A microbial Pompeii

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old teeth
The plaque on ancient teeth preserves a record of our germy past.

Apr 26, 2014 — An international team of researchers has discovered a "microbial Pompeii" on the teeth of 1000-year-old skeletons. The key to the discovery is the dental calculus (plaque) that preserves bacteria and microscopic particles of food on the surfaces of teeth, effectively creating a mineral tomb for microbiomes.

The research team discovered that the ancient human oral cavity carries numerous opportunistic pathogens and that periodontal disease is caused by the same bacteria today as in the past, despite major changes in human diet and hygiene.

More than eight centuries before the invention of the first therapeutic antibiotics in the 1940s, the ancient human oral microbiome already contained the basic genetic machinery for antibiotic resistance. As well as health information, the scientists recovered dietary DNA, allowing the identification of dietary components, such as vegetables, that leave few traces in the archaeological record.

Led by the University of Zürich, the University of Copenhagen, and the University of York, this pioneering analysis of ancient oral microbiome ecology and function involved the contributions of 32 scientists at twelve institutions in seven countries.

The research published in Nature Genetics reveals that unlike bone which rapidly loses much of its molecular information when buried, calculus grows slowly in the mouth and enters the soil in a much more stable state, helping it to preserve biomolecules. This trait let the researchers examine ancient DNA that was not compromised by the burial environment.

They used an technique known as shotgun DNA sequencing to dental calculus and reconstructed the genome of a major periodontal pathogen. The team produced possibly the first genetic evidence of dietary biomolecules to be recovered from ancient dental calculus.

"Dental calculus is a window into the past and may well turn out to be one of the best-preserved records of human-associated microbes," says Professor Christian von Mering, an author of the study and Group Director at the SIB Swiss Institute of Bioinformatics, which performed the bioinformatics analysis.

The study has wide reaching implications for understanding the evolution of the human oral microbiome and the origins of periodontal disease. Periodontal disease causes distinctive proteomic changes in the dentition and is characterized by chronic inflammation, resulting in tooth and bone loss. Dr. Enrico Cappellini of the University of Copenhagen, a senior author of the study, describes the dental calculus analyzed in this study as a kind of "battlefield archaeological site, just at the molecular scale."

Today, moderate to severe periodontal disease affects more than 10% of the world's population and is linked to diverse systemic diseases, including cardiovascular disease, stroke, pulmonary disease, and type II diabetes. Although common in humans, domestic pets, and zoo animals, periodontal disease does not typically develop in wild animals, leading to speculation that it is an oral microbiome disease resulting from modern human lifestyles.

"As we learn more about the evolution of this microbiome in response to migration and changes in diet, health and medicine," says Professor Matthew Collins, of the University of York, a member of the team, "I can imagine a future in which most archaeologists regard calculus as more interesting than the teeth themselves."

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