Microbial community structure, pigment composition, and nitrogen source of red snow in Antarctica

Contribution of Proteorhodopsin to Light-Dependent Biological Responses in Hymenobacter nivis P3T Isolated from Red Snow in Antarctica

Proteorhodopsin (PR) is a major family of microbial rhodopsins that function as light-driven outward proton pumps. PR is now widely recognized for its ecological importance as a molecule responsible for solar energy flow in various ecosystems on the earth. However, few concrete examples of the actual use of light by natural microorganisms via PR have been demonstrated experimentally. This study reveals one example of that in a cryophilic bacterium Hymenobacter nivis P3T isolated from red snow in Antarctica. The results demonstrate light-dependent biochemical and biological responses in H. nivis cells, such as the proton pump activity of H. nivis PR (HnPR), which leads to the production of proton motive force, cellular ATP production, and cell growth. In addition, the results of this study demonstrate the photochemical properties of a PR, namely, HnPR, in the membrane of a natural host bacterium. The photocycle of HnPR was much faster than other PRs even at 5 °C, indicating that the proton pump function of HnPR has adapted to the low-temperature environment of Antarctica. Although it is well-known that PR helps natural host microorganisms to use light energy, this study provides another concrete example for understanding the biological role of PR by demonstrating the link between the molecular functions of PR and the light-dependent biochemical and biological responses of a PR-bearing host.

Endometabolic profiling of pigmented glacier ice algae: the impact of sample processing

INTRODUCTION

Glacier ice algae, mainly Ancylonema alaskanum and Ancylonema nordenskiöldi, bloom on Greenland Ice Sheet bare ice surfaces. They significantly decrease surface albedo due to their purple-brown pigmentation, thus increasing melt. Little is known about their metabolic adaptation and factors controlling algal growth dynamics and pigment formation. A challenge in obtaining such data is the necessity of melting samples, which delays preservation and introduces bias to metabolomic analysis. There is a need to evaluate the physiological response of algae to melting and establish consistent sample processing strategies for metabolomics of ice microbial communities.

OBJECTIVES

To address the impact of sample melting procedure on metabolic characterization and establish a processing and analytical workflow for endometabolic profiling of glacier ice algae.

METHODS

We employed untargeted, high-resolution mass spectrometry and tested the effect of sample melt temperature (10, 15, 20 °C) and processing delay (up to 49 h) on the metabolome and lipidome, and complemented this approach with cell counts (FlowCam), photophysiological analysis (PAM) and diversity characterization.

RESULTS AND CONCLUSION

We putatively identified 804 metabolites, with glycerolipids, glycerophospholipids and fatty acyls being the most prominent superclasses (> 50% of identified metabolites). Among the polar metabolome, carbohydrates and amino acid-derivatives were the most abundant. We show that 8% of the metabolome is affected by melt duration, with a pronounced decrease in betaine membrane lipids and pigment precursors, and an increase in phospholipids. Controlled fast melting at 10 °C resulted in the highest consistency, and is our recommendation for future supraglacial metabolomics studies.

Snow viruses and their implications on red snow algal blooms

Algal blooms can give snowmelt a red color, reducing snow albedo and creating a runaway effect that accelerates snow melting. The occurrence of red snow is predicted to grow in polar and subpolar regions with increasing global temperatures. We hypothesize that these algal blooms affect virus-bacteria interactions in snow, with potential effects on snowmelt dynamics. A genomic analysis of double-stranded DNA virus communities in red and white snow from the Whistler region of British Columbia, Canada, identified 792 putative viruses infecting bacteria. The most abundant putative snow viruses displayed low genomic similarity with known viruses. We recovered the complete circular genomes of nine putative viruses, two of which were classified as temperate. Putative snow viruses encoded genes involved in energy metabolisms, such as NAD+ synthesis and salvage pathways. In model phages, these genes facilitate increased viral particle production and lysis rates. The frequency of temperate phages was positively correlated with microbial abundance in the snow samples. These results suggest the increased frequency of temperate virus-bacteria interactions as microbial densities increase during snowmelt. We propose that this virus-bacteria dynamic may facilitate the red snow algae growth stimulated by bacteria.IMPORTANCEMicrobial communities in red snow algal blooms contribute to intensifying snowmelt rates. The role of viruses in snow during this environmental shift, however, has yet to be elucidated. Here, we characterize novel viruses extracted from snow viral metagenomes and define the functional capacities of snow viruses in both white and red snow. These results are contextualized using the composition and functions observed in the bacterial communities from the same snow samples. Together, these data demonstrate the energy metabolism performed by viruses and bacteria in a snow algal bloom, as well as expand the overall knowledge of viral genomes in extreme environments.

The colonization of an irradiated environment: the case of microbial biofilm in a nuclear reactor

The investigation of the microbial community change in the biofilm, growing on the walls of a containment tank of TRIGA nuclear reactor revealed a thriving community in an oligotrophic and heavy-metal-laden environment, periodically exposed to high pulses of ionizing radiation (IR). We observed a vertical IR resistance/tolerance stratification of microbial genera, with higher resistance and less diversity closer to the reactor core. One of the isolated Bacillus strains survived 15 kGy of combined gamma and proton radiation, which was surprising. It appears that there is a succession of genera that colonizes or re-colonizes new or IR-sterilized surfaces, led by Bacilli and/or Actinobacteria, upon which a photoautotrophic and diazotrophic community is established within a fortnight. The temporal progression of the biofilm community was evaluated also as a proxy for microbial response to radiological contamination events. This indicated there is a need for better dose-response models that could describe microbial response to contamination events. Overall, TRIGA nuclear reactor offers a unique insight into IR microbiology and provides useful means to study relevant microbial dose-thresholds during and after radiological contamination.

The distribution and drivers of microbial pigments in the cryoconite of four Tibetan glaciers

Microbial pigments play a significant role in glacier albedo reduction, thereby contributing to accelerated glacier retreat. The Tibetan Plateau has experienced rapid glacier retreat in recent decades due to global warming, yet there is limited understanding of microbial pigment distribution in the region. Here, we investigated the pigment concentration and composition in cryoconite from four glaciers. Our results showed that chlorophylls were the dominant pigments in Palong No. 4 (PL) and Jiemayangzong (JMYZ) glaciers located in the south of the Tibetan Plateau, while carotenoids were dominant in Qiangyong (QY) and Tanggula (TGL) glaciers located in the central region. Additionally, the chlorophyll b to chlorophyll a ratio, which is an indicator of the algae-to-cyanobacteria ratio, was higher in PL and JMYZ compared to QY and TGL. By using Random Forest Regression and Structural Equation Modelling, we determined that the concentrations of chlorophyll a, chlorophyll b, and carotenoids were associated with autotrophic bacteria relative abundance, climatic factors, and a combination of bacterial and climatic factors, respectively. This study is the first to describe the distribution of microbial pigments in cryoconite from Tibetan glaciers, providing additional support on the influence of algal pigment on glacier retreat.

