Tuesday, May 17, 2011

IB Biology on Microbes, Biotechnology, Prokaryotes, Option F

IB Biology, Microbes, Biotechnology and Prokaryote, Option F
Quorum Sensing by Bacteria Vibrio Fischeri and Bobtail squids
Keywords are 
Symbiosis, Autoinducers, Quorum Sensing, Bioluminescence, Biofilm, Aggregates, Quorum quenching


Ted Talk on Bacteria Communication using Quorum Sensing

Quorum Sensing
Quorum Sensing was observed in Vibrio fischeri, a bioluminiscent bacterium that lives as a mutualistic symbiont in Hawaiian bobtail squid.
Bacteria used it to coordinate behavior/control their population density by producing signalling molecules known as autoinducers which are used to regulate gene expression.
How it works!
Squid has a built-in flashlight uses bacteria to help navigate night waters, hunt for prey, and hide from predators. A little cavity on squid's underside houses colonies of bacteria known as Vibrio fischeri.
Cilia sweep bacteria from water into the cavity, once the colony reaches critical density population it produces autoinducers which acts as communication tool that control gene regulation to release an bioluminescent enzyme called luciferase leading to bioluminescence.

Mutual Beneficial Symbiotic Relationship ( Endosymbiotic )
Bobtail_squid
How Bacteria Benefit from Squid?


Squid feed the bacteria with amino acids and nutrients.
How Squid Benefit from Bacteria?
At Night, squid uses bacteria light to hide its silhouette/shadow whereby bacteria able to produce enough light from the bottom (bio flashlight) to match the amount of light striking the top. (antipredator devise).


During Day, squid releases the bacteria into water and as conc of bacteria drop, conc of autoinducers drop, and it stop producing light. As day progresses, bacteria conc increases, conc autoinducers increase, and light will be produced again.
How Quorum Sensing Works
  • Bacteria population increases and start to release autoinducers
  • Autoinducers will bind to specific receptors and induce the release of enzyme luciferase
  • Enzyme luciferase will cause bioluminescence
  • Bacteria population drops, autoinducers will drops and light will not be produced.
  • Production of autoinducers/bioluminescence is dependent on population density of bacteria
  • Bacteria Communicate/Talk with each other
TedTalk, Bacteria Communication using intramolecular signal.

    Click HERE for more videos on how bacteria communicate using secreted chemical signals molecules called autoinducers. 
    Keywords from TedTalk are
    • Bacteria Communication using Quorum Sensing
    • Bacteria acts collectively using intramolecular/ intermolecular signals called autoinducers
    • Once reaches a population density, chemical signals will be released and bacteria will attack
    • Cell to cell communication signal is used to regulate production of virulence factors/biofilms
    • Develop anti-quorum sensing agent to block bacteria communication or block production of virulence factors
    • Anti-Quorum Sensing drugs as replacement for Antibiotics( most bacteria are resistant against antibiotics now)

    "Latest New Discovery News on 16 May 2011
    NASA's Endeavour space shuttle will be carrying a peculiar live cargo: a creature named, Hawaiian Bobtail Squid to study the effect of microgravity environment on the squid's ability to be colonized by the bacteria. It is important as our body is also colonised by 90 trillion and 500 different species of bacteria
    .......................................................................................................................................................
    BioFilms
    Biofilm is an aggregation of microorganisms due to secretion of a protective/adhesive extracellular matrix called extracellular polymeric substance (EPS). Biofilm protects pathogens from immune system/ antibiotics, making bacteria resistant against antibiotics. Infectious biofilm are urinary tract infections and  formation of dental plaque gingivitis.

    Examples of Biofilm producing bacteria
    Pseudomonas aeruginosa an important opportunistic pathogen found in soil
    Streptococcus mutans which causes dental plaque, material that adheres to teeth.


    Antibiotics is designed to destroy a free living/single cell bacteria but not a community of bacteria (biofilm) which is protected by a sticky layers of cells that act as a shield and prevent antibiotics from destroying the bacteria underneath. Biofilm allows colonies to be increasingly antibiotic resistant.



    Click HERE to view more biofilm formation

    How to Destroy Biofilms produced by Bacteria.
    ScienceDaily (Apr. 11, 2010) — Researchers at North Carolina State University found a chemical when used  with antibiotics, is effective in destroying biofilms produced by antibiotic-resistant strains of bacteria such as the Staphylococcus strain MRSA. Molecules known as 2-aminoimidazoles with antibiotics was effective in dispersing the biofilms created by certain bacterial strains.  
    .......................................................................................................................................................
    Endosymbiotic Theory.
    According to Theory, organelles originated as free-living bacteria were taken inside another cell as endosymbionts. Mitochondria developed from proteobacteria ( Rickettsiales ) and chloroplasts from cyanobacteria. Now, chloroplasts in green plants closely resembled cyanobacteria.
    Cyanobacteria


    2 types of cells in Cyanobacteria
    Nitrogen Fixation Cells in Heterocysts-- fix nitrogen gas into ammonia, nitrites and nitrates.

    Photosynthetic Cells-- containing pigments( phycobilins) to absorb light producing organic carbon (sugar)

    Ex: Cyanobacteria are Nostoc and Spirullina ( sold as food )


    Cyanobacteria form filaments having thick-walled heterocysts, which contain enzyme nitrogenase, vital for nitrogen fixation because enzyme is sensitive to oxygen. 
    Thick Cell Wall on heterocyst, prevents diffusion of oxygen into cells.






    Nitrogenases enzymes have iron/ sulfur (cofactor)  with a heterometal (FeMoCo), a molybdenum and iron which are easily oxidised and destroy by oxygen. Enzymes are sensitive to oxygen.





    Video, Endosymbiotic Theory and Cyanobacteria

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    EndoSymbiotic Nitrogen Fixing Bacteria with Legumes
    Rhizobium forms an endosymbiotic nitrogen fixing association with roots of legumes plants and have nitrogenase enzyme complex which is sensitive to oxygen. It is inactivated when exposed to oxygen, because this reacts with the iron component of the proteins.


    Symbiotic relationship between Rhizobium and legume plant.
    Nitrogenase enzyme contain a heterometal  FeMoCo with a central molybdenum atom which is easily oxidised when exposed to oxygen 
    Rhizobium, the root nodules can contain oxygen-scavenging molecules such as leghaemoglobin.

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