In the long list of genomic “firsts,” scientists have added another today: the oldest known pathogen ever sequenced. And it comes from perhaps the most famous “iceman,” Ötzi, who lived in the Alps of Central Europe more than 5,000 years ago. The secrets lurking in its genome suggest surprisingly recent ancient migrations of people into Europe.
Ötzi was found on September 9, 1991 by German hikers at an altitude of 10,000 feet near the Austrian-Italian border. He had a number of physical ailments: Lyme disease, high levels of arsenic, tooth decay…and yet, what killed Ötzi appeared to be an arrowhead, found in his left shoulder. The weapon must have lacerated a major artery once it entered his body.
A little over five years ago, Albert Zink and his colleagues at the European Academy of Bolzano/Bozen (EURAC) decided to look for the presence of pathogens and microorganism in Ötzi’s stomach. They were also searching for a special bacterium called Helicobacter pylori.
Our bodies are host to around 100 trillion bacteria—H. pylori is just one species, but it is present in more than 50% of the world’s population. When it was first discovered, H. pylori was thought to cause cancer and ulcers. However, most people with the bacterium do not experience symptoms or complications, despite its association with gastrointestinal problems. Instead, H. pylori appears to play an important role in the overall gut ecosystem, and the absence of it is linked to several immune and metabolic disorders.
Now, a team of scientists working with Zink and microbiologist Frank Maixner—also from the EURAC—has processed Ötzi’s genomic data to better understand the contents of his microbiome and what it can tell us about our microbial “hitchhikers” through the ages. When the team first placed samples from Ötzi’s stomach under the microscope, they were skeptical as to whether or not they would see any H. pylori strains. But once they extracted the entire DNA of the stomach’s contents, they were able to isolate the H. pylori sequence.
What the team found is that this ancient strain of H. pylori belonged to a now-extinct population of the bacterium that was first found in northern India and other parts of southern Asia. In addition, the scientists found little evidence of the African strain which is present in the modern European “admixture.”
“This puts things into wonderful perspective for us with just one genome,” said study co-author Yoshan Moodley of the University of Venda in South Africa. Since H. pylori has been floating around inside the human microbiome for a long time, it has co-evolved with humans, so genetic analyses of H. pylori strains can reflect the history of human geography as a whole. What this new discovery shows is that relatively recent migrations (after Ötzi’s time) must have occurred for the European strain of H. pylori to become what it is today.
“This genome is very unique and gives us an idea of what we can expect from the emerging field of microbiology in the future,” said Thomas Rattei of the University of Vienna. “It allows us this absolutely unique window into the Copper Age.”