CH391L/S12/Locomotion

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[[Category:CH391L_S12]]
[[Category:CH391L_S12]]
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==Locomotion==
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=Locomotion=
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===Flagella===
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==Flagella==
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[[Image:Nrmicro1900-f1.jpg | thumb | 100px| Jarrell and McBride 2008 ]]
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[[Image:Nrmicro1900-f1.jpg | thumb | 200px| Structure of ''Escherichia coli'' flagellum <cite>Jarrell2008</cite> ]]
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The bacterial flagellum is the most common and thoroughly studied prokaryotic motility structure. It resembles a spinning propeller-like structure that is used for swimming in aqueous environments and in some organisms enables swarming across solid surfaces.  The flagellum is a very complex organelle consisting of over 20 proteins (''flg'', ''flh'', ''fli'', ''flj'' variants) and as many as 30 proteins assisting in regulation and assembly.  Each ''Escherichia coli or Salmonella'' cell typically has 6-8 structures.  The export system for assembly of the structure represents a classical Type III secretion system (T3SS).  The main structure consists of 3 main substructures: the basal body, which anchors the structure in the cell membrane and contains the motor; the filament which acts as the propeller; and the hook, a joint which connects the basal body and filament.  Rotation of the filament to generate movement is driven by the proton motive force, whereby H<sup>+</sup> atoms crossing the cell membrane interact with the motor proteins (''MotA'', ''MotB''), inducing a conformational change that turns the rotor.  This rotation can reach speeds of 18,000rpm and propel the cell 25-35uM per second.
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The bacterial flagellum is the most common and thoroughly studied prokaryotic motility structure. It resembles a spinning propeller-like structure that is used for swimming in aqueous environments and in some organisms enables swarming across solid surfaces.  The flagellum is a very complex organelle consisting of over 20 proteins (''flg'', ''flh'', ''fli'', ''flj'' variants) and as many as 30 proteins assisting in regulation and assembly.  Each ''Escherichia coli or Salmonella'' cell typically has 6-8 structures.  The export system for assembly of the filament structure represents a flagellum-specific Type III secretion system (T3SS) in which flagellin subunits are passaged through the hollow flagellar filament structure to the distal end for assembly.  The main structure consists of 3 main substructures: the basal body, which anchors the structure in the cell membrane and contains the motor; the filament which acts as the propeller; and the hook, a joint which connects the basal body and filament.  Rotation of the filament to generate movement is driven by the proton motive force, whereby H<sup>+</sup> atoms crossing the cell membrane interact with the motor proteins (''MotA'', ''MotB''), inducing a conformational change that turns the rotor.  This rotation can reach speeds of 18,000rpm and propel the cell 25-35uM per second.
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====Chemotaxis====
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===Flagellar Chemotaxis===
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[[Image:CheY.jpg |left| thumb | 100px ]]
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[[Image:CheYp.png |left| thumb | 200px|Regulation of flagellar rotation<cite>Sweeney2011</cite>]]
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The rotation of the flagellum and the direction of movement is often regulated by sensory stimuli, allowing the cell to migrate towards attractive signals.  In ''E.coli'' this is achieved through a signal transduction system that controls the phosphorylation state of the response regulator protein ''CheY''.  In the absence CheY-P the flagellum rotates CWW in a "run" state.  The presence of CheY-P, signals induces a switch to CW rotation resulting in "tumbling".  When an attractant binds to a receptor it initiates a conformational change and downstream cascade that leads to decreased levels of CheY-P, in response cells tumble less frequently and will move towards the attractant.
+
The rotation of the flagellum and the direction of movement is often regulated by sensory stimuli, allowing the cell to migrate towards attractive signals.  In ''E.coli'' this is achieved through a signal transduction system that controls the phosphorylation state of the response regulator protein ''CheY''.  In the absence CheY-P the flagellum rotates CWW in a "run" state.  The presence of ''CheY-P'', induces a switch to CW rotation resulting in "tumbling" which randomly reorients the cell.  When an attractant binds to a receptor it initiates a conformational change and downstream cascade that leads to suppression of CheA, a protein that normally phosphoryates ''CheY'' to ''CheY-P''. The absence of ''CheY-P'' causes the flagellum to remain in the "run" state leading to migration towards the signal.  A third protein, ''CheZ'' helps regulate the circuit by preventing the accumulation of ''CheY-P'' through dephosphorylation.
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The 2009 Imperial College of London igem team attempted to engineer ''e.coli'' chemotaxis towards malate so that cells would migrate towards plant roots (which excrete malate).  The ''e.coli'' cells could then be taken up by the plant and deliver auxin (indole 3-acetic acid [IAA]) to promote root growth.  To do this they introduced a malate chemoreceptor from ''Pseudomonas aeruginosa'' and demonstrated that cells tended to be in the run state more often when exposed to malate [http://2011.igem.org/Team:Imperial_College_London/Tour 2009 Team Auxin].
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===Gas Vesicles===
 
