Growth-dependent analysis of the expression of AI-regulated genes at the single cell level. V. harveyi conjugants that carried one of the plasmids pCA2, pCA3, pCA4, pCA5, and pCA1 containing a promoter::gfp fusion driven by the luxC (blue), vhp (green), vscP (red), luxS (grey), or recA (dark grey) promoter, respectively, were cultivated, and at the indicated times the optical density (OD600) was determined (A) and single cell analysis was performed (B-F). At each time point the average fluorescence of the population was determined (A). The activity of luxC (B), vhp (C), vscP (D), luxS (E), and recA (F) promoters was followed in a growing population over time. Fluorescence levels were normalized for cell size and expressed in arbitrary units.