Article

Self-Produced Exopolysaccharide is a Signal that Stimulates Biofilm Formation in Pseudomonas aeruginosa

Department of Microbiology, University of Washington, Seattle, WA 98195.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 11/2012; 109(50). DOI: 10.1073/pnas.1217993109
Source: PubMed

ABSTRACT

Bacteria have a tendency to attach to surfaces and grow as structured communities called biofilms. Chronic biofilm infections are a problem because they tend to resist antibiotic treatment and are difficult to eradicate. Bacterial biofilms have an extracellular matrix that is usually composed of a mixture of polysaccharides, proteins, and nucleic acids. This matrix has long been assumed to play a passive structural and protective role for resident biofilm cells. Here we show that this view is an oversimplification and that the biofilm matrix can play an active role in stimulating its own synthesis. Working with the model biofilm bacterium Pseudomonas aeruginosa, we found that Psl, a major biofilm matrix polysaccharide for this species, acts as a signal to stimulate two diguanylate cyclases, SiaD and SadC, to produce the intracellular secondary messenger molecule c-di-GMP. Elevated intracellular concentrations of c-di-GMP then lead to the increased production of Psl and other components of the biofilm. This mechanism represents a unique positive feedback regulatory circuit, where the expression of an extracellular polysaccharide promotes biofilm growth in a manner analogous to autocrine signaling in eukaryotes.

Download full-text

Full-text

Available from: Yasuhiko Irie
  • Source
    • "While psl gene expression is directly repressed by RsmA at the translational level (Irie et al., 2010), there is no evidence of a direct effect of RsmA on the pel genes, although transcriptomic analysis showed that the active state of the Gac network (i.e., rsmA mutation) also promotes transcription of the pel operon (Brencic and Lory, 2009). The Gac system has recently been shown to positively affect the intracellular levels of the signaling molecule c-di-GMP, which also induces exopolysaccharides production (Moscoso et al., 2011, 2014; Irie et al., 2012; Frangipani et al., 2014). This second messenger regulates Pel production both at the transcriptional and post-transcriptional level, by inhibiting the activity of the transcriptional repressor FleQ (Hickman and Harwood, 2008), and activating the Pel biosynthesis protein PelD (Lee et al., 2007). "
    [Show abstract] [Hide abstract]
    ABSTRACT: In Pseudomonas aeruginosa the Gac signaling system and the second messenger cyclic diguanylate (c-di-GMP) participate in the control of the switch between planktonic and biofilm lifestyles, by regulating the production of the two exopolysaccharides Pel and Psl. The Gac and c-di-GMP regulatory networks also coordinately promote the production of the pyoverdine siderophore, and the extracellular polysaccharides Pel and Psl have recently been found to mediate c-di-GMP-dependent regulation of pyoverdine genes. Here we demonstrate that Pel and Psl are also essential for Gac–mediated activation of pyoverdine production. A pel psl double mutant produces very low levels of pyoverdine and shows a marked reduction in the expression of the pyoverdine-dependent virulence factors exotoxin A and PrpL protease. While the exopolysaccharide-proficient parent strain forms multicellular planktonic aggregates in liquid cultures, the Pel and Psl-deficient mutant mainly grows as dispersed cells. Notably, artificially induced cell aggregation is able to restore pyoverdine-dependent gene expression in the pel psl mutant, in a way that appears to be independent of iron diffusion or siderophore signaling, as well as of recently described contact-dependent mechanosensitive systems. This study demonstrates that cell aggregation represents an important cue triggering the expression of pyoverdine-related genes in P. aeruginosa, suggesting a novel link between virulence gene expression, cell–cell interaction and the multicellular community lifestyle.
    Full-text · Article · Aug 2015 · Frontiers in Microbiology
    • "decreasedinthepresenceofS.aureus(Mashburnetal.,2005).QS moleculesproducedbyP.aeruginosaprobablyinducethelysis ofS.aureusanditsuseasanironsource.Bycontrast,otherQS signalsmayactasironchelatingmolecules(Bredenbruchetal., 2006). AlongsidetheclassicQSmediators,recentstudieshave highlightedasignalingactivityfortheexopolysaccharides producedbytheB.subtilisepsoperon.Thispolymerisrecognized bytheextracellulardomainofatyrosinekinasewhichactivates itsownsyntheticpathway(Elsholzetal.,2014).Similarly,in P.aeruginosa,ithasbeendemonstratedthatthePs1polymer stimulatesmatrixproductioninneighboringcellsviac-di-GMP activation,althoughtheprecisemechanismremainsunknown (Irieetal.,2012). "
    [Show abstract] [Hide abstract]
    ABSTRACT: The better understanding of the functioning of microbial communities is a challenging and crucial issue in the field of food microbiology, as it constitutes a prerequisite to the optimization of positive and technological microbial population functioning, as well as for the better control of pathogen contamination of food. Heterogeneity appears now as an intrinsic and multi-origin feature of microbial populations and is a major determinant of their beneficial or detrimental functional properties. The understanding of the molecular and cellular mechanisms behind the behavior of bacteria in microbial communities requires therefore observations at the single-cell level in order to overcome "averaging" effects inherent to traditional global approaches. Recent advances in the development of fluorescence-based approaches dedicated to single-cell analysis provide the opportunity to study microbial communities with an unprecedented level of resolution and to obtain detailed insights on the cell structure, metabolism activity, multicellular behavior and bacterial interactions in complex communities. These methods are now increasingly applied in the field of food microbiology in different areas ranging from research laboratories to industry. In this perspective, we reviewed the main fluorescence-based tools used for single-cell approaches and their concrete applications with specific focus on food microbiology. Copyright © 2015 Elsevier B.V. All rights reserved.
    No preview · Article · Jul 2015 · International journal of food microbiology
  • Source
    • "decreasedinthepresenceofS.aureus(Mashburnetal.,2005).QS moleculesproducedbyP.aeruginosaprobablyinducethelysis ofS.aureusanditsuseasanironsource.Bycontrast,otherQS signalsmayactasironchelatingmolecules(Bredenbruchetal., 2006). AlongsidetheclassicQSmediators,recentstudieshave highlightedasignalingactivityfortheexopolysaccharides producedbytheB.subtilisepsoperon.Thispolymerisrecognized bytheextracellulardomainofatyrosinekinasewhichactivates itsownsyntheticpathway(Elsholzetal.,2014).Similarly,in P.aeruginosa,ithasbeendemonstratedthatthePs1polymer stimulatesmatrixproductioninneighboringcellsviac-di-GMP activation,althoughtheprecisemechanismremainsunknown (Irieetal.,2012). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Biofilms constitute the prevalent way of life for microorganisms in both natural and man-made environments. Biofilm-dwelling cells display greater tolerance to antimicrobial agents than those that are free-living, and the mechanisms by which this occurs have been investigated extensively using single-strain axenic models. However, there is growing evidence that interspecies interactions may profoundly alter the response of the community to such toxic exposure. In this paper, we propose an overview of the studies dealing with multispecies biofilms resistance to biocides, with particular reference to the protection of pathogenic species by resident surface flora when subjected to disinfectants treatments. The mechanisms involved in such protection include interspecies signaling, interference between biocides molecules and public goods in the matrix, or the physiology and genetic plasticity associated with a structural spatial arrangement. After describing these different mechanisms, we will discuss the experimental methods available for their analysis in the context of complex multispecies biofilms.
    Full-text · Article · Jul 2015 · Frontiers in Microbiology
Show more