The role of S-layer proteins in bacterial adhesion to solid surfaces was investigated by determining whether there was a relationship between the adsorption of S-layer protein and the attachment of the source bacteria to a series of substrata exhibiting a range of water-wettabilities. Polystyrene substrata, prepared by treatment with H2SO4, provided advancing water contact angles ranging from 76° to 46°. The test bacteria were a Pseudomonas-like strain, designated EU2, and the thermophilic bacterium Bacillus coagulans. In two out of four cases, S-layer adsorption paralleled cell attachment. Numbers of attached EU2 and amount of S-layer adsorption in phosphate buffer both increased with increasing substratum hydrophobicity. Numbers of attached B. coagulans and S-layer adsorption in distilled deionized water both decreased with increasing substratum hydrophobicity. The inconsistencies in attachment and S-layer adsorption observed in the remaining experiments were possibly due to the fact that S-layer proteins were free to adsorb by both inner and outer faces, whereas S-layer on the cell could adsorb only by the outer face. The results indicated that S-layers may play a role in bacterial adhesion to surfaces, but that the adhesiveness of S-layers depends upon their specific chemistry and environmental conditions such as medium composition and temperature.
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