Untethering and Degradation of the Polysaccharide Matrix Are Essential Steps in the Dispersion Response of Biofilms.

Biofilms are multicellular aggregates of bacteria that are encased in an extracellular matrix. The biofilm matrix of PAO1 is composed of eDNA, proteins, and the polysaccharides Pel and Psl. This matrix is thought to be degraded during dispersion to liberate cells from the biofilms, with dispersion being apparent not only by single cells escaping from the biofilm but also leaving behind eroded or hollowed-out biofilm. However, little is known of the factors involved in matrix degradation. Here, we focused on the glycoside hydrolases PelA and PslG. We demonstrate that induction of but not expression resulted in dispersion. As Psl is tethered to the matrix adhesin CdrA, we furthermore explored the role of CdrA in dispersion. mutant biofilms were hyperdispersive, while mutant biofilms were impaired in dispersion in response to glutamate and nitric oxide, indicating the presence of the surface-associated matrix protein CdrA impedes the dispersion response. In turn, insertional inactivation of enabled -induced dispersion. Lowering of the intracellular c-di-GMP level via induction of PA2133 encoding a phosphodiesterase was not sufficient to induce dispersion by wild-type strains and strains overexpressing , indicating that -induced dispersion is independent of c-di-GMP modulation and, likely, LapG. forms multicellular aggregates or biofilms encased in a matrix. We show for the first time here that dispersion by requires the endogenous expression of and , leading to the degradation of both Pel and Psl polysaccharides, with PslG-induced dispersion being CdrA dependent. The findings suggested that endogenously induced Psl degradation is a sequential process, initiated by untethering of CdrA-bound Psl or CdrA-dependent cell interactions to enable Psl degradation and ultimately, dispersion. Untethering likely involves CdrA release in a manner independent of c-di-GMP modulation and thus LapG. Our findings not only provide insight into matrix degrading factors contributing to dispersion but also identify key steps in the degradation of structural components of the biofilm matrix.