FIG 4.

Bulk viscoelasticity of B. subtilis biofilms. (A) Storage modulus values for 1-day-old biofilms of wild-type strains B. subtilis B-1 (red) and NCIB 3610 (blue) and three mutant strains of NCIB 3610 (blue); (B) storage modulus values for 1-day-old biofilms of wild-type B. subtilis strain NCIB 3610 grown in the presence or absence of γ-polyglutamate (PGA) and after different periods of exposure to ethanol (see Materials and Methods). Biofilms were not treated or were exposed to ethanol for 10 or 60 min, as indicated. Error bars denote the standard deviations for 9 samples from 3 different growth batches. P values for these data are given in Tables S2 and S3 in the supplemental material.