Better explicating the strengths and shortcomings of these models will help refine projections and improve transparency in the years ahead.
Image credit: Witsawat.S.
Contributed by David R. Nelson, May 1, 2012 (sent for review February 17, 2012)
- Fig. 1.
Schematic illustration of active (arrows) and inactive (asterisk) dislocations in an otherwise ordered peptidoglycan mesh. The dislocations with arrows attached are activated by the enzymatic machinery and move with velocity v. Those with asterisks are inactive.
- Fig. 2.
Numerical simulation of the dynamics of 30 active dislocations, with simulation parameters matching the biological ones. The dislocations are driven by a combination of chemical forces and turgor pressure in the circumferential direction, proportional to the sign of the Burgers vector. 10,000 inactive dislocations create a disordered potential for the motion of the active dislocations. The temperature is zero and
. The x and y coordinates of the dislocations were chosen randomly and uniformly along the axes, and 
. The climb to glide mobility ratio is μc/μg = 10. The red and blue points mark the starting positions of the ± b dislocations, and the red and blue lines correspond to their trajectories. The black circles mark the end of the cylinder. A snapshot of the simulation is taken after 
. The numerous inactive dislocation (marked as black dots) create a disordered energy landscape which can trap the active dislocations and inhibit further growth. In the SI Text further details regarding the simulation are given, as well as Movie S1 showing the dynamics. - Fig. 3.
(A) Active dislocation pulled past an inactive one by the enzymatic machinery. In this case an initial (inactive) dislocation pair could be created by an enzyme that cuts glycan bonds (rate constant γ4). The elongation machinery then assembles around an inactive dislocation turning it into an active one (rate constant γ2). (B) Direct insertion of a glycan strand fragment to create an active and inactive dislocation pair (rate constant Γ).
References
Dislocation-mediated growth of bacterial cell walls
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