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[[Image:Serratia gas vesicles.jpg |right| thumb | 100px | Ramsey [[PNAS]] 2011 ]]
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==Gas Vesicles==
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Some aquatic bacteria use hollow gas-filled vesicles to provide buoyancy and enable them regulate their position in the water column. Prototrophic bacteria may use the vesicles to find regions with appropriate light intensity<cite>Damerval1991</cite>, similarly aearobic bacteria may use them to float to oxygenated surface waters.  Gas vesicles are commonly observed and studied in aquatic cyanobacteria, but have recently been discovered in ''Serratia sp.'', an enterobacterium <cite>Ramsey2011</cite>.  Typically 10-14 ''gvp'' genes are involved in vesicle formation.  It has been shown that gas vesicles from ''Anabaena'' are permeable to H<sub>2</sub>, N<sub>2</sub>, 0<sub>2</sub>, C0<sub>2</sub>, CO, CH<sub>4</sub>, and Ar <cite>Walsby1971</cite>.
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[[Image:Serratia gas vesicles.jpg |right| thumb | 200px | Conical gas vesicles in ''Serratia sp''<cite>Ramsey2011</cite> ]]
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Some aquatic bacteria use hollow gas-filled vesicles to provide buoyancy and enable them regulate their position in the water column.  Prototrophic bacteria may use the vesicles to find regions with appropriate light intensity<cite>Damerval1991</cite>, similarly aearobic bacteria may use them to float to oxygenated surface waters<cite>Beard2002</cite> .  Gas vesicles are commonly observed and studied in aquatic cyanobacteria, but have recently been discovered in ''Serratia sp.'', an enterobacterium <cite>Ramsey2011</cite>.  Typically 10-14 ''gvp'' genes are involved in formation of the hollow, gas-filled cylindrical structures with conical caps.  It has been shown that gas vesicles from ''Anabaena'' are permeable to H<sub>2</sub>, N<sub>2</sub>, O<sub>2</sub>, CO<sub>2</sub>, CO, CH<sub>4</sub>, and Ar <cite>Walsby1971</cite>.
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===Cytoskeletal===
 
