Scientists thaw 5,300-year-old mummy to study ancient gut bacteria

Scientists say the famous "Iceman," a 5,300-year-old European mummy, may have been feeling a little ill on the day an unknown assailant chased him through the Alps, shot an arrow into his artery and killed him.

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A recent study shows the Copper-Age European, who is also known as Oetzi, carried a viral strain of Helicobacter pylori bacteria in his stomach, a discovery that scientists say sheds important light on both the Iceman's health and the history of human migration.

The findings were published in the journal Science on Thursday.

According to the study authors, Helicobacter pylori is one of the most common and ancient human pathogens.

Scientists estimate the bacteria has been infecting humans for at least 100,000 years. But researcher say the Iceman sample is the oldest Helicobacter pylori DNA they've ever examined in depth.

"That is why this genome is so special," study co-author Yoshan Moodley, a genetics and biology professor at South Africa's University of Venda, told reporters in a teleconference on Wednesday. "It allows us this absolutely unique window into the Copper Age. We don't have to infer it. We can see."

Helicobacter pylori can cause ulcers or gastric carcinoma, but fewer than 10 per cent of carriers actually suffer from these symptoms.

Because of this, it's unknown if Iceman actually felt the effects of his bacterial infection.

"We can't be 100 per cent sure that he really suffered from gastric disease," Moodley said. "We have clear evidence that he had immune reactions, but we can't really say to what extent."

Thawing the Iceman and extracting the samples

The Iceman's remains are usually kept in Italy's South Tyrol Museum of Archeology, where the museum imitates the Alpine conditions in which the body was preserved until hikers found it in 1991.

But in order to extract and examine bacteria from the Iceman's stomach, scientists had to temporarily thaw the mummy.

Researchers did this in a tightly controlled environment, the Iceman wasn't harmed in the process and he was later refrozen, says study co-author Albert Zink, the scientific director at the Institute for Mummies and the Iceman.

Once the body was defrosted, researchers accessed the stomach through a previously-made incision, and extracted samples from his gastrointestinal tract.

In these samples, they found the presence of Helicobacter pylori, and were able to reconstruct the bacteria's genome and examine its genetic makeup.

This analysis, the study says, led to a "surprising" new understanding of ancient Europeans' origins.

Using Helicobacter pylori to trace human migration

Because Helicobacter pylori has existed in humans for so long, scientists say its evolution reflects the way human populations have grown, migrated and changed.

"Helicobacter pylori's worldwide population structure is almost literally a mirror image of human populations," Moodley said. "So we use them as a surrogate for what humans were doing at various stages of prehistory."

Modern strains of the bacteria are categorized according to geographic location, and can be traced back to different ancestral sources.

The modern Helicobacter pylori strain in Europe, for example, comes from a combination of ancestral bacteria from Asia and Africa.

But scientists were surprised to find that the ancient bacteria in the Iceman's stomach showed only the Asian strain, not a mixture with the African variation.

Scientists say this suggests a wave of human migration arrived in Europe from Africa sometime after the Iceman's death, introducing the North African strain of bacteria to the population.

"The wave of migration that brought the African Helicobacter pylori into Europe had not occurred, or had not occurred in earnest, by the time the Iceman was alive," Moodley concluded.

'Paleomicrobiology' and examining other mummy guts

Now that scientists have successfully extracted and reconstructed bacteria from the Iceman, they hope to use similar techniques to explore other ancient gut bacteria.

"One thing we definitely want to do is to expand our investigation to other mummies," Zink said on Wednesday.

He said he and his co-researchers have already been in touch with colleagues in Northern Europe, South America and Asia, and also hope to trace the paths of ancient bacteria in Siberia.

Eventually, Zink said, he hopes this could open the doors to a "totally new" field of research, which he dubs "paleomicrobiology."


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