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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

ABSTRACT

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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    • "Significant differential expression was determined to be genes showing log 2 fold change relative to untreated controls of >1.5 or <−1.5 at a 5 % false discovery rate. Significantly differentially expressed genes are highlighted in Additional file 1iron-sulfur clusters and, in some cases, degrade them[34]. Fe-S cluster degradation by methyl viologen and other redox-active compounds has been shown to initiate wide-ranging transcriptional changes through induction of the SoxRS transcription factor system[35]. "
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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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