Bacterial characterization of the snow cover at Spitzberg, Svalbard

Bacterial diversity in a contaminated Alpine glacier as determined by culture-based and molecular approaches

Glaciers are important ecosystems, hosting bacterial communities that are adapted to cold conditions and scarcity of available nutrients. Several works focused on the composition of bacterial communities in glaciers and on the long-range atmospheric deposition of pollutants in glaciers, but it is not clear yet if ski resorts can represent a source of point pollution in near-by glaciers, and if these pollutants can influence the residing bacterial communities. To test these hypotheses, 12 samples were analyzed in Madaccio Glacier, in a 3200 ma.s.l. from two areas, one undisturbed and one close to a summer ski resort that is active since the 1930s. Chemical analyses found concentrations up to 43 ng L(-1) for PCBs and up to 168 μg L(-1) for PAHs in the contaminated area: these values are significantly higher than the ones found in undisturbed glaciers because of long-range atmospheric deposition events, and can be explained as being related to the near-by ski resort activities. Isolation of strains on rich medium plates and PCR-DGGE analyses followed by sequencing of bands allowed the identification of a bacterial community with phylogenetic patterns close to other glacier environments, with Proteobacteria and Actinobacteria the mostly abundant phyla, with Acidobacteria, Firmicutes and Cyanobacteria also represented in the culture-independent analyses. A number of isolates were identified by molecular and biochemical methods as phylogenetic related to known xenobiotic-degrading strains: glaciers subjected to chemical contamination can be important reservoirs of bacterial strains with potential applications in bioremediation.

Volatile organic compounds in Arctic snow: concentrations and implications for atmospheric processes

The role of volatile organic compounds (VOC) in the snowpack for atmospheric oxidation, gas-particle transfer and aerosol formation remains poorly understood, partly due to a lack of methodology and unavailable data. We deployed solid phase micro-extraction (SPME) gas chromatography with flame ionization detection for measurement of halogenated, aromatic and oxygenated VOC in the snow pack in Alert, NU, Canada, a High Arctic site. Maximum concentrations in snow were 39 ± 6 μg L(-1) (styrene), indicating a potential VOC contribution to atmospheric oxidation and aerosol formation. Concurrently sampled air had concentrations of up to 1.0 ± 0.3 ng L(-1) (trichloroethene). Back trajectory data showed a change of air mass source region during a depletion event of several VOC in snow (e.g., trichloroethene and benzene). Snow profiles showed an enrichment of most compounds close to the surface. During a second study in Barrow, AK, USA VOC were quantified in snow and frost flowers in the Montreal lab. In Barrow work was carried out as part of the extensive OASIS (Ocean-Atmosphere-Sea Ice-Snowpack) field campaign. Maximum VOC concentrations were up to 1.3 ± 0.1 μg L(-1) (acetophenone). Bromoform in frost flowers averaged 0.19 ± 0.04 μg L(-1), indicating the potential to contribute to bromine generation through photolysis.

Snow surface microbiome on the High Antarctic Plateau (DOME C)

The cryosphere is an integral part of the global climate system and one of the major habitable ecosystems of Earth's biosphere. These permanently frozen environments harbor diverse, viable and metabolically active microbial populations that represent almost all the major phylogenetic groups. In this study, we investigated the microbial diversity in the surface snow surrounding the Concordia Research Station on the High Antarctic Plateau through a polyphasic approach, including direct prokaryotic quantification by flow cytometry and catalyzed reporter deposition fluorescence in situ hybridization (CARD-FISH), and phylogenetic identification by 16S RNA gene clone library sequencing and 454 16S amplicon pyrosequencing. Although the microbial abundance was low (<10³ cells/ml of snowmelt), concordant results were obtained with the different techniques. The microbial community was mainly composed of members of the Alpha-proteobacteria class (e.g. Kiloniellaceae and Rhodobacteraceae), which is one of the most well-represented bacterial groups in marine habitats, Bacteroidetes (e.g. Cryomorphaceae and Flavobacteriaceae) and Cyanobacteria. Based on our results, polar microorganisms could not only be considered as deposited airborne particles, but as an active component of the snowpack ecology of the High Antarctic Plateau.

