Fig. 1.

Characterization of channels within B. subtilis biofilms. (A) Biofilm growing on the surface of an agar gel containing water and nutrients. The biofilm increases in height to hundreds of micrometers, spreads to reach a diameter of several centimeters, and forms macroscopic wrinkles. (B) Series of microscopy images of a region near the center of the biofilm. Injection of an aqueous dye reveals a network of channels beneath the wrinkles. (C) Microscopy image of a biofilm after injection of an aqueous solution containing a mixture of fluorescent beads reveals the connectivity of the channels. (D) SEM image of a wrinkle cross-section. (E) SEM image of the underside of a biofilm reveals well-defined channels. (Inset) SEM image of the microstructure of the biofilm. (F) Side view of a biofilm wrinkle reconstructed from profiles of plastic molds of the upper and lower surfaces of the biofilm and the surface of the agar.