The phenazine pyocyanin is a terminal signalling factor in the quorum sensing network of Pseudomonas aeruginosa. Mol Microbiol

Divisions of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA.
Molecular Microbiology (Impact Factor: 4.42). 10/2006; 61(5):1308-21. DOI: 10.1111/j.1365-2958.2006.05306.x
Source: PubMed


Certain members of the fluorescent pseudomonads produce and secrete phenazines. These heterocyclic, redox-active compounds are toxic to competing organisms, and the cause of these antibiotic effects has been the focus of intense research efforts. It is largely unknown, however, how pseudomonads themselves respond to - and survive in the presence of - these compounds. Using Pseudomonas aeruginosa DNA microarrays and quantitative RT-PCR, we demonstrate that the phenazine pyocyanin elicits the upregulation of genes/operons that function in transport [such as the resistance-nodulation-cell division (RND) efflux pump MexGHI-OpmD] and possibly in redox control (such as PA2274, a putative flavin-dependant monooxygenase), and downregulates genes involved in ferric iron acquisition. Strikingly, mexGHI-opmD and PA2274 were previously shown to be regulated by the PA14 quorum sensing network that controls the production of virulence factors (including phenazines). Through mutational analysis, we show that pyocyanin is the physiological signal for the upregulation of these quorum sensing-controlled genes during stationary phase and that the response is mediated by the transcription factor SoxR. Our results implicate phenazines as signalling molecules in both P. aeruginosa PA14 and PAO1.

