Spermidine is a common component of the eDNA-dependent biofilm matrix.

Biofilms are structured multicellular bacterial communities encased within an extracellular matrix comprised of exopolysaccharides, proteins, extracellular DNA (eDNA), and other biopolymers that provide protection against environmental stressors. We and others have shown that eDNA serves as a fundamental structural element common to even multispecies biofilms. During biofilm maturation, ubiquitous DNABII proteins facilitate the conversion and stabilization of eDNA into the rare and rigid Z-DNA conformation, thereby enhancing matrix integrity and rendering the underlying eDNA resistant to nucleases. We have previously shown that the removal of positively charged molecules, such as DNABII proteins, results in rapid, significant disruption of diverse biofilms. Here, we identify the polyamine spermidine as another essential positively charged molecule that, together with DNABII proteins, contributes to the development and maintenance of the eDNA-dependent extracellular matrix. We also provide evidence that SPD is present within the biofilm matrix alongside DNABII proteins in multiple bacterial pathogens. Our findings indicate that SPD and DNABII proteins cooperate to promote Z-DNA formation. Depletion of SPD and DNABII using cation exchanger P11-phosphocellulose or inhibition of SPD synthesis via dicyclohexylamine impaired biofilm formation and destabilized preformed biofilms. These results suggest that polyamine synthesis or accumulation represents a potential target for biofilm disruption and control.