By Cara Burke
Nowadays, it is well known that microorganisms reside in ice environments, but this discovery came after many years of assuming that these cold and often harsh environments could not sustain much microbial life. We now know that there is a great amount microbe biodiversity in glacial ice, and we are beginning to understand, following a recent study, that there is also a great amount of microbe diversity in snow (Garcia-Lopez & Cid, 2017).
Glaciers are home to a wide variety of microbes. The glacial environment is unique, and the species within each glacier and its diversity level depends greatly on the glacier’s location (Garcia-Lopez & Cid, 2017). The photosynthetic organisms at the surface of glaciers are primary producers and start a vertical food chain which provides for the heterotrophs (typically protists and bacteria) that reside in the middle of the glacier. These microorganisms are key to allowing plants and wildlife to colonise the land that is left when a glacier recedes, and their results will be seen as glacial ice continues to rapidly melt (Garcia-Lopez & Cid, 2017).
Microorganisms can play an important role in the formation of snow. In 2008, the most active ice nucleators were found to be biological in origin, with 69% to 100% of ice nucleators above 2 μm being biological, the majority of which bacterial (Christner et al., 2008). Ice nucleators initiate the process of ice formation by allowing molecules in a liquid to start forming clusters, which then determine how the liquid will crystalise (Esmon, 2014). However, our understanding of the biodiversity of microorganisms in white snow itself has only recently begun to develop.
Snow seems to be lacking in all of the things that make life for microbes easier – warmth, free water, and nutrients. We have been aware of snow microbes since expeditions to Antarctica in the 1950s and 1960s, where green, red and orange algal blooms were discovered in the snow. They are the result of a huge increase in the population of algae, and form large patches of colour on the white snowy surface. These algal blooms are incredibly important for the ecosystems where they occur, since they are primary producers and carbon sinks. Earlier this year, satellite observations found that Antarctica has nearly 1,700 large patches of green algae, which covered an area of almost 2 square kilometres (Gray et al., 2020). But until recently, these algae, visible to the naked eye, were considered the only algae to be found in late-season snow.
Last year, a surprising study by Shawn Brown and Ari Jumpponen revealed that the biodiversity of microorganisms in snow is much greater than previously expected. The study describes “the diverse, dynamic and metabolically active microbial communities inhabiting snow”. The study took samples from late season snowpacks across the latitudinal gradient in Fennoscandian Lapland and Colorado and used DNA extraction, amplification and sequencing to determine the species present in the snow, as well as their diversity. There were 2979 OTUs (operational taxonomic units) of bacteria, 358 OTUs of fungi, and 23 algal OTUs, which reflect a diversity much greater than previously imagined (Brown & Jumpponen, 2019). The current theory is that algae reside in white snow and can bloom when the nutritional and environmental conditions are more favourable. They help provide a good nutritional environment for bacteria and fungi – the same fungi found in white snow were found in algal blooms but to a greater extent. Overall, the sheer number of species present is a surprise, and it seems as though the species and diversity remain fairly consistent across the snow studied (Brown & Jumpponen, 2019). Because this finding is relatively new, there is still much to be discovered about the distribution and diversity of these microorganisms in snow environments across the world, as well as how active they may be.
The importance of these microorganisms for our climate and ecosystem is not yet fully known, though is now clearly an area with a great amount of potential. 80% of the terrestrial biosphere is permanently frozen. During winter, snow can cover up to 12% of the Earth’s surface (Garcia-Lopez & Cid, 2017). There is a great deal more to be discovered regarding the microorganisms which inhabit this snow and ice. They may even prove useful in further understanding the current climate crisis and finding suitable solutions.
Brown, S. P. & Jumpponen, A. (2019) Microbial Ecology of Snow Reveals Taxa-Specific Biogeographical Structure. Microbial Ecology. 77 (4), 946-958. Available from: https://doi.org/10.1007/s00248-019-01357-z. Available from: doi: 10.1007/s00248-019-01357-z.
Christner, B. C., Morris, C. E., Foreman, C. M., Cai, R. & Sands, D. C. (2008) Ubiquity of Biological Ice Nucleators in Snowfall. Science (American Association for the Advancement of Science). 319 (5867), 1214. Available from: https://search.datacite.org/works/10.1126/science.1149757. Available from: doi: 10.1126/science.1149757.
Esmon, A. (2014) The Physics of Ice: It All Begins with Nucleation. Available from: https://www.thermofisher.com/blog/biobanking/the-physics-of-ice-it-all-begins-with-nucleation/.
Garcia-Lopez, E. & Cid, C. (2017) The Role of Microbial Ecology in Glacier Retreat. Glacier Evolution in a Changing World.
Gray, A., Krolikowski, M., Fretwell, P., Convey, P., Peck, L. S., Mendelova, M., Smith, A. G. & Davey, M. P. (2020) Remote sensing reveals Antarctic green snow algae as important terrestrial carbon sink. Nature Communications. 11 (1), 2527. Available from: https://doi.org/10.1038/s41467-020-16018-w. Available from: doi: 10.1038/s41467-020-16018-w.