A latest research, published in Nature Communications, revealed that our immune systems and oral health may benefit from giant DNA loops carried by oral bacteria, which may lower our risk of developing some types of cancer.
The newly identified nucleic acid rings, known as "Inocles," seem to be a sizable form of plasmid; these genetic components are present in many microorganisms outside of the primary DNA instruction manual.
Inocles, like bonus survival kits, are likely to be crucial in assisting bacteria, in this case Streptococcus bacteria, in adapting to the biological environment in the mouth, according to a team led by researchers from the University of Tokyo.
Yuya Kiguchi, a microbiologist from University of Tokyo, said, "We know there are a lot of different kinds of bacteria in the oral microbiome, but many of their functions and means of carrying out those functions are still unknown."
"By exploring this, we discovered Inocles, an example of extrachromosomal DNA – chunks of DNA that exist in cells, in this case bacteria, but outside their main DNA," the researcher added.
A thorough analysis of 56 volunteers' saliva samples revealed the enormous DNA loops, and additional testing was done on 476 samples to ascertain the prevalence of Inocles in the general population. According to the data, about three-quarters of us may be carrying the elements.
Ironically, Inocles' remarkable size may have contributed to its lack of prior sightings. While smaller DNA fragments are easier to read, the reconstruction of larger sequences is more difficult with conventional DNA sequencing techniques.
In order to circumvent this issue, the researchers developed a custom sequencing system known as preNuc, which eliminated human DNA from the sample and decreased the quantity of bacterial DNA jigsaw pieces that needed to be sorted.
"The average genome size of [an] Inocle is 350 kilobase pairs, a measure of length for genetic sequences, so it is one of the largest extrachromosomal genetic elements in the human microbiome," said Kiguchi, adding, "Plasmids, other forms of extrachromosomal DNA, are at most a few tens of kilobase pairs."
"This long length endows Inocles with genes for various functions, including resistance to oxidative stress, DNA damage repair and cell wall-related genes, possibly involved in adapting to extracellular stress response."
Interestingly, among the larger group of saliva samples, those with head and neck cancer had significantly fewer of these DNA elements in their mouths, suggesting that the loops may be beneficial.
It is yet unknown if Inocles may be preventing cancer or if another factor may be decreasing the number of Inocles while increasing the risk of cancer.
The scientists are also eager to investigate the potential functions of the genes in Inocles, their potential for inter-individual transmission, and the potential effects they may have on oral health.
"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," concluded Kiguchi.
