Aggregate shape governs growth dynamics.

<p>Growth of the spread (<i>θ</i> = 5^<i>o</i>), semi-spread (<i>θ</i> = 90°), and rounded aggregate (<i>θ</i> = 180°) populations over the course of our simulations in the absence (<i>ρ</i> = 0 cell <i>μ</i>m⁻¹) and presence (<i>ρ</i> = 0.5 cell <i>μ</i>m⁻¹) of competition. For clarity the error bars, representing the standard deviations, are only shown for the final data points. The standard deviations at these points are maximal.</p

Cells on the outside of the aggregates grow faster because they have greater access to nutrients.

<p>(a) Cell growth rate (<i>μ</i>) distribution of the biofilm formed from the semi-spread aggregate in the absence of competition after 4h. (b) Corresponding nutrient concentration field, [<i>S</i>].</p

Our simulation set-up.

<p>Schematic representation of bacterial aggregates (green) which are initially spread on a surface to varying extents. The schematic also shows surrounding, competing, unaggregated cells (red). <i>θ</i> is the angle where the aggregate-medium (nutrient) interface meets the solid surface (see Section A in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0149683#pone.0149683.s001" target="_blank">S1 File</a>). Aggregates were generated from pre-formed biofilms by extracting cells whose coordinates lay within circular geometries (defined by <i>θ</i>) of varying size (see Section A in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0149683#pone.0149683.s001" target="_blank">S1 File</a>). Top- Rounded aggregate, <i>θ</i> = 180°; Middle- Semi-spread aggregate, <i>θ</i> = 90°; Bottom- Spread aggregate with <i>θ</i> = 5°. Note that the size of the aggregates (in terms of number of bacteria) is approximately equal.</p

Initial aggregate arrangement affects biofilm morphology.

<p>Simulation snapshots of three bacterial aggregates initially arranged on the surface and the biofilms they form after 480 h: (a) Spread, 0 h. A zoomed in image is also shown to make the shape of the aggregate easier to resolve; (b) Semi-spread, 0 h; (c) Rounded, 0 h; (d) Spread, 480 h; (e) Semi-spread, 480 h; (f) Rounded, 480 h.</p

Aggregate shape and neighbouring strain density affect biofilm morphology.

<p>Simulation snapshots of biofilms seeded from spread and rounded aggregates after 480 h growth in the presence of a low and high density inoculum of the competing strain: (a) <i>θ</i> = 5°, <i>ρ</i> = 0.01 cell <i>μ</i>m⁻¹; (b) <i>θ</i> = 180°, <i>ρ</i> = 0.01 cell <i>μ</i>m⁻¹; (c) <i>θ</i> = 5°, <i>ρ</i> = 0.5 cell <i>μ</i>m⁻¹; (d) <i>θ</i> = 180°, <i>ρ</i> = 0.5 cell <i>μ</i>m⁻¹.</p

Rounded aggregate is relatively more successful with increased competition.

<p>Relative fitness as measured by <i>N</i>/<i>N</i>₀ of rounded aggregates increases with competition. Rounded aggregates become favourable relative to spread aggregates with increasing density of competitor cells. P values and degrees of freedom computed from unpaired two tailed T-test assuming unequal variances.</p

Success of aggregates depends on shape and competition.

<p>(a) aggregate-medium interface length, s, as a function of <i>θ</i>. (b-d) Average number of progeny, <i>N</i>/<i>N</i>₀, of aggregates defined by their surface-aggregate angle <i>θ</i>, the functional from of which changes with increasing density of competitor cells: (b) <i>ρ</i> = 0 <i>μ</i>m cell⁻¹; (c) <i>ρ</i> = 0.145 <i>μ</i>m cell⁻¹; (d) <i>ρ</i> = 0.5 <i>μ</i>m cell⁻¹. Vertical bars represent the standard deviation from 20 data points.</p

Input parameters for biofilm simulations.

<p>Input parameters for biofilm simulations.</p

Gradients in individual cell growth rates emerge in our simulated biofilms during growth.

<p>Cell growth rate distributions for the spread and rounded aggregates after 480 h of growth: (a) <i>θ</i> = 5°, <i>ρ</i> = 0.0 cell <i>μ</i>m⁻¹; (b) <i>θ</i> = 5°, <i>ρ</i> = 0.01 cell <i>μ</i>m⁻¹; (c) <i>θ</i> = 5°, <i>ρ</i> = 0.5 cell <i>μ</i>m⁻¹; (d) <i>θ</i> = 180°, <i>ρ</i> = 0.0 cell <i>μ</i>m⁻¹; (e) <i>θ</i> = 180°, <i>ρ</i> = 0.01 cell <i>μ</i>m⁻¹; (f) <i>θ</i> = 180°, <i>ρ</i> = 0.5 cell <i>μ</i>m⁻¹. These distributions correspond to the configurations in Figs <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0149683#pone.0149683.g002" target="_blank">2</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0149683#pone.0149683.g004" target="_blank">4</a>. Note that the gradient in cell growth rate is so large that a log scale is used for visualisation purposes. The green dashed lines represents an approximate boundary between the aggregate cells and the surrounding competing strain.</p