FIGURE 7.
Phenotypic heterogeneity of the conjugation operon during growth of B. subtilis. A, the promoter of conjugation shows a heterogonous expression pattern in the presence of regulatory elements encoded by plasmid pLS20. Fluorescence microscopy pictures were overlaid on bright field microscopy pictures to indicate the coexistence of two states in the clonal population of pLS20-containing cells carrying a Pc-mcherry fusion. Scale bar, 4 μm. B, fluorescence distribution of the mCherry reporter protein under control of the promoter of conjugation (Pc) at different time points during growth. Histograms derived from the time course experiment show a bimodal distribution. The red box highlights the signal intensities above the threshold used to calculate the number of cells switching the conjugation operon to the ON state. Fluorescence intensities were log-transformed and plotted linearly. C, percentage of cells exceeding the fluorescence threshold during growth. Left y axis, growth of cells; right y axis, number of cells expressing the fluorescent reporter protein above the threshold. D, snapshots from a representative time lapse experiment illustrate the stable expression of the fluorescent reporter protein mCherry from the Pc promoter during microcolony development. The time scale is represented in hours, and the scale bar corresponds to 4 μm. a.U., arbitrary units.