Quorum sensing

Question 1

definition of QS behaviours

Answer 1

behaviours that are not productive as an individual but are effective by the simultaneous action of a group of cells

Question 2

systems regulated by QS (5)

Answer 2

bioluminescence
virulence factor expression
biofilm formation
sporulation
mating

Question 3

what are most QS systems based on?

Answer 3

autoinducers

simple diffusible signalling molecules

Question 4

types of autoinducer (2)

Answer 4

AHLs (acylated homoserine lactones)

short oligopeptides

Question 5

what is the difference between G-ve and G=ve autoinducers?

Answer 5

G-ve autoinducers can diffuse across the membrane while G+ve cannot

Question 6

QS in G-ve example

vibrio fischeri : LuxI/R

Answer 6

LuxI protein makes autoinducer

concentration of autoinducer increases until it binds to LuxR

LuxR becomes an active transcription factor

Turns on expression of luciferase operon (+ feedback)

Question 7

QS in G+ve example

staph aureus

Answer 7

AgrD makes the autoinducer

AgrD is actively exported from the cell through AgrB which cuts and circularises it so AgrD cannot get back in

AgrD binds to AgrC, a detector and histidine kinase

AgrC phosphorylates the RR AgrA

AgrA-P activates the transcription of target genes which includes
virulence
secreted factors
QS circuit itself (+ feedback)

ensures staph aureus will only be virulent when there are enough cells

Question 8

Summary

Answer 8

small molecules like ppGpp and cyclic di GMP are important in cell signalling

secondary messengers are: cAMP, c-di-GMP, ppGpp

they can be used in circuits to measure cell density

can serve as alarmones that bring about global changes in gene expression

Question 9

cAMP

Answer 9

when phosphorylates affects

CAP protein

produces transcription of virulence factors including motility (NOT biofilm formation), catabolism of alt. sources

CAP: Catabolite activator protein
cAMP-CAP is required for transcription activation of the lac operon (involved in catabolism)