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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