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We investigated the impact of calcium and magnesium ions on the deposition kinetics of flagellated and nonflagellated Pseudomonas aeruginosaonto an alginate conditioning film in a radial stagnation point flow system. The bacterial deposition/adhesion behavior was related to structural changes of the alginate film in the presence of the divalent cations. Our results showed that adhesion of nonmotile bacteria was governed by cation bridging interactions between high-affinity sites at the bacterial surface and either clean or alginate-conditioned substrate surfaces. For motile bacteria, the adhesion onto clean quartz was governed by electrostatic interactions while adhesion onto alginate-conditioned quartz was dependent on the structure and viscoelastic properties of the alginate film in the presence of calcium or magnesium. We demonstrate that bacterial adhesion behavior is governed both by the effects of divalent cations on the surface properties of the bacteria and the substrate and by the type of specific interactions occurring between these two surfaces. [ABSTRACT FROM AUTHOR]

A quartz crystal microbalance with dissipation (QCM-D) has been used to determine the adsorption rate of ampicillin-resistant linear and supercoiled plasmid DNA onto a silica surface coated with natural organic matter (NOM). The structure of the resulting adsorbed DNA layer was determined by analyzing the viscoelastic properties of the adsorbed DNA layers as they formed and were then exposed to solutions of different ionic composition. The QCM-D data were complemented by dynamic light scattering measurements of diffusion coefficients of the DNA molecules as a function of solution ionic composition. The obtained results suggest that electrostatic interactions control the adsorption and structural changes of the adsorbed plasmid DNA on the NOM-coated silica surface. The adsorption of DNA molecules to the NOM layer took place at moderately high monovalent (sodium) electrolyte concentrations. A sharp decrease in solution ionic strength did not result in the release of the adsorbed DNA, indicating that DNA adsorption on the NOM-coated silica surface is irreversible under the studied solution conditions. However, the decrease in electrolyte concentration influenced the structure of the adsorbed layer, causing the adsorbed DNA to adopt a less compact conformation. The linear and supercoiled DNA had similar adsorption rates, but the linear DNA formed a thicker and less compact adsorbed layer than the supercoiled DNA. [ABSTRACT FROM AUTHOR]

A quartz crystal microbalance with dissipation (QCM-D) is used to determine the adsorption rate of a supercoiled plasmid DNA onto a quartz surface and the structure of the resulting adsorbed DNA layer. To better understand the DNA adsorption mechanisms and the adsorbed layer physicochemical properties, the QCM-D data are complemented by dynamic light scattering measurements of diffusion coefficients of the DNA molecules as a function of solution ionic composition. The data from simultaneous monitoring of variations in frequency and dissipation energy with the QCM-D suggest that the adsorbed DNA layer is more rigid in the presence of divalent (calcium) cations compared to monovalent (sodium) cations. Adsorption rates are significantly higher in the presence of calcium, attaining a transport-limited rate at about 1 mM Ca2. Results further suggest that in low ionic strength solutions containing 1 mM Ca2and in moderately high ionic strength solutions containing 300 mM NaCl, plasmid DNA adsorption to negatively charged mineral surfaces is irreversible. [ABSTRACT FROM AUTHOR]

Understanding the adsorption properties of polysaccharides in terms of substrate affinity, kinetics, and layer structure is of paramount importance in numerous industrial and natural systems. The structural growth of the layers of two model polysaccharidessodium alginate and polygalacturonic acid (PGA)was characterized by quartz crystal microbalance with dissipation and atomic force microscopy. Monitoring the variations in frequency and dissipation energy provides insights into both the average adsorbed mass and the viscoelastic properties of the adsorbed layer of polyelectrolytes along with the associated ions and water molecules. Both polysaccharides had similar adsorption patterns with increasing ionic strengths and showed significant complexation of calcium ions. In the presence of calcium, the alginate gel layer exhibited significant swelling with an increasing concentration of monovalent salt that the PGA gel layer did not manifest. Basing our discussion on the “egg-box model”, we interpreted these different swelling behaviors as resulting from differences in the complexation modes of the two polysaccharides. The dimerization of the polymers by cross-linking and the weaker dimer−dimer associations play major roles in the sensitivity of the polysaccharide gel matrix to high salt concentration environments. [ABSTRACT FROM AUTHOR]