Recovered from the ice of an Alpine glacier at the end of the last century, almost everything about Ötzi was already known. That he was about 45 when he was killed from behind some 5,300 years ago. A detailed genetic study published three years ago revealed that, besides being bald, he had a dark complexion and likely came from distant Anatolia. We even know what he ate shortly before he was killed by an arrow. Now, a new study identifies the microscopic life he carried inside him. The paper, published in the journal Microbiome, shows that his bacteria were very different from those of people in modern societies. The researchers also found a number of cold-adapted fungi that have awakened thousands of years later and could threaten the mummy’s future.
“We have identified ancestral gut bacteria preserved in Ötzi that are extremely rare in people living modern, industrialized lifestyles, although they can still be found in people with traditional, non-industrialized lifestyles,” says Frank Maixner, director of the Institute for Mummy Studies at Eurac Research (Bolzano, Italy) and the study’s senior author. “These microbes give us a unique and valuable picture of what the human gut looked like in the Copper Age, before industrialization transformed our microbiota,” Maixner adds in an email.
The researchers took advantage of the rare opportunity in 2019 when Ötzi was thawed for five hours for a series of procedures on the mummy. During that time they sampled his skin and connective tissue, used about a dozen swabs on as many parts of his body, collected some of the water that melted from his interior, and reanalyzed the soil preserved since 1991 from where the mummy had been removed. They even studied the air inside the chamber where the Iceman is kept—always at the same temperature (−6º) and 99% humidity—which aims to replicate the conditions in which he was preserved for millennia.
Ötzi’s gut microbiome found now is the same one he had when he died, although postmortem species typical of decomposition have been added to it. The team found a large number and variety of the genus Clostridia, already detected in some Egyptian mummies. In both the soil and the melted water they found microorganisms well adapted to the cold. In particular, they identified four species of fungi, all yeasts, such as Glaciozyma watsonii and Phenoliferia glacialis, whose names are telling: these are psychrophilic microbes, accustomed to icy environments. Some of them had previously been found far from the Alps, in places like the Russian Arctic or Antarctica.
What is intriguing about these yeasts is that, despite accompanying Ötzi in his death, some samples showed only limited DNA damage. That would indicate that at least some of those found on the Iceman’s skin were active when they were studied. Moreover, by comparing them with samples taken in 2010, the researchers confirmed that they have not remained static—that the mummy’s microbial ecosystem did not stay frozen for 5,300 years. This leads the authors to write in their conclusions: “The crucial question now is whether these yeasts are descendants of ancient yeasts that continued to replicate over the years, or whether they were in a latent state that reactivated after the mummy was thawed.”
According to Maixner, “here we see continuity. These yeasts have accompanied Ötzi on his long journey through the millennia.” For him, this would demonstrate that the mummy “is not a static relic, but a dynamic biological system.” But it also means the mummy may be at risk. When they removed him from the ice, they used a chemical compound (phenol or carbolic acid) to decontaminate him. But, as with the arms race between antibiotics and bacteria, this may have suppressed some microorganisms while leaving the door open to others—such as these yeasts that thrive on the Iceman’s skin.
“The mummy’s conservation conditions are very stable nowadays,” says Elisabeth Vallazza, director of the South Tyrol Archaeological Museum, which oversees his preservation. “Extensive microbiological monitoring ensures the mummy does not suffer any damage. However, more research and comprehensive conservation efforts are unquestionably needed to preserve him for many more generations,” she adds in a statement.
But the study’s authors are clear that keeping Ötzi at −6º and 99% relative humidity is no longer sufficient to freeze his microbiome’s activity. “Our genomic analysis revealed that several of the microbes present—including some cold-adapted yeasts and certain bacteria—carry genes that encode enzymes capable of breaking down proteins, fats and even collagen, a key structural component of skin and connective tissue,” Maixner emphasizes, concluding: “this implies a latent biological risk to the mummy’s integrity in the long term.”
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