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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 sensing”Quorum 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
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
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.