Challenges and opportunities in elucidating the structures of biofilm exopolysaccharides: A case study of the Pseudomonas aeruginosa exopolysaccharide called Pel

Biofilm formation protects bacteria from antibiotic treatment and host immune responses, making biofilm infections difficult to treat. Within biofilms, bacterial cells are entangled in a self-produced extracellular matrix that typically includes exopolysaccharides. Molecular-level descriptions of biofilm matrix components, especially exopolysaccharides, have been challenging to attain due to their complex nature and lack of solubility and crystallinity. Solid-state nuclear magnetic resonance (NMR) has emerged as a key tool to determine the structure of biofilm matrix exopolysaccharides without degradative sample preparation. In this review, we discuss challenges of studying biofilm matrix exopolysaccharides and opportunities to develop solid-state NMR approaches to study these generally intractable materials. We specifically highlight investigations of the exopolysaccharide called Pel made by the opportunistic pathogen, Pseudomonas aeruginosa. We provide a roadmap for determining exopolysaccharide structure and discuss future opportunities to study such systems using solid-state NMR. The strategies discussed for elucidating biofilm exopolysaccharide structure should be broadly applicable to studying the structures of other glycans.