Iceman died a long time ago, but his microbes are still alive

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

In a comprehensive analysis of the DNA of microbes inside and outside Ötzi's mummified body, scientists linked several species of fungi to the cold mountain environment where he died. They probably colonized his corpse and froze with it. Fungi's natural resistance to cold has kept them dormant but still alive and able to revive even after thousands of years, according to research published last week in the journal Microbiome.

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

"In many studies of DNA from ancient human remains, microbial DNA is largely ignored, and it is often unclear whether the recovered microbial DNA is as old as the human body itself or is more recent contamination," Anders Bergström, an evolutionary genomics researcher at the University of East Anglia in the United Kingdom, told CNN in an email. "This study by Ötzi now provides some fascinating insights into this." Bergström did not participate in the new research.

Scientists have hypothesized that Ötzi had no human companions when he breathed his last in the frigid Ötztal Alps - but he was not truly alone. Trillions of microbes populated his body while alive and remained on his corpse, including some from the place where he died.

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

"We identified ancient intestinal bacteria preserved within Ötzi that are extremely rare in people living modern, industrialized lifestyles today - although they can still be found in people with traditional, non-industrialized lifestyles," Maixner told CNN in an email.

A reconstruction of Ötzi, who died 5,300 years ago - Augustin Ochsenreiter/South Tyrol Archeology Museum
For scientists, Ötzi's microbes are almost as interesting as Ötzi himself, offering clues about his microbiome and health, and suggesting 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 decomposition. After hikers discovered the mummy in 1991 on the border between Austria and Italy, the remains were stored at the South Tyrolean Archaeological Museum in Bolzano, where they were frozen at around -6 degrees Celsius (21 degrees Fahrenheit) with 99% relative humidity. These conditions were similar to those on the glacier where Ötzi was found.

However, scientists have recently questioned whether this strategy actually kept microbes in check, as some types of microbes are known to thrive in extremely cold environments. Furthermore, handling a mummy exposes it to potential contamination by modern bacteria and fungi, which further complicates understanding its microbial composition.

Managing microbes
For the new study, scientists carried out a detailed survey of Ötzi's microbes. They analyzed the water reservoirs inside his body, took samples from the mummy's outer surface and exposed internal tissues. They examined soil taken from beneath the mummy during its excavation in 1991 and consulted data from samples previously collected from inside Ötzi's intestine.

The researchers also collected and cultured microbes present in the air from the mummy's storage chamber and the room where the remains were handled. From samples and swabs, they were able to grow some of these microbes. Then, by extracting DNA from viable and non-viable specimens and examining the extent of DNA damage, scientists were able to identify fungal and bacterial species and estimate whether they were ancient or modern, unraveling which microbes originated with Ötzi, which likely migrated into his body after death, and which may have been introduced later during handling.

According to the study, the most common microbes in Ötzi's surface tissues were the bacteria Methylobacterium and Sphingomonas, introduced by humans through modern manipulation. Another type of bacteria, Staphylococcus, was also identified in the mummy's microbiome.

Microbiologist Mohamed Sarhan examines yeast colonies taken from a sample of Ötzi's stomach - Andrea De Giovanni/Eurac Research
Four yeasts - Glaciozyma, Goffeauzyma, Mrakia and Phenoliferia - were found internally and on the external surface of Ötzi. Genetic similarities with cold-adapted fungi found in places like Antarctica suggested they were environmental microbes, and significant damage to their DNA linked them to the ancient alpine ecosystem of Ötzi.

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

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

The research is "an excellent work that combines several study methods," including two types of genomic sequencing that provided detailed data on 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 I find most interesting is the one that depends on culture," Cerritos told CNN in an email. "With this method, it is possible to recover organisms, even those up to 5,300 years old."

Sarhan examines yeast cells under a microscope - Andrea De Giovanni/Eurac Research
Still, it may be premature to rule out the possibility that one of these supposedly revived ancient microbes, Staphylococcus, was acquired through recent contamination, Cerritos added, since the species is common on human skin. Sequencing the sample's genome and comparing it to DNA from historical and modern strains of Staphylococcus could clarify its age, he noted.

In the decades since Ötzi's discovery, scientists have gathered many clues about his life and violent death, around the age of 46. His last meal included grains, plants, and the meat of deer and ibex. A deep cut on his hand and an arrow lodged in his shoulder suggest that his final days were marked by violence; he likely died of hemorrhage from his shoulder wound. He had 61 tattoos, which are among the oldest in the world. Calcium deposits in his heart indicated heart problems, and his intestine contained the bacteria Helicobacter pylori, a microbe associated with gastric cancer and ulcers.

These new microbial discoveries could pave the way for future knowledge - about Ötzi and other specimens from the remote past.

"We hope that equally careful studies can be carried out on a wider range of human and animal remains, in particular on bone tissue, which serves as input material for the vast majority of ancient DNA studies," Bergström added.

"By studying how microbial communities in human remains change over time, we hope to be able to better understand which microbes were actually present at the time of the organism's death, which is ultimately what interests us most."

Source: CNN