Quorum sensing Flashcards
What are the main regulatory switches of the acute and chronic lifestyles?
Quorum sensing
Gac/Rsm system
c-di-GMP
What is quorum sensing?
Density dependent regulation of gene expression
What are the two quorum sensing regulatory networks?
AHL dependent quorum sensing
AHL independent PQS quorum sensing
What are the two systems of AHL dependent quorum sensing?
Las and Rhl
What is AHL?
N-Acyl Homoserine Lactone
What does AHL dependent quorum sensing involve?
A synthase
A transcriptional regulator
What does the synthase do?
Produces AHL
What is the AHL of the Las system?
3-oxo-C12-HSL
What is the AHL of the Rhl system?
C4-HSL
What is the synthase of the Las system?
LasI
What is the transcriptional regulator of the Las system?
LasR
What is the transcriptional regulator of the Rhl system?
RhlR
What is the synthase of the Rhl system?
RhlI
When the AHL reaches a certain extracellular concentration?
When the population level exceeds a certain level the AHL molecules exceed the threshold concentration and are recognised by transcriptional regulators. The AHL regulatory complex then leads to the expression of various virulence genes
Why are virulence genes expressed in a density dependent manner?
Only want to produce virulence effectors when there are many cells around as then the bacterium will be able to produce high enough quantities to cause an impact. If a single bacterium produced effectors alone they would simply diffuse away
LasR-HSL complex does what?
- Autoinduction by increasing LasI expression
- Induces the production of RhIR
- Activates genes e.g. those producing exotoxin A
RhIR-HSL complex does what?
- Autoinduction by increasing RhlI expression
- Activates genes e.g. those producing rhamnolipids, HCN and pyocyanin
Las system leads to the production of what virulence factors?
Exotoxin A
RhI system leads to the production of which virulence factors?
Pyocyanin, HCN, Rhamnolipids
Relationship between the Las and Rhl systems?
The Las system can directly activate the RhI system through the LasR-HSL complex which directly up-regulates RhlR transcription
What molecule links the activation of T3SS to QS?
Vfr
What is Vfr?
Virulence factor regulator
What is he coactivator of Vfr?
cAMP
Vfr can activate?
Quorum sensing and T3SS
High levels of cAMP favour which lifecycle?
The acute lifecycle
What is the signalling molecule in the AHL independent quorum sensing regulatory network?
PQS
PQS stands for?
Pseudomonas Quinolone Signal
How is PQS made?
Chorismic acid turns into HHQ which is converted into PQS via pqsH
What converts chorismic acid into HHQ?
pqsABCD proteins
What converts HHQ into PQS?
pqsH
Once a certain extracellular concentration of PQS is reached it binds?
pqsR
pqsR-PQS complex then?
Binds to DNA and leads to the activation of the pqsABCDE operon
Increase in PQS= autoinduction
Production of pqsE
Production of pyocyanin
pqsE leads to the production of?
HCN
Pyocyanin
Rhamnolipids
Overall, quorum sensing is more involved with controlling which lifestyle?
Acute lifestyle
