Discovery of Giant DNA Elements in Human Oral Microbiome Could Influence Oral Health and Disease Risks

Recent research conducted by scientists at the University of Tokyo has uncovered a remarkable presence of giant extrachromosomal DNA elements, termed Inocles, residing in the human oral microbiome. These large DNA structures, previously undetected due to technological limitations, appear to play a significant role in bacterial adaptation within the mouth's dynamic environment.

Published in the journal Nature Communications, the study reveals that Inocles are hosted by bacteria such as Streptococcus salivarius and can reach sizes of approximately 350 kilobase pairs. This makes them some of the largest extrachromosomal DNA elements found in the human microbiome, surpassing typical plasmids which are usually only a few tens of kilobase pairs.

The discovery was made possible through the application of advanced long-read sequencing techniques, combined with a novel method called preNuc, developed to effectively remove human DNA from saliva samples. This approach enabled researchers to assemble complete genomes of Inocles and analyze their genetic content, which includes genes related to resistance against oxidative stress, DNA repair, and cell wall functions—key factors in bacterial resilience and adaptation.

These findings suggest that Inocles could influence how oral bacteria colonize and persist, potentially impacting oral health issues such as cavities, gum disease, and even more systemic conditions. Furthermore, the researchers propose that Inocles could serve as biological markers for serious diseases, including cancer.

The team aims to develop methods to culture bacteria containing Inocles in the lab, to better understand their functions and possible modes of transfer between individuals. Using a combination of laboratory experiments and computational models like AlphaFold, they intend to elucidate the roles of uncharacterized genes within these elements.

Remarkably, it is estimated that approximately 74% of humans may carry Inocles, highlighting their widespread presence. This discovery opens new avenues for microbiome research and suggests that the human mouth hosts a previously hidden genetic component that could significantly influence health and disease resilience.

Source: Medical Xpress