DNA binding to hydroxyapatite: a potential mechanism for preservation of microbial DNA

Molecular methods are increasingly being deployed for analysis of the microbial flora in the root canal. Such methods are based on the assumption that recovered DNA is associated with the active endodontic infection, yet paleomicrobiology research is based on the recovery of ancient DNA from centuries-old tooth and bone samples, which points to considerable longevity of the DNA molecule in these tissues. The main component of dentin and bone is the mineral hydroxyapatite. This study assessed DNA binding to hydroxyapatite and whether this binding affinity stabilizes the DNA molecule in various media.

DNA was extracted from Fusobacterium nucleatum and added to ceramic hydroxyapatite for 90 minutes. The DNA-bound hydroxyapatite was incubated in different media (ie, water, sera, and DNase I) for up to 3 months. At predetermined intervals, the recovery of detectable DNA was assessed by releasing the DNA from the hydroxyapatite using EDTA and evaluating the presence of DNA by gel electrophoresis and polymerase chain reaction (PCR) amplification.

When incubated with hydroxyapatite, nonamplified DNA was detectable after 3 months in water, sera, and DNase I. In contrast, DNA incubated in the same media (without hydroxyapatite) decomposed to levels below the detection level of PCR within 3 weeks, with the exception of DNA in sera in which PCR revealed a weak positive amplification product.

These results confirm a specific binding affinity of hydroxyapatite for DNA. Hydroxyapatite-bound DNA is more resistant to decay and less susceptible to degradation by serum and nucleases, which may account for the long-term persistence of DNA in bone and tooth.