Formation, collective motion, and merging of macroscopic bacterial aggregates
Fig 2
Spatial structure of aggregate formation.
A-D) Spatial analysis of the aggregate pattern at 22.5 h for a subregion of the plate. (A) The aggregate area distribution is depicted, with a mean of 1.01 mm2 and standard deviation of 0.25 mm2. (B) Histogram of the nearest neighbor distance distributions of the aggregate pattern and a random point pattern for comparison. For the bacterial aggregates, a pronounced single peak shows the existence of small-scale structure in the pattern. The average is 3.33 mm, with standard deviation of 2.33 mm. The distribution of the random pattern had an average of 3.35 mm, with standard deviation of 3.00 mm and it was found to be statistically different from that of the aggregate pattern, with a two-sided Kolmogorov-Smirnov test distance 0.15 and a p-value of p = 3.69e-155. (C) Structure factor versus wavenumber. The structure factor saturates to 1 at 3 mm-1, suggesting absence of long-range order. The dotted horizontal line represents the structure factor of a random point pattern for large system size. (D) Radial pair correlation function. The pair correlation is zero for distances less than 1.7 average aggregate diameters, as no other spots are detected in that proximity. The pair correlation peaks at 3.37 mm, exhibiting short range order, and saturates to one at 7 mm, consistent with disorder at longer distances. The dotted horizontal line represents the pair correlation factor of a random point pattern for large system size.