The Gliding Motility of Myxobacteria

Nan Chen and Yi-lin Wu Advisor: Prof. Mark Alber

Center for the Study of Biocomplexity, University of Notre Dame

Proposed life cycle for Myxobacteria (Dale Kaiser,2003 )

The Gliding Motility• Social motility: puller;• Adventurous motility: pusher• A+S+: 1.6micron/min; A-

S+:0.4 micron/min; A+S-:0.6 micron/min; (all maximum rates)

(Ref: Dale Kaiser,2003)

• Cell-end reversal: both engine switch;

• Reversal rate is regulated by C-signaling;

• Plot of reversal rate versus signaling strength (FrzF activation rate) (Igoshin et al, 2004)

The mechanism of A-motility

Ref:How Myxobacteria Glide, Charles Wolgemuth Dale Kaiser et al, 2002

• Hypothesis: Slime secretion from the nozzle-like structures may provide the force needed to drive A-engine;

• The force is due to the swelling property of polyelctrolyte gels, which have be found in slime. The calculated force is 50~150 pN (calculations can be found in the handout paper)

• Not known: how slime is introduced into the nozzle?

A special case: Flailing motion• A myxobacteria cell is stuck at one end and the

free end acts as A-engine• Picture from Gliding Movements in Myxococcus

xanthus, Alfred Spormann and Dale Kaiser, 1995

Force and Flexibility of Flailing Myxobacteria Biophysical Journal, Charles Wolgemuth,2005

• Model: treating the cell as an elastic but inextensible filament of conserved length, L, and radius, a. The distance along the filament is parameterized by the arc length, s, and the shape of the filament is described by the vector r(s).

Elastic energy:

f v v n v t

t r

( )v n v t v n v t

Elastic restorative force per length:

Drag coefficients (proportionality constants for movement perpendicular to or along the tangent direction)

∧ is the tension is the filament, with ∧(L)=F, the force produced by A-engine; The following equation is required by the non-stretching curve dynamics:

Ref. of the paper: Nonlinear Dynamics of Stiff Polymers, Phys. Rev. Lett., Goldstein and Langer, 1995

( ) ( 1)v n v t v t

Nondimensionalizing (using F~A/L^2, f~F/L)

Physical parameters:

Results • There exists a critical value (F*L^2/A=37.5). Below this

value, the filament remains straight; above the value, it starts bending and flailing motion, which is consistent with experiment results.

Results• The relationship between the two parameters and flailing

amplitudes as well as frequencies• The model provide a new method to measure the A-

engine’s propulsive force of gliding bacteria.

Results

• The force F is found to be between 50-150 pN. This is consistent with the force predicted to be generated by slime extrusion. So the hypothesis that A-engine is driven by slime secretion is strengthened.

My Suggestion

• The model might be useful in studying the bending and alignment when myxobacteria collide. (The S-end can be considered stuck to the other cell)