Images such as this one and others presented at Biofilms 2003 support the concept of biofilm formation as a multicellular developmental process during which differentiation occurs.

Spatial pattern of green fluorescent protein expression (green) in a Pseudomonas aeruginosa biofilm counterstained with rhodamine to reveal the extent of the biomass independent of activity (red). Protein synthetic activity is distributed non-uniformly, in this case being located both at the periphery of cell clusters and also in the centers of some cell clusters.