Old chewing gum gives insight into people and bacteria from the past

Researchers at the University of Copenhagen have successfully extracted a complete human genome from thousands of years of chewing gum. According to the researchers, it is a new untapped source of old DNA.

During excavations on Lolland, archaeologists found a type of 5,700-year-old "chewing gum" made from birch. In a new study, researchers from the University of Copenhagen have successfully extracted a complete ancient human genome from the field.

It is the first time that an entire ancient human genome has been extracted from anything other than human bones. The new research results have been published in the scientific journal Nature Communications.

"It is amazing to have obtained a complete ancient human genome from something other than bones," said associate professor Hannes Schroeder of the Globe Institute at the University of Copenhagen, who led the research.

`` In addition, we have also recovered DNA from oral microbes and several important human pathogens, making it a very valuable source of ancient DNA, especially for periods when we have no remains humans, '' adds Hannes Schroeder.

Based on the ancient human genome, the researchers found that the pitch of birch was chewed by a female. It was genetically closer to the hunter-gatherers of continental Europe than to those who lived at the time in central Scandinavia. They also found that she probably had dark skin, dark hair and blue eyes.

Sealed in the mud

The birch field was discovered during archaeological excavations in Syltholm, east of Rødbyhavn, in southern Denmark. The excavations are carried out by the Lolland-Falster Museum as part of the construction of the Fehmarn tunnel.

“Syltholm is completely unique. Almost everything is sealed in mud, which means that the conservation of organic remains is absolutely phenomenal, '' explains Theis Jensen, postdoctoral fellow at the Globe Institute, who worked on the study for his doctorate and also participated in the excavations at Syltholm .

`` It is the largest Stone Age site in Denmark and archaeological findings suggest that the people who occupied the site heavily exploited wild resources until the Neolithic, which is the period when farm animals and domestic animals were introduced for the first time in the south of Scandinavia '', Theis Adds Jensen.

This is reflected in the DNA results, as the researchers also identified traces of plant and animal DNA in the pitch - especially hazelnuts and duck - that could be part of the individual's diet.

Bacterial evolution

In addition, the researchers successfully extracted DNA from several oral microbiota in the field, including many commensal species and opportunistic pathogens.

“The preservation is incredibly good and we have managed to extract many different bacterial species that are characteristic of an oral microbiome. Our ancestors lived in a different environment and had a different lifestyle and diet, so it is interesting to know how this is reflected in their microbiome, ”says Hannes Schroeder.

The researchers also discovered DNA that could be attributed to the Epstein-Barr virus, which is known to cause infectious mononucleosis or glandular fever. According to Hannes Schroeder, ancient "chewing gum" has great potential in research on the composition of our ancestral microbiome and the evolution of important human pathogens.

"This can help us understand how pathogens have evolved and spread over time, and what makes them particularly virulent in a given environment. At the same time, it can help predict how a pathogen will behave in the future and how it might be contained or eradicated, ”says Hannes Schroeder.

Chewing gum, all purpose glue or medicine?

• Birch pitch is a black brown substance that is produced by heating birch bark. It was commonly used in prehistoric times for chopping stone tools as a multipurpose glue. The first known use of birch pitch dates back to the Paleolithic.
• Pieces of birch pitch are often found with dental impressions suggesting that they have been chewed. As the pitch solidifies on cooling, it has been suggested that it has been chewed to make it malleable again before being used for hafting, etc.
• Other uses of birch have also been suggested. For example, one theory suggests that birch pitch could have been used to relieve toothache or other ailments because it is slightly antiseptic. Other theories suggest that people may have used it as some kind of prehistoric toothbrush, to suppress hunger, or just to have fun like chewing gum.

Journal Reference:

Theis Z. T. Jensen, Jonas Niemann, Katrine Højholt Iversen, Anna K. Fotakis, Shyam Gopalakrishnan, Åshild J. Vågene, Mikkel Winther Pedersen, Mikkel-Holger S. Sinding, Martin R. Ellegaard, Morten E. Allentoft, Liam T. Lanigan, Alberto J. Taurozzi, Sofie Holtsmark Nielsen, Michael W. Dee, Martin N. Mortensen, Mads C. Christensen, Søren A. Sørensen, Matthew J. Collins, M. Thomas P. Gilbert, Martin Sikora, Simon Rasmussen, Hannes Schroeder. A 5700 year-old human genome and oral microbiome from chewed birch pitch. Nature Communications, 2019; 10 (1) DOI: 10.1038/s41467-019-13549-9