A new paper in ISME Journal investigates the effect of resource limitations on the structure of biofilms. The authors used both mathematical modeling as well as mixed bacterial cultures to study the role of nutrient availability to spatial structuring within biofilms. For the growth experiments, the authors mixed differently colored Pseudomonas aeruginosa strains (expressing a different fluorescent protein). This resulted in some cool pictures:

Here is the link to the full paper (Open Access):

Resource limitation drives spatial organization in microbial groups
Sara Mitri, Ellen Clarke, and Kevin R Foster
The ISME Journal advance online publication, 27 November 2015; doi:10.1038/ismej.2015.208

Abstract: Dense microbial groups such as bacterial biofilms commonly contain a diversity of cell types that define their functioning. However, we have a limited understanding of what maintains, or purges, this diversity. Theory suggests that resource levels are key to understanding diversity and the spatial arrangement of genotypes in microbial groups, but we need empirical tests. Here we use theory and experiments to study the effects of nutrient level on spatio-genetic structuring and diversity in bacterial colonies. Well-fed colonies maintain larger well-mixed areas, but they also expand more rapidly compared with poorly-fed ones. Given enough space to expand, therefore, well-fed colonies lose diversity and separate in space over a similar timescale to poorly fed ones. In sum, as long as there is some degree of nutrient limitation, we observe the emergence of structured communities. We conclude that resource-driven structuring is central to understanding both pattern and process in diverse microbial communities.