Researchers have extracted the oldest complete genome sequence of a pathogen yet, from the body of the 5,300-year-old ice mummy Ötzi.
According to a 7 January paper1 in Science, the ‘Iceman’ was infected with the bacterium Helicobacter pylori, which also plagues modern humans.
Few corpses have drawn more attention from researchers than Ötzi’s, discovered in 1991 encased in ice at an altitude of more than 3,000 metres, by hikers exploring the Tyrolean Alps in Italy. The cause of his death is believed to have been an arrow in the back, but researchers have shown that Ötzi suffered from myriad health problems, including cavities, hardened arteries and possibly Lyme disease.
In 2010, researchers examining a computed tomography (CT) scan of Ötzi noticed that his stomach had been preserved. After they opened him up, they discovered that his last meal had contained ibex and wild grains. Then, a team led by biomolecular archaeologist Albert Zink at the Institute for Mummies and the Iceman in Bolzano, Italy, decided to look for H. pylori.
Roughly half of all modern humans carry the stomach bacterium, which causes ulcers in a small percentage of carriers and can lead to stomach cancer.
Using purification techniques similar to those used to extract the DNA of bubonic-plague-causing bacteria from the teeth of Black Death victims, Zink’s team obtained genetic material from Ötzi’s stomach that matched 92% of the modern pathogen’s 1.6-million-letter genome.
The strain that infected the iceman contained genes for a cellular toxin that allows modern H. pylori to cause ulcers. Zink’s team also identified protein fragments that are found in the inflamed stomach tissue of people harbouring H. pylori. This suggests that Ötzi may have been made ill by his infection.
The strain found in Ötzi was genetically distinct from the H. pylori most common in modern Europe, which is a recombinant hybrid of two strains related to those that circulate in India and North Africa. Ötzi’s H. pylori matches only the Indian strain.
Humans acquire H. pylori through close contact, usually from family members, and researchers have used the bacterium’s DNA to trace past human migrations. Zink’s team suggests that the migration that brought the North African strain to Europe occurred after Ötzi died. It is also possible that other Europeans who lived at the same time as Ötzi harboured recombinant H. pylori, the authors acknowledge.
Study co-author Yoshan Moodley, a geneticist at the University of Venda in Thohoyandou, South Africa, told journalists that the Ötzi bacterium was probably the original strain that lived in the stomachs of the first Europeans.
“This ancient HP strain has allowed us what is perhaps a unique opportunity to discover what populations of Helicobacter pylori existed in Europe during this copper age,” he told journalists. “This might never happen again that we find such a wonderfully preserved specimen where Helicobacter pylori DNA still can be extracted.”
Daniel Falush, a population geneticist at Swansea University, UK, says that the study solves an important question about when the hybrid H. pylori strain carried by modern Europeans emerged. A previous study2 proposed that it may have arisen in the Middle East as long ago as 50,000 years. It is not yet clear how a North African H. pylori strain got to Europe, Falush says. "Some of the pharaohs in the Nile Valley may have transmitted it," he jokes.
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