Abstract
IntroductionAutoinducer-2 (AI-2) quorum sensing is a bacterial communication system that responds to cell density. The system requires luxS activity to produce AI-2, which can regulate gene expression and processes such as biofilm formation.AimTo investigate the role of luxS in biofilm formation and gene expression in the nosocomial pathogen Klebsiella pneumoniae .MethodologyA ΔluxS gene deletion was made in K. pneumoniae KP563, an extensively drug-resistant isolate. AI-2 production was assessed in wild-type and ΔluxS strains grown in media supplemented with different carbohydrates. Potential roles of luxS in biofilm formation were investigated using a microtiter plate biofilm assay and scanning electron microscopy. Quantitative RT-PCR evaluated the expression of lipopolysaccharide (wzm and wbbM), polysaccharide (pgaA), and type 3 fimbriae (mrkA) synthesis genes in wild-type and ΔluxS mutant biofilm extracts.ResultsAI-2 production was dependent on the presence of luxS. AI-2 accumulation was highest during early stationary phase in media supplemented with glucose, sucrose or glycerol. Changes in biofilm architecture were observed in the ΔluxS mutant, with less surface coverage and reduced macrocolony formation; however, no differences in biofilm formation between the wild-type and ΔluxS mutant using a microtiter plate assay were observed. In ΔluxS mutant biofilm extracts, the expression of wzm was down-regulated, and the expression of pgaA, which encodes a porin for poly-β−1,6-N-acetyl-d-glucosamine (PNAG) polysaccharide secretion, was upregulated.ConclusionRelationships among AI-2-mediated quorum sensing, biofilm formation and gene expression of outer-membrane components were identified in K. pneumoniae . These inter-connected processes could be important for bacterial group behaviour and persistence.
Highlights
Autoinducer-2 (AI-2) quorum sensing is a bacterial communication system that responds to cell density
Relationships among AI-2-m ediated quorum sensing, biofilm formation and gene expression of outer-m embrane components were identified in K. pneumoniae
Comparisons were made for K. pneumoniae KP563 wild-type, ΔluxS mutant and the ΔluxS mutant complemented with pACYC184 carrying the KP563 luxS gene
Summary
Autoinducer-2 (AI-2) quorum sensing is a bacterial communication system that responds to cell density. Quorum sensing (QS) is a cell-to-cell communication system that allows bacteria to regulate biological functions in response to changes in population density, acting as a mechanism for environmental adaptation [1, 2]. The system is controlled by the production, secretion and detection of extracellular signalling molecules called autoinducers. Two main classes of autoinducers are defined by two systems, termed Type I QS and Type II QS. In Type I QS, the autoinducer-1 molecules are N-acyl homoserine lactone (AHL) derivatives. In Type II QS, the signalling molecules are known as autoinducer-2 (AI-2) [3, 4]. Unlike Type I QS, which is a highly specific system used
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