Ötzi’s Frozen Remains: Discovering Metabolically Active Microorganisms in Ancient Ice

Recent research suggests that some microorganisms in the 5,300-year-old remains of Ötzi the Iceman may be metabolically active, despite his long-term ice preservation.

Ötzi’s mummified remains were discovered in 1991, as they melted from a glacier in the Alps near the Austria-Italy border. He is estimated to have lived between 3350 and 3120 BC. Over the last 35 years, studies of his remains revealed significant insights, including his probable dark complexion and baldness, and the fact that he had numerous tattoos. An arrow wound in his shoulder indicates he was murdered.

Ötzi is currently housed at the South Tyrol Archaeological Museum in Bolzano, Italy, under conditions that replicate those of his original icy environment: -6°C (21°F) with 99% relative humidity.

Researchers, including Frank Meixner from the Eulac Institute Mummy Research Institute, analyzed skin swabs, tissue fragments, and thawed water samples from Ötzi, collected in 1992, 2010, and 2019. They compared these to soil and ice samples from the discovery site in the 1990s.

Both ancient and modern microorganisms have been identified in Ötzi, with some possibly remaining metabolically active. “We can differentiate between Ötzi’s endogenous gut bacteria and those that entered his body from the environment after death,” Meixner explains.

Metagenomic analysis of internal tissues conducted by the research team has revealed specialized bacteria that thrive in mammalian intestines without oxygen, such as Treponema and Kineotrix. The extent of DNA damage in these bacteria suggests they were living in Ötzi’s body during his lifetime.

The diverse range of microbes found in Ötzi’s gut may reflect the varied diets of Chalcolithic humans, contrasting with those of modern Western societies, according to Meixner.

Additionally, the samples contained bacteria from the Pseudomonas genus, commonly found in soil and water. The DNA damage observed indicates these bacteria likely belong to an ancient microbial community at the discovery site.

The research team identified cold-tolerant or psychrophilic yeasts in Ötzi’s external samples: Phenoripheria, Graciojima, Gofojima, and Murakia.

Analysis indicated that these yeasts are also ancient microorganisms. Notably, the presence of Graciojima increased from 2010 to 2019, suggesting it may be metabolically active or capable of reproduction under current storage conditions.

“This is compelling evidence that Graciojima has colonized the mummy post-mortem,” states Nikolai Oskolkov, although he’d like additional data points to ensure results are not influenced by experimental conditions.

The increasing prevalence of yeast is intriguing, as noted by Damra Kaptan from the University of Stavanger, Norway. “Determining if it’s active will require us to check for RNA produced from the yeast DNA,” she elaborates. “It’s possible the yeast was dormant or partially activated during thawing.”

Some yeasts possess enzymes capable of breaking down proteins and collagen, which could potentially harm the mummies; however, researchers found no evidence of such damage.

The research team also identified microorganisms containing genes that can degrade the toxic compound phenol. Professor Meixner suggests this may be linked to treatments applied to the mummy in the 1990s aimed at controlling mold growth. “When Ötzi was discovered, there was already active mold, and he was treated with phenol,” he explains. “This could have strengthened the microbiome.”

Overall, the study indicates that Ötzi is not merely a biological time capsule, but rather a complex ecosystem formed from the inheritance of his gut microbes, the glacial environment, and over 30 years of preservation. “Given these microbes have been associated with the mummy from the start, should we consider them as part of his biological makeup?” questions Meixner.

He recommends ongoing genomic monitoring, including checks for activity signs like RNA and metabolites, to determine if the microbial community is awakening and affecting Ötzi’s tissue. If this occurs, scientists may need to reassess storage conditions to mitigate microbial activity.