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Дом ученых и специалистов Реховота

декабрь, 2012 г.


Bacterium as a Model
for Biological Systems

(К докладу на семинаре в Бейт Оле 24 декабря)

 

Itzhak Fishov. Израиль

 

Properties of the LIVING SYSTEM

 

1. Increase of order and decrease of enthalpy –> flow of energy and matter.

2. Conservation of properties –> multiplication, homeostasis.

3. Adaptation, evolution –> mutations.

 

Why Bacteria may serve as a model?

  • Difference and similarity with eukariotes.

  • Simplicity

  • Growth in definite conditions Mutations

  • Genetic Exchange

    ARTHUR KORNBERG,
    Ten Commandments: Lessons
    from the Enzymology of
    DNA Replication.
    J. Bact., 2000, 182:3613–3618.

     

    II. TRUST THE UNIVERSALITY OF BIOCHEMISTRY AND THE POWER OF MICROBIOLOGY

     

    “What’s true for E. coli is true for elephants,
    and what’s not true for E. coli is not true.”


    What are Microbes?

    What are Microbes?

    relative sizes of different microorganisms:



    bacterial cell, 1 x 3 μm (Heliobacterium modesticaldum)



    (Madigan et al., Fig. 2.2)

    yeast cell, 8 μm dia (Saccharomyces cerevisiae)



    comparative structure of prokaryotic and eukaryotic cells:



    (Madigan et al., Fig 2.1)

     

    1. prokaryotic: nucleoid, no organelles

    2. eukaryotic: nucleus, organelles

     



    Bacteria in human body



    Berg RD. The indigenous gastrointestinal microflora.
    Trends Microbiol. 1996, 4(11):430-5


    impact of microorganisms on human affairs:





    A brief history of microbiology



    Prokaryotic cell structure



    Spatial organization of bacterial cell

    Dividing Escherichia coli



    1. cell
    2. nucleoid
    3. FtsZ ring

    A cycling cell is a growing cell and
    a growing cell is a cycling cell

     

    Continuous and discontinuous processes. The growth process is drawn as a circle to depict its continuity. The different sizes of the circles represent different growth rates. The discontinuous processes like DNA replication, segregation and cell division cause the cell to “cycle”.

     

    The principal questions
  • How does the growing cell trigger the initiation of DNA replication?

  • How does the cell coordinate the order of the DNA segregation and subsequent cell division?

  • How does the cell separate sister nucleoids and position the division site?

  •  

      

      

    Multiple points of coordination exist
    between cell cycle events


     

    Curr Opin Microbiol. 2008 Apr;11(2):94-9.

    The great divide: coordinating cell cycle events during bacterial growth and division.

    Haeusser DP, Levin PA.

     

    Thinking about bacterial populations as multicellular organisms



    CORE CONCEPTS OF BACTERIAL MULTICELLULARITY

    1. Bacterial cells have communication and decision-making capabilities that enable them to coordinate growth, movement, and biochemical activities

    2. Examples of communication and coordinated behaviors are widespread (possibly ubiquitous) among bacterial taxa and are not limited to a few groups with a specialized multicellular vocation.

    3. Bacterial populations derive adaptive benefits from multicellular cooperation and their ability to integrate the diverse activities of different cells. These benefits include (but are not limited to):

  • (a) More efficient proliferation resulting from a cellular division of labor;

  • (b) Access to resources and niches that cannot be utilized by isolated cells;

  • (c) Collective defense against antagonists that eliminate isolated cells; and

  • (d) Optimization of population survival by differentiation into distinct cell types.

  •  

    Quorum sensing

    * A mechanism for bacteria to monitor one another presence and to modulate gene expression in response to changes in population density.

    Quorum sensing

    Quorum sensing is the means by which bacteria “talk” to each other

    Quorum sensing

    Bacteria produce and secret autoinducer molecules that are detected by other bacteria

    As the population grows, more bacteria secret the autoinducer and its concentration rises until reaching a threshold

    After reaching the threshold autoinducer concentration the culture begins simultaneous gene expression


    Why quorum sensing?

    The advantage: regulation of behavior that is only productive when carried out by many cells together

    * Sporulation



    Secretion of virulence factors





    * Conjugation


    * Bioluminescence

    *Biofilm formation

     

    The use of those properties may be for:

  • Cooperation

  • But also competition between individuals living in the same environmentCould they serve as an interkingdom tool?

    Thinking about bacterial populations as multicellular organisms



    Bacterial fine art





    The beginnings of multicellularity and architecture?

     

    Fruiting bodies of the myxobacterium Chondromyces crocatus. The fruiting bodies of myxobacteria can contain 105–106 cells (for Myxococcus and Dictyostelium).


    Biofilm…?!

     

  • A Biofilm is a community of microorganisms attached to a solid surface in aqueous environments. A Biofilm community can include bacteria, fungi, yeasts, protozoa, and other microorganisms.

  • Although microorganisms can have an independent planktonic existence, more than 90% of bacteria reside within a Biofilm.

  • Collective behavior

     

    Complex differentiation and collective behavior have been demonstrated for a number of different organisms under a variety of different situations:

  • Myxococcus - differentiate when starved to form elaborate fruiting bodies

  • Anabaena-during heterocyst development

  • Bacillus subtilis - metamorphosis into spores

  • Serratia liquefaciens - migration of populations by means of swarming motility


  • Biofilm structure



    Why do bacteria form biofilms?



    Stages of Biofilm formation



    Biofilms and pathogenesis

     

  • 1. There are 2 cases in which treatment with antibiotics is not effective:

  • 2. Bacteria that are innately antibiotic resistant

  • Bacteria that reside within a biofilm

  • Biofilm bacteria can be up to 1,000-fold more resistant to antibiotic treatment than the same organism grown planktonically

  • 3 mechanisms:

  • 1. phenotypic changes in bacteria

  • 2. inactivation of the antibiotics by extracellular polymers

  • 3. nutrient limitation resulting in slowed growth rate


  • There is a connection between quorum sensing and biofilm maturation



    Scanning confocal microscope images of a mature P. aeruginosa wild-type biofilm (left) and a quorum-sensing mutant biofilm (right).

    This can be used to affect the bacteria’s virulence and help fight diseases

     

    декабрь, 2012 г.    

    Copyright © Itzhak Fishov



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