The hierarchy quorum sensing network in Pseudomonas aeruginosa

Abstract

Pseudomonas aeruginosa causes severe and persistent infections in immune compromised individuals and cystic fibrosis sufferers. The infection is hard to eradicate as P. aeruginosa has developed strong resistance to most conventional antibiotics. The problem is further compounded by the ability of the pathogen to form biofilm matrix, which provides bacterial cells a protected environment withstanding various stresses including antibiotics. Quorum sensing (QS), a cell density-based intercellular communication system, which plays a key role in regulation of the bacterial virulence and biofilm formation, could be a promising target for developing new strategies against P. aeruginosa infection. The QS network of P. aeruginosa is organized in a multi-layered hierarchy consisting of at least four interconnected signaling mechanisms. Evidence is accumulating that the QS regulatory network not only responds to bacterial population changes but also could react to environmental stress cues. This plasticity should be taken into consideration during exploration and development of anti-QS therapeutics.

Key words： quorum sensing; IQS; PQS; las; rhl; Pseudomonas aeruginosa; virulence; environmental factors

References

1 Abe A, Matsuzawa T, Kuwae A (2005) Type-III effectors: sophisticated bacterial virulence factors. C R Biol328: 413-428

2 Adam EC, Mitchell BS, Schumacher DU, Grant G, Schumacher U (1997) Pseudomonas aeruginosa II lectin stops human ciliary beating: therapeutic implications of fucose. Am J Respir Crit Care Med155: 2102-2104

3 Albus AM, Pesci EC, Runyen-Janecky LJ, West SE, Iglewski BH (1997) Vfr controls quorum sensing in Pseudomonas aeruginosa. J Bacteriol179: 3928-3935

4 Anba J, Bidaud M, Vasil ML, Lazdunski A (1990) Nucleotide sequence of the Pseudomonas aeruginosa phoB gene, the regulatory gene for the phosphate regulon. J Bacteriol172: 4685-4689

5 Bains M, Fernandez L, Hancock RE (2012) Phosphate starvation promotes swarming motility and cytotoxicity of Pseudomonas aeruginosa. Appl Environ Microbiol78: 6762-6768

6 Baysse C, Cullinane M, Dénervaud V, Burrowes E, Dow JM, Morrissey JP, Tam L, Trevors JT, O’Gara F (2005) Modulation of quorum sensing in Pseudomonas aeruginosa through alteration of membrane properties. Microbiology151: 2529-2542

7 Bertani I, Venturi V (2004) Regulation of the N-acyl homoserine lactone-dependent quorum-sensing system in rhizosphere Pseudomonas putida WCS358 and cross-talk with the stationaryphase RpoS sigma factor and the global regulator GacA. Appl Environ Microbiol70: 5493-5502

8 Blier A-S, Veron W, Bazire A, Gerault E, Taupin L, Vieillard J, Rehel K, Dufour A, Le Derf F, Orange N (2011) C-type natriuretic peptide modulates quorum sensing molecule and toxin production in Pseudomonas aeruginosa. Microbiology157: 1929-1944

9 Bonomo RA, Szabo D (2006) Mechanisms of multidrug resistance in Acinetobacter species and Pseudomonas aeruginosa. Clinical Infectious Diseases43(Suppl 2): 49-S56

10 Borlee BR, Geske GD, Blackwell HE, Handelsman J (2010) Identification of synthetic inducers and inhibitors of the quorum-sensing regulator LasR in Pseudomonas aeruginosa by high-throughput screening. Appl Environ Microbiol76: 8255-8258

11 Branny P, Pearson JP, Pesci EC, Kohler T, Iglewski BH, Van Delden C (2001) Inhibition of quorum sensing by a Pseudomonas aeruginosa dksA homologue. J Bacteriol183: 1531-1539

12 Brint JM, Ohman DE (1995) Synthesis of multiple exoproducts in Pseudomonas aeruginosa is under the control of RhlR-RhlI, another set of regulators in strain PAO1 with homology to the autoinducer-responsive LuxR-LuxI family. Journal of Bacteriology177: 7155-7163

13 Cabrol S, Olliver A, Pier GB, Andremont A, Ruimy R (2003) Transcription of quorum-sensing system genes in clinical and environmental isolates of Pseudomonas aeruginosa. J Bacteriol185: 7222-7230

14 Camilli A, Bassler BL (2006) Bacterial small-molecule signaling pathways. Science311: 1113-1116

15 Campodonico VL, Gadjeva M, Paradis-Bleau C, Uluer A, Pier GB (2008) Airway epithelial control of Pseudomonas aeruginosa infection in cystic fibrosis. Trends Mol Med14: 120-133

16 Cao JG, Meighen EA (1993) Biosynthesis and stereochemistry of the autoinducer controlling luminescence in Vibrio harveyi. J Bacteriol175: 3856-3862