Similar heterotrophic communities but distinct interactions supported by red and green-snow algae in the Antarctic Peninsula

Snow algae are predicted to expand in polar regions due to climate warming, which can accelerate snowmelt by reducing albedo. Green snow frequently occurs near penguin colonies, and red snow distributes widely along ocean shores. However, the mechanisms underpinning the assemblage of algae and heterotrophs in colored snow remain poorly characterized. We investigated algal, bacterial, and fungal communities and their interactions in red and green snows in the Antarctic Peninsula using a high-throughput sequencing method. We found distinct algal community structure in red and green snows, and the relative abundance of dominant taxa varied, potentially due to nutrient status differences. Contrastingly, red and green snows exhibited similar heterotrophic communities (bacteria and fungi), whereas the relative abundance of fungal pathogens was substantially higher in red snow by 3.8-fold. Red snow exhibited a higher network complexity, indicated by a higher number of nodes and edges. Red snow exhibited a higher proportion of negative correlations among heterotrophs (62.2% vs 3.4%) and stronger network stability, suggesting the red-snow network is more resistant to external disturbance. Our study revealed that the red snow microbiome exhibits a more stable microbial network than the green snow microbiome.

Functional filtering and random processes affect the assembly of microbial communities of snow algae blooms at Maritime Antarctic

The increasing temperatures at the West Antarctic Peninsula (Maritime Antarctic) could lead to a higher occurrence of snow algal blooms which are ubiquitous events that change the snow coloration, reducing albedo and in turn exacerbating melting. However, there is a limited understanding of snow algae blooms biodiversity, composition, and their functional profiles, especially in one of the world's areas most affected by climate change. In this study we used 16S rRNA and 18S rRNA metabarcoding, and shotgun metagenomics to assess the diversity, composition, and functional potential of the snow algae blooms bacterial and eukaryotic communities at three different sites of Maritime Antarctic, between different colors of the algae blooms and between seasonal and semi-permanent snowfields. We tested the hypothesis that the functional potential of snow algae blooms is conserved despite a changing taxonomic composition. Furthermore, we determined taxonomic co-occurrence patterns of bacteria and eukaryotes and assessed the potential for the exchange of metabolites among bacterial taxa. Here, we tested the prediction that there are co-occurring taxa within snow algae whose biotic interactions are marked by the exchange of metabolites. Our results show that the composition of snow algae blooms vary significantly among sites. For instance, a higher abundance of fungi and protists were detected in Fildes Peninsula compared with Doumer Island and O'Higgins. Likewise, the composition varied between snow colors and snow types. However, the functional potential varied only among sampling sites with a higher abundance of genes involved in tolerance to environmental stress at O'Higgins. Co-occurrence patterns of dominant bacterial genera such as Pedobacter, Polaromonas, Flavobacterium and Hymenobacter were recorded, contrasting the absence of co-occurring patterns displayed by Chlamydomonadales algae with other eukaryotes. Finally, genome-scale metabolic models revealed that bacteria within snow algae blooms likely compete for resources instead of forming cooperative communities.

Interfacial phenomena in snow from its formation to accumulation and shedding

Snow accumulation alters the energy budget of engineered (i.e. photovoltaic panels) and natural surfaces (i.e. earth) by affecting the amount of solar energy these surfaces can absorb. Falling of accumulated snow from overhead structures (i.e. telecommunication towers, power lines, wind turbines, and bridge cables) and slipping pedestrians and vehicles on surfaces covered with snow and ice can lead to injuries and safety issues. This review article aimed to provide an overview of snow from its nucleation/formation fundamentals to its interaction with man-made and natural surfaces leading to its accumulation, followed by its removal via shedding and/or melting. Mechanical, thermal, and thermodynamics properties of snow were reviewed providing insights on their impact on snow interaction with surfaces. Finally, currently-available active and passive techniques to mitigate issues associated with snow accumulation on surfaces were reviewed, and perspectives on challenges ahead were provided.

Spatial and Temporal Variations in Pigment and Species Compositions of Snow Algae on Mt. Tateyama in Toyama Prefecture, Japan

Snow algae are photosynthetic microbes that inhabit the melting snow surface in alpine and polar regions. We analyzed the pigment and species composition of colored snow collected on Mt. Tateyama in Japan during the melting seasons of 2015 and 2016. High-performance liquid chromatographic analyses of the pigments extracted from the colored snow showed that their composition varied within the study area and were classified into four types: Type A (astaxanthin-monoester dominant), Type B (medium astaxanthin-monoester content), Type C (abundant primary carotenoids and free-astaxanthin), and Type D (abundant primary carotenoids and astaxanthin diesters). Types A and B were most commonly observed in the study area, whereas Types C and D appeared only at specific sites. Analysis of the 18S ribosomal RNA (18S rRNA) gene revealed six major amplicon sequence variants (ASVs) of snow algae, belonging to the Sanguina, Chloromonas, and Chlainomonas groups. The relative abundance of the algal ASVs showed that Sanguina was dominant (>48%) in both Types A and B, suggesting that the difference in astaxanthin abundance between the two types was caused by the production of pigments in the algal cells. The algal community structures of Types C and D differed from those of Types A and B, indicating that the primary carotenoids and astaxanthin diesters were derived from certain algal species in these types. Therefore, astaxanthin-rich Sanguina algae mostly induced the red snow that appeared widely in this alpine area; however, they were partially dominated by Chloromonas or Chlainomonas algae, causing different pigment compositions.

Remote Sensing Phenology of Antarctic Green and Red Snow Algae Using WorldView Satellites

Snow algae are an important group of terrestrial photosynthetic organisms in Antarctica, where they mostly grow in low lying coastal snow fields. Reliable observations of Antarctic snow algae are difficult owing to the transient nature of their blooms and the logistics involved to travel and work there. Previous studies have used Sentinel 2 satellite imagery to detect and monitor snow algal blooms remotely, but were limited by the coarse spatial resolution and difficulties detecting red blooms. Here, for the first time, we use high-resolution WorldView multispectral satellite imagery to study Antarctic snow algal blooms in detail, tracking the growth of red and green blooms throughout the summer. Our remote sensing approach was developed alongside two Antarctic field seasons, where field spectroscopy was used to build a detection model capable of estimating cell density. Global Positioning System (GPS) tagging of blooms and in situ life cycle analysis was used to validate and verify our model output. WorldView imagery was then used successfully to identify red and green snow algae on Anchorage Island (Ryder Bay, 67°S), estimating peak coverage to be 9.48 × 10⁴ and 6.26 × 10⁴ m², respectively. Combined, this was greater than terrestrial vegetation area coverage for the island, measured using a normalized difference vegetation index. Green snow algae had greater cell density and average layer thickness than red blooms (6.0 × 10⁴ vs. 4.3 × 10⁴ cells ml^-1) and so for Anchorage Island we estimated that green algae dry biomass was over three times that of red algae (567 vs. 180 kg, respectively). Because the high spatial resolution of the WorldView imagery and its ability to detect red blooms, calculated snow algal area was 17.5 times greater than estimated with Sentinel 2 imagery. This highlights a scaling problem of using coarse resolution imagery and suggests snow algal contribution to net primary productivity on Antarctica may be far greater than previously recognized.

Insights into upstream processing of microalgae: A review

The aim of this review is to provide insights into the upstream processing of microalgae, and to highlight the advantages of each step. This review discusses the most important steps of the upstream processing in microalgae research such as cultivation modes, photobioreactors design, preparation of culture medium, control of environmental factors, supply of microalgae seeds and monitoring of microalgal growth. An extensive list of bioreactors and their working volumes used, elemental composition of some well-known formulated cultivation media, different types of wastewater used for microalgal cultivation and environmental variables studied in microalgae research has been compiled in this review from the vast literature. This review also highlights existing challenges and knowledge gaps in upstream processing of microalgae and future research needs are suggested.

