Pel is a cationic exopolysaccharide that cross-links extracellular DNA in thePseudomonas aeruginosabiofilm matrix

Abstract

Biofilm formation is a complex, ordered process. In the opportunistic pathogenPseudomonas 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 ofN-acetylgalactosamine andN-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-specificWisteria floribundalectin 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 knownP. aeruginosaexopolysaccharides and is instrumental in its ability to interact with other key biofilm matrix components.