Degradable GFP expression from a ribosomal promoter in a growing culture of E. coli. (A) Graphical representation of the reporter. An unstable variant of GFP was placed downstream of a ribosomal promoter, rrnB P1. (B) Stationary phase cultures of E. coli ASV and AGA, each containing a different variant of unstable GFP, were diluted (1:1000) in fresh media and cultured with aeration at 37°C. At designated timepoints samples were removed and assayed for cell counts (CFU/ml) and fluorescence (RFU, arbitrary units).