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==Chemotaxis==
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The 2009 Groningen igem team cloned the gas vesicle operon from ''Bacillus megaterium'' and put it under the control of an Arsenite sensitive promoter.  In the presence of Arsenite the cells will make gas vesicles and become buoyant [http://2009.igem.org/Team:Groningen/Project Groningen 2009].
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==Twitching Motility==
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==References==
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[[Image:twitch4.jpg |left| thumb | 150px | Mattick 2002<cite>Mattick 2002</cite> ]]
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Many species of bacteria including ''Pseudomonas aeruginosa'',''Neisseria gonorrhoeae'' and ''Myxoccocus xanthus'' use a Type IV pilus (T4P) system for motility.  Cell propulsion by T4P involves pilus extension, attachment, and then pilus retraction.  This process results in a jerky pattern of movement, hence the name "Twitching motility".  Cells move at rates of 0.05 - 1 uM per second and close proximity to other cells is usually required for efficient movement.  The process of pilus extension and retraction involves the ATP-dependent assembly or disassembly of PilA monomers in the pilus fiber.
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[[Image:twitch3.jpg |center| thumb | 200px | Kearns 2010 ]]
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[http://www.youtube.com/watch?v=m1vJKz_bV7U Video of ''Pseudomonas aeruginosa'' twitching movement]
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==Gliding Motility==
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[[Image:slime.jpg |right| thumb | 150px | Slime production in ''Myxococcus xanthus''<cite>Zussman2011</cite>]]
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Many diverse bacterial species have been to observed to be motile on a solid surface without the aid of a flagella or pilus.  Major progress in explaining this "gliding" mechanism as exemplified by ''Myxococcus xanthus'' has only recently been made.  2 models help explain the gliding movement, the slime secretion model and the focal adhesion model.  Both models likely play a role in this form of locomotion and appear to be powered by the proton motive force.
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===Slime Model===       
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It has been observed that most gliding bacteria tend to leave behind a trail of polysaccharide "slime" as they travel.  It has been hypothesized that the extrusion of this slime could provide force to push the cells forward.  Nozzle structures have been observed by electron microscopy at the cell poles with ribbons of slime exiting the structures.  However, the exact role of slime secretion in gliding motility is still a topic of much debate and speculation.
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===Focal Adhesion Model===
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[[Image:gliding.jpg |left| thumb | 150px | Focal adhesions/motor complexes in ''Myxococcus xanthus''<cite>Zussman2011</cite>]]
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In this model, large focal adhesion complexes extend from the cell and connect the extracellular surface to actin-like cytoskeletal filaments.  Motor proteins attached to the intracellular portion of the focal adhesion push backwards and move the focal adhesion along the cytoskeletal filament to move the cell forward.
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=References=
<biblio>
<biblio>
 +
#Jarrell2008 pmid=18461074
#Ramsey2011 pmid=21873216
#Ramsey2011 pmid=21873216
#Walsby1971 pmid=4337701
#Walsby1971 pmid=4337701
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#Mattick2002 pmid=12142488
#Damerval1991 pmid=1904525
#Damerval1991 pmid=1904525
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#Zussman2011 pmid=21910630
 +
#Beard2002 pmid=12167531
 +
#Sweeney2011 pmid=21933915

Current revision


Contents

Locomotion

Flagella

Structure of Escherichia coli flagellum [1]
Structure of Escherichia coli flagellum [1]

The bacterial flagellum is the most common and thoroughly studied prokaryotic motility structure. It resembles a spinning propeller-like structure that is used for swimming in aqueous environments and in some organisms enables swarming across solid surfaces. The flagellum is a very complex organelle consisting of over 20 proteins (flg, flh, fli, flj variants) and as many as 30 proteins assisting in regulation and assembly. Each Escherichia coli or Salmonella cell typically has 6-8 structures. The export system for assembly of the filament structure represents a flagellum-specific Type III secretion system (T3SS) in which flagellin subunits are passaged through the hollow flagellar filament structure to the distal end for assembly. The main structure consists of 3 main substructures: the basal body, which anchors the structure in the cell membrane and contains the motor; the filament which acts as the propeller; and the hook, a joint which connects the basal body and filament. Rotation of the filament to generate movement is driven by the proton motive force, whereby H+ atoms crossing the cell membrane interact with the motor proteins (MotA, MotB), inducing a conformational change that turns the rotor. This rotation can reach speeds of 18,000rpm and propel the cell 25-35uM per second.


Flagellar Chemotaxis

Regulation of flagellar rotation[2]
Regulation of flagellar rotation[2]

The rotation of the flagellum and the direction of movement is often regulated by sensory stimuli, allowing the cell to migrate towards attractive signals. In E.coli this is achieved through a signal transduction system that controls the phosphorylation state of the response regulator protein CheY. In the absence CheY-P the flagellum rotates CWW in a "run" state. The presence of CheY-P, induces a switch to CW rotation resulting in "tumbling" which randomly reorients the cell. When an attractant binds to a receptor it initiates a conformational change and downstream cascade that leads to suppression of CheA, a protein that normally phosphoryates CheY to CheY-P. The absence of CheY-P causes the flagellum to remain in the "run" state leading to migration towards the signal. A third protein, CheZ helps regulate the circuit by preventing the accumulation of CheY-P through dephosphorylation.


The 2009 Imperial College of London igem team attempted to engineer e.coli chemotaxis towards malate so that cells would migrate towards plant roots (which excrete malate). The e.coli cells could then be taken up by the plant and deliver auxin (indole 3-acetic acid [IAA]) to promote root growth. To do this they introduced a malate chemoreceptor from Pseudomonas aeruginosa and demonstrated that cells tended to be in the run state more often when exposed to malate 2009 Team Auxin.