Potential drivers of microbial community structure and function in Arctic spring snow

The Arctic seasonal snowpack can extend at times over a third of the Earth’s land surface. This chemically dynamic environment interacts constantly with different environmental compartments such as atmosphere, soil and meltwater, and thus, strongly influences the entire biosphere. However, the microbial community associated with this habitat remains poorly understood. Our objective was to investigate the functional capacities, diversity and dynamics of the microorganisms in snow and to test the hypothesis that their functional signature reflects the snow environment. We applied a metagenomic approach to nine snow samples taken over 2 months during the spring season. Fungi, Bacteroidetes, and Proteobacteria were predominant in metagenomic datasets and changes in community structure were apparent throughout the field season. Functional data that strongly correlated with chemical parameters like mercury or nitrogen species supported that this variation could be explained by fluctuations in environmental conditions. Through inter-environmental comparisons we examined potential drivers of snowpack microbial community functioning. Known cold adaptations were detected in all compared environments without any apparent differences in their relative abundance, implying that adaptive mechanisms related to environmental factors other than temperature may play a role in defining the snow microbial community. Photochemical reactions and oxidative stress seem to be decisive parameters in structuring microbial communities inside Arctic snowpacks.

Bacterial diversity in snow on North Pole ice floes

The microbial abundance and diversity in snow on ice floes at three sites near the North Pole was assessed using quantitative PCR and 454 pyrosequencing. Abundance of 16S rRNA genes in the samples ranged between 43 and 248 gene copies per millilitre of melted snow. A total of 291,331 sequences were obtained through 454 pyrosequencing of 16S rRNA genes, resulting in 984 OTUs at 97 % identity. Two sites were dominated by Cyanobacteria (72 and 61 %, respectively), including chloroplasts. The third site differed by consisting of 95 % Proteobacteria. Principal component analysis showed that the three sites clustered together when compared to the underlying environments of sea ice and ocean water. The Shannon indices ranged from 2.226 to 3.758, and the Chao1 indices showed species richness between 293 and 353 for the three samples. The relatively low abundances and diversity found in the samples indicate a lower rate of microbial input to this snow habitat compared to snow in the proximity of terrestrial and anthropogenic sources of microorganisms. The differences in species composition and diversity between the sites show that apparently similar snow habitats contain a large variation in biodiversity, although the differences were smaller than the differences to the underlying environment. The results support the idea that a globally distributed community exists in snow and that the global snow community can in part be attributed to microbial input from the atmosphere.

Diversity and novelty of actinobacteria in Arctic marine sediments

The actinobacterial diversity of Arctic marine sediments was investigated using culture-dependent and culture-independent approaches. A total of 152 strains were isolated from seven different media; 18 isolates were selected for phylogenetic analysis on the basis of their 16S rRNA gene sequences. Results showed that the 18 isolates belonged to a potential novel genus and 10 known genera including Actinotalea, Arthrobacter, Brachybacterium, Brevibacterium, Kocuria, Kytococcus, Microbacterium, Micrococcus, Mycobacterium, and Pseudonocardia. Subsequently, 172 rDNA clones were selected by restriction fragment length polymorphism analysis from 692 positive clones within four actinobacteria-specific 16S rDNA libraries of Arctic marine sediments, and then these 172 clones were sequenced. In total, 67 phylotypes were clustered in 11 known genera of actinobacteria including Agrococcus, Cellulomonas, Demequina, Iamia, Ilumatobacter, Janibacter, Kocuria, Microbacterium, Phycicoccus, Propionibacterium, and Pseudonocardia, along with other, unidentified actinobacterial clones. Based on the detection of a substantial number of uncultured phylotypes showing low BLAST identities (<95 %), this study confirms that Arctic marine environments harbour highly diverse actinobacterial communities, many of which appear to be novel, uncultured species.

Activity and bacterial diversity of snow around Russian Antarctic stations

The diversity and temporal dynamics of bacterial communities in pristine snow around two Russian Antarctic stations was investigated. Taxonomic analysis of rDNA libraries revealed that snow communities were dominated by bacteria from a small number of operational taxonomic units (OTUs) that underwent dramatic swings in abundance between the 54th (2008-2009) and 55th (2009-2010) Russian Antarctic expeditions. Moreover, analysis of the 55th expedition samples indicated that there was very little, if any, correspondence in abundance of clones belonging to the same OTU present in rDNA and rRNA libraries. The latter result suggests that most rDNA clones originate from bacteria that are not alive and/or active and may have been deposited on the snow surface from the atmosphere. In contrast, clones most abundant in rRNA libraries (mostly belonging to Variovorax, Janthinobacterium, Pseudomonas, and Sphingomonas genera) may be considered as endogenous Antarctic snow inhabitants.

