Extracellular DNA as a component of dental plaque

Abstract

Therapeutics that can control microbial biofilms while preserving the natural microbiota represent a promising strategy in managing biofilm-related diseases such as periodontitis. Extracellular DNA (eDNA) is an important structural component of many biofilms, including dental plaque. Bacteria within dental plaque produce deoxyribonuclease (DNase) enzymes that could digest eDNA. This project aimed to investigate whether a DNase produced by an oral bacterium can degrade eDNA in oral biofilms, thereby inhibiting the biofilm growth or disrupting mature biofilms, and compare its activity to a DNase from a non-oral bacterium. Preliminary investigations were also made into the microbial composition and immunostimulatory properties of eDNA. NucB, a DNase from a marine isolate of Bacillus licheniformis, inhibited biofilm growth and dispersed preformed biofilms of Fusobacterium nucleatum. It also inhibited the growth of model plaque biofilms, but did not affect preformed biofilms, implying that eDNA is more important or more accessible during the initial phases of the plaque biofilm formation. Furthermore, NucB inhibited the growth of anaerobic model plaque biofilms, but not those cultured in aerobic sucrose-rich conditions indicating that it may be particularly useful for reducing subgingival plaque, which is essentially anaerobic. Conversely, SsnA, a DNase from the oral bacterium Streptococcus gordonii, inhibited the growth of Fusobacterium nucleatum biofilms but did not disrupt preformed biofilms. SsnA Also lacked any antibiofilm effect with model plaque biofilms. NucB efficiently degraded various DNA substrates, whereas SsnA was only effective against single stranded and low molecular weight DNA, suggesting that eDNA in the plaque biofilm is predominantly double stranded DNA of high molecular weight. Overall, this work provided key insights into the activity of a DNase from an oral bacterium and showed that there is a scope to enhance subgingival biofilm control using exogenous DNases from non-oral bacteria.