Effect of RpfR on AHL system. (A) AHL signal production was quantified with the aid of AHL reporter strain CF11 to test the β-galactosidase activity. (B) The β-galactosidase activity of a cepI-lacZ transcriptional fusion in H111 wild-type (■), ∆rpfR (▲) and ∆rpfR supplemented with BDSF signal (◆). 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.