(D) Kymograph of fluorescence intensity AZD8186 of the left most 25 patches for strain JEK1036 (green) showing a typical pattern of landscape invasion consisting of three subsequent colonization waves (α at t ≈ 3.5 h, β at t ≈ 5 h and γ at t ≈ 6 h) followed by the expansion front (at t ≈ 6 h); scale bar = 1 mm. The inset

at the top shows an enlarged view of the α wave just after entering the habitat from the inlet; scale bar = 100 μm. Colliding waves decompose into distinct components After inoculation, the populations initially grow in the inlet holes and start to colonize the habitats after 2 to 4 hours. During the first phase of colonization typically three waves enter the habitat, as can be seen in Figure 1D. The first two waves (α and β) are of relatively low cell density (≈500 cells per wave), while the third wave (γ) is a high-density wave at the leading edge of an expansion front (Figure 1D). In most (32 out of 48) habitats, RSL3 solubility dmso three waves with densities and velocities similar to Figure 1D are seen for at least one of the two strains, while in all 48 habitats (on 11 devices of types-1 and 2, see Additional files 2 and 3) at least a single wave is observed. These colonization waves require chemotaxis, as a smooth-swimming, non-chemotactic, cheY knockout strain did not form any waves (Additional file 4A). Bacteria in a wave remain tightly packed while

traveling throughout the patchy habitat, although there is some limited dispersion of the wave profile (Additional file 5). The observed wave profiles (Additional file 5A-C) and velocities (=0.86 μm/s, Additional file 5D) compare well to those described in previous work, where wave velocities of 1.8 to 3.8 μm/s were reported for linear channels [29, 30, 43], while waves in large unstructured chambers traveled at 0.56 μm/s [33]. This indicates that a patchy spatial structure does not interfere with the formation and propagation of bacterial population waves. Interestingly, the waves span multiple (roughly

mafosfamide 5) patches, indicating that traveling populations are formed at scales larger than that of the habitat patches. When two waves coming from opposite inlets collide, they give rise to complex but reproducible spatiotemporal patterns (Figure 2). Figure 2A shows data depicting a green wave coming from the left and a red wave coming from the right. After their collision, most green cells remain grouped with other green cells, either in the reflected wave traveling back towards the left inlet, or in a large ITF2357 mw stationary population (Figure 2A, t = 7 h). The red cells show a similar post-collision distribution, consisting of a reflected wave and a stationary population spatially separated from their green counterpart (Figure 2A). As most cells stay with their original population, it is still possible to distinguish between ‘red’ and ‘green’ populations after the collision.