Topic 2-L7 - Movement of bacterial cells Flashcards
Motility:
The ability to propel your own movement
Example of bacteria that isn’t motile
Yersinia pestis.
Flagellum is a
large, complex, multi-protein machine that powers bacterial movement
Flagellum includes a
long, thin filament that acts like a propeller. It is rotated using a motor that is anchored in the cell envelope.
Rotation of flagellum propels cell, enabling the cell to
“Swim” and “swarm”
Flagella can be built at different
positions along the cell – different bacteria have different numbers/arrangements
5 types of different flagella types of cells
A) Peritrichous (many across pole/body)
B) Monotrichous or Polar (single – at pole)
C) Lophotrichous (many, all at one pole)
Not shown – amphitrichous – (both poles) Not shown – atrichous (no flagella at all)
Flagella rotate in both directions?
YES
Longer “runs” –
Counterclockwise rotation, helical bundle formed at tail of cell - cell moves forward
Short “tumbles” –
one or more flagella rotate clockwise – bundle falls apart – bacteria tumbles, assumes new, random orientation
Bacteria with a reversible flagellum, rotation in
opposite directions reverses direction of movement
unidirectional flagella –
rotation stops/starts. Random movement during “stops” change direction of bacterium
3 segments of the flagellum:
1) filament
2) hook
3) basal body
Filament
(long, thin propeller – drives movement)
Hook
(adaptor that connects filament to
the basal body)
Basal body.
Core of the structure. Powers rotation of filaments
Flagella motor function
Harnesses proton motive force to drive rotation
The Central rod in the flagella motor passes through a series of rings:
MS ring (cytoplasmic membrane) C ring (cytoplasm) P ring (peptidoglycan) L ring (outer membrane)
Stator in the flagellar motor couples the
flow of protons to rotation of the MS ring – behaves like a “proton turbine”
MS ring
rotates rod…and ultimately
hook and filament.
L/P rings act like
bearings (or bushings) to help rotation
C ring important for:
generating torque, switching motor direction, flagellin secretion
Gram Positive Flagellum lacks
P/L rings
– only contains C/MS rings
The long filament that drives movement in the flagellum is made of thousands of copies of a single protein called
flagellin
flagellin
Filament is rigid, helical and hollow
- Free at one end (out in environment) –
connected to motor (via rod, hook) at
other end - Highly conserved in bacteria
Synthesis of the flagellum
Made form inside out
Flagellin is produced in
cytoplasm
Flagellin is
secreted via the “export apparatus” through a thin pore in the basal body/hollow filament - assembles filament with help of cap proteins
The sport of flagellin through
“Type III secretion system”
“Type III secretion system”
a related system is used as a protein toxin injection system by certain
bacterial pathogens
Spirochetes have a flagellum (“axial filament”) that resides in periplasm –
rotation results in corkscrew motion of entire bacterium
Flagellar motility if often highly regulated –
even motile bacteria can adopt atrichous/non-motile state
Taxis is the
directed movement of bacteria. Accomplished using a “bias random walk”
Chemotaxis:
Movement in the direction of gradients of increasing or decreasing concentration to particular chemical(s) (via chemoreceptors)
If bacterium moving toward desirable nutrient, tumbles inhibited –
longer runs.
If bacterium moving away from desirable nutrient, tumbles inhibited –
More frequent tumbles
Phototaxis:
Movement toward/away from light
Aerotaxis:
Directed motility in response to O2
twitching motility
Non-flagellar movement
twitching motility, in which a
Type IV pilus attaches to a surface and then retracts
-Sort of like a grappling hook
