Researchers at Trinity College Dublin have recovered remarkably preserved microbiomes from two teeth dating back 4,000 years, found in an Irish limestone cave. Genetic analyzes of these microbiomes reveal important changes in the oral microenvironment from the Bronze Age to the present. Both teeth belonged to the same male individual and also provided a snapshot of his oral health.
The study, carried out in collaboration with archaeologists from the Atlantic University of Technology and the University of Edinburgh, was published today in the journal Molecular biology and evolution. The authors identified several bacteria related to gum disease and provided the first high-quality ancient genome of mutans streptococcusthe main culprit of cavities.
While S. mutans Although very common in modern mouths, it is exceptionally rare in the ancient genomic record. One reason for this may be the acid-producing nature of the species. This acid deteriorates the tooth, but it also destroys DNA and prevents plaque from fossilizing. While most ancient oral microbiomes are recovered from fossilized plaque, this study focused directly on the tooth.
Another reason for the shortage of S. mutans In old mouths it may be due to the lack of favorable habitats for this sugar-loving species. An increase in dental cavities is seen in the archaeological record after the adoption of cereal agriculture thousands of years ago, but a much more dramatic increase has only occurred in the last few hundred years, when sugary foods were introduced into the masses.
The teeth sampled were part of a larger skeletal assemblage excavated from Killuragh Cave, County Limerick, by the late Peter Woodman of University College Cork. While other teeth in the cave showed advanced decay, no decay was observed in the sampled teeth. However, one tooth produced an unprecedented amount of S. mutans DNA, a sign of an extreme imbalance in the oral microbial community.
“We were very surprised to see such a great abundance of S. mutans “In this 4,000-year-old tooth,” said Dr. Lara Cassidy, an assistant professor in Trinity’s School of Genetics and Microbiology and lead author of the study. “It is a remarkably rare finding and suggests that this man was at high risk of suffering from developing cavities just before his death.”
The researchers also found that other species of streptococci were virtually absent from the tooth. This indicates that the natural balance of the oral biofilm has been altered. mutates had outcompeted the other streptococci, leading to the pre-disease state.
The team also found evidence supporting the “disappearing microbiome” hypothesis, which proposes that modern microbiomes are less diverse than those of our ancestors. This is a cause for concern, as the loss of biodiversity can affect human health. The two Bronze Age teeth produced highly divergent tooth strains. Tannerella forsythiaa bacteria implicated in gum disease.
“These ancient single-mouth strains were more genetically different from each other than any pair of modern strains in our data set, despite modern samples derived from Europe, Japan, and the United States,” explained Iseult Jackson, a PhD candidate in Trinity, and first author of the study. “This represents a huge loss of diversity and we need to understand it better.”
Very few complete genomes of oral bacteria have been recovered before the medieval era. By characterizing prehistoric diversity, the authors were able to reveal dramatic changes in the oral microenvironment that have occurred since then.
Dr. Cassidy added: “Over the last 750 years, a single lineage of T. forsythia has become dominant throughout the world. This is the telltale sign of natural selection, where one strain rapidly increases in frequency due to some genetic advantage it possesses over others. T. forsythia Strains from the industrial era onwards contain many new genes that help bacteria colonize the mouth and cause disease.
“S. mutans It has also undergone recent lineage expansions and changes in the content of genes related to pathogenicity. These coincide with humanity’s massive consumption of sugar, although we discovered that modern S. mutans Populations have remained more diverse, with deep divisions in the S. mutans evolutionary tree prior to the Killuragh genome.”
Scientists believe this is due to differences in the evolutionary mechanisms that shape genome diversity in these species.
“S. mutans “It is very adept at exchanging genetic material between strains,” Dr. Cassidy said. “This means that an advantageous innovation can spread among S. mutans lineages like a new piece of technology. “This ability to easily share innovations may explain why this species retains many diverse lineages without one becoming dominant and replacing all the others.”
Indeed, these two disease-causing bacteria have changed dramatically from the Bronze Age to today, but it appears that very recent cultural transitions in the industrial age have had an outsized impact.