RsaL, a Novel Repressor of Virulence Gene Expression in Pseudomonas aeruginosa

Abstract

As components of a Pseudomonas aeruginosaquorum-sensing system, LasR and PAI-1 globally regulate expression of multiple virulence determinants, as well as the second P. aeruginosa quorum-sensing system. To date, no information exists on negative regulation of the quorum-sensing cascade in P. aeruginosa. Here we describe a novel gene, rsaL, which is located downstream from lasR and transcribed antisense relative to lasR. In P. aeruginosa,overexpression of rsaL results in reduced lasBexpression and decreased elastase activity. With the use of a six-His protein fusion system, we demonstrate that rsaL encodes an 11-kDa protein. Direct quantitation of PAI-1 levels in cultures and studies utilizing Escherichia coli lambda lysogens carryinglacZ transcriptional fusions reveal that RsaL specifically represses transcription of the PAI-1 autoinducer synthase gene,lasI. RsaL’s repressive effect on lasI and the associated decrease in elastase activity have important implications for the expression of all LasR–PAI-1-dependent virulence genes and the overall pathogenicity of P. aeruginosa.

Regulation of quorum sensing inPseudomonas

“…This model needs to be substantiated by the molecular analysis of events taking place at the ppuI promoter. RsaL appears to play a similar role in lasI gene expression in P. aeruginosa (see above; de Kievit et al, 1999); however, in P. putida there appears to be tighter control imposed by RsaL, resulting in lower expression levels of AHL QS. The biological role of this strong repression played by RsaL is currently unknown.…”

Quorum sensing and swarming migration in bacteria

“…Although more regulators such as Vfr (required for a basal level of lasR expression) [103], and RsaL (repression of lasI) [104] have been described in literature ( Fig. 6), only those affecting the rhl quorum sensing system and C 4 -HSL production and/or rhamnolipids or HAA will be discussed in this section as putative regulators of the P. aeruginosa swarming behaviour.…”

Characterization of the multiple molecular mechanisms underlying RsaL control of phenazine‐1‐carboxylic acid biosynthesis in the rhizosphere bacterium Pseudomonas aeruginosa PA1201

“…RsaL is a transcriptional regulator belonging to a new subfamily within the tetra-helical superclass of helixturn-helix proteins. It is recognized as the predominant repressor of the las QS system in P. aeruginosa and Pseudomonas fuscovaginae, and of the ppu QS system in Pseudomonas putida WCS358 (de Kievit et al, 1999;Rampioni et al, 2006;2007a;Mattiuzzo et al, 2011;Venturi et al, 2011;Rampioni et al, 2012). In P. aeruginosa PAO1 at high cell densities, RsaL represses the expression of lasI, the gene coding for the synthase required for the production of the signal molecule N-3oxododecanoyl-homoserine lactone (3-oxo-C12-HSL).…”

“…As a consequence, rsaL mutation in P. aeruginosa PAO1 leads to enhanced surface motility and the production of secreted virulence factors such as elastase, hemolysins, hydrogen cyanide, and PYO. Conversely, when compared with the wild type strain, the rsaL mutation decreases the ability of this pathogen to cause chronic lung infections in mice (de Kievit et al, 1999;Rampioni et al, 2009;Bond ı et al, 2014). Notably, transcriptomic analyses revealed that RsaL has a negative impact on the expression of multiple genes, including the phz1 cluster, phzM and phzS (Rampioni et al, 2007b).…”