Lenka Procházková

Colored snow caused by green algae (Chlorophyceae) is well known, but melting snowpacks can also harbor golden‐brown blooms consisting of Chrysophyceae. We collected 14 samples of cryoflora in the Austrian and Swiss Alps, the High Tatras in Slovakia, and in Arctic Svalbard. Eight laboratory unicellular flagellated strains were established from eight sites and phylogenetic analyses (18S rRNA and rbc L gene sequences) revealed new taxa belonging to the order Hydrurales (Chrysophyceae). Some formed tetrahedral swarmers; others were capsoid or amoeboid forms. Characteristics of vegetative cells and molecular markers, including the ITS2 rRNA region, supported the description of eight species: Hydrurus novisii sp. nov., H. klavenessii sp. nov., H. tatrae sp. nov., H. pulcher sp. nov., H. pascheri sp. nov., H. svalbardensis sp. nov., H. nivalis sp. nov. and H. nemcovae sp. nov. Pulse‐amplitude‐modulate (PAM) fluorometry indicated that the photosystem II of Arctic populations was adapted to high light conditions. Abundant polyunsaturated fatty acids supported cell survival at temperatures around 0°C, and the composition of these acids differed among species. The cells contained compatible solutes that could act as antifreeze agents. The main carotenoid fucoxanthin caused the overall golden‐brown pigmentation. The closest relatives of the new species were reported from snow and cold mountain streams and lakes, indicating that these Hydruralian microalgae prefer low temperatures and elevated irradiation. The large number of new species discovered during this limited sampling campaign suggests the underestimated diversity of phototrophic microbes in melting snow. Consequently, the genus Hydrurus shows a similar high relevance for snow algae blooms as Chloromonas does within the green algae.

The green alga Klebsormidium is found worldwide in terrestrial and freshwater habitats. A novel strain was isolated from biological soil crusts on Breinosa Mountain in Svalbard (High Arctic, 78°N) to investigate its adaptation to extreme Arctic conditions, characterized by low temperatures and short periods of snow-free ground. Genetic analyses confirmed the strain’s identity as Klebsormidium flaccidum, showing high genetic similarity to strains from polar and temperate habitats. This study explored the effects of nitrogen starvation, cold stress, desiccation, and freezing, focusing on molecular responses and stress resilience. Nitrogen starvation strongly impacted metabolic activity, while cold and desiccation stress had more subtle effects, with K. flaccidum showing permanent stress-related gene expression instead of acute responses. Cold acclimation was found to enhance desiccation and freezing tolerance, while nitrogen starvation worsened the effects of these stresses. These results suggest that K. flaccidum CCALA 1182 is inherently capable of withstanding fluctuating environmental stresses, highlighting its potential for survival in diverse and harsh ecosystems.

Melting glacier surfaces are increasingly affected by blooms of psychrophilic microalgae, which darken the ice and lower its albedo, accelerating melting. These microalgae contain distinct vacuoles filled with brownish pigments that were earlier described as the unusual plant phenol purpurogallin. Recently, we discovered so far unreported, large amounts of iron dissolved in aqueous extracts of the glacier ice algae Ancylonema alaskanum . Since the vacuole content was very dark but the chromatographically isolated, aforementioned phenol was only yellowish, a putative complexation of iron with purpurogallin was assumed to be the reason. Application of several protocols, including Raman microscopy on both living cells and extracts, provided strong evidence that this microalga sequesters iron and forms organic metal complexes. Consequently, substantial amounts of so far uncharacterised Fe‐complexes of purpurogallin are inferred to be present in Ancylonema , and that putative polymerisation of this compound impeded an earlier analytical discovery. This finding holds significant ecological implications for cold regions. The pigmentation not only enhances the tolerance of glacier ice algae to excessive UV and visible radiation but also influences our current understanding of the biochemical iron cycle in cryosphere‐dominated polar and alpine regions. Further downstream consequences of this biological iron source remain to be elucidated.