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Available from: Lars E. Dietrich,
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    • "The Las system is the first to become activated, and it in turn stimulates additional systems known as Rhl and PQS, which additionally regulate each other (Fig. 1) [3]. Finally, pyocyanin, a phenazine small molecule and virulence factor, acts as a terminal signaling factor in the quorum-sensing cascade [4]. Consistent with this hierarchy, inactivation of LasR, the regulatory protein of the Las quorum-sensing system, has been reported to severely attenuate quorum sensing, the production of quorum-regulated factors, and virulence in typical laboratory culture and in short-term animal models [5], [6], [7], [8], [9], [10], [11]. "
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    ABSTRACT: Secreted virulence factors of the human pathogen Pseudomonas aeruginosa are often under quorum sensing control. Cells lacking the quorum-sensing regulator LasR show reduced virulence factor production under typical laboratory conditions and are hypo-virulent in short-term animal infection models, yet lasR mutants are frequently associated with long-term infection in cystic fibrosis patients. Here, I show that in stationary-phase or slow-growth conditions, lasR cells continuously and strongly produce the important virulence factor pyocyanin while wild-type cells do not. Pyocyanin overproduction by lasR cells is permitted by loss of repression by RsaL, a LasR-dependent negative regulator. lasR cells also contribute pyocyanin in mixed cultures, even under "cheating" conditions where they depend on their wild-type neighbors for nutrients. Finally, some clinical P. aeruginosa isolates with lasR mutations can overproduce pyocyanin in the laboratory. These results imply that slow-growing clinical populations of lasR cells in chronic infections may contribute to virulence by producing pyocyanin under conditions where lasR (+) cells do not.
    PLoS ONE 02/2014; 9(2):e88743. DOI:10.1371/journal.pone.0088743 · 3.23 Impact Factor
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    • "PCN synthesis is regulated by QS, as several reports indicate that mutations in the lasI-lasR and rhlI-rhlR QS systems result in the loss of PCN production (de Kievit and Iglewski 2000; Rumbaugh et al. 2000; Schaber et al. 2004; Siehnel et al. 2010). Moreover, PCN itself functions as a QS signal, as indicated by the fact that i) it demonstrates cell density-dependent accumulation, ii) it is a small diffusible molecule that is recognized by adjacent cells, and iii) it triggers a specific transcriptional response (Dietrich et al. 2006), further complicating our understanding of its mechanisms of action. Despite in vitro studies demonstrating that PCN interferes with multiple cellular functions in animals, its importance during bacteria–plant interactions is uncertain. "
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    ABSTRACT: Pyocyanin acts as a virulence factor in Pseudomonas aeruginosa, a plant and animal pathogen. In this study we evaluated the effect of pyocyanin on growth and development of Arabidopsis seedlings. Root inoculation with P. aeruginosa PAO1 strain inhibited primary root growth in WT Arabidopsis seedlings. In contrast, single lasI- and double rhlI-/lasI- mutants of P. aeruginosa defective in pyocyanin production showed decreased root growth inhibition concomitant with an increased phytostimulation. Treatment with pyocyanin modulates root system architecture inhibiting primary root growth and promoting lateral root and root hair formation without affecting meristem viability or causing cell death. These effects correlated with altered proportions of hydrogen peroxide and superoxide in root tips and with an inhibition of cell division and elongation. Mutant analyses showed that pyocyanin modulation of root growth was likely independent of auxin, cytokinin and abscisic acid, but required ethylene signaling as the Arabidopsis etr1-1, ein2-1 and ein3-1 ethylene-related mutants were less sensitive to pyocyanin-induced root stoppage and reactive oxygen species (ROS) distribution. Our findings suggest that pyocyanin is an important factor modulating the interplay between ROS production and root system architecture by an ethylene dependent signaling.
    Molecular Plant-Microbe Interactions 11/2013; 27(4). DOI:10.1094/MPMI-08-13-0219-R · 3.94 Impact Factor
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    • "In a study to identify genes involved in the production of pyocyanin, mutation of the np20 gene which was previously shown to be a virulence determinant [20], caused deficiency in both pyocyanin and the cell-to-cell signal 2-heptyl-3-hydroxy-4-quinolone (the Pseudomonas Quinolone Signal or PQS) production [21]. Others have reported that this regulator is required for production of pyocyanin [22], and that np20 mutant strains are avirulent in both nematode [15] and mouse infection models [14]. Recently, Np20 was shown to regulate the expression of dksA2, a paralogue of global transcriptional regulator dksA, in a zinc-dependent manner [23]. "
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    ABSTRACT: Zinc is essential for all bacteria, but excess amounts of the metal can have toxic effects. To address this, bacteria have developed tightly regulated zinc uptake systems, such as the ZnuABC zinc transporter which is regulated by the Fur-like zinc uptake regulator (Zur). In Pseudomonas aeruginosa, a Zur protein has yet to be identified experimentally, however, sequence alignment revealed that the zinc-responsive transcriptional regulator Np20, encoded by np20 (PA5499), shares high sequence identity with Zur found in other bacteria. In this study, we set out to determine whether Np20 was functioning as Zur in P. aeruginosa. Using RT-PCR, we determined that np20 (hereafter known as zur) formed a polycistronic operon with znuC and znuB. Mutant strains, lacking the putative znuA, znuB, or znuC genes were found to grow poorly in zinc deplete conditions as compared to wild-type strain PAO1. Intracellular zinc concentrations in strain PAO-Zur (Δzur) were found to be higher than those for strain PAO1, further implicating the zur as the zinc uptake regulator. Reporter gene fusions and real time RT-PCR revealed that transcription of znuA was repressed in a zinc-dependent manner in strain PAO1, however zinc-dependent transcriptional repression was alleviated in strain PAO-Zur, suggesting that the P. aeruginosa Zur homolog (ZurPA) directly regulates expression of znuA. Electrophoretic mobility shift assays also revealed that recombinant ZurPA specifically binds to the promoter region of znuA and does not bind in the presence of the zinc chelator N,N',N-tetrakis(2-pyridylmethyl) ethylenediamine (TPEN). Taken together, these data support the notion that Np20 is the P. aeruginosa Zur, which regulates the transcription of the genes encoding the high affinity ZnuABC zinc transport system.
    PLoS ONE 10/2013; 8(9):e75389. DOI:10.1371/journal.pone.0075389 · 3.23 Impact Factor
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