Ultrastructural characterization of matrix development and the role of extracellular DNA in early Enterococcus faecalis biofilms

Enterococcus faecalis is a highly adaptable, gram-positive bacterium that occupies a diverse range of ecological niches. A common soil-dwelling organism, it is also inhabits the metazoan gastrointestinal tract---from insects to humans. E. faecalis is remarkably resistant to a wide range of clinically-relevant antibiotics and readily forms biofilms on both abiotic and biotic surfaces. These latter factors underlie the medical relevance of E. faecalis..;This thesis explores the ramifications of early developmental events in E. faecalis biofilm formation. Using correlative microscopy techniques, we investigated a series of mutants with ultrastructural changes in the extracellular matrix that elucidate the roles these genes play in matrix architecture. We also report that extracellular DNA plays a substantial role in stabilizing early (< 8 hr post-inoculation) E. faecalis biofilms, and that the source of this DNA is not via bulk cell lysis, but rather appears to be secreted from metabolically active cells. A putative model for this non-canonical source of DNA in the matrix is also proposed.