17 Cao H, Krishnan G, Goumnerov B, Tsongalis J, Tompkins R, Rahme LG (2001) A quorum sensing-associated virulence gene of Pseudomonas aeruginosa encodes a LysR-like transcription regulator with a unique self-regulatory mechanism. Proc Natl Acad Sci USA98: 14613-14618

18 Castric PA (1983) Hydrogen cyanide production by Pseudomonas aeruginosa at reduced oxygen levels. Can J Microbiol29: 1344-1349

19 Castric P (1994) Influence of oxygen on the Pseudomonas aeruginosa hydrogen cyanide synthase. Curr Microbiol29: 19-21

20 Castric PA, Ebert RF, Castric KF (1979) The relationship between growth phase and cyanogenesis in Pseudomonas aeruginosa. Curr Microbiol2: 287-292

21 Chernish RN, Aaron SD (2003) Approach to resistant gram-negative bacterial pulmonary infections in patients with cystic fibrosis. Curr Opin Pulm Med9: 509-515

22 Chugani S, Greenberg E (2007) The influence of human respiratory epithelia on Pseudomonas aeruginosa gene expression. Microbial pathogenesis42: 29-35

23 Chugani SA, Whiteley M, Lee KM, D’Argenio D, Manoil C, Greenberg EP (2001) QscR, a modulator of quorum-sensing signal synthesis and virulence in Pseudomonas aeruginosa. Proc Natl Acad Sci USA98: 2752-2757

24 Ciofu O, Mandsberg LF, Bjarnsholt T, Wassermann T, Høiby N (2010) Genetic adaptation of Pseudomonas aeruginosa during chronic lung infection of patients with cystic fibrosis: strong and weak mutators with heterogeneous genetic backgrounds emerge in mucA and/or lasR mutants. Microbiology156: 1108-1119

25 Coleman JP, Hudson LL, McKnight SL, Farrow JM, Calfee MW, Lindsey CA, Pesci EC (2008) Pseudomonas aeruginosa PqsA is an anthranilate-coenzyme A ligase. J Bacteriol190: 1247-1255

26 Collier DN, Anderson L, McKnight SL, Noah TL, Knowles M, Boucher R, Schwab U, Gilligan P, Pesci EC (2002) A bacterial cell to cell signal in the lungs of cystic fibrosis patients. FEMS Microbiol Lett215: 41-46

27 Cook JMI, Harragan B (1992) In: Proceedings of the 92nd annual meeting of the american society for microbiology. Paper presented at 92nd annual meeting of the american society for microbiology, New Orleans

28 Cornforth JW, James AT (1956) Structure of a naturally occurring antagonist of dihydrostreptomycin. The Biochemical Journal63: 124-130

29 Cornforth DM, Popat R, McNally L, Gurney J, Scott-Phillips TC, Ivens A, Diggle SP, Brown SP (2014) Combinatorial quorum sensing allows bacteria to resolve their social and physical environment. Proc Natl Acad Sci3(4): 220-227

30 Costerton JW (2001) Cystic fibrosis pathogenesis and the role of biofilms in persistent infection. Trends Microbiol9: 50-52

31 Daddaoua A, Fillet S, Fernández M, Udaondo Z, Krell T, Ramos JL (2012) Genes for carbon metabolism and the ToxA virulence factor in Pseudomonas aeruginosa are regulated through molecular interactions of PtxR and PtxS. PLoS One7: e39390

32 D’Argenio DA, Calfee MW, Rainey PB, Pesci EC (2002) Autolysis and autoaggregation in Pseudomonas aeruginosa colony morphology mutants. J Bacteriol184: 6481-6489

33 D’Argenio DA, Wu M, Hoffman LR, Kulasekara HD, Deziel E, Smith EE, Nguyen H, Ernst RK, Larson Freeman TJ, Spencer DH (2007) Growth phenotypes of Pseudomonas aeruginosa lasR mutants adapted to the airways of cystic fibrosis patients. Mol Microbiol64: 512-533

34 de Kievit T, Seed PC, Nezezon J, Passador L, Iglewski BH (1999) RsaL, a novel repressor of virulence gene expression in Pseudomonas aeruginosa. J Bacteriol181: 2175-2184

35 Dekimpe V, Deziel E (2009) Revisiting the quorum-sensing hierarchy in Pseudomonas aeruginosa: the transcriptional regulator RhlR regulates LasR-specific factors. Microbiology155: 712-723

36 Denervaud V, TuQuoc P, Blanc D, Favre-Bonte S, Krishnapillai V, Reimmann C, Haas D, van Delden C (2004) Characterization of cell-to-cell signaling-deficient Pseudomonas aeruginosa strains colonizing intubated patients. J Clin Microbiol42: 554-562

37 Deng Y, Wu J, Tao F, Zhang LH (2011) Listening to a new language: DSF-based quorum sensing in Gram-negative bacteria. Chem Rev111: 160-173

38 Denning GM, Wollenweber LA, Railsback MA, Cox CD, Stoll LL, Britigan BE (1998) Pseudomonas pyocyanin increases interleukin- 8 expression by human airway epithelial cells. Infect Immun66: 5777-5784

