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: 9.81). 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.

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Available from: Yasuhiko Irie, Aug 04, 2015
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    • "It appears that S. aureus cells were not able to discriminate between molecularly smooth surfaces when the average surface roughness was below 0.2 nm and hence were able to effectively colonise these surfaces. Meanwhile, regarding to the attachment behaviour of P. aeruginosa, increased EPS production is known to be one of the primary factors that allows P. aeruginosa cells to successfully colonise a surface (Irie et al. 2012; Ryder et al. 2007). We previously demonstrated that "
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    • "The ΔsadC and ΔsiaD mutants defective for SadC and/or SiaD DGC were constructed by allelic displacement as previously described (Irie et al., 2012). "
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    • "In nonmucoid strains, Psl and/or Pel are the major exopolysaccharides components of the biofilm matrix. Psl contains a repeating pentasaccharide consisting of D-man nose, D-glucose and L-rhamnose (Byrd et al., 2009), which serves as a scaffold and as a signalling molecule to stimulate biofilm formation (Irie et al., 2012). Noticeably, Psl has been shown to be produced only by certain P. aeruginosa strains, such as PAO1 but not PA14 (Friedman & Kolter, 2004b). "
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