Some ancient microbes frozen with Ötzi the Iceman are still growing - Ars Technica

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Ötzi the Iceman, Europe’s most famous mummy, is crawling with microbes, some long dead, some still eking out a living after thousands of years, and some very modern.

After he died in the Ötztal Alps, the Copper Age man now known as Ötzi lay alone and forgotten for 5,300 years, until a group of hikers stumbled on his freeze-dried remains in 1991. Since then, he’s received a lot of attention from scientists, who have sequenced his DNA, pored over his last meal and the remains of his gut microbes, and examined his clothes and his broken tools. Today, Ötzi lies in a high-tech resting place at the South Tyrol Museum of Archaeology in Italy, where, it turns out, his body is still home to a handful of cold-adapted yeast species that have probably been with him since just after he died.

Slightly morbid souvenirs from the Alps

Microbiologist Mohamed S. Sarhan (of the Institute of Mummy Studies at the private Eurac Research center) and his colleagues recently sampled material from Ötzi’s stomach and meltwater from inside his body, swabbed his skin, and even sampled airborne microbes from his frozen storage room and the lab outside it. They also took samples from a block of frozen alpine soil taken from next to Ötzi’s body back in 1991.

We already know quite a bit about Ötzi’s gut microbes thanks to a 2019 study, but Sarhan and his colleagues wanted the bigger picture. Instead of just sequencing all the microbial DNA they could find on Ötzi, the researchers wanted to understand which species were really part of his ancient one-man ecosystem and which were modern contaminants.

Sarhan and his colleagues cultured some of the samples, and also put some through a process called shotgun metagenomics, which involves sequencing all the bits of DNA floating around in a sample. Inside Ötzi’s guts, Sarhan and his colleagues—like previous studies—found ancient DNA from a host of bacteria that match what we expect of ancient, “non-Westernized” gut microbiomes. But elsewhere on and in the mummy, the team also found some microbes that weren’t actually dead.

Two mountaineers (one of them Reinhold Messner) with Otzi, Europe’s oldest natural human mummy, in the Otztal Alps between Austria and Italy in September 1991.

Credit:<br>Paul Hanny/Gamma-Rapho/Getty Images

Two mountaineers (one of them Reinhold Messner) with Otzi, Europe’s oldest natural human mummy, in the Otztal Alps between Austria and Italy in September 1991.

Credit:

Paul Hanny/Gamma-Rapho/Getty Images

Ötzi is kept in carefully maintained conditions, as close as possible to the glacier that preserved his body for more than 5,000 years. The chamber is a brisk -6º Celsius, with 99 percent humidity carefully maintained by a spray of UV-treated water. That’s enough to protect the mummy from most of the microbes that usually help decompose human remains. But Sarhan and his colleagues were surprised to find that it’s also the perfect environment for a few microbes that Ötzi carried with him down from the mountains.

In samples from the mummy, Sarhan and his colleagues found four strains of cold-tolerant yeasts, all closely related to similar yeasts found in Arctic glaciers, in Antarctica, and high in the mountains of Italy and Russia. And unlike Ötzi’s long-dead gut bacteria, which left just broken, aging fragments of DNA behind, the yeasts seem to be alive and reproducing (albeit at, ahem, a glacial pace).

“These yeasts have accompanied Ötzi on his long journey through the millennia,” said Frank Maxiner, director of the Institute for Mummy Studies at Eurac and a coauthor of the recent study, in a press release. (Ötzi probably doesn’t find that terribly comforting, but you never know.)

Thawed ancient microbes or a long-lived colony?

The yeasts—species of Phenolifera, Glaciozyma, Goffeauzyma, and Mrakia, for the mycology fans—turned up on Ötzi’s skin, in his stomach, and in water sampled from inside his body. Sarhan and his colleagues cultured live yeast from the samples, but their shotgun metagenomics results also revealed a bunch of short fragments of DNA, most bearing the kind of damage that happens when DNA molecules break down over time. That’s a hallmark of ancient DNA, which meant that the yeasts had most likely been living on and in Ötzi’s body since shortly after he died.

And when Sarhan and his colleagues compared samples taken in 2010 to those taken in 2019, they saw longer fragments and less damage, on average—in other words, there was...