Mic 428 Lecture

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Mic 428 Lecture 5 Microbial Locomotion
Behavioral Responses
(Sections 4.10., 4.11., and 4.12.)
Outline
Motility and its significance. Brief review of
microbial locomotion through flagella. Flagella
in gram-negative and gram-positive
organisms. Other motility modes Gliding
motility. Characteristics, gliding organisms,
mechanisms. Swarming motility. Swarming
organisms, mechanisms. Behavioral responses
Chemotaxis, phototaxis and other taxes.
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Mic 428 Lecture 5 Microbial Locomotion
Behavioral Responses
Basic concepts of microbial locomotion that were
covered in MIC 201, will not be repeated here. If
you need to review those concepts, please read
your textbook or take a look at my website, MIC
201, lecture 6. www.csupomona.edu/gbrelles
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Mic 201 Lecture 6 outline Cell structures and
functions

• Microbial locomotion.
• Flagella and motility.
• Different flagellar arrangements.
• Flagellar structure.

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Why do cells move? Is there any advantage in
being motile?

• Microbial locomotion.
• Flagella and motility.
• Different flagellar arrangements.

Energy expenditure
Flagellar structure the hook and the motor.
Wavelength, flagellin.
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Manner of movement in peritrichously flagellated
prokaryotes. (a) Peritrichous Forward motion is
imparted by all flagella rotating
counterclockwise (CCW) in a bundle. Clockwise
(CW) rotation causes the cell to tumble, and then
a return to counterclockwise rotation leads the
cell off in a new direction.
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Manner of movement in polarly flagellated
prokaryotes
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Gliding motility
Non-swimming, non-flagellated organisms move
across solid surfaces in a process called gliding.
Gliding prokaryotes are generally filamentous or
rod shaped. The morphology of colonies is
distinctive since cells glide and move away from
the center of the colony.
Cyanobacteria, Myxococcus xanthus, Flavobacterium
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Gliding motility
(Courtesy of Patrick Vicente, Jessica Garcia and
Ching Liv, Mic 428 students, Winter 2006)
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Mechanism of gliding motility
In Cyanobacteria slime production.
The slime appears to contact both the cell
surface and the solid surface against which the
gliding cells move.
In Flavobacterium
Movement of proteins in the cell surface likely
driven by energy release from PMF.
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Swarming motility
Typical in Proteus.
Swarming motility is recognized by concentric
rings of growth around the colony.
The mechanism involves periodic morphological
changes at approximately 1-2 hours intervals.
Short flagellated cells that periodically give
rise to highly flagellated and filamentous cells.
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Swarming motility
In Vibrio parahaemolyticus.
In liquid medium they produce polar flagella
while in high-viscosity medium, lateral flagella.
The morphological changes are under genetic
control (laf genes).
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Behavioral responses
Motile prokaryotes are attuned to the chemical
and physical state of their environment and can
move toward or away from various stimuli
presumably as a means of remaining competitively
successful.
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Behavioral responses
Directed movements of the cells to respond to
gradients of physical and chemical agents in
nature. Chemotaxis response to
chemicals. Phototaxis response to
light. Magnetotaxis response to magnetic
fields. Aerotaxis response to oxygen.
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Chemotaxis
Bacteria are too small to sense a gradient across
their body length. They respond to temporal
rather than spatial gradients.
In the absence of gradient, cells move in a
random fashion that includes runs and tumbles.
What happens when there is a gradient?
The random movement becomes biased.
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Chemotaxis in a peritrichously flagellated
bacterium (E. coli)
(a) In the absence of a chemical attractant the
cell swims randomly in runs, changing direction
during tumbles. (b) In the presence of an
attractant runs become biased, and the cell moves
up the gradient of the attractant.
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Different situation with polarly flagellated
organisms Some bacteria can reverse the rotation
of their flagella (Pseudomonas). Other cannot, so
the flagellum stops periodically and during this
time the cell becomes reoriented (Rhodobacter).
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Measuring chemotaxis
(a) Insertion of capillary into a bacterial
suspension. (b) Accumulation of bacteria in a
capillary containing an attractant. (c) Control
capillary contains a salt solution that is
neither an attractant nor a repellent. Cell
concentration inside the capillary becomes the
same as that outside. (d) Repulsion of bacteria
by a repellent. (e) Time course showing cell
numbers in capillaries containing various
chemicals.
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Phototaxis
Advantage for organisms.
Scotophobotaxis True phototaxis
Rhodospirillum centenum