The dynamic bacterial communities of a melting High Arctic glacier snowpack

Snow environments can occupy over a third of land surface area, but little is known about the dynamics of snowpack bacteria. The effect of snow melt on bacterial community structure and diversity of surface environments of a Svalbard glacier was examined using analyses of 16S rRNA genes via T-RFLP, qPCR and 454 pyrosequencing. Distinct community structures were found in different habitat types, with changes over 1 week apparent, in particular for the dominant bacterial class present, Betaproteobacteria. The differences observed were consistent with influences from depositional mode (snowfall vs aeolian dusts), contrasting snow with dust-rich snow layers and near-surface ice. Contrary to that, slush as the decompositional product of snow harboured distinct lineages of bacteria, further implying post-depositional changes in community structure. Taxa affiliated to the betaproteobacterial genus Polaromonas were particularly dynamic, and evidence for the presence of betaproteobacterial ammonia-oxidizing bacteria was uncovered, inviting the prospect that the dynamic bacterial communities associated with snowpacks may be active in supraglacial nitrogen cycling and capable of rapid responses to changes induced by snowmelt. Furthermore the potential of supraglacial snowpack ecosystems to respond to transient yet spatially extensive melting episodes such as that observed across most of Greenland's ice sheet in 2012 merits further investigation.

The dynamic arctic snow pack: an unexplored environment for microbial diversity and activity

The Arctic environment is undergoing changes due to climate shifts, receiving contaminants from distant sources and experiencing increased human activity. Climate change may alter microbial functioning by increasing growth rates and substrate use due to increased temperature. This may lead to changes of process rates and shifts in the structure of microbial communities. Biodiversity may increase as the Arctic warms and population shifts occur as psychrophilic/psychrotolerant species disappear in favor of more mesophylic ones. In order to predict how ecological processes will evolve as a function of global change, it is essential to identify which populations participate in each process, how they vary physiologically, and how the relative abundance, activity and community structure will change under altered environmental conditions. This review covers aspects of the importance and implication of snowpack in microbial ecology emphasizing the diversity and activity of these critical members of cold zone ecosystems.

Seasonal variability in bacterial and fungal diversity of the near-surface atmosphere

Bacteria and fungi are ubiquitous throughout the Earth's lower atmosphere where they often represent an important component of atmospheric aerosols with the potential to impact human health and atmospheric dynamics. However, the diversity, composition, and spatiotemporal dynamics of these airborne microbes remain poorly understood. We performed a comprehensive analysis of airborne microbes across two aerosol size fractions at urban and rural sites in the Colorado Front Range over a 14-month period. Coarse (PM10-2.5) and fine (PM2.5) particulate matter samples were collected at weekly intervals with both bacterial and fungal diversity assessed via high-throughput sequencing. The diversity and composition of the airborne communities varied across the sites, between the two size fractions, and over time. Bacteria were the dominant type of bioaerosol in the collected air samples, while fungi and plants (pollen) made up the remainder, with the relative abundances of fungi peaking during the spring and summer months. As bacteria made up the majority of bioaerosol particles, we analyzed the bacterial communities in greater detail using a bacterial-specific 16S rRNA gene sequencing approach. Overall, bacterial taxonomic richness and the relative abundances of specific bacterial taxa exhibited significant patterns of seasonality. Likewise, airborne bacterial communities varied significantly between sites and across aerosol size fractions. Source-tracking analyses indicate that soils and leaves represented important sources of bacteria to the near-surface atmosphere across all locations with cow fecal bacteria also representing an important source of bioaerosols at the more rural sites during early fall and early spring. Together, these data suggest that a complex set of environmental factors, including changes in atmospheric conditions and shifts in the relative importance of available microbial sources, act to control the composition of microbial bioaerosols in rural and urban environments.

