title: Modulation of quorum sensing in Pseudomonas aeruginosa through alteration of membrane properties.
abstract: Changes in the cellular envelope are major physiological adaptations that occur when micro-organisms encounter extreme environmental conditions. An appropriate degree of membrane fluidity is crucial for survival, and alteration of membrane lipids is an essential adaptive response. Emerging data suggest that microbial cells may recognize alterations in their membrane viscosity resulting from certain environmental changes as a trigger for adaptive cellular responses. In Pseudomonas aeruginosa, the quorum-sensing (QS) system involves a complex regulatory circuitry that coordinates the expression of genes according to a critical population density. Interestingly, it has been shown that the QS system of P. aeruginosa can also be activated by nutritional stress, independently of the cell density, and therefore may be part of a more general adaptive response to stressful environmental conditions. In order to examine the proposed link between membrane properties and stress signalling, the effects of genetically engineered alterations of the membrane phospholipid composition of P. aeruginosa PAO1 on the activation of the stringent response and the QS system were examined. The lptA gene encoding a functional homologue of PlsC, an Escherichia coli enzyme that catalyses the second step of the phospholipid biosynthesis pathway, was identified and disrupted. Inactivation of lptA altered the fatty acid profile of phospholipids and the membrane properties, resulting in decreased membrane fluidity. This resulted in a premature production of the QS signals N-butanoyl- and N-hexanoyl-homoserine lactone (C4-HSL and C6-HSL) and a repression of 2-heptyl-3-hydroxy-4-quinolone (PQS) synthesis at later growth phases. The effects on C4- and C6-HSL depended upon the expression of relA, encoding the (p)ppGpp alarmone synthase, which was increased in the lptA mutant. Together, the findings support the concept that alterations in membrane properties can act as a trigger for stress-related gene expression.
authors.affiliation: BIOMERIT Research Centre, Microbiology Department, University College Cork, National University of Ireland, Cork, Ireland.
authors.forename: Christine
authors.initials: C
authors.lastname: Baysse
authors.affiliation: BIOMERIT Research Centre, Microbiology Department, University College Cork, National University of Ireland, Cork, Ireland.
authors.forename: Méabh
authors.initials: M
authors.lastname: Cullinane
authors.affiliation: BIOMERIT Research Centre, Microbiology Department, University College Cork, National University of Ireland, Cork, Ireland.
authors.forename: Valérie
authors.initials: V
authors.lastname: Dénervaud
authors.affiliation: BIOMERIT Research Centre, Microbiology Department, University College Cork, National University of Ireland, Cork, Ireland.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Burrowes
authors.affiliation: BIOMERIT Research Centre, Microbiology Department, University College Cork, National University of Ireland, Cork, Ireland.
authors.forename: J Maxwell
authors.initials: JM
authors.lastname: Dow
authors.affiliation: BIOMERIT Research Centre, Microbiology Department, University College Cork, National University of Ireland, Cork, Ireland.
authors.forename: John P
authors.initials: JP
authors.lastname: Morrissey
authors.affiliation: Department of Environmental Biology, Rm 3220 Bovey Building, University of Guelph, Guelph, Ontario, Canada N1G 2W1.
authors.forename: Ling
authors.initials: L
authors.lastname: Tam
authors.affiliation: Department of Environmental Biology, Rm 3220 Bovey Building, University of Guelph, Guelph, Ontario, Canada N1G 2W1.
authors.forename: Jack T
authors.initials: JT
authors.lastname: Trevors
authors.affiliation: BIOMERIT Research Centre, Microbiology Department, University College Cork, National University of Ireland, Cork, Ireland.
authors.forename: Fergal
authors.initials: F
authors.lastname: O'Gara
mesh_terms: D000217:Acyltransferases / Q000235:genetics* / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D008245:Lysophospholipase / Q000235:genetics* / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism*; D009097:Multienzyme Complexes / Q000235:genetics* / Q000378:metabolism; D011550:Pseudomonas aeruginosa / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D015363:Quinolones / Q000378:metabolism*; D015398:Signal Transduction
chemical_list: D008565:Membrane Proteins; D009097:Multienzyme Complexes; D015363:Quinolones; D000217:Acyltransferases; D008245:Lysophospholipase; C021782:lysophospholipase-transacylase