In a new study published in Cell, scientists have uncovered the oldest-ever host-associated bacterial DNA, found in the remains of a mammoth that lived over 1.1 million years ago. This discovery reveals a long-lost relationship between extinct animals and the bacteria that evolved alongside them.
A Million-year-old Tooth With Hidden Secrets
The breakthrough comes from the Centre for Palaeogenetics in Sweden, a research collaboration between Stockholm University and the Swedish Museum of Natural History. Their team analyzed DNA from 483 mammoth remains, and 440 of those had never been sequenced before. One of them—a tooth from a steppe mammoth—ended up being the jackpot.
That tooth, preserved in permafrost since the Ice Age, held traces of microbial DNA that once lived inside the animal itself. Not bacteria that showed up after it died—real, living passengers from when the mammoth was alive. According to Dr. Benjamin Guinet, a postdoctoral fellow and lead author of the study, the idea of a million-year-old mammoth tooth still carrying microbial traces isn’t just speculative anymore—it’s a reality.
Some Bacteria Were Helpful, Others Maybe Not So Much
Inside that ancient DNA, the team found six types of microbes that kept showing up in different mammoth samples. These included relatives of Pasteurella, Streptococcus, Actinobacillus, and Erysipelothrix. Some of these were likely harmless parts of the mammoth’s natural gut or oral microbiome.
One Pasteurella-like microbe closely resembled a modern bacterium that still causes deadly infections in African elephants today. Since elephants are the closest living relatives of mammoths, it’s very possible mammoths were vulnerable to the same kinds of infections. In fact, this connection might help explain some of the disease challenges Ice Age animals faced.
The researchers also managed to reconstruct part of the genome of Erysipelothrix, a type of bacteria that still infects pigs, poultry, and other animals. That makes this the oldest known host-associated microbial DNA ever successfully sequenced—something no one thought was possible until now.
Cracking Ancient DNA Wasn’t Easy
Unraveling the microbial DNA was no small feat. As microbes evolve quickly, tracing their lineage across such deep timeframes is like, in the words of senior author Dr. Tom van der Valk, “following a trail that kept rewriting itself.” Yet despite degraded samples and the challenges of distinguishing post-mortem invaders from genuine cohabitants, the team managed to extract invaluable biological signals from the past.
These insights are about more than just microbes. The study suggests that ancient microbial communities were shaped by long-term co-evolution with their hosts. Some lineages appear to have accompanied mammoths across tens of thousands of years and across entire continents—from the icy plains of northern Eurasia to the final woolly mammoth populations on Wrangel Island around 4,000 years ago.
What Ancient DNA Still Teaches Us
According to Professor Love Dalén, a senior researcher on the project, the implications go far beyond just mammoths. “Not only can we study the genomes of mammoths themselves, but we can now begin to explore the microbial communities that lived inside them,” he explained. These tiny organisms may have played a role in the health, adaptation, and even extinction of their massive hosts.
What emerges is a vivid reminder that prehistoric life isn’t confined to skeletons and fossils. Microbes, often overlooked, are proving to be persistent storytellers of the ancient past—carrying with them clues about the environments, health challenges, and evolutionary paths of the animals they once inhabited.
