The Cell Body of a Bent Cell Is Represented by Three Nodes (Solid Black Dots)

<p>The cell has a length-to-width ratio of 10:1.</p

Local Order Measuring Domain

<p>Local Order Measuring Domain</p

Simulations of Cell Motion Deep Inside the Swarming Colony

<div><p>(A) Initial random distribution of cells in a square area of size 167 μm × 167 μm at the density of 50 K-S units with periodic boundary conditions.</p><p>(B) A⁺S⁻ mutant swarm after 3 h of evolution.</p><p>(C) Wild-type (A⁺S⁺) swarm after 3 h of evolution.</p><p>(D) Plot of the global order parameter Ω for the simulations of wild-type (A⁺S⁺) and A⁺S⁻ mutant swarms.</p></div

The Simulation Domain

<p>Periodic boundary conditions are used at sides a and c, while reflection boundary condition is imposed at side d (see <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.0030253#s4" target="_blank">Methods</a>). Cells at a density of 50 K-S units are shown randomly distributed in the initial area. Their initial orientations are chosen in accordance with the distribution function described in Methods, <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.0030253#pcbi-0030253-e012" target="_blank">Equation 12</a>.</p

The Dependence of Cell Number Flux on the Slime Aging Time

<p>The Dependence of Cell Number Flux on the Slime Aging Time</p

Phase-Contrast Image of the Cell Distribution at the Edge of a Young A⁻S⁺ Swarm That Is Expanding to the Right

<p>Older A⁻S⁺ swarms stop expanding when their edge becomes smooth and many layers deep. The white scale bar is 50 μm long.</p

Simulation Images and Linear Growth of Colony

<div><p>(A) and (B) are pictures of the edges of the A⁺S⁻ and wild-type (A⁺S⁺) swarms, respectively, after 200 min of simulation.</p><p>(C) Linear increase in the number of cells in the simulation domain with time. The red lines are best fits of simulation data with slopes indicated in the plot.</p></div

Picture of a Rectangular Section of a Typical Swarm Edge of Wild-Type M. xanthus Strain DK 1622 (A⁺S⁺)

<p>Several small peninsulas project outward from the edge of the swarm. The inset is a higher-magnification view of a segment of a typical swarming edge in which single cells and clusters of cells are evident. The inset was taken from a different but similar experiment. Dense clusters of cells (darker shades of gray) are evident in both pictures.</p

Diagram Showing the Two Types of Social Interactions for a Cell (Black)

<p>Although the pilus length varies with extension, retraction, and breakage, most pili are on the order of one cell length [<a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.0030253#pcbi-0030253-b039" target="_blank">39</a>]. Area I represents the pilus–cell interaction area. Its sides are taken as the average pilus length. If either the head or the tail of another cell falls within this area, it can be contacted by pili from the black cell<i>.</i> Area II is the corresponding interaction area for A motility. A bent gray cell in direct contact with a dark cell illustrates the bending and alignment due to collisions between cells. Slime trail following is illustrated by trails (light gray shaded area) inside of area II. An artificially low cell density has been used in this figure to clarify the several interactions. In reality, many cells are adjacent to each other within the interaction area.</p

Fitting Curves of Spreading Rates of Wild-Type (A⁺S⁺) Myxobacteria and Motility Mutants (Reproduced by Using Data from [10])

<p>The dots are experimental data points. The fitting functions are as follows: wild-type (A⁺S⁺), <i>f</i>(<i>x</i>) = <i>a</i> − <i>b</i> × exp(−<i>x</i> / <i>c</i>), with <i>a</i> = 1.55 ± 0.06, <i>b</i> = 1.41 ± 0.10, and <i>c</i> = 56 ± 10; A⁺S⁻ mutant, <i>g</i>(<i>x</i>) = <i>a</i> − <i>b</i> × exp(−<i>x</i> / <i>c</i>), with <i>a</i> = 0.67 ± 0.03, <i>b</i> = 0.49 ± 0.05, and <i>c</i> = 57 ± 16; and A⁻S⁺ mutant, <i>h</i>(<i>x</i>) = <i>b</i> × (1 − exp(−<i>x</i> / <i>c</i>)), with <i>b</i> = 0.46 ± 0.02 and c = 184 ± 27. The density is in K-S units, and the expansion rate is in microns per minute.</p