Microbial preference for different size classes of organic carbon: a study from Antarctic snow

Significance of carbon cycling in polar ecosystems is well recognized. Yet, bacteria in surface snow have received less attention in terms of their potential in carbon cycling. Here, we present results on carbon utilization by bacterial communities in three surface snow samples from Antarctica collected along a coastal to inland transect. Microcosm studies were conducted over 8 days at 5 ± 1°C to study carbon metabolism in different combinations of added low molecular weight (LMW (glucose, <1 kDa)) and high molecular weight (HMW (starch, >1 kDa)) substrates (final 20 ppm). The total organic carbon (TOC) in the snow samples decreased with time at rates ranging from non-detectable to 1.4 ppm day(-1) with rates highest in snow samples from inland region. In addition, carbon utilization studies were also carried out with bacterial isolates LH1, LH2, and LH4 belonging to the genus Cellulosimicrobium, Bacillus, and Ralstonia, respectively, isolated from the snow samples. Studies with strain LH2 in different amendments of glucose and starch showed that TOC decreased with time in all amendments at a rate of 0.9-1.5 ppm day(-1) with highest rates of 1.4-1.5 ppm day(-1) in amendments containing a higher proportion of starch. The bacterial isolates were also studied to determine their ability to utilize other LMW and HMW compounds. They utilized diverse substrates like carbohydrates, amino acids, amines, amides, complex polymers, etc., of molecular mass <100 Da, 100-500 Da, >500 Da-1 kDa, and >1 kDa preferring (up to 31 times) substrates with mass of >1 kDa than <1 kDa. The ability of bacteria in snow to utilize diverse LMW and HMW substrates indicates that they could be important in the uptake of similar compounds in snow and therefore potentially govern snow chemistry.

Phylogenetic clustering increases with elevation for microbes

Although phylogenetic approaches are useful for providing insights into the processes underlying biodiversity patterns, the studies of microbial phylogenetic relatedness are rare, especially for elevational gradients. Using high-throughput pyrosequencing, we examined the biodiversity patterns for biofilm bacterial communities that were scraped from stream stones along an elevational gradient from 1820 to 4050 m in China. The patterns of bacterial species richness and phylogenetic diversity were hollow towards higher elevations. The bacterial communities consisted of closer relatives than expected and displayed increasing terminal phylogenetic clustering towards mountain top. The increasing phylogenetic clustering with elevation contrasts reports for macroorganisms that revealed phylogenetic overdispersion at low or intermediate elevations. Because water temperature showed the strongest correlation with phylogenetic relatedness (r(2)  = 0.516), the elevational pattern in the bacterial phylogenetic structure indicated that environmental filtering possibly due to lower temperature or more frequent temperature fluctuations increased towards higher elevations. Evidence supporting the environmental filtering on bacteria was also reflected by the orderly succession in the relative abundance of different bacterial phyla along the elevational gradient and in the high evenness of bacterial taxa at higher elevations. Overall, our results indicated that ecological processes possibly related to temperature may play a dominant role in structuring bacterial biodiversity along the elevational gradient.

Life at the wedge: the activity and diversity of arctic ice wedge microbial communities

The discovery of polygonal terrain on Mars underlain by ice heightens interest in the possibility that this water-bearing habitat may be, or may have been, a suitable habitat for extant life. The possibility is supported by the recurring detection of terrestrial microorganisms in subsurface ice environments, such as ice wedges found beneath tundra polygon features. A characterization of the microbial community of ice wedges from the high Arctic was performed to determine whether this ice environment can sustain actively respiring microorganisms and to assess the ecology of this extreme niche. We found that ice wedge samples contained a relatively abundant number of culturable cells compared to other ice habitats (∼10(5) CFU·mL(-1)). Respiration assays in which radio-labeled acetate and in situ measurement of CO(2) flux were used suggested low levels of microbial activity, though more sensitive techniques are required to confirm these findings. Based on 16S rRNA gene pyrosequencing, bacterial and archaeal ice wedge communities appeared to reflect surrounding soil communities. Two Pseudomonas sp. were the most abundant taxa in the ice wedge bacterial library (∼50%), while taxa related to ammonia-oxidizing Thaumarchaeota occupied 90% of the archaeal library. The tolerance of a variety of isolates to salinity and temperature revealed characteristics of a psychrotolerant, halotolerant community. Our findings support the hypothesis that ice wedges are capable of sustaining a diverse, plausibly active microbial community. As such, ice wedges, compared to other forms of less habitable ground ice, could serve as a reservoir for life on permanently cold, water-scarce, ice-rich extraterrestrial bodies and are therefore of interest to astrobiologists and ecologists alike. .

