It is interesting to note that the reflected wave reverses direction within 10 minutes, without first forming a detectable stationary subpopulation, contrary to previous observations where reflected waves reverse direction on much longer time scales (~1 h), after first forming a stationary population [38]. We observe similar collision patterns between colonization waves even when both sides of the habitat are inoculated with cells from the same strain, indicating that these collisions are not an artifact of the fluorescent markers (Additional

file 4B-D).We observe that patterns of wave collisions are similar in habitats on the same device (i.e. habitats inoculated with cells from the same set of initial cultures; compare Figure 2B with D and C with E), however, there is a large variation in the collision patterns

between habitats on different devices inoculated with cells from a different set of initial MEK inhibitor drugs click here cultures (Figure 3). For each wave the post-collision outcome can be decomposed in three components: (i) part of the wave is reflected back, continuing to travel as a wave after quickly (within 10 min) having Angiogenesis inhibitor reversed its direction; (ii) part of the wave disintegrates and a local (sessile) population is formed; (iii) part of the wave is ‘refracted’, continuing to travel as a wave in the same direction as before the collision, although typically with a lower velocity. The distribution of bacteria from the incoming wave over these three components second can vary strongly between devices, as can be seen in Figure 3. For example: in Figure 3A the green and red α-waves both have strong reflected parts (49% and 29% of the cells in the red and green α-waves, respectively), in Figure 3B the red α-wave completely disintegrates and in Figure 3C a large part (46%) of the red α-wave is refracted.

The patterns can become more complex if subsequent incoming waves interact with the subpopulations formed in the initial collision. For example in Figure 3C, a red β-wave merges with a green stationary populations and a combined, two-strain wave (yellow), is formed and starts traveling to the left of the habitat. Figure 2 The collisions of colonization waves. (A) Occupancy measure (area fraction) calculated per patch for strains JEK1037 (red) and JEK1036 (green) showing the collision between two α waves (at t = 6 h, patch 54). Note how both waves branch: a part of the wave is reflected, a part forms a stationary population, and a part continuous (for a short distance) in the same direction. (B) Kymograph of fluorescence intensity for the collision shown in A. (C) Enlarged view of B, centered at the point of collision. Note how the red and green populations remain largely segregated in space, even though individual cells do mix with the other population. (D) Kymograph of fluorescence intensity of a collision in a different habitat in the same device (with separate inlets; type-2) as the habitat shown in A- C. Note the similarity between B and D.