Influence of calcium ions on the mechanical properties of a model biofilm of mucoid Pseudomonas aeruginosa

The mechanical properties of biofilms and in particular their mechanical st rength is of great importance for both biofilm reactors and for the removal of undesired biofilms as in cases of biofouling and biocorrosion. By uniax ial compression measurements. it is possible to determine the apparent elas tic or Young's modulus and the yield stress as parameters for mechanical st ability, This was performed with a recently developed device, using model b iofilms of mucoid strain Pseudomonas aeruginosa SG81. The biofilms were gro wn on membrane filters placed on nutrient agar medium with different concen trations of calcium ions. The compressive stress - strain behaviour up to f ailure was recorded at a compression speed of 1 mum s(-1). The apparent You ng's modulus, representing the stiffness of the biofilm, and the yield stre ss obtained from the stress - strain diagram were used for the description of mechanical properties of biofilms. A certain critical concentration of c alcium ions was found where the Young's modulus of the P. aeruginosa biofil ms increases strongly and subsequently remains constant for higher calcium concentrations. This behaviour is explained by the presence of calcium ions crosslinking alginate, which is the major component of the extracellular p olymeric substances produced by the mucoid P. aeruginosa strain used in thi s investigation.