Isolation and characterization of fast-growing green snow bacteria from coastal East Antarctica

Snow microorganisms play a significant role in climate change and affecting the snow melting rate in the Arctic and Antarctic regions. While research on algae inhabiting green and red snow has been performed extensively, bacteria dwelling in this biotope have been studied to a much lesser extent. In this study, we performed 16S rRNA gene amplicon sequencing of two green snow samples collected from the coastal area of the eastern part of Antarctica and conducted genotypic and phenotypic profiling of 45 fast-growing bacteria isolated from these samples. 16S rRNA gene amplicon sequencing of two green snow samples showed that bacteria inhabiting these samples are mostly represented by families Burkholderiaceae (46.31%), Flavobacteriaceae (22.98%), and Pseudomonadaceae (17.66%). Identification of 45 fast-growing bacteria isolated from green snow was performed using 16S rRNA gene sequencing. We demonstrated that they belong to the phyla Actinobacteria and Proteobacteria, and are represented by the genera Arthrobacter, Cryobacterium, Leifsonia, Salinibacterium, Paeniglutamicibacter, Rhodococcus, Polaromonas, Pseudomonas, and Psychrobacter. Nearly all bacterial isolates exhibited various growth temperatures from 4°C to 25°C, and some isolates were characterized by a high level of enzymatic activity. Phenotyping using Fourier transform infrared (FTIR) spectroscopy revealed a possible accumulation of intracellular polymer polyhydroxyalkanoates (PHA) or lipids in some isolates. The bacteria showed different lipids/PHA and protein profiles. It was shown that lipid/PHA and protein spectral regions are the most discriminative for differentiating the isolates.

Microbial community analysis with a specific statistical approach after a record breaking snowfall in Southern Italy

Purpose

Snow and ice ecosystems present unexpectedly high microbial abundance and diversity. Although arctic and alpine snow environments have been intensively investigated from a microbiological point of view, few studies have been conducted in the Apennines. Accordingly, the main purpose of this research was to analyze the microbial communities of the snow collected in two different locations of Capracotta municipality (Southern Italy) after a snowfall record occurred on March 2015 (256 cm of snow in less than 24 h).

Methods

Bacterial communities were analyzed by the Next-Generation Sequencing techniques. Furthermore, a specific statistical approach for taxonomic hierarchy data was introduced, both for the assessment of diversity within microbial communities and the comparison between different microbiotas. In general, diversity and similarity indices are more informative when computed at the lowest level of the taxonomic hierarchy, the species level. This is not the case with microbial data, for which the species level is not necessarily the most informative. Indeed, the possibility to detect a large number of unclassified records at every level of the hierarchy (even at the top) is very realistic due to both the partial knowledge about the cultivable fraction of microbial communities and limitations to taxonomic assignment connected to the quality and completeness of the 16S rRNA gene reference databases. Thus, a global approach considering information from the whole taxonomic hierarchy was adopted in order to obtain a more consistent assessment of the biodiversity.

Result

The main phyla retrieved in the investigated snow samples were Proteobacteria, Actinobacteria, Bacteroidetes, and Firmicutes. Interestingly, DNA from bacteria adapted to thrive at low temperatures, but also from microorganisms normally associated with other habitats, whose presence in the snow could be justified by wind-transport, was found. Biomolecular investigations and statistical data analysis showed relevant differences in terms of biodiversity, composition, and distribution of bacterial species between the studied snow samples.

Conclusion

The relevance of this research lies in the expansion of knowledge about microorganisms associated with cold environments in contexts poorly investigated such as the Italian Apennines, and in the development of a global statistical approach for the assessment of biological diversity and similarity of microbial communities as an additional tool to be usefully combined with the barcoding methods.

Over Winter Microbial Processes in a Svalbard Snow Pack: An Experimental Approach

Snow packs cover large expanses of Earth’s land surface, making them integral components of the cryosphere in terms of past climate and atmospheric proxies, surface albedo regulators, insulators for other Arctic environments and habitats for diverse microbial communities such as algae, bacteria and fungi. Yet, most of our current understanding of snow pack environments, specifically microbial activity and community interaction, is limited to the main microbial growing season during spring ablation. At present, little is known about microbial activity and its influence on nutrient cycling during the subfreezing temperatures and 24-h darkness of the polar winter. Here, we examined microbial dynamics in a simulated cold (−5°C), dark snow pack to determine polar winter season microbial activity and its dependence on critical nutrients. Snow collected from Ny-Ålesund, Svalbard was incubated in the dark over a 5-week period with four different nutrient additions, including glacial mineral particles, dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP) and a combined treatment of DIN plus DIP. Data indicate a consumption of dissolved inorganic nutrients, particularly DIN, by heterotrophic communities, suggesting a potential nitrogen limitation, contradictory to phosphorus limitations found in most aquatic environments. 16S amplicon sequencing also reveal a clear difference in microbial community composition in the particulate mineral treatment compared to dissolved nutrient treatments and controls, suggesting that certain species of heterotrophs living within the snow pack are more likely to associate with particulates. Particulate phosphorus analyses indicate a potential ability of heterotrophic communities to access particulate sources of phosphorous, possibly explaining the lack of phosphorus limitation. These findings have importance for understanding microbial activity during the polar winter season and its potential influences on the abundance and bioavailability of nutrients released to surface ice and downstream environments during the ablation season.

Remote sensing reveals Antarctic green snow algae as important terrestrial carbon sink

We present the first estimate of green snow algae community biomass and distribution along the Antarctic Peninsula. Sentinel 2 imagery supported by two field campaigns revealed 1679 snow algae blooms, seasonally covering 1.95 × 10⁶ m² and equating to 1.3 × 10³ tonnes total dry biomass. Ecosystem range is limited to areas with average positive summer temperatures, and distribution strongly influenced by marine nutrient inputs, with 60% of blooms less than 5 km from a penguin colony. A warming Antarctica may lose a majority of the 62% of blooms occupying small, low-lying islands with no high ground for range expansion. However, bloom area and elevation were observed to increase at lower latitudes, suggesting that parallel expansion of bloom area on larger landmasses, close to bird or seal colonies, is likely. This increase is predicted to outweigh biomass lost from small islands, resulting in a net increase in snow algae extent and biomass as the Peninsula warms.

Snow algae bloom along the coast of Antarctica and are likely to be biogeochemically important. Here, the authors produced the first map of such blooms, show that they are driven by warmer temperatures and proximity to birds and mammals, and are likely to increase given projected climate changes.

