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MICRB 265 General Microbiology. Doug McFarlane Lecture 26 – Quorum Sensing. Last Lecture. Negative and positive control of transcription Effectors in each system Global regulation s -factors Catabolite repression The lac operon Negative, positive, and global control.

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micrb 265 general microbiology

MICRB 265 General Microbiology

Doug McFarlane

Lecture 26 – Quorum Sensing

last lecture
Last Lecture
  • Negative and positive control of transcription
    • Effectors in each system
  • Global regulation
    • s-factors
    • Catabolite repression
  • The lac operon
    • Negative, positive, and global control
today s lecture
Today’s Lecture
  • Intercellular signaling – quorum sensing
    • Case study: bioluminescence by Vibrio fischeri
    • http://www.modares.ac.ir/sci/saman_h/Pages/bacterial.htm
quorum sensing
Quorum Sensing
  • Ability to sense the presence of high numbers of other bacteria in their environment
  • 8.10 in Brock; exercise 11 in lab
  • Some actions are useless unless done in coordination with large numbers of cells
    • E.g. toxin production
quorum sensing examples
Quorum Sensing – Examples
  • Biofilm formation (E.g. Pseudomonas aeruginosa in CF)
  • Production of virulence factors, such as toxins (E.g. S. aureus)
  • Secretion of extracellular enzymes (E.g. Natronococcus occultus)
  • Bioluminescence (E.g. Vibrio fischeri)

Evolutionary forerunners to hormone systems in Eukaryotes?

signaling molecules
Signaling Molecules
  • Aka “autoinducers”
  • E.g. acyl homoserine lactones (AHL)
  • Gram positives usually use small peptides
  • AI-1, AI-2
case study bioluminescence
Case Study – Bioluminescence
  • Bioluminescent bacteria – Photobacterium spp., Vibrio fischeri
  • Can be free-living or symbiotic

Bobtail squid

bug 16 vibrio fischeri
Bug #16 – Vibrio fischeri
  • Bacteria; Gram-negative
  • Free-living or symbiont of the bobtail squid – colonizes light organs
  • Luminescence takes place only when [bacteria] reaches a certain threshold  quorum sensing
  • Expelled from squid in the morning
  • New culture grows up at night  quorum
bug 16 vibrio fischeri1

Vibrio auto-inducer

Bug #16 – Vibrio fischeri
  • AHL – autoinducer molecule (VAI)
  • Lux operon:
    • Negative control
    • Positive control

LuxI = autoinducer synthase

LuxR = repressor protein

LuxAB = luciferase

LuxCDE = proteins involved in recycling fatty acid to aldehyde

light producing reaction
Light-Producing Reaction
  • FMNH2 + aldehyde + O2

FMN + H2O + fatty acid + light

    • Catalyzed by luciferase
  • FMNH2 produced when oxidizing energy source (like NADH+)
  • Facultative anaerobes, but require O2 for bioluminescence
biotech applications of the lux system
Biotech Applications of the lux System
  • Can be used to…
    • Track cells in a body
    • “Tag” proteins or cell components
    • Biosensor system (e.g. Ptod - toluene)
    • Find/study promoters
  • Example paper
  • Similar to the b-galactosidase reporter system used in lab (Ex. 11)
biosensor toluene
Biosensor – Toluene
  • Ptod – lux C D A B E
  • Transcription regulated by repressor protein – blocks Ptod
  • Inducer: toluene
  • Immobilized cells with biosensor plasmid
  • Expose cells to industrial effluent
  • Light detection  positive for toluene
bacterial communications
Bacterial Communications
  • Not always species-specific (cross-talk)
  • Some “eavesdropping”
  • Sensing what else is out there to establish survival strategy
    • More “us” than “them”?
  • Some signaling molecules also serve as bacteriocides
  • Potential targets for new antimicrobial drugs
next topic
Next Topic
  • Signal Transduction
  • 2-component regulatory systems
    • E.g. Omp C/F in E. coli
    • E.g. chemotaxis sensing