Study Distinguishes Ötzi the Iceman’s Ancient Gut Bacteria from Post-Mortem Colonizing Fungi, Finds Potentially Active Tissue-Degrading Yeast

Researchers have identified bacteria that probably lived inside Ötzi the Iceman when he was alive and cold-loving yeasts that colonized his body after death. Ötzi’s mummified remains were discovered in 1991 thawing from an Alpine glacier near the Austria-Italy border. He is estimated to have lived between 3350 and 3120 BC.

The body is kept at the South Tyrol Museum of Archaeology in Bolzano, Italy, at a constant temperature of -6°C and 99 per cent relative humidity. Frank Maixner at Eurac Research’s Institute for Mummy Studies in Bolzano and colleagues examined skin swabs, tissue fragments and internal thawed water samples collected in 1992, 2010 and 2019.

They also compared these with soil and ice samples taken from the discovery site in the 1990s.

Metagenomic analysis of internal tissues revealed specialist bacteria that thrive without oxygen inside the mammalian gut, including species of Treponema and Kineothrix. The level of DNA damage in these bacteria indicates they probably lived inside Ötzi during his lifetime.

Pseudomonas bacteria were found in all samples, and their DNA damage pattern suggests they belong to an ancient community from the discovery site.

On external samples the team found cold-loving yeasts including Phenoliferia, Glaciozyma, Goffeauzyma and Mrakia. DNA damage showed these were ancient microbes. The abundance of Glaciozyma increased between 2010 and 2019 and became the dominant strain while its DNA damage level dropped, suggesting it may be metabolically active under current conservation conditions.

“We can really distinguish between the Iceman’s endogenous gut bacteria and microbes that joined from the environment as soon as he died,” Frank Maixner said. He added that the wide variety of microbes may reflect the more varied diet of Copper Age humans compared with modern Western societies.

Nikolay Oskolkov at Lund University said the data provide good evidence that Glaciozyma colonised the mummy post mortem.

Damla Kaptan at the University of Stavanger noted that RNA analysis would be needed to confirm whether the yeast is active. Some of the yeasts encode enzymes for breaking down protein and collagen. Some microbes contain genes required for degrading the toxic compound phenol.

Researchers in the 1990s treated the mummy with a phenol-containing substance after active mould formation was observed when the body was found. Frank Maixner said the study shows that Ötzi is not a biologically frozen time capsule but a complex ecosystem shaped by the succession of his gut microbes after death, infiltration of organisms from the glacier over thousands of years and three decades of conservation.

He recommends regular genomic surveillance, including tests for RNA and metabolites, to monitor whether microbial communities are degrading the mummy’s tissues.

1186/s40168-026-02417-6.