Natural Communities of Carotenogenic Chlorophyte Haematococcus lacustris and Bacteria from the White Sea Coastal Rock Ponds

Haematococcus lacustris is a biotechnologically important green unicellular alga producing widely used keta-karotenoid astaxanthin. In natural habitats, it exists in the form of algal-bacterial community, and under laboratory conditions, it is also accompanied by bacteria. The issue of the bacterial composition of industrial algal cultures is widely recognized as important. However, there is a dearth of information about bacterial composition of H. lacustris communities. In current work, we analyze the composition of natural H. lacustris communities from the White Sea coastal temporal rock ponds. For the first time, a 16S rRNA gene-based metagenome of natural H. lacustris bacterial communities has been generated. Main results of its analysis are as follow. Bacterial families Comamonadaceae, Cytophagaceae, Xanthomonadaceae, Acetobacteraceae, Rhodobacteraceae, and Rhodocyclaceae were observed in all studied H. lacustris natural communities. They also contained genera Hydrogenophaga and Cytophaga. Bacteria from the Hydrogenophaga genus were present in H. lacustris cultures after their isolation under the conditions of laboratory cultivation. Similar to other planktonic microalgae, H. lacustris forms a phycosphere around the cells. In this zone, bacteria attached to the algal surface. The contact between H. lacustris and bacteria is maintained even after sample drying. The study provides information about possible members of H. lacustris core microbiome, which can be presented in the industrial and laboratory cultures of the microalga.

Snow and Glacial Algae: A Review1

Snow or glacial algae are found on all continents, and most species are in the Chlamydomonadales (Chlorophyta) and Zygnematales (Streptophyta). Other algal groups include euglenoids, cryptomonads, chrysophytes, dinoflagellates, and cyanobacteria. They may live under extreme conditions of temperatures near 0°C, high irradiance levels in open exposures, low irradiance levels under tree canopies or deep in snow, acidic pH, low conductivity, and desiccation after snow melt. These primary producers may color snow green, golden-brown, red, pink, orange, or purple-grey, and they are part of communities that include other eukaryotes, bacteria, archaea, viruses, and fungi. They are an important component of the global biosphere and carbon and water cycles. Life cycles in the Chlamydomonas-Chloromonas-Chlainomonas complex include migration of flagellates in liquid water and formation of resistant cysts, many of which were identified previously as other algae. Species differentiation has been updated through the use of metagenomics, lipidomics, high-throughput sequencing (HTS), multi-gene analysis, and ITS. Secondary metabolites (astaxanthin in snow algae and purpurogallin in glacial algae) protect chloroplasts and nuclei from damaging PAR and UV, and ice binding proteins (IBPs) and polyunsaturated fatty acids (PUFAs) reduce cell damage in subfreezing temperatures. Molecular phylogenies reveal that snow algae in the Chlamydomonas-Chloromonas complex have invaded the snow habitat at least twice, and some species are polyphyletic. Snow and glacial algae reduce albedo, accelerate the melt of snowpacks and glaciers, and are used to monitor climate change. Selected strains of these algae have potential for producing food or fuel products.

Investigating Algal Communities in Lacustrine and Hydro-Terrestrial Environments of East Antarctica Using Deep Amplicon Sequencing

Antarctica has one of the most extreme environments on Earth, with low temperatures and low nutrient levels. Antarctica’s organisms live primarily in the coastal, ice-free areas which cover approximately 0.18% of the continent’s surface. Members of Cyanobacteria and eukaryotic algae are important primary producers in Antarctica since they can synthesize organic compounds from carbon dioxide and water using solar energy. However, community structures of photosynthetic algae in Antarctica have not yet been fully explored at molecular level. In this study, we collected diverse algal samples in lacustrine and hydro-terrestrial environments of Langhovde and Skarvsnes, which are two ice-free regions in East Antarctica. We performed deep amplicon sequencing of both 16S ribosomal ribonucleic acid (rRNA) and 18S rRNA genes, and we explored the distribution of sequence variants (SVs) of these genes at single nucleotide difference resolution. SVs of filamentous Cyanobacteria genera, including Leptolyngbya, Pseudanabaena, Phormidium, Nodosilinea, Geitlerinama, and Tychonema, were identified in most of the samples, whereas Phormidesmis SVs were distributed in fewer samples. We also detected unicellular, multicellular or heterocyst forming Cyanobacteria strains, but in relatively small abundance. For SVs of eukaryotic algae, Chlorophyta, Cryptophyta, and Ochrophyta were widely distributed among the collected samples. In addition, there was a red colored bloom of eukaryotic alga, Geminigera cryophile (Cryptophyta), in the Langhovde coastal area. Eukaryotic SVs of Acutuncus antarcticus and/or Diphascon pingue of Tardigrada were dominant among most of the samples. Our data revealed the detailed structures of the algal communities in Langhovde and Skarvsnes. This will contribute to our understanding of Antarctic ecosystems and support further research into this subject.

Labilibaculum antarcticum sp. nov., a novel facultative anaerobic, psychrotorelant bacterium isolated from marine sediment of Antarctica

A novel facultative anaerobic and facultative psychrophilic bacterium, designated SPP2^T, was isolated from an Antarctic marine sediment. Cells of the isolate were observed to be long rods (0.5 × 5-10 μm), Gram-stain negative and to have gliding motility. For growth, the optimum NaCl concentration was found to be 2-3% and the optimum temperature to be 18-22 °C. Strain SPP2^T cannot use sulfate and nitrate as electron acceptors in the presence of lactate. The G+C content of the genomic DNA was determined to be 36.0 mol%.. The major cellular fatty acids were identified as anteiso-C_15:0 and iso-C_15:0. MK-7 was found to be the predominant respiratory quinone. Phylogenetic analysis based on the 16S rRNA gene revealed that the novel strain belongs to the family Marinifilaceae and to be closely related to Labilibaculum manganireducens 59.10-2M^T with 16S rRNA gene sequence identity of 98%. The OrthoANI and dDDH values between the genome sequences of strain SPP2^T and its close relative were 84% and 27.3%, which are lower than the threshold values for species delineation. On the basis of phylogenetic and phenotypic characterisation, Labilibaculum antarcticum sp. nov. is proposed with the type strain SPP2^T (= NBRC 111151^T = CECT 9460^T).

Snow algae communities in Antarctica: metabolic and taxonomic composition

Snow algae are found in snowfields across cold regions of the planet, forming highly visible red and green patches below and on the snow surface. In Antarctica, they contribute significantly to terrestrial net primary productivity due to the paucity of land plants, but our knowledge of these communities is limited. Here we provide the first description of the metabolic and species diversity of green and red snow algae communities from four locations in Ryder Bay (Adelaide Island, 68°S), Antarctic Peninsula. During the 2015 austral summer season, we collected samples to measure the metabolic composition of snow algae communities and determined the species composition of these communities using metabarcoding. Green communities were protein-rich, had a high chlorophyll content and contained many metabolites associated with nitrogen and amino acid metabolism. Red communities had a higher carotenoid content and contained more metabolites associated with carbohydrate and fatty acid metabolism. Chloromonas, Chlamydomonas and Chlorella were found in green blooms but only Chloromonas was detected in red blooms. Both communities also contained bacteria, protists and fungi. These data show the complexity and variation within snow algae communities in Antarctica and provide initial insights into the contribution they make to ecosystem functioning.