39 Deziel E, Lepine F, Milot S, He J, Mindrinos MN, Tompkins RG, Rahme LG (2004) Analysis of Pseudomonas aeruginosa 4-hydroxy-2-alkylquinolines (HAQs) reveals a role for 4-hydroxy-2-heptylquinoline in cell-to-cell communication. Proc Natl Acad Sci USA101: 1339-1344

40 Déziel E, Gopalan S, Tampakaki AP, Lépine F, Padfield KE, Saucier M, Xiao G, Rahme LG (2005) The contribution of MvfR to Pseudomonas aeruginosa pathogenesis and quorum sensing circuitry regulation: multiple quorum sensing-regulated genes are modulated without affecting lasRI, rhlRI or the production of Nacyl-l-homoserine lactones. Mol Microbiol55: 998-1014

41 Diggle SP, Winzer K, Lazdunski A, Williams P, Camara M (2002) Advancing the quorum in Pseudomonas aeruginosa: MvaT and the regulation of N-acylhomoserine lactone production and virulence gene expression. J Bacteriol184: 2576-2586

42 Diggle SP, Winzer K, Chhabra SR, Worrall KE, Cámara M, Williams P (2003) The Pseudomonas aeruginosa quinolone signal molecule overcomes the cell density-dependency of the quorum sensing hierarchy, regulates rhl-dependent genes at the onset of stationary phase and can be produced in the absence of LasR. Mol Microbiol50: 29-43

43 Diggle SP, Matthijs S, Wright VJ, Fletcher MP, Chhabra SR, Lamont IL, Kong X, Hider RC, Cornelis P, Cámara M (2007) The Pseudomonas aeruginosa 4-quinolone signal molecules HHQ and PQS play multifunctional roles in quorum sensing and iron entrapment. Chem Biol14: 87-96

44 Doshi HK, Chua K, Kagda F, Tambyah PA (2011) Multi drug resistant pseudomonas infection in open fractures post definitive fixation leading to limb loss: a report of three cases. International Journal of Case Reports and Images (IJCRI)2: 1-6

45 Dubern JF, Diggle SP (2008) Quorum sensing by 2-alkyl-4-quinolones in Pseudomonas aeruginosa and other bacterial species. Mol Biosyst4: 882-888

46 Eberhard A (1972) Inhibition and activation of bacterial luciferase synthesis. J Bacteriol109: 1101-1105

47 Eberhard A, Burlingame AL, Eberhard C, Kenyon GL, Nealson KH, Oppenheimer NJ (1981) Structural identification of autoinducer of Photobacterium fischeri luciferase. Biochemistry20: 2444-2449

48 Farrow JM 3rd, Sund ZM, Ellison ML, Wade DS, Coleman JP, Pesci EC (2008) PqsE functions independently of PqsR-Pseudomonas quinolone signal and enhances the rhl quorum-sensing system. J Bacteriol190: 7043-7051

49 Filloux A, Bally M, Soscia C, Murgier M, Lazdunski A (1988) Phosphate regulation in Pseudomonas aeruginosa: cloning of the alkaline phosphatase gene and identification of phoB-and phoRlike genes. Mol Gen Genet212: 510-513

50 Frisk A, Schurr JR, Wang G, Bertucci DC, Marrero L, Hwang SH, Hassett DJ, Schurr MJ (2004) Transcriptome analysis of Pseudomonas aeruginosa after interaction with human airway epithelial cells. Infect Immun72: 5433-5438

51 Fuqua C (2006) The QscR quorum-sensing regulon of Pseudomonas aeruginosa: an orphan claims its identity. J Bacteriol188: 3169-3171

52 Fuqua WC, Winans SC, Greenberg EP (1994) Quorum sensing in bacteria: the LuxR-LuxI family of cell density-responsive transcriptional regulators. J Bacteriol176: 269-275

53 Gallagher LA, McKnight SL, Kuznetsova MS, Pesci EC, Manoil C (2002) Functions required for extracellular quinolone signaling by Pseudomonas aeruginosa. J Bacteriol184: 6472-6480

54 Gambello MJ, Iglewski BH (1991) Cloning and characterization of the Pseudomonas aeruginosa lasR gene, a transcriptional activator of elastase expression. J Bacteriol173: 3000-3009

55 Gambello MJ, Kaye S, Iglewski BH (1993) LasR of Pseudomonas aeruginosa is a transcriptional activator of the alkaline protease gene (apr) and an enhancer of exotoxin A expression. Infect Immun61: 1180-1184

56 Gentry DR, Cashel M (1996) Mutational analysis of the Escherichia coli spoT gene identifies distinct but overlapping regions involved in ppGpp synthesis and degradation. Mol Microbiol19: 1373-1384

57 Haddad A, Jensen V, Becker T, Haussler S (2009) The Pho regulon influences biofilm formation and type three secretion in Pseudomonas aeruginosa. Environ Microbiol Rep1: 488-494

