Effects of shear stress and substrate loading rate on Pseudomonas aeruginosa biofilm thickness and density

Thickness, roughness, and density data were obtained from monopopulation Pseudomonas aeruginosa biofilms grown in an annular reactor under different substrate loading rates and shear stresses. Biofilm thickness showed significant increases, up to approx. 30 mu m, with increasing substrate loading rate. Shear stress had no significant effect on thickness. Biofilm roughness, as measured by the standard deviation of the thickness, increased with increasing thickness. Areal mass density significantly increased with substrate loading rate and was not significantly affected by shear stress. Substrate loading and shear stress did not significantly affect volumetric mass density. A numerical expression that describes changes volumetric density as a function of biofilm depth is presented.