Fig. 3: Concentration-dependent antibiotic and anti-curli effects of bacillaene.

a W3110 macrocolonies grown in close proximity to paper discs containing purified bacillaene, extract from the pksL mutant (control) or methanol (solvent control). Bacillaene shows inhibitory effects on growth or curli production on a distance scale that reflects a differential action of the metabolite depending on its concentration. Scale bar represents 5 mm and is applicable to all images in the panel. b The top image shows results of the effects of bacillaene or pksL extract on the formation of curli-dependent biofilms of E. coli W3110 on microtiter wells. Volumes indicated correspond to a 700 μg/ml solution of purified bacillaene or to pksL extract. Bacillaene concentrations indicated in parentheses are final concentrations (fc) in wells. The image, which shows the presence or absence of biofilms on the well walls after CV staining, reveals that bacillaene also inhibits -at different concentration- the formation of submerged biofilms. The bottom graphic presents the quantification of E. coli biofilm formation and associated planktonic growth in each well determined by measuring the absorbance (A₅₅₀) of solubilized CV and optical density (OD₅₇₈), respectively. Data shows that at high concentrations bacillaene inhibits growth, whereas at lower concentrations it inhibits curli synthesis. The data are means ± standard deviations of A₅₅₀ and OD₅₇₈ values derived from the analysis of three independent experiments (n = 3).