In-Field Implementation of a Recombinant Factor C Assay for the Detection of Lipopolysaccharide as a Biomarker of Extant Life within Glacial Environments

The discovery over the past two decades of viable microbial communities within glaciers has promoted interest in the role of glaciers and ice sheets (the cryosphere) as contributors to subglacial erosion, global biodiversity, and in regulating global biogeochemical cycles. In situ or in-field detection and characterisation of microbial communities is becoming recognised as an important approach to improve our understanding of such communities. Within this context we demonstrate, for the first time, the ability to detect Gram-negative bacteria in glacial field-environments (including subglacial environments) via the detection of lipopolysaccharide (LPS); an important component of Gram-negative bacterial cell walls. In-field measurements were performed using the recently commercialised PyroGene^® recombinant Factor C (rFC) endotoxin detection system and used in conjunction with a handheld fluorometer to measure the fluorescent endpoint of the assay. Twenty-seven glacial samples were collected from the surface, bed and terminus of a low-biomass Arctic valley glacier (Engabreen, Northern Norway), and were analysed in a field laboratory using the rFC assay. Sixteen of these samples returned positive LPS detection. This work demonstrates that LPS detection via rFC assay is a viable in-field method and is expected to be a useful proxy for microbial cell concentrations in low biomass environments.

Culturable bacteria isolated from snow cores along the 1300 km traverse from Zhongshan Station to Dome A, East Antarctica

The abundance and community composition of culturable bacteria in four snow cores along the 1300 km traverse from Zhongshan Station to Dome A, East Antarctica, were investigated through the combination of liquid and solid media and small subunit 16S rRNA sequences. Under aerobic cultivation conditions, the average concentrations of bacterial colonies from each snow core varied from 0.008 to 0.32 CFU mL(-1). A total of 37 and 15 isolates with different morphologic characteristics were recovered from solid and liquid media PYGV, respectively. The phylogenetic analysis of 14 representatives with different ARDRA patterns from RFLP showed that all the isolates were affiliated with five phylogenetic groups: Firmicutes, Actinobacteria, Alphaproteobacteria, Gammaproteobacteria and Bacteroidetes. Actinobacteria represented the largest cluster with 43% of strains, and these strains exhibited unique phenotypic properties. The community compositions of culturable bacteria in the four snow cores were distinctly different from each other and the concentrations and community sizes of culturable bacteria along the traverse decreased with increases of latitude, altitude and distance from coast, which likely reflected the different bacterial sources and biogeographies under the different regional climate conditions in the snow cover of East Antarctica.

Structure and diversity of bacterial, eukaryotic and archaeal communities in glacial cryoconite holes from the Arctic and the Antarctic

The cryosphere presents some of the most challenging conditions for life on earth. Nevertheless, (micro)biota survive in a range of niches in glacial systems, including water-filled depressions on glacial surfaces termed cryoconite holes (centimetre to metre in diameter and up to 0.5 m deep) that contain dark granular material (cryoconite). In this study, the structure of bacterial and eukaryotic cryoconite communities from ten different locations in the Arctic and Antarctica was compared using T-RFLP analysis of rRNA genes. Community structure varied with geography, with greatest differences seen between communities from the Arctic and the Antarctic. DNA sequencing of rRNA genes revealed considerable diversity, with individual cryoconite hole communities containing between six and eight bacterial phyla and five and eight eukaryotic 'first-rank' taxa and including both bacterial and eukaryotic photoautotrophs. Bacterial Firmicutes and Deltaproteobacteria and Epsilonproteobacteria, eukaryotic Rhizaria, Haptophyta, Choanomonada and Centroheliozoa, and archaea were identified for the first time in cryoconite ecosystems. Archaea were only found within Antarctic locations, with the majority of sequences (77%) related to members of the Thaumarchaeota. In conclusion, this research has revealed that Antarctic and Arctic cryoconite holes harbour geographically distinct highly diverse communities and has identified hitherto unknown bacterial, eukaryotic and archaeal taxa, therein.

Glaciers and ice sheets as a biome

The tundra is the coldest biome described in typical geography and biology textbooks. Within the cryosphere, there are large expanses of ice in the Antarctic, Arctic and alpine regions that are not regarded as being part of any biome. During the summer, there is significant melt on the surface of glaciers, ice caps and ice shelves, at which point microbial communities become active and play an important role in the cycling of carbon and other elements within the cryosphere. In this review, we suggest that it is time to recognise the cryosphere as one of the biomes of Earth. The cryospheric biome encompasses extreme environments and is typified by truncated food webs dominated by viruses, bacteria, protozoa and algae with distinct biogeographical structures.

