MMI 301 Quorum Sensing

  1. What is quorum sensing
    Cell-cell signaling used to control specific genes, allows coordination of group activities
  2. Best studied system for QS?
    • acyl-homoserine lactone (AHL) QS in proteobacteria
    •     -Many species
    •     -Signals are dedicated
    •     -Made by AHL synthases, bind to protein receptors
    •     -Regulate different things in different species
  3. How does it work (basic)
    All cells send out signals, only when signal concentration is high enough (enough nearby cells) does the gene get transcribed.
  4. How does Pseudomonas aeruginosa us QS?
    When high density, activate genes for virulence and biofilm formation
  5. Biofilms
    • Produced in response to high QS, made of extracellular polysaccharide matrix
    • Large '3D' structures
  6. What kind of QS do Gram +/- use
    • AHL-type=Gram -
    • Peptide-type= Gram +
  7. What synthesizes AHL QS molecules?
    LuxI protein homologs
  8. QS systems in Vibrio fischeri
    • LuxI-->C6-->LuxR
    • AinS-->C8-->AinR
    • Synthase-->Signal-->Regulatory protein
  9. C8 signal pathway
    • C8-->luxO-->litR-->luxR-->luxlCDABEG-->bioluminescence
    • .......................................................C6---^
    • C8 INHIBITS luxO
    • luxO INHIBITS litR
    • litR STIMULATES luxR
    • luxR and C6 STIMULATE luxlCDABEG
  10. Purposes of bioluminescence
    Avoid predators, Attract prey, Interspecies communication
  11. Bobtail squid use what bacteria for light
    Vibrio fischeri
  12. What fischeri strains will survive in bobtail organ
    Ones that produce light (despite being less fit in a 'vacuum')
  13. What are the strains of Fischeri
    GFP and RFP, green and red fluorescent proteins
  14. How to assay for bacterial colonization of bobtail
    • Inoculate squid. 
    • wait.

    either plate/count light organ homogenate or measure light given off by squid.
  15. How is luminescence produced
    • FMNH2+O+RCHO+luciferase->FMN+H2O+RCOOH+Light
    • reduced flavin to oxidized flavin and aldehyde to acid

    In general you have a luciferin turning into an oxy luciferin
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MMI 301 Quorum Sensing
MMI 301