1887

Abstract

In , 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 [-(3-oxododecanoyl)--homoserine lactone] and c4-hsl (-butanoyl--homoserine lactone), which are produced by LasI and RhlI, respectively. The exoenzyme S regulon of , 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 ′- 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 gene was examined. Evidence is provided for downregulation of during biofilm formation of PAO1. The mutant PDO100 and mutant PDO111, but not the mutant PDO-JP1, showed approximately twofold upregulation of the ′- reporter in comparison to PAO1. Upregulation of ′- 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 expression. As RhlR/C4-HSL is also involved in regulation of RpoS, the mutant SS24 was examined and the ′- 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 biofilms.

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2004-04-01
2024-03-29
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