Genetic Secrets Explored From 4,000-year-old Human Molars: Evidence of Tooth Decay-causing Bacteria Discovered

Get inside the time machine and buckle up your seat belts! Today, I am driving you back to the Bronze Age!

An incredible group of researchers from Trinity College, Dublin, found evidence of tooth decay-causing bacteria in 4,000-year-old ancient human molars. They discovered this evidence by examining the remarkably preserved microbiomes in them.

Discovered in an Irish limestone cave, these teeth belonged to the same individual and offered a fascinating glimpse into his oral health and the ancient microbial world.

The team in collaboration with archaeologists from the Atlantic Technological University and the University of Edinburgh, uncovered significant changes in our oral microbiomes from the Bronze Age to the present.

The teeth were part of a larger skeletal collection excavated from Killuragh Cave in County Limerick by the late Peter Woodman of University College Cork.

A Rare Find: Ancient Streptococcus mutans

One of the most surprising discoveries was the presence of an exceptionally high amount of Streptococcus mutans DNA in one of the ancient teeth.

S. mutans is the primary culprit behind tooth decay and is incredibly common in modern mouths but rare in the ancient genomic record.

Its acid-producing nature not only decays teeth but also destroys DNA, preventing plaque from fossilizing. However, this study focused on only the tooth bypassing the usual difficulties in preserving ancient S. mutans.

Dr. Lara Cassidy, an assistant professor in Trinity's School of Genetics and Microbiology and senior author of the study, found it a remarkably rare find.

She suggested that this man was at a high risk of developing cavities right before his death!

Oral Microbiome Imbalance

Interestingly, while other teeth from the same cave showed advanced dental decay, the sampled teeth did not have visible cavities.

Yet, one tooth contained an unprecedented amount of S. mutans DNA, indicating an extreme imbalance in the oral microbial community.

Other streptococcal species were virtually absent, suggesting that S. mutans had outcompeted them, leading to a pre-disease state.

This discovery supports the "disappearing microbiome" hypothesis, which proposes that modern microbiomes are less diverse than those of our ancestors.

The two Bronze Age teeth yielded highly divergent strains of Tannerella forsythia, another bacterium linked to gum disease.

These ancient strains were more genetically different from each other than any modern strains in the researchers' dataset, which spanned Europe, Japan, and the USA.

Evolutionary Insights and Modern Implications

There have been dramatic changes in our oral microbiomes over the centuries.

Over the last 750 years, a single lineage of T. forsythia has become dominant worldwide.

This dominance is a sign of natural selection, where one strain rises rapidly due to genetic advantages.

T. forsythia strains from the industrial era contain new genes that help them colonize the mouth and cause disease.

Similarly, S. mutans has also undergone significant changes, particularly in response to humanity's increased sugar consumption.

Despite these changes, modern S. mutans populations have remained diverse, with deep evolutionary splits predating the Killuragh genome.

S. mutans's ability to swap genetic material between strains allows advantageous innovations to spread like new technology.

This adaptability might explain why S. mutans maintains many diverse lineages without one becoming completely dominant.

A Window into the Past

This study offers a unique window into how our oral microbiomes have evolved and adapted from the Bronze Age to today.

It underscores how recent cultural shifts, particularly during the industrial era, have profoundly impacted our oral health.

These changes help us appreciate the complexity and resilience of our microbial companions.

It highlights the importance of maintaining a balanced and diverse microbiome for our overall health.

Post inspiration: Trinity College Dublin. (2024, March 27). Scientists extract genetic secrets from 4,000-year-old teeth to illuminate the impact of changing human diets over the centuries. ScienceDaily. Retrieved July 19, 2024