Pel is a cationic exopolysaccharide that cross-links extracellular DNA in the <i>Pseudomonas aeruginosa</i> biofilm matrix

TLDR

Biofilm formation in *Pseudomonas aeruginosa* involves the exopolysaccharides Psl and Pel and extracellular DNA, yet Pel’s chemical structure and spatial localization within mature biofilms remain unknown. Using specialized carbohydrate analyses, the authors identified Pel as a positively charged exopolysaccharide composed of partially acetylated 1→4 linkages of N‑acetylgalactosamine and N‑acetylglucosamine, and then developed a visualization tool combining Pel‑specific Wisteria floribunda lectin staining with confocal microscopy. Pel cross‑links extracellular DNA in the biofilm stalk through ionic interactions, and its distinct cationic charge enables it to interact with other key matrix components.

Abstract

Biofilm formation is a complex, ordered process. In the opportunistic pathogen Pseudomonas aeruginosa, Psl and Pel exopolysaccharides and extracellular DNA (eDNA) serve as structural components of the biofilm matrix. Despite intensive study, Pel's chemical structure and spatial localization within mature biofilms remain unknown. Using specialized carbohydrate chemical analyses, we unexpectedly found that Pel is a positively charged exopolysaccharide composed of partially acetylated 1→4 glycosidic linkages of N-acetylgalactosamine and N-acetylglucosamine. Guided by the knowledge of Pel's sugar composition, we developed a tool for the direct visualization of Pel in biofilms by combining Pel-specific Wisteria floribunda lectin staining with confocal microscopy. The results indicate that Pel cross-links eDNA in the biofilm stalk via ionic interactions. Our data demonstrate that the cationic charge of Pel is distinct from that of other known P. aeruginosa exopolysaccharides and is instrumental in its ability to interact with other key biofilm matrix components.