Researchers have recovered remarkably preserved microbiomes from two teeth dating back 4,000 years, found in an Irish limestone cave. Genetic analyses of these microbiomes reveal major changes in the oral microenvironment from the Bronze Age to today. The authors identified several bacteria linked to gum disease and provided the first high-quality ancient genome of Streptococcus mutans, the major culprit behind tooth decay. While S. mutans is 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 decays the tooth, but also destroys DNA and stops plaque from fossilising. While most ancient oral microbiomes are retrieved from fossilised plaque, this study targeted the tooth directly. Another reason for the scarcity of S. mutans in ancient mouths may be the lack of favourable habitats for this sugar-loving species. An uptick of dental cavities is seen in the archaeological record after the adoption of cereal agriculture thousands of years ago, but a far more dramatic increase has occurred only in the past few hundred years when sugary foods were introduced to the masses.