Microbial Ecology of Snow Reveals Taxa-Specific Biogeographical Structure

Snows that persist late into the growing season become colonized with numerous metabolically active microorganisms, yet underlying mechanisms of community assembly and dispersal remain poorly known. We investigated (Illumina MiSeq) snow-borne bacterial, fungal, and algal communities across a latitudinal gradient in Fennoscandia and inter-continental distribution between northern Europe and North America. Our data indicate that bacterial communities are ubiquitous regionally (across Fennoscandia), whereas fungal communities are regionally heterogeneous. Both fungi and bacteria are biogeographically heterogeneous inter-continentally. Snow algae, generally thought to occur in colorful algae blooms (red, green, or yellow) on the snow surface, are molecularly described here as an important component of snows even in absence of visible algal growth. This suggests that snow algae are a previously underestimated major biological component of visually uncolonized snows. In contrast to fungi and bacteria, algae exhibit no discernible inter-continental or regional community structure and exhibit little endemism. These results indicate that global and regional snow microbial communities and their distributions may be dictated by a combination of size-limited propagule dispersal potential and restrictions (bacteria and fungi) and homogenization of ecologically specialized taxa (snow algae) across the globe. These results are among the first to compare inter-continental snow microbial communities and highlight how poorly understood microbial communities in these threatened ephemeral ecosystems are.

Antarctic heterotrophic bacterium Hymenobacter nivis P3T displays light-enhanced growth and expresses putative photoactive proteins

Hymenobacter nivis P3^T is a heterotrophic bacterium isolated from Antarctic red snow generated by algal blooms. Despite being non-photosynthetic, H. nivis was dominantly found in the red snow environment that is exposed to high light and UV irradiation, suggesting that this species can flourish under such harsh conditions. In order to further understand the adaptive strategies on the snow surface environment of Antarctica, the genome of H. nivis P3^T was sequenced and analyzed, which identified genes putatively encoding for light-reactive proteins such as proteorhodopsin, phytochrome, photolyase and several copies of cryptochromes. Culture-based experiments revealed that H. nivis P3^T growth was significantly enhanced under light conditions, while dark conditions had increased extracellular polymeric substances. Furthermore, the expression of several putative light-reactive proteins was determined by proteomic analysis. These results indicate that H. nivis P3^T is able to potentially utilize light, which may explain its dominance on the red snow surface environment of Antarctica. ORIGINALITY-SIGNIFICANCE STATEMENT: The role of proteorhodopsin in heterotrophic bacteria is not well-characterized, as only a handful of proteorhodopsin-harbouring isolates were shown to have a light-enhanced phenotype through culture-based experiments to date. This is the first study that demonstrates light-stimulated growth and protein expression evidence of photoactive proteins for a non-marine psychrophile and for a member of the genus Hymenobacter. It is also the first study that provides comprehensive proteome information for this genus. This study presents significant results in understanding the adaptive mechanism of a heterotrophic non-photosynthetic bacterium thriving on the snow surface environment of Antarctica as well as demonstrating the role of light-utilization in promoting growth, possibly through proteorhodopsin.

What color should glacier algae be? An ecological role for red carbon in the cryosphere

Red-colored secondary pigments in glacier algae play an adaptive role in melting snow and ice. We advance this hypothesis using a model of color-based absorption of irradiance, an experiment with colored particles in snow, and the natural history of glacier algae. Carotenoids and phenols-astaxanthin in snow-algae and purpurogallin in ice-algae-shield photosynthetic apparatus by absorbing overabundant visible wavelengths, then dissipating the excess radiant energy as heat. This heat melts proximal ice crystals, providing liquid-water in a 0°C environment and freeing up nutrients bound in frozen water. We show that purple-colored particles transfer 87%-89% of solar energy absorbed by black particles. However, red-colored particles transfer nearly as much (85%-87%) by absorbing peak solar wavelengths and reflecting the visible wavelengths most absorbed by nearby ice and snow crystals; this latter process may reduce potential cellular overheating when snow insulates cells. Blue and green particles transfer only 80%-82% of black particle absorption. In the experiment, red-colored particles melted 87% as much snow as black particles, while blue particles melted 77%. Green-colored snow-algae naturally occupy saturated snow where water is non-limiting; red-colored snow-algae occupy drier, water-limited snow. In addition to increasing melt, we suggest that esterified astaxanthin in snow-alga cells increases hydrophobicity to remain surficial.

Microbial Community Analysis of Colored Snow from an Alpine Snowfield in Northern Japan Reveals the Prevalence of Betaproteobacteria with Snow Algae

Psychrophilic algae blooms can be observed coloring the snow during the melt season in alpine snowfields. These algae are important primary producers on the snow surface environment, supporting the microbial community that coexists with algae, which includes heterotrophic bacteria and fungi. In this study, we analyzed the microbial community of green and red-colored snow containing algae from Mount Asahi, Japan. We found that Chloromonas spp. are the dominant algae in all samples analyzed, and Chlamydomonas is the second-most abundant genus in the red snow. For the bacterial community profile, species belonging to the subphylum Betaproteobacteria were frequently detected in both green and red snow, while members of the phylum Bacteroidetes were also prominent in red snow. Furthermore, multiple independently obtained strains of Chloromonas sp. from inoculates of red snow resulted in the growth of Betaproteobacteria with the alga and the presence of bacteria appears to support growth of the xenic algal cultures under laboratory conditions. The dominance of Betaproteobacteria in algae-containing snow in combination with the detection of Chloromonas sp. with Betaproteobacteria strains suggest that these bacteria can utilize the available carbon source in algae-rich environments and may in turn promote algal growth.

The microbiome of glaciers and ice sheets

Glaciers and ice sheets, like other biomes, occupy a significant area of the planet and harbour biological communities with distinct interactions and feedbacks with their physical and chemical environment. In the case of the glacial biome, the biological processes are dominated almost exclusively by microbial communities. Habitats on glaciers and ice sheets with enough liquid water to sustain microbial activity include snow, surface ice, cryoconite holes, englacial systems and the interface between ice and overridden rock/soil. There is a remarkable similarity between the different specific glacial habitats across glaciers and ice sheets worldwide, particularly regarding their main primary producers and ecosystem engineers. At the surface, cyanobacteria dominate the carbon production in aquatic/sediment systems such as cryoconite holes, while eukaryotic Zygnematales and Chlamydomonadales dominate ice surfaces and snow dynamics, respectively. Microbially driven chemolithotrophic processes associated with sulphur and iron cycle and C transformations in subglacial ecosystems provide the basis for chemical transformations at the rock interface under the ice that underpin an important mechanism for the delivery of nutrients to downstream ecosystems. In this review, we focus on the main ecosystem engineers of glaciers and ice sheets and how they interact with their chemical and physical environment. We then discuss the implications of this microbial activity on the icy microbiome to the biogeochemistry of downstream ecosystems.

