Tokyo: Led by microbiologist Yuya Kiguchi, the research team uncovered large genetic loops, around 350,000 base pairs long, in saliva samples from 56 volunteers. The presence of these DNA rings was later confirmed in 476 additional samples, showing that roughly 75 percent of people may carry them unknowingly.

“These loops are so large that conventional sequencing methods missed them,” Kiguchi explained. “We developed a new technique to filter out human DNA and isolate bacterial DNA, which finally revealed their existence.”

The endonuclease DNA carries genes that help bacteria withstand oxidative stress, repair DNA damage, and adapt to the changing oral environment. This protective role also appears to benefit human hosts. Strikingly, the team found that patients with head and neck cancers had fewer of these genetic loops, sparking questions about their role in reducing cancer risks.

The findings highlight a potential link between bacterial genetics and human health, opening the door to new treatments or preventive strategies for oral diseases and certain cancers. Researchers stress that further studies are needed to determine whether endonuclease directly reduces cancer risk or if its scarcity is a consequence of other factors.