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Iceman’s Gut Microbes Shed Light on Ancient Human Geography

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Researchers Eduard Egarter-Vigl and Albert Zink take a sample from the Iceman mummy in November 2010. | © EURAC/Marion Lafogler

Analysis of bacteria from the gut of the "Iceman," a famous 5300-year-old European glacial mummy, provides an intriguing glimpse at ancient human migrations, according to a study published in the 8 January issue of Science.

Frank Maixner of the Institute for Mummies and the Iceman and colleagues took samples from the gut of the ancient man frozen in the Alps, analyzing the samples in the hopes of detecting evidence of Helicobacter pylori. H.pylori is a bacterium that has resided within its human host for so many generations that different strains have evolved as humans migrated around the world, meaning that genetic analysis of strains of this bacterium can be used to map the history of human geography. It is passed on from one person to another by close contact; for example, in children who play with each other.

Nowadays, H. pylori only rarely causes symptoms such as ulcers and inflammation of the stomach, but it seems that the strain within the Iceman was producing virulent factors, suggesting that he may have felt a bit ill on the day that he was murdered. Previous analyses from other teams of researchers suggest that the Iceman suffered numerous wounds before his death, but a blow to the head is likely what killed him.

Furthermore, the strain of H. pylori that the Iceman harbored shares a high level of ancestry with an ancient Asian strain of the bacterium that originated around modern-day India. This comes as a surprise because most modern-day Europeans harbor a hybrid strain of H. pylori that shares both Asian and African ancestry.

Until now, researchers could only speculate about when H. pylori within Europeans became a hybrid African and Asian strain. Successfully deciphering the genome of the ancient strain within the Iceman provides the first evidence that the Asian and African strains had not mixed during the Iceman's lifetime, 5300 years ago.

 
frank Maixner discusses how the Iceman's gut bacteria can be used to time certain human migrations. | © EURAC

If the Iceman's H. pylori strain is representative of local Europeans during the Copper Age, which data strongly suggest, these results imply that African strains mixed with European strains within the past few thousand years.

Yoshan Moodley of Max Planck Institute for Infection Biology, a researcher involved with the study, noted that these new data address questions that researchers have been trying to answer for years. "This puts things into wonderful perspective for us with just one genome. We can say that the waves of migrations that brought the African H. pylori into Europe had not occurred, or had not occurred in earnest, by the time the Iceman was alive."

Previously, piecing together ancient bacterial genomes to depict the historical migration of humans would seem near impossible — the researchers had to correctly identify the right type of bacteria and piece together its fragmented DNA. But thanks to evolving techniques, researchers have better means to decipher these ancient genomes. Maixner noted that the study marks the most ancient genome of H. pylori that has been published to date.

"This was really challenging and I was not sure we could succeed in the reconstruction of such an ancient genome," Maixner said. "Now that we are aware of how [to analyze these ancient genomes], we are keen to continue. Several research projects to take place in South America and Asia are currently at the planning stage."

The team is contacting researchers on these continents to see if they will be able to analyze samples from other ancient, well-preserved mummies that may harbor strains of H. pylori, to gain even more insights into ancient human migration worldwide.

[Credit for associated teaser image: © EURAC/Marion Lafogler]