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Quorum sensing in bacterial populations

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Khaled Touny
Khaled Touny

Quorum sensing allows bacteria to communicate via small diffusible molecules and regulate gene expression in response to cell population density. In Gram-negative bacteria, these signaling molecules are usually acylated homoserine lactones. Quorum sensing plays an important role in biofilm formation, allowing bacteria to synchronize behaviors like polysaccharide synthesis and adherence as the biofilm matures.

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Quorum sensing Mechanism of cell to cell signaling or density sensing in bacteria Small diffusible molecules secreted by bacterial cells which when cell density becomes sufficient can be detected by other cells in the population In Gram negative bacteria these molecules are usually derivatives of acylated homoserine lactone (AHL( In Gram positives they are often small peptides A universal autoinducer AI-2 is produced by a number of bacteria and may mediate cross-
adherenceadherence microcolonymicrocolony Synthesis of theSynthesis of the polysacharidepolysacharide biofilmbiofilm Quorum sensingQuorum sensing homoserine -homoserine - lactonelactone NutrientNutrient OxygenOxygen Bacteria lacking lasI produce a loose and easily disrupted biofilmBacteria lacking lasI produce a loose and easily disrupted biofilm
Quorum sensing Autoinducer systems Gram-negative bacteria: - LuxI (autoinducer synthase) - LuxR (activator) - AHL (autoinducer/ co- activator) Bassler (2002) Cell 109: 421. Gram-positive bacteria: - propropeptide - two component system - peptide autoinducer Acylated homoserin e lactone (AHL) Oligo -peptid e Vibrio fisheri Staphylococcus aureus
LuxR/LuxI quorum sensing Gram-negative bacteria(passive diffusion in and out of the cell)
Quorum sensing in Gram positive bacteria Similar to Gram negative bacteria Signal is a peptide Peptide is detected at the cell surface by a two component regulatory system
Quorum sensing in a biofilm
Quorum sensing in a biofilm

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Quorum sensing in bacterial populations

  • 1. Quorum sensing Mechanism of cell to cell signaling or density sensing in bacteria Small diffusible molecules secreted by bacterial cells which when cell density becomes sufficient can be detected by other cells in the population In Gram negative bacteria these molecules are usually derivatives of acylated homoserine lactone (AHL( In Gram positives they are often small peptides A universal autoinducer AI-2 is produced by a number of bacteria and may mediate cross-
  • 2. adherenceadherence microcolonymicrocolony Synthesis of theSynthesis of the polysacharidepolysacharide biofilmbiofilm Quorum sensingQuorum sensing homoserine -homoserine - lactonelactone NutrientNutrient OxygenOxygen Bacteria lacking lasI produce a loose and easily disrupted biofilmBacteria lacking lasI produce a loose and easily disrupted biofilm
  • 3. Quorum sensing Autoinducer systems Gram-negative bacteria: - LuxI (autoinducer synthase) - LuxR (activator) - AHL (autoinducer/ co- activator) Bassler (2002) Cell 109: 421. Gram-positive bacteria: - propropeptide - two component system - peptide autoinducer Acylated homoserin e lactone (AHL) Oligo -peptid e Vibrio fisheri Staphylococcus aureus
  • 4. LuxR/LuxI quorum sensing Gram-negative bacteria(passive diffusion in and out of the cell)
  • 5. Quorum sensing in Gram positive bacteria Similar to Gram negative bacteria Signal is a peptide Peptide is detected at the cell surface by a two component regulatory system
  • 6. Quorum sensing in a biofilm
  • 7. Quorum sensing in a biofilm

Editor's Notes

  1. 50 species of gram-negative bacteria produce AHL that differ only in the acyl side chain moiety. Each LuxR is highly selective for the cognate AHL signal molecule. Gram-positive actively transport peptide autoinducer out of the cell. Phosphorelay system highly specific for given peptide signal.