Quorum Sensing

Quorum Sensing

Dr. Abdelraouf A. Elmanama

Being part of a community  Bacteria

are single celled microorganisms  Thought of being small independent factories

Dr. Abdelraouf A. Elmanama

Scale of microbial interaction

 Vast  Microbes

interact with each other and their environment  Never get a microbe on its own, always present in communities  Interaction is crucial for microbial cell survival

Dr. Abdelraouf A. Elmanama

?Some justified questions  Why

is it important for bacteria to communicate?  What sort of mechanisms can they use to do this?  How is specificity achieved?

Dr. Abdelraouf A. Elmanama

Strange behaviors There were some questions regarding the behavior of some types of bacteria   

Luminescent bacteria (light production) Staphylococcus aureus (toxin production) Pseudomonas aeruginosa (virulence factors)

Dr. Abdelraouf A. Elmanama

Answers From the bacteria point of view Why waste energy to produce light when that light is not enough to attract attention

Dr. Abdelraouf A. Elmanama

Answers From the bacteria point of view Why produce toxin when in fact the amount is not enough to produce disease. In the contrary, this small amount of toxin will induce immune response and lead to their destruction

Dr. Abdelraouf A. Elmanama

Conclusion Bacteria are some sort of smart cells or more correctly were created to be smart Bacteria communicate so that they can orchestrate activity that cannot be achieved by a single cell

The question remain how they knew that their number is small

Dr. Abdelraouf A. Elmanama

Quorum Sensing Bacteria use quorum sensing to mastermind behaviors, including • Mating • Releasing toxins • Causing disease (virulence)

Dr. Abdelraouf A. Elmanama

The language HSLshomoserine lactone

N-(3-oxohexanoyl) homoserine lactone (OHHL)

Dr. Abdelraouf A. Elmanama

Families of HSLs 

There are many N-acyl homoserine lactones (AHLs)



It is a diffusible molecule and is found in the growth medium of Gram –ve bacteria



There are many related molecules in the AHL family and they differ from each other by the length of the acyl side chains (4, 6, 8,10, 12, 14C) and substitutions (oxo or hydroxy) at the C3 position of the N-linked acyl side chain

Dr. Abdelraouf A. Elmanama

Role of HSL in bioluminescence in Vibrio fischeri

 At

low cell densities, V. fischeri is not bioluminescent  As cells reach late exponential, early stationary phase, luminescence is induced and persists into late stationary phase

Dr. Abdelraouf A. Elmanama

Bioluminescence

Bioluminescent bacteria can be cultured on both liquid and solid medium. When they have reached a high cell density their light emission can be visualised by the naked eye.

Dr. Abdelraouf A. Elmanama

Induction of bioluminescence inVibrio fischeri

3 growth OD600 nm

2 bioluminescence 1 10

Dr. Abdelraouf A. Elmanama

Time (h)

30

40

Genes encoding luminescence Thelux operon

R

I

C

D

A

B

E

Gene luxA luxB

encodes for 2 subunits of luciferase enzyme

luxC luxD luxE

multi-enzyme fatty acid reductase

luxI luxR

regulatory elements

Dr. Abdelraouf A. Elmanama

General principle of density-dependant signalling  Cells

make a signalling molecule (AHL) constitutively  The AHL diffuses freely out of the cell into the surrounding medium  As the population of the cells grow, so does the concentration of AHL in the growth medium  When the population (and hence AHL) concentration reaches a threshold, the AHL moves back down its concentration gradient into the cell Dr. Abdelraouf A. Elmanama

.Cont

 The

concentration of AHL inside the cell now increases and AHL can bind to luxR – the transcriptional activator protein  The luxR-AHL conjugate activates gene expression  This system is often referred to as “autoinduction”

Dr. Abdelraouf A. Elmanama

Autoinduction Vibrio fischeri produces AHLs

a self induced molecular “gene on” switch

outside inside

Autoinducer N-acyl homoserone lactones LuxI is an enzyme capable of synthesising AHLs

LuxI OFF lux genes

Autoinduction Vibrio fischeri produces AHLs

a self induced molecular on switch

AHLs

outside inside

LuxI AHLs are small molecules which rapidly diffuse out from the cell

OFF lux genes

Autoinduction a self induced molecular on switch

Vibrio fischeri + High concentrations of AHLs, diffuse back into the cell down its concentration gradient

AHLs outside LuxR

LuxR transcriptional regulator unable to activate lux operon without AHLs

OFF lux genes

inside

Autoinduction Vibrio fischeri + High concentrations of AHLs

a self induced molecular on switch

outside inside luciferase

LuxR-AHL complex binds to promoter region of the lux operon, activating transcription

ON LuxR lux genes

When does autoinduction occur? When AHLs reach a critical level

Critical [AHL] Specific Genes ON

i.e. target genes regulated in a cell densitydependent manner

[AHLs]

Increasing Cell Density

Low cell density AHLs below critical level

High cell density AHLs at critical level

Opportunities

  

AHL signalling is involved in expression of virulence of many human (and other) pathogens Interfering with such signalling may be the basis of a new class of anti-microbials Natural inhibitors have already been identified – a furanone isolated from a marine algal species (luminescent marine bacteria are never found forming biofilms on the surface of marine algae)

Dr. Abdelraouf A. Elmanama

 New

Drug Lead Fights Bacteria that Can Be Lethal by Disrupting Quorum Sensing and Biofilms

Dr. Abdelraouf A. Elmanama

‫وإن من شيء إل يسبح بحمده ولكن‬ ‫ل تفقهون تسبيحهم‬ ‫) السراء‪(44:‬‬

‫‪Dr. Abdelraouf A. Elmanama‬‬