Quorum sensing

Question 1

processes dependent on sufficient population size

Answer 1

virulence factor production

biofilms

bioluminescence

ABs

Question 2

bacterial communication

• mediated by
• signal intensity shows
• used to regulate…?

Answer 2

production + sensing of chemical signals

population density

gene expression

Question 3

symbiotic example

• what is it?
• benefits

Answer 3

V. fischeri colonise specialised crypt (light organs) of bobtail squid

bacteria - get nutrients
squid - get bioluminescence
(counter-illumination)

Question 4

V. fischeri

- when do they produce light?

Answer 4

at certain cell density
- waste of time to produce if just 1 cell

only in squid
- squid survives -> bacteria survive

Question 5

quorum sensing

Answer 5

LuxI produces autoinducer molecules (Als)

favourable enviro -> bacteria increase -> more Als

• > activates LuxR
• > transcribes genes

Question 6

autoinducers (AIs)

• what are they?
• types in Gram -ve and +ve
• universal types

Answer 6

signalling molecules
- same core region but different chain lengths

Gram -ve
= acyl-homoserine lactones

Gram +ve
= oligo peptides

Universal
= furanosyl borate diester

Question 7

QS systems

- 3 key principles

Answer 7

1. members of community generate AIs
2. AIs detected by receptors on membrane/in cytoplasm
3. AI detection
   -> further AI production (feed-forward effect)
   + activation of QS regulated traits

Question 8

feed forward effect

Answer 8

increases signal intensity
-> facilitates synchronisation

(all cells in population can detect AIs + upregulate gene expression)

Question 9

2 component systems
- what do they do?

• most common e.g.

Answer 9

senses external signals + relays into cell

sensor kinase (SK) system

Question 10

sensor kinase system

Answer 10

1. SK recognises signal
2. internal kinase domain phosphorylated at His residue
3. interacts with response regulator + transfers P
4. active response regulate modulates gene expression

Question 11

2nd component of SK system

Answer 11

response regulator

Question 12

QS control of virulence in P. aeruginosa

Answer 12

opportunistic G-ve pathogen

in CF lung infections

forms biofilm

virulence regulated by QS
- 3 circuits interact

Question 13

P. aeruginosa

- 3 interacting circuits

Answer 13

las IR circuit
rhl IR circuit
PQS circuit

Question 14

exploiting QS to control bacteria

• QS interfering drug
• key principle

Answer 14

Las + Rhl
= targets for anti-virulence/ anti-biofilm agents
-> develop receptor inhibitors

disrupt bacterial communication + coordination of gene expression

Question 15

G+ve QS systems

Answer 15

AIPs synthesised as inactive precursors

-> activated in transporter or after secretion

Question 16

S. aureus

Answer 16

commensal

- opportunistic

Question 17

QS in S. aureus

Answer 17

low densities
= low AI conc
-> cells express adhesins
.:. stick during initial phases of infection

high densities
= high AI conc
-> express toxins
.:. release more nutrients + move to new site