The influence of fluid shear and AlCl3 on the material properties of Pseudomonas aeruginosa PAO1 and Desulfovibrio sp. EX265 biofilms

An understanding of the material properties of biofilms is important when describing how biofilms physically interact with their environment. In this study, aerobic biofilms of Pseudomonas aeruginosa PAO1 and anaerobic sulfate-reducing bacteria (SRB) biofilms of Desulfovibrio sp. EX265 were grown under different fluid shear stresses (τ_g) in a chemostat recycle loop. Individual biofilm microcolonies were deformed by varying the fluid wall shear stress (τ_w). The deformation was quantified in terms of strain (ε), and the relative strength of the biofilms was assessed using an apparent elastic coefficient (E_app) and residual strain (ε_r) after three cycles of deformation. Aluminium chloride (AlCl₃) was then added to both sets of biofilm and the tests repeated. Biofilms grown under higher shear were more rigid and had a greater yield shear stress than those grown under lower shear. The addition of AlCl₃ resulted in a significant increase in E_app and also increased the yield point. We conclude that the strength of the biofilm is in part dependent on the shear under which the biofilm was grown and that the material properties of the biofilm may be manipulated through cation cross-linking of the extracellular polysaccharide (EPS) slime matrix.