58 Hamood AN, Griswold J, Colmer J (1996) Characterization of elastase-deficient clinical isolates of Pseudomonas aeruginosa. Infect Immun64: 3154-3160

59 Hauser AR, Cobb E, Bodí M, Mariscal D, Vallés J, Engel JN, Rello J (2002) Type III protein secretion is associated with poor clinical outcomes in patients with ventilator-associated pneumonia caused by Pseudomonas aeruginosa. Crit Care Med30: 521-528

60 Henry RL, Mellis CM, Petrovic L (1992) Mucoid Pseudomonas aeruginosa is a marker of poor survival in cystic fibrosis. Pediatr Pulmonol12: 158-161

61 Hense BA, Kuttler C, Muller J, Rothballer M, Hartmann A, Kreft JU (2007) Does efficiency sensing unify diffusion and quorum sensing? Nature Rev Microbiol5: 230-239

62 Heurlier K, Dénervaud V, Pessi G, Reimmann C, Haas D (2003) Negative control of quorum sensing by RpoN (σ54) in Pseudomonas aeruginosa PAO1. J Bacteriol185: 2227-2235

63 Hoffman LR, Kulasekara HD, Emerson J, Houston LS, Burns JL, Ramsey BW, Miller SI (2009)Pseudomonas aeruginosa lasR mutants are associated with cystic fibrosis lung disease progression. J Cyst Fibros8: 66-70

64 Hsieh Y-J, Wanner BL (2010) Global regulation by the sevencomponent Pi signaling system. Curr Opin Microbiol13: 198-203

65 Huang JJ, Petersen A, Whiteley M, Leadbetter JR (2006) Identification of QuiP, the product of gene PA1032, as the second acylhomoserine lactone acylase of Pseudomonas aeruginosa PAO1. Appl Environ Microbiol72: 1190-1197

66 Hueck CJ (1998) Type III protein secretion systems in bacterial pathogens of animals and plants. Microbiol Mol Biol Rev62: 379-433

67 Jackowski JT, Szepfalusi Z, Wanner DA, Seybold Z, Sielczak MW, Lauredo IT, Adams T, Abraham WM, Wanner A (1991) Effects of P. aeruginosa-derived bacterial products on tracheal ciliary function: role of O2 radicals. Am J Physiol260: L61-L67

68 Jackson AA, Gross MJ, Daniels EF, Hampton TH, Hammond JH, Vallet-Gely I, Dove SL, Stanton BA, Hogan DA (2013) Anr and its activation by PlcH activity in Pseudomonas aeruginosa host colonization and virulence. J Bacteriol195: 3093-3104

69 Jensen V, Löns D, Zaoui C, Bredenbruch F, Meissner A, Dieterich G, Münch R, Häussler S (2006) RhlR expression in Pseudomonas aeruginosa is modulated by the Pseudomonas quinolone signal via PhoB-dependent and-independent pathways. J Bacteriol188: 8601-8606

70 Jones S, Yu B, Bainton NJ, Birdsall M, Bycroft BW, Chhabra SR, Cox AJ, Golby P, Reeves PJ, Stephens S (1993) The lux autoinducer regulates the production of exoenzyme virulence determinants in Erwinia carotovora and Pseudomonas aeruginosa. EMBO J12: 2477-2482

71 Joseleau-Petit D, Vinella D, D’Ari R (1999) Metabolic alarms and cell division in Escherichia coli. J Bacteriol181: 9-14

72 Jude F, Kohler T, Branny P, Perron K, Mayer MP, Comte R, van Delden C (2003) Posttranscriptional control of quorum-sensing-dependent virulence genes by DksA in Pseudomonas aeruginosa. J Bacteriol185: 3558-3566

73 Juhas M, Wiehlmann L, Huber B, Jordan D, Lauber J, Salunkhe P, Limpert AS, von Gotz F, Steinmetz I, Eberl L (2004) Global regulation of quorum sensing and virulence by VqsR in Pseudomonas aeruginosa. Microbiology150: 831-841

74 Kessler E, Safrin M, Olson JC, Ohman DE (1993) Secreted LasA of Pseudomonas aeruginosa is a staphylolytic protease. J Biol Chem268: 7503-7508

75 Kim EJ, Sabra W, Zeng AP (2003) Iron deficiency leads to inhibition of oxygen transfer and enhanced formation of virulence factors in cultures of Pseudomonas aeruginosa PAO1. Microbiology149: 2627-2634

76 Kiratisin P, Tucker KD, Passador L (2002) LasR, a transcriptional activator of Pseudomonas aeruginosa virulence genes, functions as a multimer. J Bacteriol184: 4912-4919

77 Konings AF, Martin LW, Sharples KJ, Roddam LF, Latham R, Reid DW, Lamont IL (2013) Pseudomonas aeruginosa uses multiple pathways to acquire iron during chronic infection in cystic fibrosis lungs. Infect Immun81: 2697-2704

