The structural role of bacterial eDNA in the formation of biofilm streamers

Abstract

Across diverse habitats, bacteria are mainly found as biofilms, surface-attached communities embedded in a self-secreted matrix of extracellular polymeric substances (EPS), which enhances bacterial resistance to antimicrobial treatment and mechanical stresses. In the presence of flow and geometric constraints such as corners or constrictions, biofilms take the form of long, suspended threads known as streamers, which bear important consequences in industrial and clinical settings by causing clogging and fouling. The formation of streamers is thought to be driven by the viscoelastic nature of the biofilm matrix. Yet, little is known about the structural composition of streamers and how it affects their mechanical properties. Here, using a microfluidic platform that allows growing and precisely examining biofilm streamers, we show that extracellular DNA (eDNA) constitutes the backbone and is essential for the mechanical stability of Pseudomonas aeruginosa s streamers. This finding is supported by the observations that DNA-degrading enzymes prevent the formation of streamers and clear already formed ones, and that the antibiotic ciprofloxacin promotes their formation by increasing the release of eDNA. Furthermore, using mutants for production of the exopolysaccharide Pel, an important component of P. aeruginosa s EPS, we reveal a new, although indirect role of Pel, in tuning the mechanical properties of the streamers. Taken together, these results highlight the importance of eDNA and of its interplay with Pel in determining the mechanical properties of P. aeruginosa streamers, and suggest that targeting the composition of streamers can be an effective approach to control the formation of these biofilm structures.