Primary productivity of snow algae communities on stratovolcanoes of the Pacific Northwest

The majority of geomicrobiological research conducted on glacial systems to date has focused on glaciers that override primarily carbonate or granitic bedrock types, with little known of the processes that support microbial life in glacial systems overriding volcanic terrains (e.g., basalt or andesite). To better constrain the role of the supraglacial ecosystems in the carbon and nitrogen cycles, to gain insight into microbiome composition and function in alpine glacial systems overriding volcanic terrains, and to constrain potential elemental sequestration or release through weathering processes associated with snow algae communities, we examined the microbial community structure and primary productivity of snow algae communities on stratovolcanoes in the Cascade Range of the Pacific Northwest. Here, we present the first published values for carbon fixation rates of snow algae communities on glaciers in the Pacific Northwest. We observed varying levels of light-dependent carbon fixation on supraglacial and periglacial snowfields at Mt. Hood, Mt. Adams, and North Sister. Recovery of abundant 18S rRNA transcripts affiliated with photoautotrophs and 16S rRNA transcripts affiliated with heterotrophic bacteria is consistent with previous studies indicating the majority of primary productivity on snow and ice can be attributed to photoautotrophs. In contrast to previous observations of glacial ecosystems, our geochemical, isotopic, and microcosm data suggest these assemblages are not limited by phosphorus or fixed nitrogen availability. Furthermore, our data indicate these snow algae communities actively sequester Fe, Mn, and P leached from minerals sourced from the local rocks. Our observations of light-dependent primary productivity on snow are consistent with similar studies in polar ecosystems; however, our data may suggest that DIC may be a limiting nutrient in contrast to phosphorus or fixed nitrogen as has been observed in other glacial ecosystems. Our data underscore the need for similar studies on glacier surfaces and seasonal snowfields to better constrain the role of local bedrock and nutrient delivery on carbon fixation and biogeochemical cycling in these ecosystems.

Linking microbial diversity and functionality of arctic glacial surface habitats

Distinct microbial habitats on glacial surfaces are dominated by snow and ice algae, which are the critical players and the dominant primary colonisers and net producers during the melt season. Here for the first time we have evaluated the role of these algae in association with the full microbial community composition (i.e., algae, bacteria, archaea) in distinct surface habitats and on 12 glaciers and permanent snow fields in Svalbard and Arctic Sweden. We cross-correlated these data with the analyses of specific metabolites such as fatty acids and pigments, and a full suite of potential critical physico-chemical parameters including major and minor nutrients, and trace metals. It has been shown that correlations between single algal species, metabolites, and specific geochemical parameters can be used to unravel mixed metabolic signals in complex communities, further assign them to single species and infer their functionality. The data also clearly show that the production of metabolites in snow and ice algae is driven mainly by nitrogen and less so by phosphorus limitation. This is especially important for the synthesis of secondary carotenoids, which cause a darkening of glacial surfaces leading to a decrease in surface albedo and eventually higher melting rates.

Microbial communities associated with Antarctic snow pack and their biogeochemical implications

Snow ecosystems represent a large part of the Earth's biosphere and harbour diverse microbial communities. Despite our increased knowledge of snow microbial communities, the question remains as to their functional potential, particularly with respect to their role in adapting to and modifying the specific snow environment. In this work, we investigated the diversity and functional capabilities of microorganisms from 3 regions of East Antarctica, with respect to compounds present in snow and tested whether their functional signature reflected the snow environment. A diverse assemblage of bacteria (Proteobacteria, Actinobacteria, Firmicutes, Bacteroidetes, Deinococcus-Thermus, Planctomycetes, Verrucomicrobia), archaea (Euryarchaeota), and eukarya (Basidiomycota, Ascomycota, Cryptomycota and Rhizaria) were detected through culture-dependent and -independent methods. Although microbial communities observed in the three snow samples were distinctly different, all isolates tested produced one or more of the following enzymes: lipase, protease, amylase, β-galactosidase, cellulase, and/or lignin modifying enzyme. This indicates that the snow pack microbes have the capacity to degrade organic compounds found in Antarctic snow (proteins, lipids, carbohydrates, lignin), thus highlighting their potential to be involved in snow chemistry.

Metagenomic Analysis of Bacterial Communities of Antarctic Surface Snow

The diversity of bacteria present in surface snow around four Russian stations in Eastern Antarctica was studied by high throughput sequencing of amplified 16S rRNA gene fragments and shotgun metagenomic sequencing. Considerable class- and genus-level variation between the samples was revealed indicating a presence of inter-site diversity of bacteria in Antarctic snow. Flavobacterium was a major genus in one sampling site and was also detected in other sites. The diversity of flavobacterial type II-C CRISPR spacers in the samples was investigated by metagenome sequencing. Thousands of unique spacers were revealed with less than 35% overlap between the sampling sites, indicating an enormous natural variety of flavobacterial CRISPR spacers and, by extension, high level of adaptive activity of the corresponding CRISPR-Cas system. None of the spacers matched known spacers of flavobacterial isolates from the Northern hemisphere. Moreover, the percentage of spacers with matches with Antarctic metagenomic sequences obtained in this work was significantly higher than with sequences from much larger publically available environmental metagenomic database. The results indicate that despite the overall very high level of diversity, Antarctic Flavobacteria comprise a separate pool that experiences pressures from mobile genetic elements different from those present in other parts of the world. The results also establish analysis of metagenomic CRISPR spacer content as a powerful tool to study bacterial populations diversity.

Microbiology: lessons from a first attempt at Lake Ellsworth

During the attempt to directly access, measure and sample Subglacial Lake Ellsworth in 2012-2013, we conducted microbiological analyses of the drilling equipment, scientific instrumentation, field camp and natural surroundings. From these studies, a number of lessons can be learned about the cleanliness of deep Antarctic subglacial lake access leading to, in particular, knowledge of the limitations of some of the most basic relevant microbiological principles. Here, we focus on five of the core challenges faced and describe how cleanliness and sterilization were implemented in the field. In the light of our field experiences, we consider how effective these actions were, and what can be learnt for future subglacial exploration missions. The five areas covered are: (i) field camp environment and activities, (ii) the engineering processes surrounding the hot water drilling, (iii) sample handling, including recovery, stability and preservation, (iv) clean access methodologies and removal of sample material, and (v) the biodiversity and distribution of bacteria around the Antarctic. Comparisons are made between the microbiology of the Lake Ellsworth field site and other Antarctic systems, including the lakes on Signy Island, and on the Antarctic Peninsula at Lake Hodgson. Ongoing research to better define and characterize the behaviour of natural and introduced microbial populations in response to deep-ice drilling is also discussed. We recommend that future access programmes: (i) assess each specific local environment in enhanced detail due to the potential for local contamination, (ii) consider the sterility of the access in more detail, specifically focusing on single cell colonization and the introduction of new species through contamination of pre-existing microbial communities, (iii) consider experimental bias in methodological approaches, (iv) undertake in situ biodiversity detection to mitigate risk of non-sample return and post-sample contamination, and (v) address the critical question of how important these microbes are in the functioning of Antarctic ecosystems.

Integrated 'Omics', Targeted Metabolite and Single-cell Analyses of Arctic Snow Algae Functionality and Adaptability

Snow algae are poly-extremophilic microalgae and important primary colonizers and producers on glaciers and snow fields. Depending on their pigmentation they cause green or red mass blooms during the melt season. This decreases surface albedo and thus further enhances snow and ice melting. Although the phenomenon of snow algal blooms has been known for a long time, large aspects of their physiology and ecology sill remain cryptic. This study provides the first in-depth and multi-omics investigation of two very striking adjacent green and red snow fields on a glacier in Svalbard. We have assessed the algal community composition of green and red snow including their associated microbiota, i.e., bacteria and archaea, their metabolic profiles (targeted and non-targeted metabolites) on the bulk and single-cell level, and assessed the feedbacks between the algae and their physico-chemical environment including liquid water content, pH, albedo, and nutrient availability. We demonstrate that green and red snow clearly vary in their physico-chemical environment, their microbial community composition and their metabolic profiles. For the algae this likely reflects both different stages of their life cycles and their adaptation strategies. Green snow represents a wet, carbon and nutrient rich environment and is dominated by the algae Microglena sp. with a metabolic profile that is characterized by key metabolites involved in growth and proliferation. In contrast, the dry and nutrient poor red snow habitat is colonized by various Chloromonas species with a high abundance of storage and reserve metabolites likely to face upcoming severe conditions. Combining a multitude of techniques we demonstrate the power of such complementary approaches in elucidating the function and ecology of extremophiles such as green and red snow algal blooms, which play crucial roles in glacial ecosystems.

