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Chapter 18 : Alternative Autoinducer-2 Quorum-Sensing Response Circuits: Impact on Microbial Community Development

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Abstract:

Caries and periodontal disease are biofilm-mediated diseases that remain widespread and serious health problems. The dental biofilm is a complex microbial community that can comprise up to 700 bacterial species. Recent studies have made substantial progress in defining these signaling circuits and the impact that bacterial communication has on the formation and persistence of the dental biofilm. Several distinct classes of autoinducers have been identified, including numerous structurally distinct acylhomoserine lactones (AHLs), oligopeptides, quinolones, and derivatives of tetrahydrofuran. LuxS is an enzyme in the activated methyl cycle which functions in the turnover of S-adenosylhomocysteine (SAH) and generation of S-adenosylmethionine. To determine if influenced virulence properties, the expression of several genes that contribute to virulence was analyzed after inactivation of . Real-time PCR revealed that the expression of numerous genes encoding proteins involved in iron acquisition and storage was significantly altered in the mutant. Biofilm growth was restored to wild-type levels either by transforming the mutant strain with a functional copy of or by the addition of partially purified AI-2 to the growth medium. To determine if AI-2 represents a true quorum-sensing signal, Rezzonico and Duffy compiled and searched a microbial genome database for known AI-2 receptors, i.e., LuxQP and LsrB, and then compared the distribution of these proteins with published studies that examined quorum-sensing phenotypes in the organisms. The widespread distribution of LuxS in both gram-negative and gram-positive bacteria has led to the suggestion that AI-2 represents a universal quorum-sensing system that mediates interspecies communication.

Citation: Demuth D, Novak E, Shao H. 2011. Alternative Autoinducer-2 Quorum-Sensing Response Circuits: Impact on Microbial Community Development, p 263-280. In Kolenbrander P (ed), Oral Microbial Communities. ASM Press, Washington, DC. doi: 10.1128/9781555817107.ch18

Key Concept Ranking

Gene Expression and Regulation
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Confocal Laser Scanning Microscopy
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Figures

Image of FIGURE 1
FIGURE 1

The AI-2 quorum-sensing circuit of is integrated with two other quorum-sensing pathways that respond to an AHL signal (HAI-1) and a signal of unknown structure (CAI-1). AI-2 is bound by the periplasmic receptor LuxP, which interacts with the sensor kinase LuxQ. At low cell density (LCD), LuxQ functions as a kinase and initiates a phosphorelay through LuxU and the σ-dependent response regulator LuxO. Activation of LuxO results in the induction of a family of small quorum regulatory RNAs (Qrr sRNAs), which, in conjunction with Hfq, regulate the expression of LuxR, the master regulator of the AI-2 response. At high cell density (HCD), LuxQ functions as a phosphatase and phosphate flow is reversed. The expression of the sRNAs is reduced, leading to increased expression of LuxR and induction of the luciferase operon and other AI-2-dependent genes.

Citation: Demuth D, Novak E, Shao H. 2011. Alternative Autoinducer-2 Quorum-Sensing Response Circuits: Impact on Microbial Community Development, p 263-280. In Kolenbrander P (ed), Oral Microbial Communities. ASM Press, Washington, DC. doi: 10.1128/9781555817107.ch18
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Image of FIGURE 2
FIGURE 2

Biofilm growth of fimbriated is AI-2 dependent. Biofilms of wild-type (DF2200N) and LuxS-deficient (DF2200N_luxS) strains were grown for 16 h in 96-well polystyrene plates and quantified by staining with crystal violet and measuring the optical density at 575 nm (O.D.575nm). Total biomass was greater for the fimbriated strains than for afimbriated strains (not shown) but exhibited the same dependency for AI-2. Sham-infected wells were incubated with brain heart infusion (BHI) broth without bacteria.

Citation: Demuth D, Novak E, Shao H. 2011. Alternative Autoinducer-2 Quorum-Sensing Response Circuits: Impact on Microbial Community Development, p 263-280. In Kolenbrander P (ed), Oral Microbial Communities. ASM Press, Washington, DC. doi: 10.1128/9781555817107.ch18
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Image of FIGURE 3
FIGURE 3

Potential model integrating LsrR-mediated regulation of genes involved in the cellular response to AI-2 and the operon itself in ( ) and proposed for This mechanism is dependent on LsrR interaction with both unphosphorylated and phosphoryated forms of AI-2. At low cell density, LsrR represses the operon as well as numerous other genes that contribute to biofilm formation. As cell density increases, AI-2 is imported via an Lsr-independent mechanism and intracellular concentrations of the signal increase but remain below the level at which AI-2 is efficiently phosphorylated by LsrK. Binding of AI-2 by LsrR results in derepression of quorum-sensing-regulated genes such as those involved in biofilm growth. As cell density increases further, intracellular levels of AI-2 increase, AI-2 is phosphorylated by LsrK, and the operon is derepressed. As a result, extracellular AI-2 is rapidly internalized by the Lsr transporter and catabolized by LsrFG, effectively terminating the quorum-sensing response.

Citation: Demuth D, Novak E, Shao H. 2011. Alternative Autoinducer-2 Quorum-Sensing Response Circuits: Impact on Microbial Community Development, p 263-280. In Kolenbrander P (ed), Oral Microbial Communities. ASM Press, Washington, DC. doi: 10.1128/9781555817107.ch18
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References

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Tables

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TABLE 1

Biofilm growth of quorum-sensing mutants

Citation: Demuth D, Novak E, Shao H. 2011. Alternative Autoinducer-2 Quorum-Sensing Response Circuits: Impact on Microbial Community Development, p 263-280. In Kolenbrander P (ed), Oral Microbial Communities. ASM Press, Washington, DC. doi: 10.1128/9781555817107.ch18

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