78 Kosorok MR, Zeng L, West SE, Rock MJ, Splaingard ML, Laxova A, Green CG, Collins J, Farrell PM (2001) Acceleration of lung disease in children with cystic fibrosis after Pseudomonas aeruginosa acquisition. Pediatr Pulmonol32: 277-287

79 Krieg DP, Helmke RJ, German VF, Mangos JA (1988) Resistance of mucoid Pseudomonas aeruginosa to nonopsonic phagocytosis by alveolar macrophages in vitro. Infect Immun56: 3173-3179

80 Laarman AJ, Bardoel BW, Ruyken M, Fernie J, Milder FJ, van Strijp JA, Rooijakkers SH (2012) Pseudomonas aeruginosa alkaline protease blocks complement activation via the classical and lectin pathways. J Immunol188: 386-393

81 Latifi A, Winson MK, Foglino M, Bycroft BW, Stewart GS, Lazdunski A, Williams P (1995) Multiple homologues of LuxR and LuxI control expression of virulence determinants and secondary metabolites through quorum sensing in Pseudomonas aeruginosa PAO1. Mol Microbiol17: 333-343

82 Latifi A, Foglino M, Tanaka K, Williams P, Lazdunski A (1996) A hierarchical quorum-sensing cascade in Pseudomonas aeruginosa links the transcriptional activators LasR and RhIR (VsmR) to expression of the stationary-phase sigma factor RpoS. Mol Microbiol21: 1137-1146

83 Lau GW, Ran H, Kong F, Hassett DJ, Mavrodi D (2004) Pseudomonas aeruginosa pyocyanin is critical for lung infection in mice. Infect Immun72: 4275-4278

84 Ledgham F, Soscia C, Chakrabarty A, Lazdunski A, Foglino M (2003a) Global regulation in Pseudomonas aeruginosa: the regulatory protein AlgR2 (AlgQ) acts as a modulator of quorum sensing. Res Microbiol154: 207-213

85 Ledgham F, Ventre I, Soscia C, Foglino M, Sturgis JN, Lazdunski A (2003b) Interactions of the quorum sensing regulator QscR: interaction with itself and the other regulators of Pseudomonas aeruginosa LasR and RhlR. Mol Microbiol48: 199-210

86 Lee J, Wu J, Deng Y, Wang J, Wang C, Wang J, Chang C, Dong Y, Williams P, Zhang LH (2013) A cell-cell communication signal integrates quorum sensing and stress response. Nature Chem Biol9: 339-343

87 Lépine F, Milot S, Déziel E, He J, Rahme LG (2004) Electrospray/ mass spectrometric identification and analysis of 4-hydroxy-2- alkylquinolines (HAQs) produced by Pseudomonas aeruginosa. J Am Soc Mass Spectrom15: 862-869

88 Lequette Y, Greenberg EP (2005) Timing and localization of rhamnolipid synthesis gene expression in Pseudomonas aeruginosa biofilms. J Bacteriol187: 37-44

89 Li LL, Malone JE, Iglewski BH (2007) Regulation of the Pseudomonas aeruginosa quorum-sensing regulator VqsR. J Bacteriol189: 4367-4374

90 Lightbown JW, Jackson FL (1956) Inhibition of cytochrome systems of heart muscle and certain bacteria by the antagonists of dihydrostreptomycin: 2-alkyl-4-hydroxyquinoline N-oxides. Biochem J63: 130-137

91 Mattmann ME, Blackwell HE (2010) Small molecules that modulate quorum sensing and control virulence in Pseudomonas aeruginosa. J Org Chem75: 6737-6746

92 McEwan DL, Kirienko NV, Ausubel FM (2012) Host translational inhibition by Pseudomonas aeruginosa exotoxin A triggers an immune response in Caenorhabditis elegans. Cell Host Microbe11: 364-374

93 McKnight SL, Iglewski BH, Pesci EC (2000) The Pseudomonas quinolone signal regulates rhl quorum sensing in Pseudomonas aeruginosa. J Bacteriol182: 2702-2708

94 Nealson KH, Platt T, Hastings JW (1970) Cellular control of the synthesis and activity of the bacterial luminescent system. J Bacteriol104: 313-322

95 Ng WL, Bassler BL (2009) Bacterial quorum-sensing network architectures. Annu Rev Genet43: 197-222

96 Ochsner UA, Reiser J (1995) Autoinducer-mediated regulation of rhamnolipid biosurfactant synthesis in Pseudomonas aeruginosa. Proc Natl Acad Sci USA92: 6424-6428

97 Ochsner UA, Wilderman PJ, Vasil AI, Vasil ML (2002) GeneChip® expression analysis of the iron starvation response in Pseudomonas aeruginosa: identification of novel pyoverdine biosynthesis genes. Mol Microbiol45: 1277-1287

98 Oglesby AG, Farrow JM, Lee J-H, Tomaras AP, Greenberg E, Pesci EC, Vasil ML (2008) The influence of iron on Pseudomonas aeruginosa Physiology: a regulatory link between iron and quorum sensing. J Biol Chem283: 15558-15567