Total mercury and methylmercury in high altitude surface snow from the French Alps

Surface snow samples were collected weekly from the 31st of December 2008 to the 21st of June 2009 from Lake Bramant in the French Alps. Total mercury (THg), total dissolved mercury (THgD), methylmercury (MeHg) and particle distributions in surface snow were analyzed. Results showed that THg concentrations, MeHg concentrations and particle load increased with snow surface temperature, which is an indicator of rising temperatures as the season progresses. Significant correlations between MeHg and snow surface temperature and MeHg and total particles greater than 10 μm were observed. This suggests that the MeHg found in the snow originates from atmospheric deposition processes rather than in situ snowpack sources. This study suggests that an important post-winter atmospheric deposition of MeHg and THg occurs on summital zones of the French Alps and it is likely that this contamination originates from the surrounding valleys.

Microbial diversity in the snow, a moraine lake and a stream in Himalayan glacier

The microbial diversity and abundance in surface snow at different altitudes (5300 and 5504 m above sea level), a moraine lake and a glacial stream in the Yala Glacier on the southern slope of the Himalayas were investigated through a 16S rRNA gene clone library and flow cytometry approaches. Cell abundance in different habitats changed from 1.1 × 10(4) to 25 × 10(4) cells mL(-1), with the highest abundance in the moraine lake and the lowest abundance in the snow at 5504 m. Microbial communities in the snow were significantly different from those in the moraine lake and stream, although they were similar within snow and within the aquatic habitats. The two snow libraries were both dominated by Cyanobacteria, which accounted for about half of the total, followed by the Alphaproteobacteria and Firmicutes. The moraine lake and stream libraries were dominated by the Bacteroidetes and Betaproteobacteria, followed by the Actinobacteria. The results indicated that snow and water were highly diverse systems even in the same glacier. Microbial communities in the snow on the Yala Glacier were distinctly different from those in the East Rongbuk Glacier on the northern slope of Himalayas. However, microbes in the moraine lakes at two glaciers had similar community features. The snow habitat was easily affected by various environmental factors, while the aquatic habitats were comparatively stable in different glaciers.

Microbes in high arctic snow and implications for the cold biosphere

We applied molecular, microscopic, and culture techniques to characterize the microbial communities in snow and air at remote sites in the Canadian High Arctic (Ward Hunt Island, Ellesmere Island, and Cornwallis Island, latitudes 74 to 83(o)N). Members of the Bacteria and Eukarya were prevalent in the snow, and their small subunit (SSU) rRNA gene signatures indicated strong local aerial transport within the region over the preceding 8 months of winter snowpack accumulation. Many of the operational taxonomic units (OTUs) were similar to previously reported SSU rRNA gene sequences from the Arctic Ocean, suggesting the importance of local aerial transport processes for marine microbiota. More than 47% of the cyanobacterial OTUs in the snow have been previously found in microbial mats in the region, indicating that this group was also substantially derived from local sources. Viable cyanobacteria isolated from the snow indicated free exchange between the snow and adjacent mat communities. Other sequences were most similar to those found outside the Canadian Arctic but were from snow, lake and sea ice, glaciers and permafrost, alpine regions, Antarctica, and other regions of the Arctic, supporting the concept of global distribution of microbial ecotypes throughout the cold biosphere.

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.

Diversity and characterization of mercury-resistant bacteria in snow, freshwater and sea-ice brine from the High Arctic

It is well-established that atmospheric deposition transports mercury from lower latitudes to the Arctic. The role of bacteria in the dynamics of the deposited mercury, however, is unknown. We characterized mercury-resistant bacteria from High Arctic snow, freshwater and sea-ice brine. Bacterial densities were 9.4 × 10(5), 5 × 10(5) and 0.9-3.1 × 10(3) cells mL(-1) in freshwater, brine and snow, respectively. Highest cultivability was observed in snow (11.9%), followed by freshwater (0.3%) and brine (0.03%). In snow, the mercury-resistant bacteria accounted for up to 31% of the culturable bacteria, but <2% in freshwater and brine. The resistant bacteria belonged to the Alpha-, Beta- and Gammaproteobacteria, Firmicutes, Actinobacteria, and Bacteriodetes. Resistance levels of most isolates were not temperature dependent. Of the resistant isolates, 25% reduced Hg(II) to Hg(0). No relation between resistance level, ability to reduce Hg(II) and phylogenetic group was observed. An estimation of the potential bacterial reduction of Hg(II) in snow suggested that it was important in the deeper snow layers where light attenuation inhibited photoreduction. Thus, by reducing Hg(II) to Hg(0), mercury-resistant bacteria may limit the supply of substrate for methylation processes and, hence, contribute to lowering the risk that methylmercury is being incorporated into the Arctic food chains.

