Fig. 1: eDNA is key to Pseudomonas aeruginosa biofilm elasticity, pre and post dissolution in ionic liquid.
Photographs of P. aeruginosa A rugose small colony variant (RSCV) pellicle (22 °C, 3 days) and B wild-type liquid culture (37 °C, 3 days) biofilms grown under static conditions in 500 mL conical flasks, showing exopolymer-mediated phase separation of biomass, at the surface of and in the liquid of the growth medium, respectively. C Frequency dependence rheogram (n = 2, where n is the number of biological replicates) showing that tan (δ) for wild-type, RSCV pellicle static biofilms, isolated eDNA gel and wild-type static biofilm digested with heat-inactivated DNaseI at 22 °C (250 μm plate gap) is <1 across the frequency range (red dashed line), indicating that all are viscoelastic gels. Tan (δ) could not be measured for DNaseI-treated biofilms as they were not in the viscoelastic region. Error bars represent the standard deviation. D Non-linear elasticity as representative (n = 2) normal stress difference (ΔN = N1 − N2) and E viscosity dependencies on shear rate, for P. aeruginosa biofilm wild type, PDO300, Δpsl and Δpel, biofilm in 1-ethyl-3-methylimidazolium acetate (40 mg/mL) at 25 °C with 250 µm gap. F Representative (n = 2) normal stress difference (ΔN = N1 − N2) and G viscosity against shear rate for P. aeruginosa biofilm wild type, pronase, RNase and DNaseI-digested wild-type biofilm in 1-ethyl-3-methylimidazolium acetate (40 mg/mL) at 25 °C with 250 µm gap. Normal force is measured as a function of shear stress from 10 to 1000 Pa. ΔN is not described for DNaseI-digested biofilm in F and Supplementary Figure 1B, as their normal force (FN) is less than the resolution of the rheometer (i.e. 0.1 N) and set to zero for calculating ΔN. Both the ΔN and viscosity data are fitted with the FENE-P model, a rigid dumbbell model for polymer solutions. Fitting parameters are shown in Supplementary Table 2.