Multiple adaptations to polar and alpine environments within cyanobacteria: a phylogenomic and Bayesian approach

Cyanobacteria are major primary producers in the polar and alpine regions contributing significantly to nitrogen and carbon cycles in the cryosphere. Recent advancements in environmental sequencing techniques have revealed great molecular diversity of microorganisms in cold environments. However, there are no comprehensive phylogenetic analyses including the entire known diversity of cyanobacteria from these extreme environments. We present here a global phylogenetic analysis of cyanobacteria including an extensive dataset comprised of available small subunit (SSU) rRNA gene sequences of cyanobacteria from polar and high altitude environments. Furthermore, we used a large-scale multi-gene (135 proteins and 2 ribosomal RNAs) genome constraint including 57 cyanobacterial genomes. Our analyses produced the first phylogeny of cold cyanobacteria exhibiting robust deep branching relationships implementing a phylogenomic approach. We recovered several clades common to Arctic, Antarctic and alpine sites suggesting that the traits necessary for survival in the cold have been acquired by a range of different mechanisms in all major cyanobacteria lineages. Bayesian ancestral state reconstruction revealed that 20 clades each have common ancestors with high probabilities of being capable of surviving in cold environments.

Biogeography of photoautotrophs in the high polar biome

The global latitudinal gradient in biodiversity weakens in the high polar biome and so an alternative explanation for distribution of Arctic and Antarctic photoautotrophs is required. Here we identify how temporal, microclimate and evolutionary drivers of biogeography are important, rather than the macroclimate features that drive plant diversity patterns elsewhere. High polar ecosystems are biologically unique, with a more central role for bryophytes, lichens and microbial photoautotrophs over that of vascular plants. Constraints on vascular plants arise mainly due to stature and ontogenetic barriers. Conversely non-vascular plant and microbial photoautotroph distribution is correlated with favorable microclimates and the capacity for poikilohydric dormancy. Contemporary distribution also depends on evolutionary history, with adaptive and dispersal traits as well as legacy influencing biogeography. We highlight the relevance of these findings to predicting future impacts on diversity of polar photoautotrophs and to the current status of plants in Arctic and Antarctic conservation policy frameworks.

Extremophilic micro-algae and their potential contribution in biotechnology

Micro-algae have potential as sustainable sources of energy and products and alternative mode of agriculture. However, their mass cultivation is challenging due to low survival under harsh outdoor conditions and competition from other, undesired, species. Extremophilic micro-algae have a role to play by virtue of their ability to grow under acidic or alkaline pH, high temperature, light, CO2 level and metal concentration. In this review, we provide several examples of potential biotechnological applications of extremophilic micro-algae and the ranges of tolerated extremes. We also discuss the adaptive mechanisms of tolerance to these extremes. Analysis of phylogenetic relationship of the reported extremophiles suggests certain groups of the Kingdom Protista to be more tolerant to extremophilic conditions than other taxa. While extremophilic microalgae are beginning to be explored, much needs to be done in terms of the physiology, molecular biology, metabolic engineering and outdoor cultivation trials before their true potential is realized.

Microbial diversity on Icelandic glaciers and ice caps

Algae are important primary colonizers of snow and glacial ice, but hitherto little is known about their ecology on Iceland's glaciers and ice caps. Due do the close proximity of active volcanoes delivering large amounts of ash and dust, they are special ecosystems. This study provides the first investigation of the presence and diversity of microbial communities on all major Icelandic glaciers and ice caps over a 3 year period. Using high-throughput sequencing of the small subunit ribosomal RNA genes (16S and 18S), we assessed the snow community structure and complemented these analyses with a comprehensive suite of physical-, geo-, and biochemical characterizations of the aqueous and solid components contained in snow and ice samples. Our data reveal that a limited number of snow algal taxa (Chloromonas polyptera, Raphidonema sempervirens and two uncultured Chlamydomonadaceae) support a rich community comprising of other micro-eukaryotes, bacteria and archaea. Proteobacteria and Bacteroidetes were the dominant bacterial phyla. Archaea were also detected in sites where snow algae dominated and they mainly belong to the Nitrososphaerales, which are known as important ammonia oxidizers. Multivariate analyses indicated no relationships between nutrient data and microbial community structure. However, the aqueous geochemical simulations suggest that the microbial communities were not nutrient limited because of the equilibrium of snow with the nutrient-rich and fast dissolving volcanic ash. Increasing algal secondary carotenoid contents in the last stages of the melt seasons have previously been associated with a decrease in surface albedo, which in turn could potentially have an impact on the melt rates of Icelandic glaciers.

Biodiversity and physiological characteristics of Antarctic and Arctic lichens-associated bacteria

The diversity and physiological characteristics of culturable bacteria associated with lichens from different habitats of the Arctic and Antarctica were investigated. The 68 retrieved isolates could be grouped on the basis of their 16S rRNA gene sequences into 26 phylotypes affiliated with the phyla Actinobacteria, Bacteroidetes, Deinococcus-Thermus, and Firmicutes and with the classes Alphaproteobacteria, Betaproteobacteria, and Gammaproteobacteria. Isolates belonging to the Alphaproteobacteria were the most abundant, followed by those belonging to Actinobacteria, Betaproteobacteria, Gammaproteobacteria, Bacteroidetes, Firmicutes, and Deinococcus-Thermus. Phylogenetic analysis showed that approximately 21 % of the total isolates represented a potentially novel species or genus (≤97 % sequence similarity). Strains belonging to the genera Sphingomonas, Frondihabitans, Hymenobacter, and Burkholderia were recovered from lichen samples from both geographic locations, implying common and important bacterial functions within lichens. Extracellular protease activities were detected in six isolates, affiliated with Burkholderia, Frondihabitans, Hymenobacter, Pseudomonas, and Rhodanobacter. Extracellular lipase activities were detected in 37 isolates of the genera Burkholderia, Deinococcus, Frondihabitans, Pseudomonas, Rhodanobacter, Sphingomonas, and Subtercola. This is the first report on the culturable bacterial diversity present within lichens from Arctic and Antarctica and the isolates described herein are valuable resources to decode the functional and ecological roles of bacteria within lichens. In addition, the low similarity (≤97 %) of the recovered isolates to known species and their production of cold-active enzymes together suggest that lichens are noteworthy sources of novel bacterial strains for use in biotechnological applications.

