Figure 2 Effect of RpfF Bc on AHL synthase gene cepI expression. (A) The β-galactosidase activity of a cepI-lacZ transcriptional fusion in H111 wild-type (■), ∆rpfFBc (▲) and ∆rpfFBc supplemented with BDSF PF-02341066 mouse signal (◆). SYN-117 (B) Western blotting assay of CepI protein level. The data presented are the means of three replicates and error bars represents the standard deviation. BDSF system controls AHL signal production through its receptor RpfR Previous studies showed that two BDSF sensors, BCAM0227 and RpfR (BCAM0580), are involved in the BDSF-mediated QS. Among them, BCAM0227, which was originally characterized in B.
cenocepacia strain J2315, controls only a subset of the BDSF-regulated phenotypes and target genes , whereas RpfR was shown to be
a major receptor of BDSF as null mutation of RpfR results in similar mutant phenotypes as the BDSF-minus mutants . These results suggest that two BDSF signaling pathways may be operating in B. cenocepacia, which motivated us to investigate which BDSF signaling pathway plays a role in regulation of the cepI expression. Significantly, deletion of the BDSF receptor gene rpfR caused a similar reduction in AHL signal production as the deletion mutant of rpfF Bc that encodes a BDSF synthase (Figure 3A). Analysis JPH203 of the cepI expression profile using its promoter fused with the lacZ reporter gene showed that RpfR controlled the cepI expression at the transcriptional level (Figure 3B). Importantly, in contrast to the deletion mutant of rpfF Bc , which could be rescued by addition of BDSF (Figure 2A), addition of BDSF to the
rpfR mutant had no effect on the cepI expression (Figure 3B). The data are consistent with the idea that BDSF modulates AHL signal production through its cognate receptor RpfR. Agreeable with our recent finding that BCAM0227 has a negligible role in BDSF signaling , deletion of this gene however did not reveal any effect on cepI expression in B. cenocepacia H111 (Additional file 1: Figure S1). Figure 3 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. BDSF system controls AHL signal production and biological functions through regulation of intracellular c-di-GMP level RpfR is a modular protein with PAS-GGDEF-EAL domains. Among these domains, PAS is the domain interacting with BDSF, and GGDEF and EAL domains are associated with c-di-GMP metabolism .