Ötzi the Iceman is long dead, but some of his ancient microbes are still alive

Ötzi the Iceman, the well-preserved and well-studied mummy of a man who died 5,300 years ago, is a "dynamic ecosystem" of microbes, some of which have stayed viable for millennia, according to new research.

In a comprehensive DNA analysis of the microbes inside and out of Ötzi's mummified body, scientists linked several species of fungi to the chilly mountain environment where he died; they likely colonized his corpse and froze with it. The fungi's natural resistance to cold kept them dormant but still alive and capable of reviving, even after thousands of years, according to research published last week in the journal Microbiome.

In fact, some of the microbes "are not merely dormant relics" but may be multiplying slowly in micropockets of mummy moisture, the study authors reported. This growth suggests that microbial longevity and activity in ancient remains may be greater than once thought and should be taken into account during such remains' storage and handling, according to the study.

"In many studies of DNA from ancient human remains, the microbial DNA is largely ignored, and it's often not clear if the microbial DNA that is recovered is as old as the human body itself or more recent contamination," Anders Bergström, a researcher in evolutionary genomics at the UK's University of East Anglia, told CNN in an email. "This study of Ötzi now provides some fascinating insights into this." Bergström was not involved in the new research.

Scientists hypothesized that Ötzi had no human companions with him when he breathed his last on the frigid Ötztal Alps — but he wasn't truly alone. Trillions of microbes populated his living body and lingered in his corpse, including some that came from the site where he died.

"These microbes give us a unique and precious snapshot of what the human gut looked like in the Copper Age, before industrialization reshaped our microbiome," said senior study author Frank Maixner, head of the Institute for Mummy Studies at Eurac Research in Bolzano, Italy, where the work on the mummy was conducted.

"We identified ancient gut bacteria preserved inside Ötzi that are extremely rare in people living modern, industrialized lifestyles today — though they can still be found in people with traditional, non-industrialized ways of life," Maixner told CNN in an email.

To scientists, Ötzi's microbes are almost as interesting as Ötzi himself, offering clues about his microbiome and health, and hinting at the diversity of microbial communities in ancient environments.

But when it comes to preserved organic remains, microbes can also cause problems. For millennia, glacial ice and freezing temperatures protected Ötzi's body — and microbes — from degradation and decay. After hikers discovered the mummy in 1991 along the Austrian-Italian border, the remains were stored at the South Tyrol Museum of Archaeology in Bolzano, where it was frozen at about 21 degrees Fahrenheit (minus 6 degrees Celsius) with 99% relative humidity. These conditions were similar to those in the glacier where Ötzi was found.

However, scientists recently questioned if that strategy truly kept microbes in check, as some types of microbes are known to thrive in extremely cold environments. What's more, handling a mummy exposes it to potential contamination from modern bacteria and fungi, further clouding the picture of its microbial makeup.

Managing microbes

For the new study, scientists conducted a detailed survey of Ötzi's microbes. They probed water reservoirs inside his body, swabbed the mummy's exterior and sampled exposed internal tissues. They examined soil taken from underneath the mummy during its 1991 excavation, and they referenced data from samples that were previously collected from deep inside Ötzi's gut.

The researchers also collected and cultured airborne microbes from the mummy's storage chamber and from the room where the remains were handled. From their swabs and samples, they were able to culture some of the microbes. Then, by extracting DNA from viable and nonviable specimens alike and examining the extent of DNA damage, the scientists could identify species of fungi and bacteria and estimate whether they were ancient or modern, teasing out which microbes originated with Ötzi, which likely migrated onto his body after death and which may have been introduced later through handling.

The most common microbes on Ötzi's surface tissues were the bacteria Methylobacterium and Sphingomonas, which were introduced by humans through modern handling, according to the study. Another type of bacteria, Staphylococcus, was ascribed to the mummy's microbiome.

Four yeasts — Glaciozyma, Goffeauzyma, Mrakia and Phenoliferia — were found internally and on Ötzi's exterior. Genetic similarities to cold-adapted fungi found in places such as Antarctica suggested that these were environmental microbes, and their significant DNA damage linked them to Ötzi's ancient Alps ecosystem.

"Our results provide the baseline for future microbial surveys of the Iceman," Maixner said. Now that the scientists know which microbes are present, they hope to better understand what these fungi and bacteria are doing and how they might be interacting in the "ecosystem" of Ötzi's body, he explained.

One of the yeasts, Glaciozyma, was more abundant on the mummy than it was in 2010 and showed less DNA damage, suggesting that it could replicate despite the deep freeze of museum storage. And with the exception of Mrakia, the yeasts all had genes enabling them to feed on compounds that were once used to protect ancient remains as well as organic matter. Though the mummy shows no signs of damage, this discovery raises concerns about its future safety and conservation.

The research is "an excellent piece of work that combines several study methods," including two types of genomic sequencing that provided detailed data for the fungi and bacteria, said René Cerritos, a research professor at the National Autonomous University of Mexico, who was not involved in the new research.

"The analysis that I find most interesting is the culture-dependent one," Cerritos told CNN in an email. "From this method, organisms can be recovered, even those as old as 5,300 years."

Still, it may be too soon to rule out that one of those purportedly revived ancient microbes, Staphylococcus, was not acquired through recent contamination, Cerritos added, as the species is common on human skin. Sequencing the sample's genome and comparing it to DNA in historical and modern strains of Staphylococcus could shed light on its age, he noted.

In the decades since Ötzi's discovery, scientists have pieced together many clues about his life and violent death, around the age of 46. His last meal included grain, plants and meat from deer and ibex. A deep cut on his hand and an arrow lodged in his shoulder suggest his final days were marked by violence; he likely bled to death from the shoulder wound. He had 61 tattoos, which are among the oldest in the world. Calcium deposits in his heart hinted at cardiac trouble, and his gut contained Helicobacter pylori, a microbe linked to gastric cancer and ulcers.

These new microbial findings could open a door to future insights — for Ötzi and other specimens from the distant past.

"Hopefully similarly careful studies can be performed on a wider range of human and animal remains, in particular on bone tissue which serves as the input material for the vast majority of ancient DNA studies," Bergström added.

"By studying how microbial communities on remains change over time, we can hopefully better understand what microbes were actually present at the time of death of the organism, which is what we are ultimately the most interested in."

Mindy Weisberger is a science writer and media producer whose work has appeared in Live Science, Scientific American and How It Works magazine. She is the author of "Rise of the Zombie Bugs: The Surprising Science of Parasitic Mind-Control" (Hopkins Press).

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