T WUNDERLIN¹, B FERRARI², M POWER<sup>3

1</sup>Molecular Ecology, Agroscope Reckenholz, 8046 Zurich, Switzerland, ²School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney 2052, Australia, ³Department of Biological Sciences, Macquarie University, Sydney 2109, Australia

Approximately 12% of the Earth’s surface is seasonally snow-covered, yet little is known about microbial life in snow. The long-standing hypothesis of snow being near sterile has recently been challenged by demonstrations of actual microbial activity in snow. These findings on the one hand are surprising, because the extreme environmental conditions make life in snow very challenging. On the other hand, the existence of active snow microbes is coherent with the fact that every living organism today has ancestors who survived during Snowball earth.
In this study, we explored abundance and diversity of bacteria in alpine snow and revealed biogeographic distribution patterns. For this, we collected surface snow from two sites in Switzerland (Jungfraujoch (n=2) and Rosstock (5)) and two sites in Australia (Mt. Kosciuszko and Thredbo(10;5)). Bacterial abundance was 6.9 ± 0.7 x 10^5 cells/ml, which corresponds to previously determined cell numbers in alpine snow. Biomass in melted snow was filtered, subjected to DNA extraction and Illumina sequencing (V1-V3 amplicon of 16S rRNA gene). Short of 1.8 Mio. sequences were obtained, resulting in 703 to 64’699 seqs/sample. Substantially diverse bacterial communities (up to 2286 taxonomic units) were detected, which spanned across 25 bacterial phyla, with Alpha- and Betaproteobacteria, Acido-, Cyano-, Actinobacteria, Bacteroidetes and Firmicutes, accounting for 72-98% of the abundance. Isolations of strains directly from snow were also performed and their distribution corresponded to the one obtained by amplicon sequencing, with exception of Gammaproteobacteria, which were most abundant among the isolates, but rarely detected in sequence data. Detailed analysis of community patterns show that there is a significant variation in alpine snow communities across hemispheres, regional and local positioning. Surrounding vegetation and exposition to wind seem to influence the bacterial community. In addition to athmospherically deposited bacteria our results suggest the existence of cosmopolitan taxa that have previously been associated with snow or cold environments, ie. there may be cold-adapted bacterial ecotypes in snow.