Identification of genes controlled by quorum sensing in Pseudomonas aeruginosa

Abstract

Bacteria communicate with each other to coordinate expression of specific genes in a cell density-dependent fashion, a phenomenon called quorum sensing and response. Although we know that quorum sensing via acyl-homoserine lactone (HSL) signals controls expression of several virulence genes in the human pathogen Pseudomonas aeruginosa, the number and types of genes controlled by quorum sensing have not been studied systematically. We have constructed a library of random insertions in the chromosome of a P. aeruginosa acyl-HSL synthesis mutant by using a transposon containing a promoterless lacZ. This library was screened for acyl-HSL induction of lacZ. Thirty-nine quorum sensing-regulated genes were identified. The genes were organized into classes depending on the pattern of regulation. About half of the genes appear to be in seven operons, some seem organized in large patches on the genome. Many of the quorum sensing-regulated genes code for putative virulence factors or production of secondary metabolites. Many of the genes identified showed a high level of induction by acyl-HSL signaling. Many host-associated bacteria use chemical signals to monitor their own species population density and control expression of specific genes in response to population density. This type of gene regulation is termed quorum sensing (1). Several Gram-negative bacteria use acylated homoserine lactone (HSL) signals in quorum sensing. Quorum sensing in Pseudomonas aeruginosa, an opportunistic human pathogen responsible for persistent and often incurable infections in immunocompromised people and individuals with cystic fibrosis, has been well studied. The sequence of the P. aeruginosa genome is available publicly. Expression of a number of extracellular virulence factors produced by P. aeruginosa is controlled by quorum sensing (for recent reviews see refs. 2 and 3).Two quorum sensing systems, the las and rhl systems, have been identified in P. aeruginosa. In the las quorum sensing system, the lasI gene product directs the formation of the diffusible extracellular signal, N-(3-oxododecanoyl)-L-HSL (3OC 12 -HSL) (4), which interacts with LasR (5, 6) to activate a number of virulence genes, including lasB, lasA, apr, toxA, and lasI itself (6-10). Synthesis of the siderophore pyoverdine also is activated by the las system (11). P. aeruginosa strains lacking a functional LasR are avirulent in animal models (12). Although 3OC 12 -HSL is diffusible, it appears to partition into cell membranes, and P. aeruginosa efflux pumps aid in the movement of this signal to the external environment (13,14).The rhlI product catalyzes the synthesis of N-butyryl-L-HSL (C 4 -HSL) (15,16). This diffusible signal (14) in conjunction with RhlR activates expression of the rhlAB rhamnolipid synthesis genes, rhlI, and to some extent lasB (17)(18)(19)(20). Other virulence factors and secondary metabolites, including pyocyanin, cyanide, and chitinase, are positively regulated by the rhl system (18, 21), although direct transcriptional regulation of the genes in...

Altered expression of two light-dependent genes in a microcystin-lacking mutant of Microcystis aeruginosa PCC 7806

“…The LuxR\ LuxI type of quorum-sensing regulation has been shown to control the expression of an increasing number of genes, including peptide synthetase genes, exopolysaccharide genes and virulence factors, especially in host-associated bacteria such as Pseudomonas aeruginosa, Erwinia carotovora and Agrobacterium tumefaciens (Rhizobium tumefaciens) (Whiteley et al, 1999 ;Bassler, 1999). In Gram-negative bacteria quorumsensing systems consist of an N-acylhomoserine lactone (AHL) signal molecule (autoinducer), which is synthesized by a LuxI homologue, and requires an autoinducer-dependent transcriptional activator protein, as represented by LuxR (Whiteley et al, 1999). At least two different types of AHLs were shown to regulate the rhiABC operon in a cell-density-dependent manner (Rodelas et al, 1999).…”

Identification of a Pseudomonas sp. that Inhibits RHL System of Quorum Sensing

“…Up to 11 % of the P. aeruginosa genome is subjected to QS-dependent regulation [18]. Inhibition of QS offers a new hope for combating multi-antibiotic-resistant bacteria, because it does not impose harsh selective pressure for the development of resistance.…”

“…The Pseudomonas aeruginosa is highly tolerant to antibiotic treatment largely due to the biofilm [16]. Since QS system was found to be essential for creation of mature, (1) 1.51 %, (2) 1.817 %, and (3) 96.673 % differentiated biofilms [17], we also tested if the final extract of strain 4001 exhibited a similar inhibition effect on biofilm formation.…”

Metabolite transfer with the fermentation product 2,3-butanediol enhances virulence by Pseudomonas aeruginosa

“…Next, we tested whether quorum sensing, which controls virulence, antimicrobial activity, and biofilm formation for P. aeruginosa (Whiteley et al, 1999;Wagner et al, 2003), was upregulated with 2,3-butanediol compared with glucose. Quorum sensing in P. aeruginosa is mediated by diffusible acylhomoserine lactones that are produced by LasI, which synthesizes 3-oxo-dodecadonyl homoserine lactone (3O-C12-HSL), and RhlI, which synthesizes n-butyryl homoserine lactone (C4-HSL).…”

“…Research had already indicated that reduced PCA and PYO were considerably more reactive with Fe(III) and O 2 , respectively, than vice versa (Wang and Newman, 2008). Importantly, the quorum-sensing cascade regulates phenazine production by P. aeruginosa (Whiteley et al, 1999), and thus has an effect on the redox activity of the produced phenazines (Venkataraman et al, 2010).…”