Ski tourism shapes the snow microbiome on ski slopes in the Italian Central Alps

Winter sports can lead to strong anthropogenic pressures on the snow microbiome, with cascading effects on the entire alpine ecosystem. In particular, the massive usage of artificial snow, human occupation and the release of xenobiotics such as microplastics on ski tracks can profoundly shape the ecology of snow microbial ecosystems. Here, we reconstructed the temporal dynamics of the snow microbiome at 3 sites in the Italian Alps, namely inside and outside a ski track at the impacted site of Santa Caterina Valfurva and near Cancano lake as an unimpacted control, using epifluorescence microscopy, 16S rRNA amplicon sequencing and inferred metagenomics. Interestingly, the snow microbiome inside the track was featured by a higher load of prokaryotes and viruses. More specifically, known N2-fixing microorganisms from cryospheric environments and host-associated taxa, such as the gut symbionts Terrisporobacter, Clostridium sensu stricto, Enterococcus and Muribaculaceae and the opportunistic pathogen Citrobacter, characterized the impacted site. These microorganisms could be derived from the contamination of river water used for the production of artificial snow during the winter season. In addition to demonstrating the complexity and multifunctionality of the snow microbiome, where microorganisms with different ecological propensities can coexist, our findings show that ski tourism has a detectable impact on this ecosystem, favoring the enrichment of human-derived taxa, highlighting the need for more systematic monitoring – and protection – of the snow microbiome in the Alpine environment from anthropogenic threats.