Combinatorial control of biofilm development by quorum-sensing and nutrient-sensing regulators in Pseudomonas aeruginosa

Abstract

ABSTRACTPseudomonas aeruginosa is a leading cause of hospital-acquired infections and formation of sessile antibiotic-resistant communities called biofilms is required for virulence in this pathogen. Biofilm formation is modulated by various environmental stimuli including nutrient availability, and population density and composition monitored via the cell-cell communication process of quorum sensing. Previous work has shown that the RhlR quorum-sensing receptor as well as CbrA/CbrB two-component system required for nutritional adaptation repress biofilm formation. How the information encoded in multiple sensory inputs is extracted and integrated to control biofilms is largely mysterious. Here, we use biofilm analyses, RNA-seq studies, and reporter assays to explore the combined effect of information flow through the RhlR quorum-sensing and CbrA nutrient-sensing pathways on biofilm development. We find that when both RhlR and CbrA are inactive, the resulting biofilm is unstable and readily evolves into a variant that mimics the absence of RhlR. Using genetic suppressor analysis and whole genome sequencing, we have identified the carbon catabolite repression protein Crc as the molecular convergence point for quorum and nutrient sensing. Crc promotes the expression of Pel exopolysaccharide, Functional amyloid protein and Cup fimbriae components of the biofilm matrix but does so only in the absence of both RhlR and CbrA. These results uncover a regulatory link between nutritional adaption and quorum sensing with potential implications for anti-biofilm targeting strategies.