Ötzi, Europe’s most famous mummy, has been lying in a high-tech resting place at the South Tyrol Museum of Archaeology in Italy for over two decades. The Copper Age man was discovered in 1991 by a group of hikers in the Ötztal Alps and has since received extensive attention from scientists.
Microbiologist Mohamed S. Sarhan and his colleagues sampled material from Ötzi’s stomach, meltwater from inside his body, swabbed his skin, and even collected airborne microbes from his frozen storage room and the lab outside it. They also took samples from a block of frozen alpine soil taken from next to Ötzi’s body in 1991.
The researchers used a process called shotgun metagenomics to sequence all the bits of DNA floating around in each sample. This allowed them to understand which species were really part of Ötzi’s ancient one-man ecosystem and which were modern contaminants.
Inside Ötzi’s guts, the team found ancient DNA from a host of bacteria that match what we expect of ancient, ‘non-Westernized’ gut microbiomes. However, elsewhere on and in the mummy, they also found some microbes that weren’t actually dead. The yeasts seem to be alive and reproducing, albeit at a glacial pace.
The four strains of cold-tolerant yeasts found on Ötzi are closely related to similar yeasts found in Arctic glaciers, Antarctica, and high in the mountains of Italy and Russia. Unlike Ötzi’s long-dead gut bacteria, which left just broken, aging fragments of DNA behind, the yeasts seem to be alive and reproducing.
Thawed ancient microbes or a long-lived colony? The researchers cultured live yeast from the samples, but their shotgun metagenomics results also revealed a bunch of short fragments of DNA, most bearing the kind of damage that happens when DNA molecules break down over time. This suggests that the yeasts had most likely been living on and in Ötzi’s body since shortly after he died.
When Sarhan and his colleagues compared samples taken in 2010 to those taken in 2019, they saw longer fragments and less damage, on average—in other words, there was more recent DNA in the mix. This suggests that the yeasts were slowly but persistently growing.
The researchers believe that the yeasts probably lay dormant in between brief thawing sessions, when they proliferated in transient patches of meltwater or moist tissue. The yeasts may have actually gotten some help from modern efforts to preserve Ötzi’s remains. Three out of the four species can break down phenol, an antifungal compound that conservators used to treat the mummy in 1991.
The central question now is whether these yeasts are descendants of ancient yeasts that maintained their multiplication along the years or if they were in a dormant state that was revived after thawing the mummy. The researchers have reportedly made sourdough using cultures of at least one of the yeast species they identified on Ötzi, but they almost certainly didn’t use actual cultures taken from the mummy.
Source: Original article