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
