Quorum sensing negatively controls type III secretion regulon expression in Pseudomonas aeruginosa PAO1

Abstract

A systematic analysis of the type III secretion (T3S) genes of Pseudomonas aeruginosa strain PAO1 revealed that they are under quorum-sensing control. This observation was supported by the down-regulation of the T3S regulon in the presence of RhlR-C4HSL and the corresponding advanced secretion of ExoS in a rhlI mutant.

FIG. 1.

Expression of the transcriptional fusions pC-lacZ from pPP4 (A) and pD-lacZ from pSB305 (B and C) in P. aeruginosa strain PAO1 (diamonds), PAO1exsA (squares), PAO1rhlI (triangles), or PAO1lasR (crosses). Cultures were grown at 37°C in the absence (closed symbols, I) or presence (open symbols, NI) of Ca²⁺ and with exogenously added 10 μM C₄-HSL (grey symbols). The results represent a single experiment, which was repeated three times without variations. The level of β-galactosidase activity from PAO1/pMP220 (circles) was recorded after growth under T3S-inducing conditions. (D) Intracellular immunodetection of PscF in P. aeruginosa strain PA103 grown under T3S-inducing (−Ca²⁺) or noninducing (+Ca²⁺) conditions. The equivalent of an OD₆₀₀ of 0.4 was loaded in each case.

FIG. 2.

Expression of the transcriptional fusions pS-lacZ from pSB307 (A), pT-lacZ from pSB302 (B), pY-lacZ from pSB303 (C), pG-lacZ from pSB308 (D), and pN-lacZ from pSB313 (E) in P. aeruginosa strains PAO1 (diamonds) and PAO1rhlI (triangles). See the legend of Fig. 1 for more information.

FIG. 3.

Immunodetection of ExoS in culture supernatants of PAO1 or PAO1rhlI grown at 37°C under T3S-inducing conditions and with exogenously added 10 μM C₄-HSL where indicated. Samples were taken each 30 min over a 4-h growth period. The equivalent of an OD₆₀₀ of 1 was loaded on a sodium dodecyl sulfate-polyacrylamide gel electrophoresis gel.