99 Park PW, Pier GB, Preston MJ, Goldberger O, Fitzgerald ML, Bernfield M(2000) Syndecan-1 shedding is enhanced by LasA, a secreted virulence factor of Pseudomonas aeruginosa. J Biol Chem275: 3057-3064

100 Parkins MD, Ceri H, Storey DG (2001) Pseudomonas aeruginosa GacA, a factor in multihost virulence, is also essential for biofilm formation. Mol Microbiol40: 1215-1226

101 Passador L, Cook JM, Gambello MJ, Rust L, Iglewski BH (1993) Expression of Pseudomonas aeruginosa virulence genes requires cell-to-cell communication. Science260: 1127-1130

102 Pearson JP, Gray KM, Passador L, Tucker KD, Eberhard A, Iglewski BH, Greenberg EP (1994) Structure of the autoinducer required for expression of Pseudomonas aeruginosa virulence genes. Proc Natl Acad Sci USA91: 197-201

103 Pearson JP, Passador L, Iglewski BH, Greenberg EP (1995) A second N-acylhomoserine lactone signal produced by Pseudomonas aeruginosa. Proc Natl Acad Sci USA92: 1490-1494

104 Pereira CS, Thompson JA, Xavier KB (2013) AI-2-mediated signalling in bacteria. FEMS Microbiol Rev37: 156-181

105 Pesci EC, Pearson JP, Seed PC, Iglewski BH (1997) Regulation of las and rhl quorum sensing in Pseudomonas aeruginosa. J Bacteriol179: 3127-3132

106 Pesci EC, Milbank JB, Pearson JP, McKnight S, Kende AS, Greenberg EP, Iglewski BH (1999) Quinolone signaling in the cell-to-cell communication system of Pseudomonas aeruginosa. Proc Natl Acad Sci USA96: 11229-11234

107 Pessi G, Haas D (2000) Transcriptional control of the hydrogen cyanide biosynthetic genes hcnABC by the anaerobic regulator ANR and the quorum-sensing regulators LasR and RhlR in Pseudomonas aeruginosa. J Bacteriol182: 6940-6949

108 Pessi G, Williams F, Hindle Z, Heurlier K, Holden MT, Cámara M, Haas D, Williams P (2001) The global posttranscriptional regulator RsmA modulates production of virulence determinants and N-acylhomoserine lactones in Pseudomonas aeruginosa. J Bacteriol183: 6676-6683

109 Rabin HR, Butler SM, Wohl MEB, Geller DE, Colin AA, Schidlow DV, Johnson CA, Konstan MW, Regelmann WE (2004) Pulmonary exacerbations in cystic fibrosis. Pediatr Pulmonol37: 400-406

110 Rahme LG, Tan M-W, Le L, Wong SM, Tompkins RG, Calderwood SB, Ausubel FM (1997) Use of model plant hosts to identify Pseudomonas aeruginosa virulence factors. Proc Natl Acad Sci USA94: 13245-13250

111 Rahme LG, Ausubel FM, Cao H, Drenkard E, Goumnerov BC, Lau GW, Mahajan-Miklos S, Plotnikova J, Tan MW, Tsongalis J (2000) Plants and animals share functionally common bacterial virulence factors. Proc Natl Acad Sci USA97: 8815-8821

112 Rampioni G, Schuster M, Greenberg EP, Bertani I, Grasso M, Venturi V, Zennaro E, Leoni L (2007) RsaL provides quorum sensing homeostasis and functions as a global regulator of gene expression in Pseudomonas aeruginosa. Mol Microbiol66: 1557-1565

113 Redfield RJ (2002) Is quorum sensing a side effect of diffusion sensing? Trends Microbiol10: 365-370

114 Reimmann C, Beyeler M, Latifi A, Winteler H, Foglino M, Lazdunski A, Haas D (1997) The global activator GacA of Pseudomonas aeruginosa PAO positively controls the production of the autoinducer N-butyryl-homoserine lactone and the formation of the virulence factors pyocyanin, cyanide, and lipase. Mol Microbiol24: 309-319

115 Roy-Burman A, Savel RH, Racine S, Swanson BL, Revadigar NS, Fujimoto J, Sawa T, Frank DW, Wiener-Kronish JP (2001) Type III protein secretion is associated with death in lower respiratory and systemic Pseudomonas aeruginosa infections. J Infect Dis183: 1767-1774

116 Ryall B, Davies JC, Wilson R, Shoemark A, Williams HD (2008) Pseudomonas aeruginosa, cyanide accumulation and lung function in CF and non-CF bronchiectasis patients. Eur Respir J32: 740-747

117 Sauer K, Cullen MC, Rickard AH, Zeef LA, Davies DG, Gilbert P (2004) Characterization of nutrient-induced dispersion in Pseudomonas aeruginosa PAO1 biofilm. J Bacteriol186: 7312-7326

