Figure 6
From: Resource limitation drives spatial organization in microbial groups
Quantifying the cellular diffusion constant Ds. (a) For each colony from both the original experiment and the experiment with varying inoculum size, we automatically traced the boundaries between sectors and determined the distance r and angle α of each point along the boundary with respect to the center of the colony. For each boundary, we plotted 1/Ri−1/Rf on the x axis, where Rf and Ri are the distance of the furthest and closest point in a boundary to the center, respectively, and the variance in the angle α for all points along the boundary on the y axis. We then binned boundaries into intervals of 8x10−5 on the x axis, took the mean of all variances within each bin (red dots) and fit a line through these means (green dots are >3 s.ds. from the mean and were discarded from the fit), in addition to a point at the origin (red line). The slope of this line was 2Ds/v. By multiplying the slope by v/2, we obtained Ds. (b) Output of edge detection algorithm. Boundary colors were assigned randomly to improve visualization. These boundaries, together with the boundaries from 95 other colonies, are used to generate the data in panel (a). (c) Ds correlates positively with nutrient concentrations (Spearman’s correlation test, ρ=1, P<0.001). Ds/v showed no significant correlation with nutrient concentrations (ρ=0.024, P=0.98), suggesting that the colony expansion velocity determines the cellular diffusion rate Ds. The error bars show s.e. of the fit.
