Keeping our teeth clean has been a pain for thousands of years, and some particularly painful methods have historically been used to care for munchies. Two 4,000-year-old human teeth unearthed in a limestone cave in Ireland were recently found to contain “unprecedented amounts” of bacteria that can cause cavities and gum disease. Genetic analysis of these well-conserved microbiomes reveals how dietary changes have shaped our oral health from the Bronze Age to today. Here are the findings: The study was published March 27 in the journal molecular biology and evolution.
Fossilized dental plaque has been one of the most well-studied ancient human body parts. but, Few complete genomes exist Bacteria from pre-medieval teeth oral bacteria have been discovered. This means scientists have limited data on how the human oral microbiome was affected by changes in diet and events such as the spread of agriculture about 10,000 years ago. do.
Acid-producing bacteria that munch on sugar
Both The teeth belonged to the same male individual. A person who lived in what is now Ireland during the Bronze Age. Teeth contain bacteria that cause periodontal disease.
High quality ancient genome Streptococcus mutans (Streptococcus mutans). This oral bacteria is one of the main causes of tooth decay.
Streptococcus mutans Although very common in modern human mouths, it is extremely rare in the ancient genomic record. One potential reason for it being so sparse is: How do bacteria produce acid?. Acid rots teeth, but it also destroys DNA and prevents plaque from fossilizing and hardening over time. Most ancient oral microbiomes are found inside these fossilized plaques, but this new study looked directly at teeth.
[Related: Vikings filed their teeth to cope with pain.]
Another reason Streptococcus mutans It may not have existed in ancient mouths, but that may have been because it lacked sweet mouths to breed from. Streptococcus mutans We love sugar, and the archaeological record shows that tooth decay has increased since humans started growing grains. But an even more dramatic increase has occurred in the past few centuries. Sweet foods became very popular.
Microbiome extinction hypothesis
The teeth were part of a larger skeleton discovered by the deceased in Killer Caves, County Limerick. Peter Woodman, University College Cork. Other teeth in the cave showed advanced decay, but there was no evidence of cavities or early cavities. It turns out that a single tooth contains a large amount of information mutans sequence.
“We were very surprised to see such a large amount of material present. Streptococcus mutans These 4,000-year-old teeth,” says study co-author Lara Cassidy, a geneticist at Trinity College in Dublin. stated in a statement. “This is an extremely rare finding and suggests that this man was at high risk for developing tooth decay shortly before death.”
The cool, dry, and alkaline conditions of the cave may have contributed to its preservation. Streptococcus mutans DNA. on the other hand, Streptococcus mutans DNA was abundant and other streptococcal species were almost absent in the tooth samples. This indicates that the natural balance or oral biofilm has changed.mutans outcompeted other bacterial species.
According to the research team, this study Microbiome extinction hypothesis. This idea suggests that our ancestors’ microbiomes were actually more diverse than ours today. Further evidence supporting this hypothesis is Tannerella forsythia (Forsythia) The team built it from the teeth. Forsythia still exists and causes periodontal disease.
“The two sampled teeth contained quite different distortions. Forsythia” Study co-author Isolt Jackson, PhD candidate at Trinity College Dublin stated in a statement. “Even though these modern samples originate from Europe, Japan, and the United States, these strains from a single ancient mouth are more abundant than any modern strain in our dataset. They were genetically different from each other. This is interesting because loss of biodiversity can have negative effects on the oral environment and human health.”
Genes and oral changes
Both reconstructed genomes reveal dramatic changes in the oral microenvironment over the past 750 years.one lineage Forsythia This is a sign of what geneticists call a selective episode. This is when a particular genetic advantage causes a strain of bacteria to increase rapidly in frequency.of Forsythia Genomes, especially those that emerged after the Industrial Revolution, acquired genes that help colonize the mouth and cause disease.
[Related: Bronze Age cauldrons show we’ve always loved meat, dairy, and fancy cookware.]
Streptococcus mutans They also found evidence of recent lineage expansion and changes in gene content that coincided with the spread of sugar.However, modern Streptococcus mutans Population remains diverse Forsythiaincluding some deep splits Streptococcus mutans An evolutionary tree older than the genome discovered in Ireland. The research team believes this is caused by evolutionary differences behind the genomic diversity of these bacterial species.
“Streptococcus mutans “We’re very adept at exchanging genetic material between lineages,” Cassidy said. “This allows advantageous innovations to be distributed across lineages. S. mutans Rather than one lineage becoming dominant and replacing all others, lineages change. ”
Both of these pathogens have changed dramatically in nature from the Bronze Age to today. However, very recent cultural changes, such as increased consumption of sugar, seem to be having a major impact.
