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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?
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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