Quorum sensing

Question 1

how does Bioluminescence work?

Answer 1

• Caused by bioluminescent bacteria of genera Vibrio and Photmicrobium
• its the bacterial luciferin that causes it and it occurs due to chemical reaction

(FMNH2 + O2 + RCHO (luciferin) →FMN +RCOOH (oxy luciferin) + H2O + blue light).

-The reaction is catalyzed by luciferase (luxA/B).

Question 2

Give an example of symbiotic relations with bioluminescence bacteria and animals

Answer 2

• V. fischeri and bobtail squid

during the day it bobtail squid spits out V. fischeri and burrows to avoid predators and at night once their poulation size is larger it uses luminescence to lure in its prey

• luminescence only occurs once a lot of bacteria which is evidence that QUORUM SENSING is occurring

Question 3

what are the 4 main types of signal molecules in Quorum Sensing

Answer 3

• Acyl-homoserine lactones (AHL)
• Streptomyces gamma-butrolactones
• AI-2 family
• Oligopeptide autoinducers

Question 4

what are the other types of singalling molecules of Quorum sensing

Answer 4

• 2-heptyl-3-hydroxy-4-quinolone (Pseudomonas QS signal or PQS
• cis-11-methyl-2-dodecenoic acid from Xanthomonas (diffusible signal factor or DSF)
• 3-hydroxy-palmitate methyl ester, (3-OH-PAME) from Ralstonia
• diketopiperazines cyclo-(L-Leu-L-Val) and cyclo( -Ala-L-Val), respectively, from Pseudomonas

Question 5

What are the quorum sensing regulatory functions controlled in Gram negatives

Answer 5

• Bioluminescence
• Virulence factors
• Conjugal plasmid transfer
• motility
• cell aggregation
• starvation response
• symbiosis with plants

Question 6

Why are IIA Biofilms important in human infection

Answer 6

• Dental biofilms caries gigivitis and periodontitis
• Causes pneumonia in CF patients
• Artificial surfaces on humans in catheters, contact lenses and prothetic joints
• difficult to eradicate as antibiotic resistant and resist phagocytosis

Question 7

how is IIa biofilm formed

Answer 7

• single planktonic cell sticks in environmental cues and initial interaction
• developmental signals between cells
• mature biofilm formed
• detached cells start new biofilms

pilA gene is essential for growth into mushroom stalks and WT expressed at the tops

Question 8

How are signals transmitted into the cells

Answer 8

the signal can either bind to protein and bind to cell receptor or bind directly to receptor itself and mediate a response

or can diffuse straight through or pass through import protein to start a response.

Question 9

Quorum sensing in Vibrio fischeri

Answer 9

• LuxR is the cytoplasmic receptor of AHL and transcriptional activator of the luciferase luxICDABE operon
• Luxl is AHL synthase
• AHL membrane permeable signal

Question 10

Quorum sensing using peptides and two component regulatory systems

Answer 10

• Gram Positives communicate using modified Oligopeptides as signals and two component type membrane bound histidine kinase receptors. the signalling is mediated by phosphorylation cascade that influences the activity of a DNA binding transcriptional regulatory protein ( response regulator)
• peptides can be used with ABC transporter which incorporates with other proteins as precursor locus to regulate DNA

Question 11

Quorum Sensing in Staphylococcus aureus

Answer 11

• using TCR detects external peptides AIP. which regulates P2 and P3.
• P2 controls expression of RNAIII which increases secreted factors and inhibits cell adhesion proteins.

P3 contoles expression of agrB/D/C/A

• AgrA is the response regulator
• AgrC is receptor protein with histidine Kinase

Question 12

Quorum sensing in V. harveyi QS

Answer 12

• its a hybrid system with two circuits in parallel which converge to regulate common set of target genes
• Luxs and AI-2 present in many G-s
• 4 possible input states AL-1 + AL-2
  Al-2, AL-1, nothing.
• alteration in gene expression requires both autoinducers concurrently

Question 13

Quorum sensing in P. aeruginosa QS

Answer 13

Series circuit controls virulence factor production

• Amplification: LasR positivly regulates LasI
• Temporal control: LasR regulates RhI

Question 14

How in quorum sensing detected between different cells species

Answer 14

• GFP implanted into ones DNA after promoter QS regulated promoter
• Biosensor used to detect it.

Question 15

Example of higher organism listening to bacterial communication

Answer 15

• swr regulatory system of serratia liquefaciens MG1 regulates biocontrol activity against the shoot pathogen alternaria alternata

Question 16

Whats Quorum Quenching

Answer 16

• role of quorum sensing is global control of physiology of bacterial populations.
• in niches in which populations compete the ability for one to disrupt quorum sensing gives one bacterial advantage
• likewise a hosts ability to stop sensing prevents colonisation

Question 17

examples of quorum Quenching

Answer 17

Prokaryote-prokaryote
- bacterial antagonists (s.aureus)

Proteases

• Lactonases (AiiA) and acylases (AACs) are found in AHL producers/ non producers
• bacillus AiiA destroys AHLs required for plant pathogen virulence factors roduction
• Transgenic potato and tobacco plants expressing AiiA are resistant to Erwinia infections

Eukaryote-prokaryote

seaweed
- halogenated furanones inhibit pseudomonas biofilms and seeatia swimming

Human airway epithelial cells

• Membrane associated activity that degrades Pseudomonas C12 HSL but not C4 HSL
• synthetic halogenated furanones abrogate pneumonia in mouse model

Question 18

Degradation of homoserine lactones by active enzymes (quorum sensing)

Answer 18

Little has been known about the degradation of AHLs until recently a lactonase has been identified from bacillus which opens the lactone ring. So the AHL is no longer active. Lactonase from A, A, B, K have been isolated and shown to be active. There are 11 putative lactonases fromgenome sequence analysis. All these lactonases have a conserved motif of HXHXDH_H which have some similarity to glyoxalaseII and to B-lactamse. These proteins are known to bind zinc and the lactonases are also proposed to be a metalloenzyme.

Question 19

Plant derived Quorum sensing blockers (quorum quenching)

Answer 19

• Delisea pulchra is rarely fouled in nature due to the production of halogenated secondary metabolites that exibit strong anti fouling properties
• Furanone C56 blocks quorum sensing and biofilm production.
  P.aeruginosa PAO1 was grown in flow chambers in the presence or absence of C56
  when C56 is added the AHL production decreases and later population size follows.

Question 20

Whats the effect of C-30 on growth and expression of virulence factors

Answer 20

• growth isnt changed
• Exoprotease decreased
• pyoverdin decreased
• chitinase decreased

used to clear lungs of P aeruginosa

Question 21

What is the effect of galic on P. aeruginosa biofilms

Answer 21

Decreases the resistance and pathogenicity

Question 22

Why is quorum sensing a good thing

Answer 22

• used instead of anitbiotics to reduce resistance

- used in industry to increase yields (aIIA expression in tobacco and potato)