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Flagella
Slender rigid structures
Approx. 20 nm across and
up to 20 m long
Used for locomotion
(Hair is 57-120 m across)
Flagella distribution
Bacteria differ regarding the
arrangement of flagella
Monotrichous = one
Polar = located at the end
Amphitrichous = one on
each pole
Flagella distribution
Lophotrichous = tuft at one
or both ends
Peritrichous = spread evenly
over the entire surface
Arrangement can be useful
in identification
Flagella ultrastructure
Composed of three parts:
Filament
Hook
Basal body
Some bacteria have sheaths
surrounding their flagella
Flagella ultrastructure
Flagella ultrastructure
Flagella ultrastructure
C-ring contains proteins involved in the rotation of the flagella
Flagella ultrastructure
Gram negative
Gram positive
Have four rings
Have two rings
Flagella synthesis
Involves more than 20 genes
Mechanism related to type
III secretion systems
Filament is a hollow tube
composed of flagellin and
ending with a capping
protein
Flagella synthesis
The hook is made of
different protein subunits
Basal body is composed of
several different proteins
Flagella synthesis
Other proteins are involved
in the transport of subunits
across the membrane
Protein subunits travel down
the hollow filament and are
incorporated into the end of
the growing flagella
Flagella synthesis
Chemotaxis
Rotation of flagella propels
cell through the environment
E. coli flagella can rotate
270 rps
V. alginolyticus flagella can
rotate 1,100 rps
Chemotaxis
Rotation of flagella in
counter-clockwise direction
usually results in
running/swimming
Rotation in opposite
direction results in tumbling
(random movement)
Chemotaxis
When in the presence of a
gradient of attractant,
amount of time spent in run
vs. tumble mode increases
Chemotaxis
Exact mechanism of flagella
movement not yet
understood
Basal body may rotate
within a membrane bound
ring of proteins (rotor and
stator)
Chemotaxis
Rotation is driven by proton
and sodium ion gradients
and not ATP
Chemotaxis
Controlled by a twocomponent phosphorelay
system
Chemicals bind to
chemoreceptor on cell
surface
Che A = sensor kinase
Che Y = response regulator
Chemotaxis
Different levels of
phosphorylation of proteins
in response to the presence
of attractant or repellent
influences the direction of
rotation
Chemotaxis
Attractant
Repellent
Archaeal flagella
Are quite different from bacterial flagella
Subunits may be added to filament from the cytoplasmic side
(like pili)
Pili/fimbriae
Conjugation pili differ from
other pili/fimbriae
Conjugation pili are usually
wider and longer than other
pili/fimbriae (9-10 nm wide
vs. 3-10 nm wide)
Pili/fimbriae
Are composed primarily of a
single protein
Many have special adhesive
proteins located on the tip
Can aid in attachment to
various surfaces
Pili/fimbriae
Many pathogenic bacteria are dependent on pili/fimbriae for their
ability to cause disease
e.g. urinary tract and kidney infections
Pili also help bacteria to attach to surfaces in the environment
Attachment often followed by production of a slime layer/biofilm
Pili/fimbriae
Unlike flagella, pilus
subunits are added to the
growing rod from the
bottom
Outer membrane complex
required in gram-negative
bacteria
Pili/fimbriae
Some pili/fimbriae are
responsible for a type of
motility referred to as
twitching motility
(Type
IV pili)
Caused by extension and
retraction of adherent pili