Roommates from 5,300 years ago: microorganisms still live and grow in the famous glacier mummy Ötzi – despite the cold chamber and preservation measures. Analyzes have now revealed that some bacteria and yeasts that migrated from the glacier ice into Ötzi’s tissue thousands of years ago can still multiply even in sub-zero temperatures. These microbes feed on Ötzi’s tissue and sometimes even on the toxic preservative phenol and could thus endanger the preservation of the unique ice mummy.
The glacier mummy “Ötzi” is probably the best-studied prehistoric man in Europe: the remains of this man, his clothing and equipment, preserved in glacier ice for 5,300 years, provide unique information about the appearance, lifestyle, diseases and diet of people in the Copper Age. In 2023, DNA analyzes also revealed that Ötzi was almost 90 percent descended from Anatolian farmers and had rather dark skin.
Because of its immense value for research, the famous glacier mummy is kept under special conditions: Ötzi lies in a largely sterile room that has been cooled down to minus six degrees and has 99 percent humidity. This is intended to help prevent microbes from decomposing the glacier mummy. “These conditions are very similar to those in the glacier where the mummy was found,” report Mohamed Sarhan and his colleagues from the Eurac Research Institute for Mummy Research in Bolzano.
Are Ötzi’s microbes still active today?
“However, one crucial question remains unanswered: Do the current preservation conditions really prevent microbial growth or do they still enable cold-adapted microorganisms to engage in metabolic activity?” explain the researchers. If the latter is the case, this could jeopardize the preservation of the mummy. Although Ötzi’s surface and interior have been analyzed several times for microbial DNA, no distinction was made between resting, dead and metabolically active cells.
It was therefore unclear whether Öztzi’s microbial roommates would also grow and thrive in the cold chamber. That’s why Sarhan and his colleagues have now examined Ötzi’s microbiome again in more detail. Among other things, they analyzed swabs, ice and melt water from various parts of the mummy’s surface and from its interior. For comparison, they also evaluated older data from tissue samples and Ötzi’s stomach contents and analyzed a soil sample taken from the site in 1991.
Prehistoric intestinal flora and glacial microbes
The analyzes revealed a variety of very different traces of microbes in the glacier mummy samples. Some species detected in the stomach and intestines come from Ötzi’s original intestinal flora, as the researchers report. These bacteria are extremely rare in modern humans, but are similar to the intestinal flora of the few other prehistoric humans sampled to date. “This suggests that Ötzi’s gut forms a largely protected microenvironment that has preserved the ancient microbial signatures themselves over five millennia,” the team writes.
Other microorganisms, primarily soil bacteria and yeast fungi, probably entered the ice mummy’s body from the glacier environment. These microbes are adapted to cold and only occur in icy and alpine environments, as the researchers explain. These bacteria and fungi probably colonized Ötzi’s tissue shortly after his death and have survived to this day. “We see a continuity here,” explains senior author Frank Maixner from Eurac Research: “These yeasts accompanied Ötzi on his long journey through the millennia, so to speak.”
Still active
But in addition to heavily degraded and therefore probably several thousand years old DNA from the cold-adapted glacier microbes, the team also discovered fresh DNA from these species – especially in the yeast fungi. “This suggests that these microbes are not just dormant relics,” explain Sarhan and his colleagues. Instead, these organisms appear to be slowly but persistently reproducing in and on the glacier mummy.
In other words: Despite preservation measures, some microorganisms live and grow in Ötzi’s body and tissues. However, these active microorganisms pose a danger to Ötzi: “Their active metabolism is a direct threat to the structural integrity of the mummy,” according to the team. The genes for fat- and protein-degrading enzymes detected in the samples suggest that some of these microbes feed on Ötzi’s tissues.
Preservatives as food
Also interesting: Some of the microbes still active in the glacier mummy could benefit from the measures that are actually intended to kill all microbial life. One type of bacteria and three of the four cold-adapted yeasts in Ötzi’s samples feed partly on phenol. This toxic and corrosive organic chemical was previously used for disinfection. The glacier mummy was also repeatedly sprayed with phenol for years to prevent fungal infestation.
But this poison apparently did not harm at least some microbes – on the contrary: because they have genes that enable them to break down phenol, these bacteria and fungi even benefited from the disinfectant phenol treatment. “It created a selective microenvironment that favored these specialized decomposers,” explain the Eurac researchers.
Complex ecosystem instead of static time capsule
“Overall, our comprehensive survey reveals that Ötzi the Iceman is not a frozen biological time capsule, but represents a complex ecosystem,” say Sarhad and his colleagues. The microbiome of the glacier mummy reflects the millennia-old history of Ötzi, but also modern influences such as the preservation measures or microorganisms from the air in the clean room.
But what does this mean for the protection of the valuable glacier mummy? In any case, the researchers recommend keeping a close eye on Ötzi’s microbial roommates. “Close microbiological monitoring ensures that the mummy is not damaged,” comments Elisabeth Vallazza, director of the South Tyrolean Archeology Museum. “But further research and full conservation efforts are certainly required to preserve them for many future generations.”
Source: Mohamed Sarhan et al. (Eurac Research – Institute for Mummy Research, Bolzano), Microbiome, 2026; doi: 10.1186/s40168-026-02417-6