Scientists have discovered the DNA of ancient microbes inside of the remains of woolly and steppe mammoths. This microbial DNA, which may be one million years old or more, may be among the oldest DNA of this type ever discovered. Some of these microbes may have even been pathogens that sickened mammoths.
Reporting in Cell, researchers analyzed microbial DNA obtained from 483 samples of mammoths; this was the first time that 440 of these samples had been sequenced. The oldest sample was a steppe mammoth estimated to have lived about 1.1 million years ago. The investigators used various tools and techniques to differentiate between microbes that lived when the mammoths did, and microbes that were introduced after the death of the mammoths and later.
This work faced some challenges; some of the DNA had degraded, and there are not many similar microbial samples from that era that these novel sequences can be compared to. But it still provides us with an amazing look at how microbes have coexisted with animals, including mammoths, for millennia.
The analysis revealed six groups of microbes that have been linked to mammoths before, such as Actinobacillus, Erysipelothrix, Pasteurella, and Streptococcus. Some of these microbes may have been infectious pathogens, the scientists suggested.
Some microbial species likely lived in symbiosis with mammoths over extensive geographic lengths and time, probably for over one million years until the last mammoths died on Wrangel Island around 4,000 years ago.
This study found one bacterium related to Pasteurella that is a close relative of a pathogenic bacterium that sickens and kills African elephants. The closest living relatives of mammoths are African and Asian elephants, so it is possible that mammoths were vulnerable to some bacterial infections as well.
"Imagine holding a million-year-old mammoth tooth. What if I told you it still carries traces of the ancient microbes that lived together with this mammoth? Our results push the study of microbial DNA back beyond a million years, opening up new possibilities to explore how host-associated microbes evolved in parallel with their hosts," said first study author Benjamin Guinet, a postdoctoral fellow at the Center for Paleogenetics at the Swedish Museum of Natural History.
"This work opens a new chapter in understanding the biology of extinct species. Not only can we study the genomes of mammoths themselves, but we can now begin to explore the microbial communities that lived inside them," added penultimate study author Love Dalén, a Professor of Evolutionary Genomics at the Center for Paleogenetics.
Sources: Stockholm University, Cell
