Functions Required for Extracellular Quinolone Signaling by Pseudomonas aeruginosa

Abstract

A set of 30 mutants exhibiting reduced production of the phenazine poison pyocyanin were isolated following transposon mutagenesis of Pseudomonas aeruginosa PAO1. The mutants could be subdivided into those with defects in the primary phenazine biosynthetic pathway and those with more pleiotropic defects. The largest set of pleiotropic mutations blocked the production of the extracellular Pseudomonas quinolone signal (PQS), a molecule required for the synthesis of secondary metabolites and extracellular enzymes. Most of these pqs mutations affected genes which appear to encode PQS biosynthetic functions, although a transcriptional regulator and an apparent response effector were also represented. Two of the genes required for PQS synthesis (phnA and phnB) had previously been assumed to encode phenazine biosynthetic functions. The transcription of one of the genes required for PQS synthesis (PA2587/pqsH) was regulated by the LasI/R quorum-sensing system, thereby linking quorum sensing and PQS regulation. Others of the pleiotropic phenazine-minus mutations appear to inactivate novel components of the quorum-sensing regulatory network, including one regulator (np20) previously shown to be required for virulence in neutropenic mice.A complex network of regulatory factors governs the production of secondary metabolites and other virulence factors in the opportunistic pathogen Pseudomonas aeruginosa. This network regulates gene expression in response to stimuli such as growth phase, culture density, and oxygen and iron availability (12,26,28,37). Central components of the network are the las and rhl quorum-sensing systems, which activate gene expression in response to culture density (13). Each system is made up of two genes, one encoding an enzyme which produces a specific acylated homoserine lactone autoinducer (lasI/rhlI), and a second encoding a transcriptional activator that binds the corresponding autoinducer (lasR/rhlR). The las system directs expression of virulence factors such as elastases A and B and alkaline protease (16,25). The rhl system directs expression of rhamnolipid biosynthesis enzymes, pyocyanin biosynthesis enzymes, and hydrogen cyanide synthase (3,24,28). In addition, LasI/R regulates expression of both itself and rhlI (1, 26). The las and rhl systems together have been shown to influence the expression of over two hundred genes (36).Recently, a third signaling system based on 2-heptyl-3-hydroxy-4-quinolone, designated the Pseudomonas quinolone signal (PQS), has been shown to be a part of the quorumsensing regulatory network in P. aeruginosa (27). The production of PQS depends on lasR (27), and exogenous PQS strongly induces expression of elastase B and rhlI in a lasR mutant background (22). These results place PQS between the las and rhl quorum-sensing systems in the quorum-sensing regulatory network (22).We have described a process ("paralytic killing") in which P. aeruginosa PAO1 rapidly kills the nematode Caenorhabditis elegans by cyanide poisoning (8, 14). Previous studies of a different P....

Proteomic analysis of Pseudomonas aeruginosa grown under magnesium limitation

“…Recently, a non-HSL P. aeruginosa intercellular signal, 2-heptyl 3-hydroxy 4-quinolone (PQS, Pseudomonas quinolone signal), a component of the P. aeruginosa quorum sensing hierarchy, has been described [19]. A chromosomal region encoding five proteins (PA0996 -1000) was recently shown to be essential for the production of PQS [30,31]. Four proteins encoded by this operon (PA0996 -PA0999) were synthesized at increased levels when P. aeruginosa was grown in low magnesium (Table 2 and Figure 1).…”

Mutation analysis of the Pseudomonas aeruginosa mvfR and pqsABCDE gene promoters demonstrates complex quorum-sensing circuitry

“…mvfR mutants exhibit decreased virulence in different host models, including plants, insects and mammals (Cao et al, 2001;Gallagher & Manoil, 2001;Lau et al, 2003;Mahajan-Miklos et al, 1999;Rahme et al, 1997). MvfR is required to produce virulence factors, such as pyocyanin and hydrogen cyanide (Gallagher & Manoil, 2001;Rahme et al, 1997), and a large family of 4-hydroxy-2-alkylquinolines (HAQs), including the intercellular signals 3,4-dihydroxy-2-heptylquinoline (PQS) and 4-hydroxy-2-heptylquinoline (HHQ) (Déziel et al, 2004;Gallagher et al, 2002;Lépine et al, 2004), which function in the transcriptional regulation of multiple virulence genes (Déziel et al, 2004;Gallagher et al, 2002;McKnight et al, 2000;.…”

“…While MvfR controls the pqsABCDE and phnAB operons, which encode proteins mediating HAQ biosynthesis (Déziel et al, 2004;Gallagher et al, 2002), the final step of PQS production, HHQ hydroxylation, appears Abbreviations: HAQ, 4-hydroxy-2-alkylquinoline; HHQ, 4-hydroxy-2-heptylquinoline; LTTR, LysR-type transcriptional regulator; MvfR, multiple virulence factor regulator; PQS, 3,4-dihydroxy-2-heptylquinoline; QS, quorum sensing; WT, wild-type.…”

The effect of pmpR on the type III secretion system in Pseudomonas aeruginosa

“…The transcription of these two operons is regulated by the PQS transcriptional regulator PqsR, also known as MvfR [8]. Mutations in pqsR interfere with PQS synthesis and affect the production of pyocyanin and other QS-controlled virulence factors [8,9].…”