Scientists have discovered huge mysterious DNA fragments in oral microbiome – a population of bacteria and other microbes that live in our mouths – and they say this giant DNA can influence the human immune system.
It is well known that the mouth is home to a variety of bacteria, and these microbes can have both positive and negative effects on our oral and overall health.
The study represents “a new piece of the puzzle that is a step forward in understanding the oral microbiome, human health and disease.” Floyd Dewhurstprofessor at the ADA Forsyth Institute, who was not involved in the study, told Live Science via email.
Microbiome Researchthat have flourished in the last decade have shown that microbiomes throughout the body play an important role in human health and disease. Researchers have determined the types and proportions of different types of microbes that live in places like our planet. mouths And gutsand then used this data to see how differences in these functions relate to our health.
The genomes of these species have been studied extensively over the years, but traditional genetic analyzes have not yet been able to explain all the links between our microbiome and overall health.
Researchers in Yutaka Suzuki The University of Tokyo lab wanted to explore these missing data and were inspired by the recent discovery of giant extrachromosomal elements (ECEs) in soil-dwelling bacteria. ECEs are sections of DNA that are separate from the main genome of an organism. In humans, our mitochondrial DNA, stored in the powerhouses of our cells, is ECE. In bacteria, the commonly known small ECE is called a plasmid.
Lead author of the study Yuya Kiguchiwho is now a researcher at Stanford University, and his colleagues in the Suzuki laboratory predicted that giant ECEs could be found in bacteria living in places other than soil.
“It's possible that many of these giant extra chromosomal elements are found in the environment, in the microbiome field, or in pathogens,” Kiguchi told Live Science. “But we don’t know of any examples of these kinds of giant extra chromosomal elements in commensals. [human] Microbiome.” Commensal microbes are those microbes that live in symbiosis with or on the human body.
Using saliva samples from hundreds of people, researchers have discovered for the first time that giant ECEs also exist in our oral microbiome. The research team called these giant pieces of DNA “inocles”; the name means “Vthe sequence of certificates is encoded; Oral origin; circuscl Genomic structure”. They also found that approximately 74% of the people in their study had these grafts in their oral microbiome.
So why were inocles first discovered? Most genetic experiments on bacteria use short-read DNA sequencing techniques. This involves cutting a cell's DNA into smaller pieces, reading their code, and then assembling those pieces into a complete genome using a computer. Although this sequencing method can easily detect small ECUs such as typical bacterial plasmids, inoclines are too large and complex to be detected by short-read sequencing.
Using long-length DNA sequencing—a more expensive and labor-intensive method that sequences and stitches together much larger pieces of DNA—the scientists were able to identify these large pieces of extrachromosomal DNA in bacteria from human saliva samples. By comparing these results with blood samples from the same people, they also found that differences in inocles levels were associated with differences in the immune system, including the immune response to certain bacterial and viral infections.
Sixty-eight people in the study had either a type of head and neck cancer or colorectal cancer, and these people had lower levels of inoclets in their oral microbiomes compared to people without these cancers. This opens up the possibility of using these newly discovered giant DNA fragments as future cancer biomarkers, the study authors suggest.
As a next step, the researchers intend to grow these inocula in the laboratory to further study their function and how they might spread between bacteria and people.
“Now that we know that inocles exist, we can try to figure out their functions and potential roles in health and disease,” Dewhurst said.
