Ötzi, a 5300-year old man found frozen in the Alps, has become the latest long-dead human to have his complete nuclear genome sequenced. Researchers previewed the Tyrolean Iceman’s genome sequence on 21 and 22 October at the Bolzano Mummy Congress in Italy.
Discovered 20 years ago near the Austrian-Italian border, Ötzi must be among the world’s most closely inspected corpses. We now know that he suffered from arthrosclerosis and cavities, bore mysterious tattoos, and gorged on ibex before dying with an arrow lodged in his back. There was also a lawsuit and a purported death curse linked to his remains.
In 2008, scientists reported the complete sequence of his mitochondrial genome. It suggests that his maternal lineage was similar to that of some modern Central Europeans, but the genome also contained mutations not found in present-day populations that have been surveyed.
To get a better grip on his ancestry and predisposition to disease, Albert Zink, head of the Institute for Mummies and the Iceman in Bolzano, and his team sequenced Ötzi’s 3 billion base pair nuclear genome from a shard of hip bone. Their sequence covers more than 90 percent of the Iceman’s genome. Their team also analysed DNA preserved in Ötzi’s stomach in hopes of revealing the microbes that colonized his gut.
Zink says his team is keeping most of the results of these studies under wraps, pending publication. They had hoped to have the paper out in time for last week’s Mummy Congress and a television special called Iceman Murder Mystery.
His team plans to use the sequence to determine Ötzi’s status for genetic variations linked to diseases in modern humans, particularly arthrosclerosis. A full nuclear genome will also paint a more detailed picture of the Iceman’s ancestry and his relationship to present-day humans. Zink’s team will ask whether Ötzi is an ancestor of people living in Central Europe today, or whether he and his kin died out and were replaced by migrants from elsewhere, such as the Middle East. To buff up this analysis, they are analysing DNA preserved in the skeletons of other ancient inhabitants of central Europe.
Ötzi’s genome has also been subject to genetic navel-gazing: Like many southern Europeans, he lacked mutations that would have helped him break down lactose as an adult, and he had brown hair and eyes (presumably this agrees with his frozen corpse).
Having just finished a feature story on the bacteria that caused the Black Death (which should be online later today), I am particularly interested in the microbes that may have colonized Ötzi. Zink’s team has found hints that he was infected with Borrelia burgdorferi, the bacterium that causes lyme disease, however Zink says this conclusion is preliminary. They have also found sequences matching Escherichia coli (a common gut microbe) and Clostridium bacteria (found in soil as well as the guts of some animals, including giant pandas).
Discerning true pathogen and symbiotic bacteria from soil microbes that have invaded ancient samples can be difficult, and some scientists have been dubious of previous claims — including some of Zink’s previous work on Egyptian mummy pathogens — that reported ancient microbes. However new technologies in DNA sequencing have led to a renaissance in ancient microbes research, and many once-sceptical researchers are leading the charge. Zink says the analysis of Ötzi’s microbiome could keep his team busy for another year.
Image courtesy of South Tyrol Museum of Archaeology