118 Schaber JA, Carty NL, McDonald NA, Graham ED, Cheluvappa R, Griswold JA, Hamood AN (2004) Analysis of quorum sensingdeficient clinical isolates of Pseudomonas aeruginosa. J Med Microbiol53: 841-853

119 Schafhauser J, Lepine F, McKay G, Ahlgren HG, Khakimova M, Nguyen D (2014) The stringent response modulates 4-hydroxy-2-alkylquinoline biosynthesis and quorum-sensing hierarchy in Pseudomonas aeruginosa. J Bacteriol196: 1641-1650

120 Schertzer JW, Boulette ML, Whiteley M (2009) More than a signal: non-signaling properties of quorum sensing molecules. Trends Microbiol17: 189-195

121 Schuster M, Greenberg EP (2006) A network of networks: quorumsensing gene regulation in Pseudomonas aeruginosa. Int J Med Microbiol296: 73-81

122 Schuster M, Greenberg EP (2007) Early activation of quorum sensing in Pseudomonas aeruginosa reveals the architecture of a complex regulon. BMC Genomics8: 287

123 Schuster M, Lostroh CP, Ogi T, Greenberg EP (2003) Identification, timing, and signal specificity of Pseudomonas aeruginosa quorum-controlled genes: a transcriptome analysis. J Bacteriol185: 2066-2079

124 Schuster M, Urbanowski ML, Greenberg EP (2004) Promoter specificity in Pseudomonas aeruginosa quorum sensing revealed by DNA binding of purified LasR. Proc Natl Acad Sci USA101: 15833-15839

125 Seet Q, Zhang LH (2011) Anti-activator QslA defines the quorum sensing threshold and response in Pseudomonas aeruginosa. Mol Microbiol 80: 951-965

126 Siehnel R, Traxler B, An DD, Parsek MR, Schaefer AL, Singh PK (2010) A unique regulator controls the activation threshold of quorum-regulated genes in Pseudomonas aeruginosa. Proc Natl Acad Sci USA107: 7916-7921

127 Sio CF, Otten LG, Cool RH, Diggle SP, Braun PG, Bos R, Daykin M, Camara M, Williams P, Quax WJ (2006) Quorum quenching by an N-acyl-homoserine lactone acylase from Pseudomonas aeruginosa PAO1. Infect Immun74: 1673-1682

128 Smith EE, Buckley DG, Wu Z, Saenphimmachak C, Hoffman LR, D’Argenio DA, Miller SI, Ramsey BW, Speert DP, Moskowitz SM (2006) Genetic adaptation by Pseudomonas aeruginosa to the airways of cystic fibrosis patients. Proc Natl Acad Sci USA103: 8487-8492

129 Solomonson LP (1981) Cyanide as a metabolic inhibitor. In: Vennesland EECB, Knowles CJ, Westley J, Wissing F(eds) Cyanide in biology. Academic Press, London, pp 11-28

130 Stewart GS, Williams P (1992) lux genes and the applications of bacterial bioluminescence. Journal of general microbiology138: 1289-1300

131 Strempel N, Neidig A, Nusser M, Geffers R, Vieillard J, Lesouhaitier O, Brenner-Weiss G, Overhage J (2013) Human host defense peptide LL-37 stimulates virulence factor production and adaptive resistance in Pseudomonas aeruginosa. PLoS One8: e82240

132 Svitil AL, Cashel M, Zyskind JW (1993) Guanosine tetraphosphate inhibits protein synthesis in vivo. A possible protective mechanism for starvation stress in Escherichia coli. J Biol Chem268: 2307-2311

133 Tan TT (2008) “Future” threat of gram-negative resistance in Singapore. Ann Acad Med Singap37: 884-890

134 Thompson LS, Webb JS, Rice SA, Kjelleberg S (2003) The alternative sigma factor RpoN regulates the quorum sensing gene rhlI in Pseudomonas aeruginosa. FEMS Microbiol Lett220: 187-195

135 Toder DS, Gambello MJ, Iglewski BH (1991) Pseudomonas aeruginosa LasA: a second elastase under the transcriptional control of lasR. Mol Microbiol5: 2003-2010

136 Van Delden C, Iglewski BH (1998) Cell-to-cell signaling and Pseudomonas aeruginosa infections. Emerg Infect Dis4: 551-560

137 Van Delden C, Pesci EC, Pearson JP, Iglewski BH (1998) Starvation selection restores elastase and rhamnolipid production in a Pseudomonas aeruginosa quorum-sensing mutant. Infect Immun66: 4499-4502

138 van Delden C, Comte R, Bally AM (2001) Stringent response activates quorum sensing and modulates cell density-dependent gene expression in Pseudomonas aeruginosa. J Bacteriol183: 5376-5384

139 Ventre I, Ledgham F, Prima V, Lazdunski A, Foglino M, Sturgis JN (2003) Dimerization of the quorum sensing regulator RhlR: development of a method using EGFP fluorescence anisotropy. Mol Microbiol48: 187-198

