrations of GFP bias (GFI/RFI/FSC) were calculated from the distributions shown in (a). The cells precultured in IPTG-free (closed circles) or IPTG-supplied (30 μM IPTG, open circles) medium showed different trajectories of averaged concentrations of GFP bias. (c) Fluorescence images of colony formation. The cells initially grown in IPTG-free or IPTG-supplied (30 μM) medium were inoculated onto the agar plates containing various concentrations of IPTG (from 0 to 30 μM). Aliquots of approximately 100 cells were inoculated on each plate. The newly formed single colonies were observed under a microscope. NIBA and WIG indicate the filters used to detect green and red fluorescence, respectively. (d) Ratio of green and red colonies. The cells initially grown in IPTG-free (closed circles) or IPTG-supplied (30 μM IPTG, open circles) medium showed different ratios of the newly formed green and red colonies.
