Life traces: psychrophilic and psychrotolerant bacteria in the Iceman

Ancient mummies have already been investigated using molecular methods, contributing to the rise of a new field called molecular paleontology. A particular sector within studies is the investigation of the DNA of ancient microorganisms, which improves the knowledge of issues such as the spread of disease, the mummification mechanisms involved, and the effect of diet on human paleo-populations. However, literature regarding the opportunistic microorganisms and their ability to colonize and deteriorate ancient bodies is scarce. In recent studies, molecular analysis has enabled the detection of bacterial species related to the putrefaction of human remains. In this study, the presence and diversity of psychrophilic and psychrotolerant bacteria in the Iceman (5350-5100 years before present, currently preserved in Bolzano, Italy) were investigated, and two strategies were utilized. The first strategy was based on conventional microbiological techniques, i.e. growth of bacterial cells on solid and liquid media. The second one was based on the isolation of DNA from small mummy specimens and microbiological cultures and putative identification of bacteria via DNA sequencing. In addition, the DNA extracted directly from the mummy‘s tissue was treated with uracil-N-glycosylase (UNG) to detect the repairing activity. As result, microbial cultivation has made it possible to identify several bacterial genera such as Ralstonia, Arthrobacter, Methylobacterium, Bradyrhizobium, Bacillus and Pseudomonas. On the other hand, DNA analysis showed that the mummy‘s tissue contain DNA of Clostridium at an elevated concentration. There is thus a sharp distinction between metabolically-active (cultivable) and non-active bacteria. This research can help setting up an optimal preservation condition for the mummy.