Microbial Analyses of a Pre-Industrial Ice Core from Weißseespitze, Tyrol

Ice cores represent valuable archives of past climatic, chemical, and biological conditions. Beyond their role in paleoclimate reconstruction, alpine ice cores enable the investigation of microbial biodiversity in extreme frozen environments and natural baselines of antibiotic resistance. This study analyses an alpine ice core from Weißseespitze (Ötztal Alps, Tyrol, Austria) (46°50’46.61393"N, 10°43’00.42181"E) to assess depth-dependent changes in bacterial and fungal communities and antibiotic resistance traits of bacteria.

The ice core was extracted in June 2025 using thermal drilling. It was 5.42 m long and covers a period from ~450–480 years before present at the surface to ~6000 years before present at the base. As a cold-based ice cap, the Weißseespitze is a suitable and well established study site in the Eastern Alps for ice core research. Until now, research has focused on gathering physical and chemical data; therefore, this study aims to provide the first biological information.

The biodiversity of bacteria is evaluated via 16S rRNA gene sequencing using the primers 16S-V3/4 and full-length 16S, while fungal biodiversity is evaluated with ITS regions using the ITS_Fung primer. Nanopore sequencing is used for both assessments. Antibiotic resistance is investigated using a cultivation-based strategy with a disk diffusion test at 20°C and 4°C. The antibiotics tested are of natural, semi-synthetic, and synthetic origin. Subsequently, selected resistant isolates are analysed genetically. 

First results of this study showed a low amount of DNA in the samples. It has also already been demonstrated that bacterial cell abundance varies along the depth profile, as do dissolved organic carbon (DOC) concentrations. In general, we hypothesize that microbial community composition and antibiotic resistance traits vary with depth in response to changes in ice structure, depositional processes, and climatic conditions, while upper layers may additionally reflect anthropogenic influence. This study contributes to a better understanding of microbial persistence in cryospheric environments, natural reservoirs of antibiotic resistance, and potential implications for downstream ecosystems and astrobiological research.