Melting snow and glacier surfaces host microalgal blooms in polar and mountainous regions. The aim of this study was to determine the dominant taxa at the species level in the European Arctic and the Alps. A standardized protocol for amplicon metabarcoding using the 18S rRNA gene and ITS2 markers was developed. This is important because previous biodiversity studies have been hampered by the dominance of closely related algal taxa in snow and ice. Due to the limited resolution of partial 18S rRNA Illumina sequences, the hypervariable ITS2 region was used to further discriminate between the genotypes. Our results show that red snow was caused by the cosmopolitan Sanguina nivaloides (Chlamydomonadales, Chlorophyta) and two as of yet undescribed Sanguina species. Arctic orange snow was dominated by S. aurantia, which was not found in the Alps. On glaciers, at least three Ancylonema species (Zygnematales, Streptophyta) dominated. Golden-brown blooms consisted of Hydrurus spp. (Hydrurales, Stramenophiles) and these were mainly an Arctic phenomenon. For chrysophytes, only the 18S rRNA gene but not ITS2 sequences were amplified, showcasing how delicate the selection of eukaryotic ‘universal’ primers for community studies is and that primer specificity will affect diversity results dramatically. We propose our approach as a ‘best practice’.

Snow algae blooms often form green or red coloured patches in melting alpine and polar snowfields worldwide, yet little is known about their biology, biogeography, and species diversity. We investigated eight isolates collected from red snow in northern Norway, using a combination of morphology, 18S rRNA gene and internal transcribed spacer 2 (ITS2) genetic markers. Phylogenetic and ITS2 rRNA secondary structure analyses assigned six isolates to the species Raphidonema nivale, Deuterostichococcus epilithicus, Chloromonas reticulata, and Xanthonema bristolianum. Two novel isolates belonging to the family Stichococcaceae (ARK-S05-19) and the genus Chloromonas (ARK-S08-19) were identified as potentially new species. In laboratory cultivation, differences in the growth rate and fatty acid profiles were observed between the strains. Chlorophyta were characterized by abundant C18:3n-3 fatty-acids with increases in C18:1n-9 in the stationary phase, whilst Xanthonema (Ochrophyta) was characterized by a large proportion of C20:5n-3, with increases in C16:1n-7 in the stationary phase. In a further experiment, lipid droplet formation was studied in C. reticulata at the single-cell level using imaging flow cytometry. Our study establishes new cultures of snow algae, reveals novel data on their biodiversity and biogeography, and provides an initial characterization of physiological traits that shape natural communities and their ecophysiological properties.

Melting glacier surfaces are unique ecosystems for specialized microbes, frequently harbouring blooms of microalgae with pigments contributing to the darkening of ice surfaces, reducing albedo and enhancing melt rates. The main cause of this phenomenon is algae of the genus Ancylonema. Prior investigation depended on field-collected material because these algae resisted cultivation. To enhance research on how these algae dominate melting ice, we established a strain of Ancylonema alaskanum from an alpine glacier and exposed to temperatures around the freezing point at irradiations of ~10% of full sunlight. The morphology of the culture changed, with the cells becoming longer and turning green by losing their brownish pigmentation, indicating that these dark phenols are crucial for survival in the cryosphere. Photophysiological comparisons of strain and glacial material showed adaptation of the photosynthetic apparatus to prevailing conditions. This laboratorial strain opens possibilities for a wide range of comparative ‘omics’ research.

Seasonally slowly melting mountain snowfields are populated by extremophilic microalgae. In alpine habitats, high‐light sensitive, green phytoflagellates are usually observed in subsurface layers deeper in the snowpack under dim conditions, while robust orange to reddish cyst stages can be seen exposed on the surface. In this study, uncommon surface green snow was investigated in the High Tatra Mountains (Slovakia). The monospecific community found in the green surface bloom consisted of vegetative Chloromonas cells (Volvocales, Chlorophyta). Molecular data demonstrated that the field sample and the strain isolated and established from the bloom were conspecific, and they represent a new species, Chloromonas kaweckae sp. nov., which is described based on the morphology of the vegetative cells and asexual reproduction and on molecular analyses of the strain. Cells of C. kaweckae accumulated approximately 50% polyunsaturated fatty acids, which is advantageous at low temperatures. In addition, this new species performed active photosynthesis at temperatures close to the freezing point showed a light compensation point of 126 ± 22 μmol photons · m⁻² · s⁻¹ and some signs of photoinhibition at irradiances greater than 600 μmol photons · m⁻² · s⁻¹. These data indicate that the photosynthetic apparatus of C. kaweckae could be regarded as adapted to relatively high light intensities, otherwise unusual for most flagellate stages of snow algae.