Effect of eDNA on biofilm formation

Aims: The aim of this study was to clarify the effects of homologous and heterologous extracellular DNAs (eDNAs) and histone-like DNA binding protein (HLP) on Streptococcus intermedius biofilm development and rigidity. Methods and Results: Formed biofilm mass was measured with 0.1% crystal violet staining method and observed with a scanning electron microscope. The localizations of eDNA and extracellular HLP (eHLP) in formed biofilm were detected by staining with 7-hydoxyl-9H-(1,3-dichloro-9,9-dimethylacridin-2-one) and anti-HLP antibody without fixation, respectively. DNase I treatment (200 U ml-1) markedly decreased biofilm formation and cell density in biofilms. Co-localization of eHLP and eDNA in biofilm was confirmed. The addition of eDNA (up to 1 μg ml-1) purified from S. intermedius, other Gram-positive, –negative bacteria, or human KB cells into the S. intermedius culture increased the biofilm mass of all tested strains of S. intermedius, wild-type, HLP down-regulated strain, and control strains. In contrast, the addition of eDNA (> 1 μg ml-1) decreased the biofilm mass of all S. intermedius strains. Conclusions: These findings demonstrated that eDNA and eHLP play crucial roles in biofilm development and its rigidity. Significance and Impact of the Study: eDNA- and HLP-targeting strategies may be applicable to novel treatments for bacterial biofilm-related infectious diseases