Effect of intracellular c-di-GMP level on AHL signal production. In trans expression of the c-di-GMP synthases, WspR from P. aeruginosa or the GGDEF domain of RpfR, in wild type H111 led to decreased AHL signal production; while overexpression of the c-di-GMP phosphodiesterases, RocR from P. aeruginosa or the EAL domain of RpfR resulted in increased AHL signal biosynthesis in BDSF-minus mutant ∆rpfFBc. Quantification of AHL signal production was performed with the aid of AHL reporter strain CF11. For convenient comparison, the AHL signal production of wild-type strain was defined as 100% and used to normalize the AHL signal production of other strains. The data presented are the means of three replicates and error bars represents the standard deviation.