The kinky propulsion of Spiroplasma Anna Tuttle
Microbiology Journal Club
October 13, 2008
How do bacteria move?   Flagellar– helical propellor driven by
rotary motor
 Some, like Spirochetes, have internal
flagellum
  Twitching– extension and retraction of
Type IV pili
  Gliding– slime secretion pushes the cell
forward
All About Spiroplasma   Genus of Mollicutes
  No cell wall
  Cell membrane has cholesterol
  Internal cytoskeleton
  Helical structure
  Descendents of Gram-positives
  Very small genomes
  0.78-2.22 Mb
All About Spiroplasma   Insect, plant, tick,
crustacean hosts
  Plant diseases
  Citris stubborn
disease
  Corn stunt disease
  Many in obligate
insect/ plant
transmission cycles
All About Spiroplasma   Insect diseases
  Sex-ratio
abnormality in
Drosophila
  Suckling mouse
cataract agent
  Cause millions in
damage in CA alone
  Difficult to treat
All About Spiroplasma   1972, found to be
causative agent of Corn
Stunt Disease
  Found to be helical,
motile, and
representative of new
group of pathogens
How do Spiroplasma move? How do Spiroplasma move?   Regular extension and contraction within limits
of helical symmetry
  Spontaneous and random change of helical sense
originating at random sites along the cell
  Forming a deformation on one of the helical turns
and propagating it along the cell
  Random bending, flexing, and twitching
How do Spiroplasma move?   Regular extension and
contraction within
limits of helical
symmetry
  Spontaneous and random
change of helical sense
originating at random sites
along the cell
  Forming a deformation on one
of the helical turns and
propagating it along the cell
  Random bending, flexing, and
twitching
How do Spiroplasma move?   Regular extension and
contraction within limits of
helical symmetry
  Spontaneous and
random change of
helical sense
originating at random
sites along the cell
  Forming a deformation on one
of the helical turns and
propagating it along the cell
  Random bending, flexing, and
twitching
How do Spiroplasma move?   Regular extension and
contraction within limits of
helical symmetry
  Spontaneous and random
change of helical sense
originating at random sites
along the cell
  Forming a deformation
on one of the helical
turns and propagating it
along the cell
  Random bending, flexing, and
twitching
How do Spiroplasma move?   Regular extension and
contraction within limits of
helical symmetry
  Spontaneous and random
change of helical sense
originating at random sites
along the cell
  Forming a deformation on
one of the helical turns and
propagating it along the cell
  Random bending,
flexing, and twitching
Filamentous Structures Underneath the Cell Membrane   Thick and thin
filaments arranged in
parallel
  Anchored to the cell
membrane
  Run the length of the
cell
Determining the Number and Spacing of Individual Filaments   Outer ribbons
  5 thick filaments
  11 nm spacing
  Inner ribbon
  9 thin filaments
  4 nm spacing
Ribbon Arrangement Through the Cell   Ribbons (red and green)
follow helical path from
one end to the other
  One shorter than the
other
  Simultaneous
conformational
changes of adjacent
filament subunits
  Leads to helicity and
ability to change
handedness
How the Cytoskeleton Enables Movement   Assumptions:
  Ribbons connected to
each other
  Inner thin filament ribbon
functions elastically
  Filament length changes
of outer ribbons occur
simultaneously by
switching between 2
conformational states of
filament subunits
How the Cytoskeleton Enables Movement   One ribbon becomes tense by
shortening while the other
relaxes
  Handedness switches at
position where state of
tension and relaxation
reverses
  That point of transition
travels the length of the cell
“Pathogenesis is linked to the ability of
an infectious organism to move
around. If we understand how a
pathogen moves, we can figure out how
to disrupt its movements and decrease
its ability to infect other organisms.”
--- Joshua Shaevitz
Swimming driven by propagaFon of kinks down body of cell Cells and Kink PosiFons Over Time Cell Swimming Parameters Conclusions   Propulsion by waves of lateral displacement that
propagate down the length of the cell
  Waves created by change in handedness of the cell
body that creates 111° bend
  Swimming uses bistable helical cytoskeleton
  New method for movement
QuesFons?