Inocles: Giant DNA rings discovered in the oral microbiome
A new form of genetic material has been discovered in the human oral microbiome: so-called inocles. These are ring-shaped DNA elements that exist within oral bacteria and are not part of the main genome. What does this mean?
Researchers at the University of Tokyo found that almost 75% of all people carry such inocles in their oral bacteria. This discovery is remarkable because it adds a new genetic layer to the oral microbiome. It helps to understand how oral bacteria adapt to their changing environment and thereby influence our health.
A survival kit for bacteria
With up to 395,000 DNA base pairs, inocles are the largest known extrachromosomal DNA elements in the human microbiome. Plasmids, the usual small DNA rings of bacteria, which are also not part of the bacterial chromosome, usually only contain a few thousand base pairs. Inocles have a correspondingly large number of additional genes, some of which have unique functions. A real survival package for bacteria in the harsh oral cavity.
In contrast to the small plasmids, they probably cannot be exchanged between bacteria (horizontal gene transfer), but are only passed on during cell division.
Why have they only been discovered now?
Inocles remained undiscovered because standard sequencing simply overlooked the large pieces of DNA. Only new sequencing technologies such as long-read technology and modern laboratory methods brought them to light.
Does Inocles only exist in the oral microbiome?
So far, they have mainly been discovered there. In the study, 74% of all samples contained such giant rings in the oral bacteria. However, they probably also exist in other human microbiomes. They have already been found in small quantities in the intestinal microbiome, in the vagina and on the skin.
Which bacteria carry these inocles?
So far, they have only been reliably detected in Streptococcus salivarius. There is a certain probability that they will also be found in other bacterial species as soon as further work is carried out on this topic.
What do the bacteria gain from this?
Their gene pool is significantly expanded. The bacteria receive a powerful upgrade to their abilities, so to speak. Inocles do not carry essential genes, but they do give the bacteria additional abilities. This is a clear evolutionary advantage. For example, functional genes have been discovered that make the bacteria resistant to stress and protect them from oxidative stress. Genes that influence cell wall synthesis and interaction with oral epithelial cells have also been discovered.
Good or evil?
This is a crucial question. Current results indicate that the ability to possess inocles has a positive effect on the good bacteria, as they become more resistant. In cancer patients, for example, the number of Inocles was found to be significantly reduced. This could mean that the Inocles make the host more stress-resistant and less susceptible to disease.
Potential impact on health and everyday life
The research is still in its infancy. At this early stage, it is still quite normal for initial hypotheses to be discarded and new ones to be added. Nevertheless, it is at least possible to imagine what this discovery could mean, even if these are not yet data-based at this stage.
Oral health
Inocles could help the oral flora to remain resistant. The discovery shows that oral hygiene is not just about “fighting bacteria”. In future, useful germs could be promoted with such extra genes rather than destroying them with alcohol-based mouthwashes.
Vaginal microbiome
If inocles are also found in other microbiomes, this could explain why some women are more susceptible to vaginal dysbiosis than others.
Nutrition
Inocles could help their host bacteria to react more flexibly to changing environmental conditions in the oral cavity – such as changes in pH or nutrient supply. This would not only help to make the oral microbiome more stable, but would also mean improved nutrient uptake.
Diagnostics
Fewer inocles were found in the saliva of certain cancer patients. Perhaps these DNA rings will be useful as an early warning sign of cancer in the future. Future tests would not only determine the bacterial species, but also their inocle status. This would then provide clear indications as to whether the microbiome of the person being examined has genetic flexibility and regenerative capacity. An inocle-rich profile could then be considered an indication of a resilient and healthy microbiome.
Probiotics
Good oral bacteria with Inocles could serve as particularly robust probiotics – provided that such DNA rings can be passed on in a targeted manner.
The most important facts at a glance
- Inocles are giant DNA rings in the bacteria of the oral microbiome
- Your oral flora is complex – pay attention to thorough oral hygiene, but avoid alcoholic mouth solutions.
- Inocles offer the bacteria huge advantages: they could explain why some people are more resistant to disease.
- Inocles act as an ingenious upgrade for bacteria.
- The discovery shows the enormous role played by the microbiome: new findings are being added every day.
- In future, tests could not only determine the types of bacteria, but also their inoculum status.
- This would provide information on the genetic flexibility and regenerative capacity of the microbiome.
- An “Inocle-rich” profile could be a sign of a resilient, healthy microbiome.
So make sure you have a healthy microbiome – take care of it!
Related article: Mouthwash in the crossfire
Source
Kiguchi, Y., Hamamoto, N., Kashima, Y. et al. Giant extrachromosomal element “Inocle” potentially expands the adaptive capacity of the human oral microbiome. Nat Commun 16, 7397 (2025). https://doi.org/10.1038/s41467-025-62406-5
