Figure 4

Simultaneous monitoring of AI-regulated bioluminescence and induction of P _vhp :: gfp . The P _vhp ::gfp reporter strain enables simultaneous measurement of two AI-dependent phenotypes, bioluminescence and exoproteolysis. Cells were cultivated, and single cell analysis was performed at the transition to the stationary phase. Panels A-C show a representative set of images of the same field viewed by phase contrast (A), luminescence (B), and fluorescence (C) microscopy. The yellow circle marks a cell with medium luminescence and fluorescence intensity. The blue circle indicates a cell with high luminescence intensity and no fluorescence. The green circle surrounds a cell with high fluorescence intensity and no luminescence. The red circle marks a dark cell (no fluorescence, no luminescence). The bar is 2.5 μm. Luminescence and fluorescence intensities (in a.u./cell) were quantitatively analyzed for 1,150 cells. For each channel the cells were grouped according to their signal intensity in no, medium, or high. (The separation in these groups is described in detail in the results part). Panel D shows the distribution of the various intensity classes plotted as percentage of the total number of cells analyzed.