Variations of algal communities cause darkening of a Greenland glacier

We have assessed the microbial ecology on the surface of Mittivakkat glacier in SE-Greenland during the exceptional high melting season in July 2012 when the so far most extreme melting rate for the Greenland Ice Sheet has been recorded. By employing a complementary and multi-disciplinary field sampling and analytical approach, we quantified the dramatic changes in the different microbial surface habitats (green snow, red snow, biofilms, grey ice, cryoconite holes). The observed clear change in dominant algal community and their rapidly changing cryo-organic adaptation inventory was linked to the high melting rate. The changes in carbon and nutrient fluxes between different microbial pools (from snow to ice, cryoconite holes and glacial forefronts) revealed that snow and ice algae dominate the net primary production at the onset of melting, and that they have the potential to support the cryoconite hole communities as carbon and nutrient sources. A large proportion of algal cells is retained on the glacial surface and temporal and spatial changes in pigmentation contribute to the darkening of the snow and ice surfaces. This implies that the fast, melt-induced algal growth has a high albedo reduction potential, and this may lead to a positive feedback speeding up melting processes.

LC-MS/APCI identification of glucoside esters and diesters of astaxanthin from the snow alga Chlamydomonas nivalis including their optical stereoisomers

HPLC methods (LC-MS/APCI and chiral HPLC) were used for the identification of astaxanthin derivatives from the red snow alga Chlamydomonas nivalis collected in Austrian Alps, Slovak High Tatra Mountains and Bulgarian Pirin. We observed a striking difference in the composition of astaxanthin optical isomers in C. nivalis collected in geographically distinct regions. Furthermore, algae from the Pirin Mountains differed in the dominance of astaxanthin diglucoside diesters, suggesting an alternative strategy to enhance cell viability at low temperatures.

Elemental and fatty acid composition of snow algae in Arctic habitats

Red, orange or green snow is the macroscopic phenomenon comprising different eukaryotic algae. Little is known about the ecology and nutrient regimes in these algal communities. Therefore, eight snow algal communities from five intensively tinted snow fields in western Spitsbergen were analysed for nutrient concentrations and fatty acid (FA) composition. To evaluate the importance of a shift from green to red forms on the FA-variability of the field samples, four snow algal strains were grown under nitrogen replete and moderate light (+N+ML) or N-limited and high light (−N+HL) conditions. All eight field algal communities were dominated by red and orange cysts. Dissolved nutrient concentration of the snow revealed a broad range of NH⁺₄ (<0.005–1.2 mg N l⁻¹) and only low PO³⁻₄ (<18 μg P l⁻¹) levels. The external nutrient concentration did not reflect cellular nutrient ratios as C:N and C:P ratios of the communities were highest at locations containing relatively high concentrations of NH⁺₄ and PO³⁻₄. Molar N:P ratios ranged from 11 to 21 and did not suggest clear limitation of a single nutrient. On a per carbon basis, we found a 6-fold difference in total FA content between the eight snow algal communities, ranging from 50 to 300 mg FA g C⁻¹. In multivariate analyses total FA content opposed the cellular N:C quota and a large part of the FA variability among field locations originated from the abundant FAs C18:1n-9, C18:2n-6, and C18:3n-3. Both field samples and snow algal strains grown under −N+HL conditions had high concentrations of C18:1n-9. FAs possibly accumulated due to the cessation of growth. Differences in color and nutritional composition between patches of snow algal communities within one snow field were not directly related to nutrient conditions. We propose that the highly patchy distribution of snow algae within and between snow fields may also result from differences in topographical and geological parameters such as slope, melting water rivulets, and rock formation.

Characterization of an UV- and VIS-absorbing, purpurogallin-derived secondary pigment new to algae and highly abundant in Mesotaenium berggrenii (Zygnematophyceae, Chlorophyta), an extremophyte living on glaciers

Mesotaenium berggrenii is one of few autotrophs that thrive on bare glacier surfaces in alpine and polar regions. This extremophilic alga produces high amounts of a brownish vacuolar pigment, whose chemical constitution and ecological function is largely unknown until now. Field material was harvested to isolate and characterize this pigment. Its tannin nature was determined by photometric methods, and the structure determination was carried out by means of HPLC-MS and 1D- and 2D-NMR spectroscopy. The main constituent turned out to be purpurogallin carboxylic acid-6-O-β-d-glucopyranoside. This is the first report of such a phenolic compound in this group of algae. Because of its broad absorption capacities of harmful UV and excessive VIS radiation, this secondary metabolite seems to play an important role for the survival of this alga at exposed sites. Attributes and abundances of the purpurogallins found in M. berggrenii strongly suggest that they are of principal ecophysiological relevance like analogous protective pigments of other extremophilic microorganisms. To prove that M. berggrenii is a true psychrophile, photosynthesis measurements at ambient conditions were carried out. Sequencing of the 18S rRNA gene of this alpine species and of its arctic relative, the filamentous Ancylonema nordenskiöldii, underlined their distinct taxonomic position within the Zygnematophyceae.

Community variability of bacteria in alpine snow (Mont Blanc) containing Saharan dust deposition and their snow colonisation potential

Microorganisms uplifted during dust storms survive long-range transport in the atmosphere and could colonize high-altitude snow. Bacterial communities in alpine snow on a Mont Blanc glacier, associated with four depositions of Saharan dust during the period 2006-2009, were studied using 16S rRNA gene sequencing and flow cytometry. Also, sand from the Tunisian Sahara, Saharan dust collected in Grenoble and Mont Blanc snow containing no Saharan dust (one sample of each) were analyzed. The bacterial community composition varied significantly in snow containing four dust depositions over a 3-year period. Out of 61 phylotypes recovered from dusty snow, only three phylotypes were detected in more than one sample. Overall, 15 phylotypes were recognized as potential snow colonizers. For snow samples, these phylotypes belonged to Actinobacteria, Proteobacteria and Cyanobacteria, while for Saharan sand/dust samples they belonged to Actinobacteria, Bacteroidetes, Deinococcus-Thermus and Proteobacteria. Thus, regardless of the time-scale, Saharan dust events can bring different microbiota with no common species set to alpine glaciers. This seems to be defined more by event peculiarities and aeolian transport conditions than by the bacterial load from the original dust source.

Diversity and ecology of psychrophilic microorganisms

Cold environments represent the majority of the biosphere on Earth and have been successfully colonized by psychrophilic microorganisms that are able to thrive at low temperatures and to survive and even maintain metabolic activity at subzero temperatures. These microorganisms play key ecological roles in their habitats and include a wide diversity of representatives of all three domains (Bacteria, Archaea, Eukarya). In this review, we summarize recent knowledge on the abundance, on the taxonomic and functional biodiversity, on low temperature adaptation and on the biogeography of microbial communities in a range of aquatic and terrestrial cold environments.

Characterization of Hymenobacter isolates from Victoria Upper Glacier, Antarctica reveals five new species and substantial non-vertical evolution within this genus

We isolated several Hymenobacter-like strains from Victoria Upper Glacier, Antarctica, basal ice that diverged substantially from currently defined Hymenobacter species according to their 16S rRNA and gyrB gene phylogenies. All strains were psychrotolerant, heterotrophic aerobes which grew preferentially on low salt and low nutrient strength agar. Further phenotypic and chemotaxonomic characterization of these isolates supported their assignment as five novel species: H. algoricola sp. nov., H. antarcticus sp. nov., H. elongatus sp. nov., H. fastidiosus sp. nov., and H. glaciei sp. nov. Remarkable among these data was the prevalence of horizontal gene transfers and phenotypic variation, even between apparently closely related strains. These results suggest extensive non-vertical evolution within the genus Hymenobacter, and may reflect evolutionary trajectories resulting from dormancy, e.g., during interment in glacial ice.