Ultrasound guided percutaneous thrombin injection for the treatment of iatrogenic pseudoaneurysms

The second messenger, cyclic dimeric GMP (c-di-GMP) regulates biofilm formation and surface attachment for many bacteria. Biofilm formation of Pseudomonas fluorescens Pf0-1 is controlled by the transfer of c-di-GMP to the inner-membrane protein, LapD. LapD-bound c-di-GMP in turn inhibits proteolytic cleavage of the adhesin LapA by the periplasmic protease LapG, which allows localization of LapA to the cell surface and thereby promotes biofilm formation. LapD is central to a complex network of c-di-GMP-mediated biofilm formation. In this study, we examine how signaling specificity of c-di-GMP by a DGC is achieved by small ligand sensing through characterization of the calcium channel chemotaxis (CACHE) receptor of the DGC, GcbC. We provide evidence that biofilm formation is enhanced by the environmentally relevant organic acid citrate, in a GcbC-dependent manner through enhanced LapA localization to the cell surface. In the presence of citrate, the GcbC shows enhanced physical interaction with LapD. GcbC also shows increased c-di-GMP production when LapD is present, and this enhanced GcbC-LapD interaction by citrate further drives c-di-GMP synthesis. Given that LapD can interact with a dozen different DGCs of P. fluorescens, many of which have ligand-binding domains, the ligand-mediated enhanced signaling of LapD-GcbC described here is likely a conserved mechanism of signaling in this network. Significance Statement Biofilm formation is a highly regulated event controlled by c-di-GMP signaling. In many bacteria, dozens of DGCs produce this dinucleotide signal, however it is unclear how undesired cross-talk is mitigated in the context of this soluble signal, and how c-di-GMP signaling is regulated in the context of environmental inputs. Here we show a ligand-mediated mechanism of signaling specificity whereby citrate enhances catalysis of the c-di-GMP synthesizing diguanylate cyclase (DGC) via increased physical interaction with its cognate receptor. We envision a scenario wherein a “cloud” of weakly interacting DGCs can increase specific interaction with their receptor in response to appropriate environmental signals, concomitantly boosting c-di-GMP production, ligand-specific signaling and biofilm formation.