Intracellular c-di-GMP The untreated P. aeruginosa PAO1 PcdrA gfp c-di-GMP reporter strain showed a >fourfold increase in GFP expression between 3 and 5 h after the beginning of biofilm development, suggesting that this corresponded with maximal c-di-GMP expression at this time. By 7 h, c-di-GMP production was slightly lower than at 5 h (black bars in Fig. 7a). The addition of 3 mM CAD significantly (P value