Fig. 5.
Mixed-morphotype colonies reproduce the layering phenomena predicted by simulations. (A) Pseudocolor confocal images show that GFP-labeled WT E. coli (shown in blue) are able to burrow beneath shorter, wider AK mutants (red), leading to the WT cells’ enrichment at the base of the colony. (B) The same is true when fluorescent labels are reversed. Images correspond to vertical colony sections (A and B, top row) and horizontal slices taken at successive depths (A and B, bottom row). (C) We quantify layering effects by measuring the volume fraction of GFP-labeled cells as a function of depth in the colony, using automated image segmentation (Materials and Methods). (D) The gradients of these traces, corresponding to the percentage gain (or loss) of GFP signal per unit depth, are compared for various binary shape combinations. Cell micrographs in A, B, and D are taken with permission from ref. 44. (Scale bars: 20 m.) Confocal images and data taken after 48 h of growth.