Fig. 2.

A time-series of EPS⁺ cells (red) growing in a biofilm with EPS^– cells (blue). The initial frequency of EPS⁺ cells is <5%, and its final frequency is >90%. At 36 h the upper surfaces of some EPS⁺ cell clusters appear flat because they have reached the ceiling of the chamber in which they are growing. Grid boxes are 11 μm on a side.