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MICRB 265 General Microbiology

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

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  1. MICRB 265 General Microbiology Doug McFarlane Lecture 26 – Quorum Sensing

  2. 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

  3. Other Global Controls

  4. Today’s Lecture • Intercellular signaling – quorum sensing • Case study: bioluminescence by Vibrio fischeri • http://www.modares.ac.ir/sci/saman_h/Pages/bacterial.htm

  5. 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

  6. 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?

  7. Signaling Molecules • Aka “autoinducers” • E.g. acyl homoserine lactones (AHL) • Gram positives usually use small peptides • AI-1, AI-2

  8. How it Works…

  9. Case Study – Bioluminescence • Bioluminescent bacteria – Photobacterium spp., Vibrio fischeri • Can be free-living or symbiotic Bobtail squid

  10. Anglerfish

  11. 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

  12. Cell-Density vs. Light Emission

  13. 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

  14. 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

  15. 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)

  16. 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

  17. 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

  18. Next Topic • Signal Transduction • 2-component regulatory systems • E.g. Omp C/F in E. coli • E.g. chemotaxis sensing

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