Surface Motility

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Surface Motility
a) Swarming - flagella
b) Twitching Type IV pili (Retractile
motility)
c) Gliding - ?
d) Spreading - passive
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Harshey, 2003, Ann Rev. Microbiol
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In 1980, Bradley proposed that pili retract based
on the following observations with pili-tropic
phages of P. aeruginosa 1. Phage-resistant
mutants had either no pili or were
hyperpiliated. 2. Both kinds of mutants did not
twitch. 3. Non-piliated mutants did not bind
phage. 4. Wild-type cells had phage located at
junction of pili and cell pole. 5. Hyperpiliated
mutants had phage at random points along pili but
not at the base. These mutants were later
shown to be defective in pilT, required for pili
retraction. 6. Antibodies to pili inhibited both
twitching and phage infection.
Conclusion Pili are necessary but not
sufficient retraction is required for both
phage infection and twitching
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Pili are thinner than flagella
Fluorescently labeled Type IV pili of P.
aeruginosa
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Model of Type IV pili assembly and retraction
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P. aeruginosa fliC gmR Cells labeled with
Cy3, an amino-specific fluorescent dye Placed
on quartz slide and observed at quartz-water
interphase
Skerer and Berg, PNAS, 2002
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Movies (http//www.rowland.o
rg/labs/bacteria/index_movies.html ) Individual
pili on the same cell appeared to extend and
retract independently. Extension per se was not
associated with cell movement, but rather with
retraction after attachment at their distal
tip. Filaments that emerge after retraction are
just as fluorescent, suggesting that the
subunits are recycled. Some cells moved,
others didnt. Might be due to how strongly the
cell body was stuck to the quartz. Apparently,
the distal tip is serving as a non-specific
adhesin. Unlike flagella, which push a cell from
the rear, pili pull a cell from the front
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P. aeruginosa has 4 Che operons and 26 MCPs!
Chp operon controls twitching and pili biogenesis
in P. aeruginosa
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Life Cycle of Myxococcus xanthus
Vegetative growth A and S motility
Starvation S motility to aggregate, and
then fruiting body development
A adventurous gliding motility by single
cells S social Type IV pili-mediated motility
by groups of cells
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Adventurous vs Social motility
http//cmgm.stanford.edu/devbio/kaiserlab/about_my
xo/about_myxococcus.html
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Fruiting Body Development
http//cmgm.stanford.edu/devbio/kaiserlab/about_my
xo/about_myxococcus.html
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Pili retraction observed in M. xanthus
using bright field microscopy Cell can be
tethered from either A or B end and move forward
from either end
Hypothesis Pili can alternate ends!
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Extracellular polysaccharides mediate pilus
retraction during social motility of
Myxococcus xanthus Li et al. 2003
PNAS 100 5443-5448
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• S motility requires
• TFP
• Extracellular fibril material
• 3. LPS (O-antigen)

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M. xanthus has 9 Che operons!
Frz controls cell reversals and chemotaxis Dif
controls fibril biogenesis Others control
development Functions inferred from homologies
to E. coli. Details unknown.
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What is the role of fibrils in twitching motility?
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Lack of fibrils does not affect pilus synthesis
Western blot of Pilin
A whole cells B Cell surface 1 Wild
type Rest Fibril mutants
Fibril mutants have more pilin on the cell surface
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TEM
Wild-type Fibril mutant 3-5
pili 9-10 pili 3-5 mM gt20
mM
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Rescue of hyperpiliation with wild-type cells or
fibril
A wt fibril-(hyperpiliated) B pil-
fibril- C 1-3 fibril- 4 O antigen-
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TEM
Wild-type Fibril mutant Mutant
fibril 3-5 pili 9-10 pili
3-5 mM gt20 mM
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Is the fibril material degrading
pilin? OR Is the pilus retracting like in the
movie?
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A purified pilin, - and fibril B suface
pilin from wt or fibril- pilT (retraction-
mutant) C wt does not rescue the
hyperpiliation on the pilT mutant
Fibril material is not degrading pilin but likely
helping its retraction
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Model of Type IV pili assembly and retraction
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Fibril treated with protease (lane 2) still
rescues hyperpiliation
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Why are fibril- mutants hyperpiliated?
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Binding appears to be separate from the pulling
force
What is this force and how is binding sensed?
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Che-Dif system communicates TFP signals to
EPS-Dif system
Black et al., Mol. Microbiol. 2006
TFP positively regulate EPS, EPS triggers TFP
retraction
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Pole-to-Pole Oscillations of a Bacterial Gliding
Motility Protein Science 2005, 310855-857
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Surface Motility
a) Swarming - flagella
b) Twitching Type IV pili (Retractile
motility)
c) Gliding - ?
d) Spreading - passive
Mycoplasma