Subsequently, the images are converted to binary images using this threshold and the occupancy value, which ranges from 0 (strain absent from patch) to 1 (strain fully covering patch), is calculated for each color-channel. The result of this procedure can be seen in Figure 2: Figure 2B shows the acquired fluorescence image, while Figure 2A shows NVP-BSK805 mw the calculated occupancy values for

the red channel (top) and green channel (bottom, see also Figure 3). It should be noted that the occupancy is not a linear measure of population density, as it cannot distinguish between mono- and multilayers of cells, causing it to saturate at high bacterial densities. Furthermore, the green channel has typically a higher background fluorescence intensity compared to the red channel, this can lead to differences in the detection of faint or

motion blurred cells between the two channels. Nevertheless, we believe that occupancy is a more reliable estimate of population density than fluorescence intensity due to its relative insensitivity to differences in the per-cell fluorescence intensity between fluorescent proteins and with growth phase. Quantitative similarity measure between spatiotemporal patterns of occupancy To estimate the degree of similarity between cell distributions in two habitats, the Euclidean distance between their occupancy kymographs is calculated. Each pixel in the occupancy kymographs represents a vector [r(t,k);g(t,k)] of the occupancies of the green strain (JEK1036, g(t,k)) and red strain (JEK1037, r(t,k)) for a given patch (k) at a given time MYO10 (t). MEK162 mouse The difference (d) between kymographs is calculated by taking, for each pixel and

color channel, the square of the difference in occupancies between the two habitats and summing this over all pixels: where r 1 (t,k) and r 2 (t,k) are the occupancies of strain JEK1037 in patch k at time t obtained for habitats 1 and 2 respectively. Similarly, g 1 (t,k) and g 2 (t,k) are the occupancies of strain JEK1036 in patch k at time t calculated for habitats 1 and 2 respectively. The factor 2 M (where M is the total number of pixels in the kymograph) normalizes d, such that it ranges from 0 for identical patterns to 1 for maximally different patterns. The difference is calculated over the period between 3 and 18 hours after inoculation. The first 3 hours are excluded as this time is required to setup the image acquisition and the end limit of 18 hours is chosen as most patterns have stabilized by this time (Additional files 2, 3 and 12). It should be noted that the Euclidean distance between two patterns is mostly affected by differences in high-density regions occupying large VS-4718 nmr expanses (in space and/or time, e.g., the expansion fronts), it is therefore hardly affected by more subtle aspects of the colonization pattern (e.g., the colonization waves).