The role of eDNA in the formation of biofilm streamers

Across many different habitats, bacteria are often found as sessile communities embedded in a self-secreted matrix of extracellular polymeric substances (EPS). The biofilm matrix enhances bacterial resistance to harsh environmental conditions and antimicrobial treatments. Nevertheless, little is known about how environmental features shape its microstructure and chemical composition.
Here, we show that a laminar flow of a diluted suspension of Pseudomonas aeruginosa PA14 around a pillar can trigger the formation of suspended filamentous biofilm structures known as streamers and that extracellular DNA (eDNA) plays a fundamental structural role in streamer formation. By varying the composition of the biofilm matrix using mutant strains of PA14 and by applying targeted enzyme treatments, we could shed light on the structural role of the different biochemical components: eDNA is essential for streamers formation, while Pel, a positively charged exopolysaccharide which binds to eDNA, affects the filament morphology. In addition, we could probe the shear-induced deformation of streamers to investigate the material properties of each component. Finally, we could promote streamers formation by adding sublethal concentration of an antibiotic commonly used to treat PA infections.