Expression of Pseudomonas aeruginosa exoS is controlled by quorum sensing and RpoS.
In Pseudomonas aeruginosa, virulence determinants and biofilm formation are coordinated via a hierarchical quorum sensing cascade, which involves the transcriptional regulators LasR and RhlR and their cognate homoserine lactone activators C12-HSL [N-(3-oxododecanoyl)-L-homoserine lactone] and c4-hsl (n-butanoyl-L-homoserine lactone), which are produced by LasI and RhlI, respectively. The exoenzyme S regulon of P. aeruginosa, comprises genes for a type III secretion system and for four anti-host effector proteins (ExoS, T, U and Y), which are translocated into host cells. It is a reasonable assumption that this ExoS regulon should be downregulated in the biofilm growth state and thus should also be under the regulatory control of the Las/Rhl system. Therefore, an exoS'-gfp reporter construct was used, and the influence of the Las and Rhl quorum sensing systems and the effect of the stationary-phase sigma factor RpoS on regulation of the exoS gene was examined. Evidence is provided for downregulation of exoS during biofilm formation of P. aeruginosa PAO1. The rhlI mutant PDO100 and rhlR mutant PDO111, but not the lasI mutant PDO-JP1, showed approximately twofold upregulation of the exoS'-gfp reporter in comparison to PAO1. Upregulation of exoS'-gfp in the PDO100 mutant could be repressed to normal level by adding C4-HSL autoinducer, indicating a negative regulatory effect of RhlR/C4-HSL on exoS expression. As RhlR/C4-HSL is also involved in regulation of RpoS, the P. aeruginosa rpoS mutant SS24 was examined and the exoS'-gfp reporter was found to be fivefold upregulated in comparison to PAO1. For the first time evidence is reported for a regulatory cascade linking RhlR/RhlI and RpoS with the expression of the anti-host effector ExoS, part of the exoenzyme S regulon. Moreover, these data suggest that the exoenzyme S regulon may be downregulated in P. aeruginosa biofilms.
Hogardt
Michael
M
Max von Pettenkofer-Institut für Hygiene und Medizinische Mikrobiologie, Ludwig-Maximilians University Munich, Pettenkoferstraße 9a, D-80336 Munich, Germany.
Roeder
Maximilian
M
Max von Pettenkofer-Institut für Hygiene und Medizinische Mikrobiologie, Ludwig-Maximilians University Munich, Pettenkoferstraße 9a, D-80336 Munich, Germany.
Schreff
Anna Maria
AM
Max von Pettenkofer-Institut für Hygiene und Medizinische Mikrobiologie, Ludwig-Maximilians University Munich, Pettenkoferstraße 9a, D-80336 Munich, Germany.
Eberl
Leo
L
Max von Pettenkofer-Institut für Hygiene und Medizinische Mikrobiologie, Ludwig-Maximilians University Munich, Pettenkoferstraße 9a, D-80336 Munich, Germany.
Heesemann
Jürgen
J
Max von Pettenkofer-Institut für Hygiene und Medizinische Mikrobiologie, Ludwig-Maximilians University Munich, Pettenkoferstraße 9a, D-80336 Munich, Germany.
D015107:4-Butyrolactone / Q000031:analogs & derivatives* / Q000378:metabolism; D036002:ADP Ribose Transferases / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001427:Bacterial Toxins / Q000235:genetics / Q000378:metabolism*; D018441:Biofilms; D003470:Culture Media; D015964:Gene Expression Regulation, Bacterial; D049452:Green Fluorescent Proteins; D006801:Humans; D008025:Ligases; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D010933:Plankton; D011550:Pseudomonas aeruginosa / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012808:Sigma Factor / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
D001426:Bacterial Proteins; D001427:Bacterial Toxins; D003470:Culture Media; D008164:Luminescent Proteins; C092312:N-butyrylhomoserine lactone; D011993:Recombinant Fusion Proteins; C086515:RhlR protein, Pseudomonas aeruginosa; D012808:Sigma Factor; D014157:Transcription Factors; C069567:sigma factor KatF protein, Bacteria; C088386:homoserine lactone; D049452:Green Fluorescent Proteins; D036002:ADP Ribose Transferases; C444820:exoenzyme S; D008025:Ligases; C096955:RHLI protein, Pseudomonas aeruginosa; D015107:4-Butyrolactone