Abstract
While the array of emergent properties assigned to biofilms is extensive (e.g. antimicrobial tolerance), the mechanisms that underpin these are largely unknown. In particular, the extracellular matrix, a defining feature of biofilms, remains poorly understood in terms of its composition and contribution to biofilm structure and function. Here we demonstrate that extracellular DNA exists in a complex with RNA that forms the main cross-linking exopolymer of Pseudomonas biofilms, and explains biofilm elasticity. The RNA has a high purine content and our solid-state NMR data indicate the formation of Hoogsteen guanine base pairs. This may suggest the presence of G-quadruplexes, which is also corroborated by the enhancement of biofilm formation in the presence of potassium. The finding that non-canonical interactions mediate networking of matrix-forming extracellular nucleic acids addresses how eDNA is organized and contributes to matrix biophysical properties. This understanding will allow for the development of more effective biofilm control strategies.