Interaction forces between spores and planar surfaces in aqueous solutions

Bacterial spore interactions with planar surfaces in aquatic environments, including adhesive forces and force–distance profiles, are influenced by the geometry and physicochemical properties of the system. The characteristics of spores of Bacillus thuringiensis (Bt) are determined using electron microscopy and electrokinetic measurements. The average size of the spores is 1.57 μm long and 0.86 μm wide, and the zeta potential values are negative for the solutions used in this work. The zeta potentials of the spores and mica surfaces used in the experiments are measured as a function of pH and ionic strength. The Derjaguin, Landau, Verwey and Overbeek (DLVO) theory is employed to predict the interaction force between the spores and planar surfaces as a function of the separation distance, and a force balance is used to explain the adhesive force. Theoretical estimations are compared to experimental measurements obtained from atomic force microscopy (AFM). The DLVO-based calculations are consistent with AFM force measurements, while the calculated adhesive force shows some deviations from the measurements. The deviations can be minimized by considering the roughness of the Bt spore and substrate surfaces. Results are important in the understanding of spore interactions with environmental surfaces in aquatic systems.