Microbial sequences retrieved from environmental samples from seasonal arctic snow and meltwater from Svalbard, Norway

16S rRNA gene (rrs) clone libraries were constructed from two snow samples (May 11, 2007 and June 7, 2007) and two meltwater samples collected during the spring of 2007 in Svalbard, Norway (79 degrees N). The libraries covered 19 different microbial classes, including Betaproteobacteria (21.3%), Sphingobacteria (16.4%), Flavobacteria (9.0%), Acidobacteria (7.7%) and Alphaproteobacteria (6.5%). Significant differences were detected between the two sets of sample libraries. First, the meltwater libraries had the highest community richness (Chao1: 103.2 and 152.2) and Shannon biodiversity indices (between 3.38 and 3.59), when compared with the snow libraries (Chao1: 14.8 and 59.7; Shannon index: 1.93 and 3.01). Second, integral-LIBSHUFF analyses determined that the bacterial communities in the snow libraries were significantly different from those of the meltwater libraries. Despite these differences, our data also support the theory that a common core group of microbial populations exist within a variety of cryohabitats. Electronic supplementary material The online version of this article (doi:10.1007/s00792-009-0299-2) contains supplementary material, which is available to authorized users.

Bacterial biodiversity from Roopkund Glacier, Himalayan mountain ranges, India

The bacterial diversity of two soil samples collected from the periphery of the Roopkund glacial lake and one soil sample from the surface of the Roopkund Glacier in the Himalayan ranges was determined by constructing three 16S rRNA gene clone libraries. The three clone libraries yielded a total of 798 clones belonging to 25 classes. Actinobacteria was the most predominant class (>10% of the clones) in the three libraries. In the library from the glacial soil, class Betaproteobacteria (24.2%) was the most predominant. The rarefaction analysis indicated coverage of 43.4 and 41.2% in the samples collected from the periphery of the lake thus indicating a limited bacterial diversity covered; at the same time, the coverage of 98.4% in the glacier sample indicated most of the diversity was covered. Further, the bacterial diversity in the Roopkund glacier soil was low, but was comparable with the bacterial diversity of a few other glaciers. The results of principal component analysis based on the 16S rRNA gene clone library data, percentages of OTUs and biogeochemical data revealed that the lake soil samples were different from the glacier soil sample and the biogeochemical properties affected the diversity of microbial communities in the soil samples.

Microorganisms in dry polar snow are involved in the exchanges of reactive nitrogen species with the atmosphere

The snowpack is a complex photochemical reactor that emits a wide variety of reactive molecules to the atmosphere. In particular, the photolysis of nitrate ions, NO(3)(-), produces NO, NO(2), and HONO, which affects the oxidative capacity of the atmosphere. We report measurements in the European High Arctic where we observed for the first time emissions of NO, NO(2), and HONO by the seasonal snowpack in winter, in the complete or near-complete absence of sunlight and in the absence of melting. We also detected unusually high concentrations of nitrite ions, NO(2)(-), in the snow. These results suggest that microbial activity in the snowpack is responsible for the observed emissions. Isotopic analysis of NO(2)(-) and NO(3)(-) in the snow confirm that these ions, at least in part, do not have an atmospheric origin and are most likely produced by the microbial oxidation of NH(4)(+) coming from clay minerals into NO(2)(-) and NO(3)(-). These metabolic pathways also produce NO. Subsequent dark abiotic reactions lead to NO(2) and HONO production. The snow cover is therefore not only an active photochemical reactor but also a biogeochemical reactor active in the cycling of nitrogen and it can affect atmospheric composition all year round.

