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 d escribing how biofilms physically interact with their environment. In this study, aerobic biofilms of Pseudomonas aeruginosa PAO1 and anaerobic sulfat e-reducing bacteria (SRB) biofilms of Desulfovibrio sp. EX265 were grown un der different fluid shear stresses (iota (g)) in a chemostat recycle loop. Individual biofilm microcolonies were deformed by varying the fluid wall sh ear stress (iota (w)).The deformation was quantified in terms of strain (ep silon), and the relative strength of the biofilms was assessed using an app arent elastic coefficient (E,p,) and residual strain (E,) after three cycle s of deformation. Aluminium chloride (AlCl3) was then added to both sets of biofilm and the tests repeated. Biofilms grown under higher shear were mor e rigid and had a greater yield shear stress than those grown under lower s hear. 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 biofi lm 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 cati on cross-linking of the extracellular polysaccharide (EPS) slime matrix.