Fig. 1.

Nystatin and surfactin induce biofilm formation. (A) Nystatin induces B. subtilis biofilm formation. Images of culture wells (1.8-cm diameter) are shown. B. subtilis forms a pellicle when cultured in MSgg but not in LB. Supplementing LB medium with 60 μM nystatin leads to pellicle formation. (B) Chemical structures of the polyene polyketides nystatin and filipin and the N-acylated nonribosomal peptides surfactin and iturin. Nystatin and surfactin induce B. subtilis biofilm formation whereas filipin and iturin do not. (C) Surfactin does not induce biofilm formation as a surfactant but rather as a signaling molecule. A mutant unable to make surfactin displays defective pellicle morphology in MSgg medium (compare Left and Center). This phenotype can be reversed by the addition of nystatin, which is not a surfactant (see Right).