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-

talk between species

adherenceadherence microcolonymicrocolony

Synthesis of theSynthesis of thepolysacharidepolysacharide

biofilmbiofilm

“ “Quorum sensing”Quorum sensing”

homoserine -homoserine -lactonelactone

NutrientNutrientOxygenOxygen

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 homoserine lactone (AHL)

Oligo -peptide

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