As in a batch of kombucha or a barrel of sherry, microbes can assemble into a mat-like layer at the boundary between air and liquid. In laboratory culture, the bacterium Pseudomonas fluorescens SBW25 is widely known for doing exactly that: starting from a non-mat-forming original type, it evolves—through genetic mutations—into forms that construct a mat at the air–liquid interface, and it does so with striking regularity within just a few days.
