Interfacial assembly of marine exopolysaccharide EPS MO245 reduces Pseudomonas aeruginosa adhesion on silica

Marine exopolysaccharides are increasingly explored as non-biocidal anti-adhesive agents, yet how their assembly at the solid–liquid interface, rather than their intrinsic chemistry alone, governs this performance remains poorly understood. Here we compare the adsorption of the marine exopolysaccharide EPS MO245 and hyaluronic acid (HA) on silica and examine how the resulting interfacial layers control the adhesion of Pseudomonas aeruginosa PAO1. Quartz crystal microbalance with dissipation (QCM-D) measurements show that EPS MO245 adsorbs onto bare silica under specific physicochemical conditions, promoted at low pH and high ionic strength, whereas HA shows no measurable adsorption under the same conditions. Although both polysaccharides are negatively charged, these contrasting behaviors demonstrate that electrostatic interactions alone cannot account for their interfacial assembly. Purification and ion-complexation experiments indicate that natively associated species, including divalent cations, contribute to EPS MO245 adsorption but do not fully explain it, pointing to an additional role for short-range interactions arising from the heterogeneous structure of the native EPS. HA could be immobilized only after deposition of a cationic poly(L-lysine) (PLL) interlayer, forming a hydrated, viscoelastic HA-containing film. Bacterial adhesion assays show that EPS MO245-coated surfaces strongly reduce colonization and weaken the mechanical coupling of adherent cells to the substrate, whereas HA/PLL-coated surfaces remain substantially colonized. These results suggest that anti-adhesive performance is set at the interface, by the polymer's ability to form a stable, hydrated, and mechanically compliant layer, as much as by its chemistry, and identify EPS MO245 as a promising marine-derived candidate for non-biocidal anti-adhesive coatings.