Gas Vesicles

Conical gas vesicles in Serratia sp[3]
Conical gas vesicles in Serratia sp[3]

Some aquatic bacteria use hollow gas-filled vesicles to provide buoyancy and enable them regulate their position in the water column. Prototrophic bacteria may use the vesicles to find regions with appropriate light intensity[4], similarly aearobic bacteria may use them to float to oxygenated surface waters[5] . Gas vesicles are commonly observed and studied in aquatic cyanobacteria, but have recently been discovered in Serratia sp., an enterobacterium [3]. Typically 10-14 gvp genes are involved in formation of the hollow, gas-filled cylindrical structures with conical caps. It has been shown that gas vesicles from Anabaena are permeable to H2, N2, O2, CO2, CO, CH4, and Ar [6].


The 2009 Groningen igem team cloned the gas vesicle operon from Bacillus megaterium and put it under the control of an Arsenite sensitive promoter. In the presence of Arsenite the cells will make gas vesicles and become buoyant Groningen 2009.

Twitching Motility

Mattick 2002[7, 8]
Mattick 2002[7, 8]

Many species of bacteria including Pseudomonas aeruginosa,Neisseria gonorrhoeae and Myxoccocus xanthus use a Type IV pilus (T4P) system for motility. Cell propulsion by T4P involves pilus extension, attachment, and then pilus retraction. This process results in a jerky pattern of movement, hence the name "Twitching motility". Cells move at rates of 0.05 - 1 uM per second and close proximity to other cells is usually required for efficient movement. The process of pilus extension and retraction involves the ATP-dependent assembly or disassembly of PilA monomers in the pilus fiber.

Kearns 2010
Kearns 2010

Video of Pseudomonas aeruginosa twitching movement


Gliding Motility

Slime production in Myxococcus xanthus[9]
Slime production in Myxococcus xanthus[9]

Many diverse bacterial species have been to observed to be motile on a solid surface without the aid of a flagella or pilus. Major progress in explaining this "gliding" mechanism as exemplified by Myxococcus xanthus has only recently been made. 2 models help explain the gliding movement, the slime secretion model and the focal adhesion model. Both models likely play a role in this form of locomotion and appear to be powered by the proton motive force.

Slime Model

It has been observed that most gliding bacteria tend to leave behind a trail of polysaccharide "slime" as they travel. It has been hypothesized that the extrusion of this slime could provide force to push the cells forward. Nozzle structures have been observed by electron microscopy at the cell poles with ribbons of slime exiting the structures. However, the exact role of slime secretion in gliding motility is still a topic of much debate and speculation.

Focal Adhesion Model

Focal adhesions/motor complexes in Myxococcus xanthus[9]
Focal adhesions/motor complexes in Myxococcus xanthus[9]


In this model, large focal adhesion complexes extend from the cell and connect the extracellular surface to actin-like cytoskeletal filaments. Motor proteins attached to the intracellular portion of the focal adhesion push backwards and move the focal adhesion along the cytoskeletal filament to move the cell forward.





References

  1. Jarrell KF and McBride MJ. . pmid:18461074. PubMed HubMed [Jarrell2008]
  2. Sweeney EG and Guillemin K. . pmid:21933915. PubMed HubMed [Sweeney2011]
  3. Ramsay JP, Williamson NR, Spring DR, and Salmond GP. . pmid:21873216. PubMed HubMed [Ramsey2011]
  4. Damerval T, Castets AM, Houmard J, and Tandeau de Marsac N. . pmid:1904525. PubMed HubMed [Damerval1991]
  5. Beard SJ, Hayes PK, Pfeifer F, and Walsby AE. . pmid:12167531. PubMed HubMed [Beard2002]
  6. Walsby AE. . pmid:4337701. PubMed HubMed [Walsby1971]
  7. Nan B and Zusman DR. . pmid:21910630. PubMed HubMed [Zussman2011]
  8. Mattick JS. . pmid:12142488. PubMed HubMed [Mattick2002]
All Medline abstracts: PubMed HubMed
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