Iceman Otzi's gut bug sheds light on human migration

He was brutally murdered over 5,300 years ago, but analysis of microbes from the gut of the "Iceman," a famous European glacial mummy, is now offering insights into historical human geography.

The Iceman, also known as Otzi, is a mummified corpse that was discovered in 1991 by two German hikers in the Italian Alps, near the border of Austria. Otzi lived in the so-called Copper Age and died when he was around 40 to 50 years old. Scientists believe that he was exhumed by glaciers melting.

"He seems to have been on the run, pursued across a high altitude alpine landscape when he was caught and brutally murdered," said Caroline Ash, senior editor at the journal Science, which published the new research.

"Thanks to being buried in the ice for the intervening millennia, his well-preserved remains have provided some extraordinary hints of the life and times of ancient Europeans," added Ash.

Scientists started to examine the Iceman's stomach several years ago and were able to detect what he ate for his last meal. Then they started to examine his guts for the presence of different pathogens and microorganisms.

That's when they discovered that he was infected with a bacterium found only in humans called the Helicobacter pylori, which causes ulcers.

Microbes and human migration

Helicobacter pylori has resided within humans for so long, over 100,000 years, that different strains have evolved as humans migrated around the world and can be used as a way to track human distribution.

The analysis of the Iceman's stomach showed the presence of Helicobacter pylori that's somewhat different from the strain found in modern Europeans.

Modern Europeans harbor a strain that shares much more ancestry with North African strains.

That suggests that in the last 5,000 years, since Otzi's death, population mixing with more recent waves of human migration into Europe have affected the Helicobacter pylori genomes in modern day Europeans.

"We can say now that the waves of migration that brought these African Helicobacter pylori into Europe had not occurred, or at least not occurred in earnest, by the time the Iceman was around," said Yoshan Moodley, a senior author on the paper and professor at the University of Venda in South Africa, at a news conference organized by the journal.

Extracting gut tissue from a frozen mummy

Finding that out wasn't easy.

"One of the first challenges was then to obtain samples from the stomach without doing any damage to the mummy," said Albert Zink, senior author on the study and head of the Institute for Mummies and the Iceman.

"We had to completely defrost the mummy and we finally could get access to the mummy by an opening by an incision that was already done by a previous study," added Zink.

A detailed genetic analysis of the stomach led to the discovery of H. pylori DNA. The difficulty was distinguishing between ancient and modern DNA.

"We needed to make sure that we really have extracted the Iceman's bacteria and not any modern contamination," said Thomas Rattei, a senior author on the paper and the head of the division of computational systems biology at the University of Vienna.

By examining the DNA, scientists were able to show through the type of DNA sequence present and the degradation of the DNA that the bacteria was from the Iceman and not some other form of contaminant.

Nasty, brutish and short life

The Iceman not only died in a brutal fashion, but he also lived a harsh life. Analysis shows that the Iceman had intestinal parasites and a lot of degenerative diseases.

"He had several heel drop fractures, degenerative arthritis, vascular calcification and the presence of an arrowhead in his left shoulder was detected," said Zink.

To boot the iceman was lactose-intolerant and had a genetic predisposition for an increased risk of coronary heart disease said Zink.