It was a quick death: an arrow severed a major artery as it entered the Iceman’s chest. If it hadn’t been for his location in the Italian Alps, his body would have decomposed soon after his death 5 300 years ago. Instead, the Iceman, often referred to as Ötzi after the mountain range, is the world’s oldest natural mummy, with his body tissues and insides freeze dried and well preserved.
By sequencing the genome of some gut bacteria in Ötzi, researchers have cast doubt on accepted theories about how and when different population groups migrated out of Africa.
The international team, whose findings were published in the journal Science on Thursday, sequenced the genome of a species of gut bacteria in Ötzi’s stomach. These are still present in many people today but because bacteria evolve more quickly than humans, different populations have different strains of the bacteria: our gut bacteria moved with us as we migrated around the world.
More than half of today’s population has Helicobacter pylori bacteria in their stomach, but, while some H. pylori are asymptomatic, others cause ulcers and other acute stomach problems, depending on the strain.
The project to determine the contents of the Iceman’s stomach began in 2010, and the international team included South African geneticist Yoshan Moodley, a professor of zoology at the University of Venda.
Moodley said: “This gut pathogen can only live in humans and, from the structure of the pathogen, you can figure out what the people were doing [in terms of migration]. The bacteria’s genetics are almost a mirror image of our genetics. It’s a fascinating little thing.”
According to the paper, “H. pylori is a bacterium that has resided in humans for so long 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.”
Current European populations of H. pylori are a hybrid of Asian and African bacteria strains, which people brought with them when they migrated into Europe, but there are question marks about when and where this hybridisation happened.
However, the genome of the bacteria sequenced from the Iceman is a “nearly pure representative” of Asian-derived H. pylori, suggesting that African populations arrived in Europe in the past few thousand years, which is later than previously supposed. Previous research on Ötzi has ruled out the possibility that he was a traveller from the north Indian region where this bacteria strain is common.
Sequencing the genome from Ötzi’s desiccated stomach was also a feat. “Separating the H. pylori sequences from all other genetic material – food, microbiome, other pathogens and soil bacteria – was like searching a needle in a haystack,” said Professor Thomas Rattei, the head of computational systems biology at the University of Vienna.
Unfortunately for the Iceman, he was infected by a particularly malignant strain of H. pylori, and would have been feeling very poorly on the day that he was killed. “He was infected by a single, virulent strain of this bacterium,” Rattei said.