Bacillus subtilis EpsA-O: A novel exopolysaccharide structure acting as an efficient adhesive in biofilms
Iztok Dogša, Barbara Bellich, Mojca Blaznik, Cristina Lagatolla, Neil Ravenscroft, Roberto Rizzo, David Stopar, Paola Cescutti
Abstract
Abstract Extracellular polysaccharides are crucial components for biofilm development. Although Bacillus subtilis is one of the most characterized Gram-positive biofilm model system, the structure-function of its exopolysaccharide, EpsA-O, remains to be elucidated. By combining chemical analysis, NMR spectroscopy, rheology, and molecular modeling, high-resolution data of EpsA-O structure from atom to supramolecular scale was obtained. The repeating unit is composed of the trisaccharide backbone [→3)-β- d -Qui p NAc4NAc-(1→3)-β- d -Gal p NAc-(1→3)-α- d -Glc p NAc-(1] n , and the side chain β- d -Gal p (3,4- S -Pyr)-(1→6)-β- d -Gal p (3,4- S -Pyr)-(1→6)-α- d -Gal p -(1→ linked to C4 of GalNAc. Close agreement between the primary structure and rheological behavior allowed us to model EpsA-O macromolecular and supramolecular solution structure, which can span the intercellular space forming a gel that leads to a complex 3D biofilm network as corroborated by a mutant strain with impaired ability to produce EpsA-O. This is a comprehensive structure-function investigation of the essential biofilm adhesive exopolysaccharide that will serve as a useful guide for future studies in biofilm architecture formation.