140 von Bodman SB, Willey JM, Diggle SP (2008) Cell–cell communication in bacteria: united we stand. J Bacteriol190: 4377-4391

141 Wade DS, Calfee MW, Rocha ER, Ling EA, Engstrom E, Coleman JP, Pesci EC (2005) Regulation of Pseudomonas quinolone signal synthesis in Pseudomonas aeruginosa. J Bacteriol187: 4372-4380

142 Westblade LF, Ilag LL, Powell AK, Kolb A, Robinson CV, Busby SJ (2004) Studies of the Escherichia coli Rsd-sigma70 complex. J Mol Biol335: 685-692

143 Whitchurch CB, Beatson SA, Comolli JC, Jakobsen T, Sargent JL, Bertrand JJ, West J, Klausen M, Waite LL, Kang PJ (2005) Pseudomonas aeruginosa fimL regulates multiple virulence functions by intersecting with Vfr-modulated pathways. Mol Microbiol55: 1357-1378

144 Whitehead NA, Barnard AM, Slater H, Simpson NJ, Salmond GP (2001) Quorum-sensing in Gram-negative bacteria. FEMS Microbiol Rev25: 365-404

145 Whiteley M, Greenberg EP (2001) Promoter specificity elements in Pseudomonas aeruginosa quorum-sensing-controlled genes. J Bacteriol183: 5529-5534

146 Whiteley M, Lee KM, Greenberg EP (1999) Identification of genes controlled by quorum sensing in Pseudomonas aeruginosa. Proc Natl Acad Sci USA96: 13904-13909

147 Whiteley M, Parsek MR, Greenberg EP (2000) Regulation of quorum sensing by RpoS in Pseudomonas aeruginosa. J Bacteriol182: 4356-4360

148 Williams P, Bainton NJ, Swift S, Chhabra SR, Winson MK, Stewart GS, Salmond GP, Bycroft BW (1992) Small molecule-mediated density-dependent control of gene expression in prokaryotes: bioluminescence and the biosynthesis of carbapenem antibiotics. FEMS Microbiol Lett100: 161-167

149 Winson MK, Camara M, Latifi A, Foglino M, Chhabra SR, Daykin M, Bally M, Chapon V, Salmond GP, Bycroft BW (1995) Multiple N-acyl-L-homoserine lactone signal molecules regulate production of virulence determinants and secondary metabolites in Pseudomonas aeruginosa. Proc Natl Acad Sci USA92: 9427-9431

150 Winzer K, Falconer C, Garber NC, Diggle SP, Camara M, Williams P (2000) The Pseudomonas aeruginosa lectins PA-IL and PA-IIL are controlled by quorum sensing and by RpoS. J Bacteriol182: 6401-6411

151 Wolz C, Hohloch K, Ocaktan A, Poole K, Evans RW, Rochel N, Albrecht-Gary AM, Abdallah MA, Doring G (1994) Iron release from transferrin by pyoverdin and elastase from Pseudomonas aeruginosa. Infect Immun62: 4021-4027

152 Wu L, Estrada O, Zaborina O, Bains M, Shen L, Kohler JE, Patel N, Musch MW, Chang EB, Fu YX (2005) Recognition of host immune activation by Pseudomonas aeruginosa. Science 309: 774-777

153 Xiao G, Deziel E, He J, Lepine F, Lesic B, Castonguay MH, Milot S, Tampakaki AP, Stachel SE, Rahme LG (2006a) MvfR, a key Pseudomonas aeruginosa pathogenicity LTTR-class regulatory protein, has dual ligands. Mol Microbiol62: 1689-1699

154 Xiao G, He J, Rahme LG (2006b) Mutation analysis of the Pseudomonas aeruginosa mvfR and pqsABCDE gene promoters demonstrates complex quorum-sensing circuitry. Microbiology152: 1679-1686

155 Yanagihara K, Tomono K, Kaneko Y, Miyazaki Y, Tsukamoto K, Hirakata Y, Mukae H, Kadota J, Murata I, Kohno S (2003) Role of elastase in a mouse model of chronic respiratory Pseudomonas aeruginosa infection that mimics diffuse panbronchiolitis. Journal of medical microbiology52: 531-535

156 Zaborin A, Romanowski K, Gerdes S, Holbrook C, Lepine F, Long J, Poroyko V, Diggle SP, Wilke A, Righetti K (2009) Red death in Caenorhabditis elegans caused by Pseudomonas aeruginosa PAO1. Proc Natl Acad Sci USA106: 6327-6332

157 Zaborina O, Lepine F, Xiao G, Valuckaite V, Chen Y, Li T, Ciancio M, Zaborin A, Petrof EO, Turner JR (2007) Dynorphin activates quorum sensing quinolone signaling in Pseudomonas aeruginosa. PLoS Pathog3: e35

158 Zhang L, Murphy PJ, Kerr A, Tate ME (1993) Agrobacterium conjugation and gene regulation by N-acyl-L-homoserine lactones. Nature362: 446-448