Regulation of Autolysis-Dependent Extracellular DNA Release by <i>Enterococcus faecalis</i> Extracellular Proteases Influences Biofilm Development

TLDR

Enterococcus faecalis is a major hospital‑acquired pathogen that forms biofilms on medical devices, with its Fsr quorum system regulating biofilm formation via gelatinase, though the underlying mechanism remains unclear. Our study shows that gelatinase (GelE) and serine protease (SprE) jointly control biofilm development by modulating autolysis and extracellular DNA release, with GelE deficiency reducing biomass and eDNA, SprE deficiency accelerating biofilm growth through increased autolysis and eDNA, and DNase I treatment confirming eDNA’s essential role.

Abstract

Enterococci are major contributors of hospital-acquired infections and have emerged as important reservoirs for the dissemination of antibiotic resistance traits. The ability to form biofilms on medical devices is an important aspect of pathogenesis in the hospital environment. The Enterococcus faecalis Fsr quorum system has been shown to regulate biofilm formation through the production of gelatinase, but the mechanism has been hitherto unknown. Here we show that both gelatinase (GelE) and serine protease (SprE) contribute to biofilm formation by E. faecalis and provide clues to how the activity of these proteases governs this developmental process. Confocal imaging of biofilms suggested that GelE(-) mutants were significantly reduced in biofilm biomass compared to the parental strain, whereas the absence of SprE appeared to accelerate the progression of biofilm development. The phenotype observed in a SprE(-) mutant was linked to an observed increase in autolytic rate compared to the parental strain. Culture supernatant analysis and confocal microscopy confirmed the inability of mutants deficient in GelE to release extracellular DNA (eDNA) in planktonic and biofilm cultures, whereas cells deficient in SprE produced significantly more eDNA as a component of the biofilm matrix. DNase I treatment of E. faecalis biofilms reduced the accumulation of biofilm, implying a critical role for eDNA in biofilm development. In conclusion, our data suggest that the interplay of two secreted and coregulated proteases--GelE and SprE--is responsible for regulating autolysis and the release of high-molecular-weight eDNA, a critical component for the development of E. faecalis biofilms.