Interactions of biofilm polysaccharides produced by human infective bacteria with molecules of the quorum sensing system. A microscopy and NMR study

Biofilms are the most common lifestyle adopted by bacterial communities where cells live embedded in a selfproduced hydrated matrix. Although polysaccharides are considered essential for matrix architecture, their possible functional roles are still rather unexplored. The primary structure of polysaccharides produced by Klebsiella pneumoniae and species of the Burkholderia cepacia Complex revealed a composition rich in rhamnose. The methyl group on carbon 6 of rhamnose units lowers the polymer hydrophilicity and can form low polarity regions on the polysaccharide chains. These regions promote chain-chain interactions that contribute to the biofilm matrix stability, but may also act as binding sites for low-polarity molecules, aiding their mobility through the hydrated matrix. In particular, quorum sensing system components crucial for the biofilm life cycle often display poor solubility in water. Therefore, cis-11-methyl-2-dodecenoic acid and L-homoserine-lactones were investigated by NMR spectroscopy for their possible interaction with polysaccharides. In addition, the macromolecular morphology of the polysaccharides was assessed using atomic force and electron microscopies to define the role of Rha residues on the three-dimensional conformation of the polymer. NMR data revealed that quorum sensing components interact with Rhamnose-rich polysaccharides, and the extent of interaction depends on the specific primary structure of each polysaccharide.