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PRESENTATION ON
QUORUM SENSING
What is Quorum sensing?
The ability of a bacteria to communicate with other bacteria is called QUORUM SENSING
Instead of a language, bacteria use signaling molecules to communicate
These signaling molecules are released into the environment
Bacteria also measure the number of signaling molecules
BACTERIAL TALK
The biological definition of QUORUM SENSING
The phenomenon whereby the accumulation of signaling molecules enable a single cell to sense the number of bacteria
These bacteria use various different types of signaling molecules
QUORUM SENSING is intensively studied in different organisms e.g Marine bacteria and several pathogenic bacteria
Why do bacteria talk to each other?QUORUM SENSING enables bacteria
to co-ordinate with each otherTo respond quickly in order to survive
the environmental changesResponses include: Adaptation to availability of nutrients Biofilm formation (defense) Avoidance of toxic compounds
Types of signaling molecules
Oligopeptides in gram-positive bacteria
N-Acyl Homoserine Lactones in gram-negative bacteria
Family of auto-inducers in both gram-positive and gram-negative
Diseases associated with biofilm include: Chronic bacterial prostatitis Chronic rhinosinusitis Cystic fibrosis pneumonia
Mechanism:
QS bacteria secrete signaling molecules and has receptors that detect the signaling molecules
Inducer + Receptor —› Trancription of certain
genes(inducer
synthesis)
Mechanism
Signaling molecules secreted Detected by surrounding bacteria
Activation of receptor only when inducer conc. Passes a threshold
Up-regulation if specific genes Transcription in all cells at same time
Cell – Cell communication
E.g Bioluminescence in V.fischeri
History of Auto-inducers
Marine bioluminescence bacteria -V.fischeri cultured in liquid medium
Shows bioluminescence in high conc. Conclusion: Inhibitor in the media removed by
high cell density Scientists – Kempner & Hamson
worked(1968)
Other Scientists: Nealson & Eberhard detected the presence of (activator molecules) AUTO-INDUCERS instead of inhibitors in the media
Molecule produced in V.fischeri was 1st isolated and characterized by Eberhard (1981)
Identified as N-(3-oxohexanoyl)-homoserine lactone (3-oxo-C6-HSL).
V.fischeri
Marine bacteriumFree-living or in symbiotic
association with fish /squidColonises in specialised light organs
causing bioluminescenceHelp the squid Euprymna scolopes to
attract prey and camoflage.No bioluminescence in free-living
state
V.fischeri
Quorum sensing in V.fischeri At low cell densities, the luxICDABE genes (luxCDABE
genes are responsible for bioluminescence) are transcribed at a low level and the small amounts of 3-oxo-C6-HSL produced diffuse out of the cell
At high cell densities, 3-oxo-C6-HSL accumulates in the local environment and therefore also inside the cell.
Transcription of luxICDABE appears to be increased by a complex of the LuxR protein and 3-oxo-C6-HSL binding to a region of DNA called the lux box. In this way the 3-oxo-C6-HSL autoinduces its own synthesis and hence amplifies the quorum sensing signal.
Quorum sensing in V.fischeri
V.harveyi
Rod-shaped,gram-negative, bioluminescent,marine
No growth at 4 ̊C and above 35 ̊C found free-swimming in tropical marine
waterscommensally in the gut microflora of
marine animals, and as both a primary and opportunistic pathogen of marine animals
Milky seas effect
The cellular structure of V. harveyi, whose polar flagella help to facilitate quorum sensing by allowing it to move rapidly towards an attractant (other V. harveyi cells) and establish high cell densities.The cellular structure of V. harveyi, whose polar flagella help to facilitate quorum sensing by allowing it to move rapidly towards an attractant (other V. harveyi cells) and establish high cell densities.The cellular structure of V. harveyi, whose polar flagella help to facilitate quorum sensing by allowing it to move rapidly towards an attractant (other V. harveyi cells) and establish high cell densities.
V.harveyi
Quorum sensing in V.harveyi
Applications
Degrade the signaling molecules preventing bacteria to communicate called QUORUM QUENCHING
Prevent bacteria to become pathogenic thus finally prevent cell inflamation,damage and toxicity
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