Quorum sensing Flashcards
how does Bioluminescence work?
- 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).
Give an example of symbiotic relations with bioluminescence bacteria and animals
- 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
what are the 4 main types of signal molecules in Quorum Sensing
- Acyl-homoserine lactones (AHL)
- Streptomyces gamma-butrolactones
- AI-2 family
- Oligopeptide autoinducers
what are the other types of singalling molecules of Quorum sensing
- 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
What are the quorum sensing regulatory functions controlled in Gram negatives
- Bioluminescence
- Virulence factors
- Conjugal plasmid transfer
- motility
- cell aggregation
- starvation response
- symbiosis with plants
Why are IIA Biofilms important in human infection
- 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
how is IIa biofilm formed
- 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
How are signals transmitted into the cells
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.
Quorum sensing in Vibrio fischeri
- LuxR is the cytoplasmic receptor of AHL and transcriptional activator of the luciferase luxICDABE operon
- Luxl is AHL synthase
- AHL membrane permeable signal
Quorum sensing using peptides and two component regulatory systems
- 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
Quorum Sensing in Staphylococcus aureus
- 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
Quorum sensing in V. harveyi QS
- 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
Quorum sensing in P. aeruginosa QS
Series circuit controls virulence factor production
- Amplification: LasR positivly regulates LasI
- Temporal control: LasR regulates RhI
How in quorum sensing detected between different cells species
- GFP implanted into ones DNA after promoter QS regulated promoter
- Biosensor used to detect it.
Example of higher organism listening to bacterial communication
- swr regulatory system of serratia liquefaciens MG1 regulates biocontrol activity against the shoot pathogen alternaria alternata
Whats Quorum Quenching
- 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
examples of quorum Quenching
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
Degradation of homoserine lactones by active enzymes (quorum sensing)
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.
Plant derived Quorum sensing blockers (quorum quenching)
- 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.
Whats the effect of C-30 on growth and expression of virulence factors
- growth isnt changed
- Exoprotease decreased
- pyoverdin decreased
- chitinase decreased
used to clear lungs of P aeruginosa
What is the effect of galic on P. aeruginosa biofilms
Decreases the resistance and pathogenicity
Why is quorum sensing a good thing
- used instead of anitbiotics to reduce resistance
- used in industry to increase yields (aIIA expression in tobacco and potato)
