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Combinatorial quorum sensing allows bacteria to resolve their social and physical environment.

ABSTRACT: Quorum sensing (QS) is a cell-cell communication system that controls gene expression in many bacterial species, mediated by diffusible signal molecules. Although the intracellular regulatory mechanisms of QS are often well-understood, the functional roles of QS remain controversial. In particular, the use of multiple signals by many bacterial species poses a serious challenge to current functional theories. Here, we address this challenge by showing that bacteria can use multiple QS signals to infer both their social (density) and physical (mass-transfer) environment. Analytical and evolutionary simulation models show that the detection of, and response to, complex social/physical contrasts requires multiple signals with distinct half-lives and combinatorial (nonadditive) responses to signal concentrations. We test these predictions using the opportunistic pathogen Pseudomonas aeruginosa and demonstrate significant differences in signal decay between its two primary signal molecules, as well as diverse combinatorial responses to dual-signal inputs. QS is associated with the control of secreted factors, and we show that secretome genes are preferentially controlled by synergistic "AND-gate" responses to multiple signal inputs, ensuring the effective expression of secreted factors in high-density and low mass-transfer environments. Our results support a new functional hypothesis for the use of multiple signals and, more generally, show that bacteria are capable of combinatorial communication.

SUBMITTER: Cornforth DM

PROVIDER: S-EPMC3964068 | biostudies-literature | 2014 Mar

REPOSITORIES: biostudies-literature

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Combinatorial quorum sensing allows bacteria to resolve their social and physical environment.

Cornforth Daniel M DM Popat Roman R McNally Luke L Gurney James J Scott-Phillips Thomas C TC Ivens Alasdair A Diggle Stephen P SP Brown Sam P SP

Proceedings of the National Academy of Sciences of the United States of America 20140304 11

Quorum sensing (QS) is a cell-cell communication system that controls gene expression in many bacterial species, mediated by diffusible signal molecules. Although the intracellular regulatory mechanisms of QS are often well-understood, the functional roles of QS remain controversial. In particular, the use of multiple signals by many bacterial species poses a serious challenge to current functional theories. Here, we address this challenge by showing that bacteria can use multiple QS signals to ...[more]

PMID: 24594597

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Project description:Quorum-sensing (QS) is a cell-cell communication system that controls gene expression in many bacterial species, mediated by diffusible signal molecules. While the intracellular regulatory mechanisms of QS are often well-understood, the functional roles of QS remain controversial. In particular, the use of multiple signals by many bacterial species poses a serious challenge to current functional theories. Here we address this challenge by showing that bacteria can use multiple QS signals to infer both their social (density) and physical (mass-transfer) environment. Analytical and evolutionary simulation models show that the detection of and response to complex social/physical contrasts requires multiple signals with distinct half-lives and combinatorial (non-additive) responses to signal concentrations. We test these predictions using the opportunistic pathogen Pseudomonas aeruginosa, and demonstrate significant differences in signal decay between its two primary signal molecules as well as diverse combinatorial responses to dual signal inputs. QS is associated with the control of secreted factors, and we show that secretome genes are preferentially controlled by synergistic M-bM-^@M-^XAND-gateM-bM-^@M-^Y responses to multiple signal inputs, ensuring the effective expression of secreted factors in high density and low mass-transfer environments. Our results support a novel functional hypothesis for the use of multiple signals and, more generally, show that bacteria are capable of combinatorial communication. The two primary signal molecules of P. aeruginosa are the homoserine lactones N-(3-oxododecanoyl)-L-homoserine lactone (3-oxo-C12-HSL) and N-butyryl-homoserine lactone (C4-HSL). Effects of the different signal molecules was assessed using a double QS synthase mutant of Pseudomonas aeruginosa PAO1 lasI/rhlI grown at 37M-BM-0C in 25 ml LB broth and 250 ml flasks with shaking at 200 r.p.m. in four treatments, each with a replicate: (a) no addition; (b) 3-oxo- C12-HSL; (c) C4-HSL; and (d) both 3-oxo-C12-HSL and C4-HSL.

Project description:The human pathogen Pseudomonas aeruginosa, a leading cause of hospital-acquired infections, inhabits and forms sessile antibiotic-resistant communities called biofilms in a wide range of biotic and abiotic environments. In this study, we examined how two global sensory signaling pathways-the RhlR quorum-sensing system and the CbrA/CbrB nutritional adaptation system-intersect to control biofilm development. Previous work has shown that individually these two systems repress biofilm formation. Here, we used biofilm analyses, RNA-seq, and reporter assays to explore the combined effect of information flow through RhlR and CbrA on biofilm development. We find that the ΔrhlRΔcbrA double mutant exhibits a biofilm morphology and an associated transcriptional response distinct from wildtype and the parent ΔrhlR and ΔcbrA mutants indicating codominance of each signaling pathway. The ΔrhlRΔcbrA mutant gains suppressor mutations that allow biofilm expansion; these mutations map to the crc gene resulting in loss of function of the carbon catabolite repression protein Crc. Furthermore, the combined absence of RhlR and CbrA leads to a drastic reduction in the abundance of the Crc antagonist small RNA CrcZ. Thus, CrcZ acts as the molecular convergence point for quorum- and nutrient-sensing cues. We find that in the absence of antagonism by CrcZ, Crc promotes the expression of biofilm matrix components-Pel exopolysaccharide, and CupB and CupC fimbriae. Therefore, this study uncovers a regulatory link between nutritional adaption and quorum sensing with potential implications for anti-biofilm targeting strategies.IMPORTANCEBacteria often form multicellular communities encased in an extracytoplasmic matrix called biofilms. Biofilm development is controlled by various environmental stimuli that are decoded and converted into appropriate cellular responses. To understand how information from two distinct stimuli is integrated, we used biofilm formation in the human pathogen Pseudomonas aeruginosa as a model and studied the intersection of two global sensory signaling pathways-quorum sensing and nutritional adaptation. Global transcriptomics on biofilm cells and reporter assays suggest parallel regulation of biofilms by each pathway that converges on the abundance of a small RNA antagonist of the carbon catabolite repression protein, Crc. We find a new role of Crc as it modulates the expression of biofilm matrix components in response to the environment. These results expand our understanding of the genetic regulatory strategies that allow P. aeruginosa to successfully develop biofilm communities.

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Combinatorial quorum sensing allows bacteria to resolve their social and physical environment.

Publications

Combinatorial quorum sensing allows bacteria to resolve their social and physical environment.

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