Ecology of microalgae on tropic glaciers and in slushy snow

Extremophilic microalgae exclusively living in melting snow and on wet glacier surfaces are primary producers of ecosystems with harsh abiotic conditions. They developed a plethora of morphological, metabolic and molecular mechanisms to cope with low temperatures or exposure to extreme visible and ultraviolet irradiance. While snow algae of the Chlorophyceae causing green to red discolorations have been studied well in the last decades, two different phenomena still deserve attention: First, equatorial tropic glaciers in South America with recently discovered populations of unknown streptophytic algae (Zygnematophyceae), which darken the ice surface due to their pigmentation. The cells are different to what is known from polar and mid-latitude glaciers. Second, golden-brown snow slush caused by unicellular Chrysophyceae related to Hydrurus, which are hardly understood. Arctic blooms are characteristic for remarkable large populations that appear in short time. Both habitats will be ecophysiologically investigated to understand how cells sustain the prevailing conditions. Preliminary data of the applicants indicate the presence of several snow and glacial algae new to science, which could also be of biotechnological interest. Tropical glaciers developed a distinct eukaryotic cryoflora, adapted to the specific local conditions of a diurnal climate cycle. The aim is to assess this habitat for the first time for demonstrating physiologic and taxonomic differences to non-tropic glaciers. Likewise, the diversity and metabolism of chrysophytes causing golden-brown slush will be investigated to understand the high productivity and principal stress response mechanisms. Field populations will be surveyed for primary productivity, community diversity, the transcriptome, presence of key metabolites like pigments or compatibles solutes, and the cell architecture. Lab strains will be studied for life cycles and testing physiologic optima. The methods used include chlorophyll fluorometry, radio-nucleotide uptake, metagenomics by Illumina amplicon high-throughput- sequencing, analytical screening of organic extracts by chromatographic protocols, light- and electron microscopy. The phototrophic eukaryotes unique to tropical glacier surfaces have never been investigated before, and are extremely endangered to be extinct as these exotic habitats will disappear due to global warming. Likewise, Chrysophyceae abundantly causing tinted slush have been almost scientifically neglected so far, despite they play a significant role in otherwise low-productive terrestrial polar ecosystems.

This project investigated highly specialised microalgae that can cause colourful blooms in shades of green, yellow, red or brown on thawing snow and ice surfaces in mountainous or polar regions. The focus was, on the one hand, on biodiversity - that is, how many and which species are found there - and, on the other, on their physiological adaptation to these cold, exposed habitats. The emphasis was on two subgroups of this phenomenon: namely, previously little-studied golden-yellow algae, which are predominantly found in slush, and equally under-documented ice algae on tropical glaciers near the equator, whose existence is threatened by global warming. Research expeditions to the Arctic (Spitsbergen), the Alps and the High Tatras led to the characterisation and cultivation of eight new, golden-yellow algae of the genus 'Hydrurus'. The closest relative of these species lives in cold streams. Common to these species is a high content of unsaturated fatty acids and sugar alcohols; both classes of compounds protect against cellular cold damage. As, unexpectedly, a new species of algae could be described from every sampled site, it can be assumed that biodiversity in this type of rapidly melting, wet snow has been underestimated until now. During an expedition to the Colombian Andes, we were able to study the 'cryoflora' of three different tropical glaciers at altitudes of just under 5,000 metres. The ice algae of the genera 'Ancylonema' and 'Cylindrocystis' living there were compared with specimens from Europe and the Arctic using microscopy and molecular DNA sequencing. We found, on the one hand, species that are widespread and reproduce and form blooms on melting ice worldwide, and, on the other hand, those with a more limited geographical distribution, which are so far known only from South America and Antarctica. The latter are certainly to be regarded as new species of the genus Ancylonema, suggesting that biodiversity among glacial ice algae is higher than previously thought. Another major success of the project was that, for the first time, we were able to cultivate a glacial ice algae, Ancylonema alaskanum, in the laboratory. As it has been deposited in the 'CCCryo' type collection in Potsdam, this is the first publicly accessible culture for all interested researchers wishing to investigate adaptations to cold and radiation, for example. Together with our collaboration partner James Raymond, we were able to identify a protein in ice algae that is secreted by the cells and thus prevents the formation of sharp-edged ice crystals in their surroundings through accretion. The smoothed crystals pose less of a danger.