Role of LytF and AtlS in eDNA Release by Streptococcus gordonii

Extracellular DNA (eDNA) is an important component of the biofilm matrix produced by many bacteria. In general, the release of eDNA is associated with the activity of muralytic enzymes leading to obvious cell lysis. In the Gram-positive oral commensal Streptococcus gordonii, eDNA release is dependent on pyruvate oxidase generated hydrogen peroxide (H(2)O(2)). Addition of H(2)O(2) to cells grown under conditions non-permissive for H(2)O(2) production causes eDNA release. Furthermore, eDNA release is maximal under aerobic growth conditions known to induce pyruvate oxidase gene expression and H(2)O(2) production. Obvious cell lysis, however, does not occur. Two enzymes have been recently associated with eDNA release in S. gordonii. The autolysin AtlS and the competence regulated murein hydrolase LytF. In the present report, we investigated the role of both proteins in the H(2)O(2) dependent eDNA release process. Single and double mutants in the respective genes for LytF and AtlS released less eDNA under normal growth conditions, but the AtlS mutant was still inducible for eDNA release by external H(2)O(2). Moreover, we showed that the AtlS mutation interfered with the ability of S. gordonii to produce eDNA release inducing amounts of H(2)O(2). Our data support a role of LytF in the H(2)O(2) eDNA dependent release of S. gordonii as part of the competence stress pathway responding to oxidative stress.