Ötzi the Iceman has been frozen for 5,300 years, and something on him is still capable of growing.
Researchers at Eurac Research in Bolzano, Italy, took Europe's oldest natural mummy out of its chamber in April 2019 and held it at 4 degrees Celsius for five hours until the ice shell covering the body melted. They collected that meltwater and surface ice, swabbed 12 anatomical sites, took soft tissue, and cultured what came off. Four species of cold-loving yeast grew in the dish. Their findings appeared in the journal Microbiome on June 3.
The mummy is normally kept at minus 6 degrees Celsius and 99% relative humidity. That regime was designed to stop decomposition. It does stop most of it. What it does not stop, the analysis shows, is a small, specialized community that evolved for exactly those conditions.
Sorting Copper Age Gut Bacteria from Three Decades of Museum Handling
The scientific problem was separating Ötzi's own microbes from everything humans have introduced since hikers found him in the Ötztal Alps in 1991.
The team combined 16S rRNA sequencing, shotgun metagenomics and cultivation, then leaned on a chemical fingerprint of age: ancient DNA accumulates cytosine-to-thymine damage at fragment ends. Anaerobic bacteria recovered from internal tissue showed deamination frequencies frequently above 10% and reaching 20%, confirming genuine antiquity.
Inside the intestines, they found Romboutsia hominis, Clostridium moniliforme, Ruminococcus bromii, Treponema succinifaciens, Huintestinicola butyrica and species of Kineothrix and Eubacterium. These closely resemble the gut communities of non-Westernized populations and are uncommon in people eating modern industrialized diets.
The exterior told a different story. Spray water used to keep the chamber humid was dominated by Methylobacterium, and the study concludes that this routine treatment introduced a Methylobacterium and Sphingomonas signature that now dominates the mummy's outer surfaces. The conservation protocol itself reshaped the microbiome it was meant to suppress.
A Rare Baseline for What Human Guts Looked Like Before Processed Food
The health relevance sits here. Researchers studying the modern microbiome constantly ask what a "normal" gut looked like before antibiotics, refined carbohydrates, and industrialized food processing. Ötzi's intestinal tract, sealed and frozen, is one of the few honest reference points available, and it has already yielded the 5,300-year-old Helicobacter pylori genome reported in 2016.
He is not the only such reference. Earlier work characterized the gut microbiome of an 11th-century Andean mummy, and the authors note that the Clostridium species dominating Ötzi's internal tissues are commonly reported in mummies recovered from cold environments. But the Iceman remains unusual for the completeness of his internal preservation.
None of this yields a diet prescription. A single individual from Copper Age Europe cannot define a healthy microbiome, and the researchers make no such claim.
The Yeast Population Shifted Between 2010 and 2019
The most striking finding was temporal. Comparing a 2010 skin sample with one taken in 2019, the researchers watched one yeast take over.
Glaciozyma rose from 85% to 98% of the yeast reads. More telling, the DNA fragments assigned to it got longer and showed less damage in the newer sample, the opposite of what happens when old genetic material simply degrades in place. The pattern is consistent with cells that have recently replicated.
The four cultured species were Glaciozyma watsonii, Mrakia robertii, Phenoliferia glacialis and a Goffeauzyma species. Genomic comparison placed them near strains from Antarctica, Arctic glaciers and high-altitude sites in Italy and Russia, supporting a glacial origin rather than modern laboratory contamination. Scientific American reported that the team revived yeast in a refrigerator and used it to bake sourdough.
Then came the detail that made conservators uneasy. After Ötzi's 1991 recovery, he was treated with a phenol-containing solution to suppress fungal growth. The genomic screen found phenol hydroxylase and catechol dioxygenase genes, the machinery for degrading phenols, in Pseudomonas sp. 5C2 and in the yeasts Glaciozyma watsonii and Phenoliferia glacialis. The historical disinfectant may have selected for organisms that can consume it.
Other genes raise a slower concern. Clostridium algidicarnis, a species normally associated with spoilage of chilled vacuum-packed meat, carries a collagenase gene. Collagen is a primary structural component of the mummy's skin and connective tissue.
What This Does and Does Not Mean
These are psychrophiles, adapted to sub-zero conditions. Genomic comparison confirmed they are specialized cold-environment organisms rather than clinical or food-borne contaminants, and the Eurac Research announcement frames them as a conservation question and a potential industrial resource for low-temperature fermentation, not a public health threat.
The limitations are real, and the authors list them. Genomic potential is not proven activity. Finding a collagenase gene shows capability, not that tissue is currently being degraded. The team could not distinguish metabolically active cells from dormant ones and recommends RNA sequencing and viability filtering as next steps. Ethical constraints on sampling an irreplaceable specimen meant no replicate samples per site, and the temporal comparison rests on just two time points.
Their recommendation is a shift in how museums think about ancient remains: from static storage to ongoing genomic surveillance, catching the transition from dormancy to activity before damage becomes visible.
Key Questions Answered
Are the microbes on Ötzi actually alive?
Four yeast species were successfully cultured, so those cells were viable. Evidence that they are actively multiplying under storage conditions is strong but indirect, based on rising abundance and declining DNA damage between 2010 and 2019.
Could these organisms infect people?
There is no indication of that. They are cold-adapted environmental species, and the study frames them as a preservation concern rather than an infectious risk.
What did his gut bacteria reveal?
Internal tissues held anaerobic species resembling those in non-industrialized human populations, offering a rare reference point for what human gut communities looked like in the Copper Age.
Why does the preservative matter?
Phenol was applied in 1991 to stop fungal growth. Several resident microbes carry genes for breaking phenols down, suggesting the treatment may have favored organisms able to tolerate or consume it.
Is the mummy in danger?
Not immediately. The researchers identified genomic capacity for tissue degradation and called for tighter monitoring and stricter environmental control as a precaution.
What comes next?
RNA sequencing to measure gene activity directly, viability testing to separate living from dead cells, and longitudinal sampling at more than two time points.
