Understanding the molecular interactions of lipopolysaccharides during E. coli initial adhesion with a surface forces apparatus
Lipopolysaccharides (LPS) occupy 75% of the surface of Gram-negative bacteria. This work investigates the role of LPS during bacterial adhesion to solid substrates. Two model lipopolysaccharides, LPS1 and LPS2, were examined. LPS1 from E. coliJM109 has a full LPS chain consisting of lipid A, core polysaccharides, and O-antigen; LPS2 from K12 has a truncated chain without the O-antigen portion. Interactions between an LPS layer prealigned on polystyrene (PS) and three different substrates (mica, PS-coated mica, and 3-aminopropyltriethoxysilane (APTES)-functionalized mica) in 0.1 M NaCl were measured using a surface forces apparatus (SFA). The PS-supported LPS showed strong adhesion to APTES, weak adhesion to mica, and strong repulsion to PS substrate. Electrostatic interaction and steric effects contribute significantly to the interactions between the LPS and different substrates. The presence of long O-antigen chains in LPS1 reduces bacterial adhesion to various substrates because of the presence of an energetic barrier during the adsorption process, which is caused by the affinity of hydrophilic neutral O-antigen chains to water and the steric entropic barrier of LPS chains on the cell membrane surface.