Scientists have discovered giant loops of DNA in bacteria living in our mouths that may help protect oral health and reduce cancer risk.
These loops, named Inocles, are a newly identified type of extrachromosomal DNA that appears to give bacteria genetic “survival kits.” Unlike normal bacterial DNA, Inocles exist outside the main chromosome, functioning much like large plasmids.
What Are Inocles?
Inocles were identified in Streptococcus bacteria, which are common inhabitants of the human mouth. Researchers from the University of Tokyo describe them as unusually large rings of DNA, averaging 350 kilobase pairs in size.
Most plasmids are just a few tens of kilobase pairs long, making Inocles among the largest extrachromosomal genetic elements discovered in the human microbiome.
How Were They Discovered?
To uncover these massive DNA loops, scientists examined saliva samples from 56 volunteers. They then expanded their study to 476 additional samples to gauge prevalence in the wider population.
The findings showed that around three-quarters of people may carry Inocles in their oral bacteria.
One reason these DNA structures had remained hidden could be their extraordinary size. Standard sequencing methods chop DNA into fragments, which makes reconstructing very large sequences difficult.
To overcome this, the team developed a new sequencing system called preNuc, designed to remove human DNA from saliva samples. This allowed researchers to focus specifically on bacterial DNA and successfully piece together the Inocles structure.
Why Inocles Matter
Researchers believe the genetic material inside Inocles carries important functions, including:
- Resistance to oxidative stress
- DNA damage repair
- Genes linked to bacterial cell walls and extracellular stress responses
These abilities may help bacteria survive in the harsh environment of the mouth, which is constantly exposed to food, oxygen, and immune activity.
Links to Cancer and Immunity
A surprising finding emerged when scientists compared samples from people with head and neck cancer. Those patients had significantly fewer Inocles compared to cancer-free participants.
This raises the possibility that Inocles may contribute to cancer protection, either by supporting a healthy oral microbiome or by influencing immune responses.
However, researchers caution that it is too early to confirm whether Inocles directly lower cancer risk. It is also possible that cancer-related changes reduce the presence of Inocles instead.
Future Research Directions
The discovery opens several important questions for future studies:
- How do Inocles function within the bacterial community of the mouth?
- Can they spread between individuals?
- What role do they play in oral and overall immune health?
Researchers believe that unlocking these answers could help shape new approaches to oral healthcare and possibly cancer prevention.
As study co-author Kiguchi explains, “It’s like finding a book with extra footnotes stapled to it, and we’re just starting to read them to find out what they do.”
A New Frontier in Microbiome Science
The discovery of Inocles highlights how much remains unknown about the human microbiome. These DNA loops may prove vital not only for understanding oral health but also for uncovering new strategies to reduce cancer risks.
With further research, Inocles could one day lead to targeted therapies that strengthen bacterial resilience, enhance immunity, and protect against disease.