Abundance and community of snow bacteria from three glaciers in the Tibetan Plateau

Bacterial abundance and diversity in snow of East Rongbuk, Laohugou and Hailuogou glaciers on the Tibetan Plateau were investigated through epifluorescence microscope and denaturing gradient gel electrophoresis. Cell abundance ranged from 4.0 x 10(3) to 290.2 x 10(3) cells/mL. The phylogenetic trees placed the 16S rRNA sequences in four major groups: Proteobacteria, Firmicutes, Actinobacteria and Bacteroidetes. Brevundimonas, Flavobacterium, Hymenobacter, Bacillus, Polaromonas, Rhodoferax and Streptomyces were widely distributed bacteria in glaciers from different cold regions. The remaining five genera of Hylemonella, Delftia, Zoogloea, Blastococcus and Rhodococcus were endemism, only recovered from our investigated glaciers. It is proposed that the three glaciers on the Tibetan Plateau provide a specific ecological niche for prolonging survival of diverse microbial lineages.

Altitudinal changes in a bacterial community on Gulkana Glacier in Alaska

To clarify altitudinal changes in the bacterial community on Gulkana Glacier in Alaska, we analyzed bacterial 16S rRNA gene by low-cycle PCR amplification, denaturing gradient gel electrophoresis (DGGE), and culturing in a snowmelt medium at 4°C. Low-cycle PCR-based cloning revealed the presence of 100 bacterial OTUs; however, 41 OTUs were identified only in a single clone, suggesting that their abundance was limited because of difficulty in predominating on the glacier. In contrast, 17 major OTUs accounted for 57-87% of the clone library at each site, suggesting that they accounted for the major part of the bacteria on the glacier. In addition, five of the 17 OTUs were included in the 21 OTUs cultured in the snowmelt medium. Based on the dominant phylotypes and DGGE results, the bacterial community on the glacier could be divided into three types, corresponding to the snow-covered, snow- and ice-covered, and bare-ice areas of the glacier. Our results suggest that a relatively limited number of bacteria predominate and that each phylotype is adapted to a distinct set of conditions on the glacier.

Dominant bacteria and biomass in the Kuytun 51 Glacier

Dominant bacteria in the different habitats in the Kuytun 51 Glacier were investigated using a 16S rRNA gene clone library sequencing technique. Results showed diverse bacteria on the glacial surface, with the dominant phyla being Proteobacteria, Cyanobacteria, and Bacteroidetes. UniFrac data showed distinct community patterns between the Kuytun and Himalayan Rongbuk glaciers.

Bacterial diversity and bioprospecting for cold-active lipases, amylases and proteases, from culturable bacteria of kongsfjorden and Ny-alesund, Svalbard, Arctic

Culturable bacterial diversity of seven marine sediment samples of Kongsfjorden and a sediment and a soil sample from Ny-Alesund, Svalbard, Arctic was studied. The bacterial abundance in the marine sediments of Kongsfjorden varied marginally (0.5 x 10(3)-1.3 x 10(4) cfu/g sediment) and the bacterial number in the two samples collected from the shore of Ny-Alesund also was very similar (0.6 x 10(4) and 3.4 x 10(4), respectively). From the nine samples a total of 103 bacterial isolates were obtained and these isolates could be grouped in to 47 phylotypes based on the 16S rRNA gene sequence belonging to 4 phyla namely Actinobacteria, Bacilli, Bacteroidetes and Proteobacteria. Representatives of the 47 phylotypes varied in their growth temperature range (4-37 degrees C), in their tolerance to NaCl (0.3-2 M NaCl) and growth pH range (2-11). Representatives of 26 phylotypes exhibited amylase and lipase activity either at 5 or 20 degrees C or at both the temperatures. A few of the representatives exhibited amylase and/or lipase activity only at 5 degrees C. None of the phylotypes exhibited protease activity. Most of the phylotypes (38) were pigmented. Fatty acid profile studies indicated that short chain fatty acids, unsaturated fatty acids, branched fatty acids, the cyclic and the cis fatty acids are predominant in the psychrophilic bacteria.

A field-based cleaning protocol for sampling devices used in life-detection studies

Analytical approaches to extant and extinct life detection involve molecular detection often at trace levels. Thus, removal of biological materials and other organic molecules from the surfaces of devices used for sampling is essential for ascertaining meaningful results. Organic decontamination to levels consistent with null values on life-detection instruments is particularly challenging at remote field locations where Mars analog field investigations are carried out. Here, we present a seven-step, multi-reagent decontamination method that can be applied to sampling devices while in the field. In situ lipopolysaccharide detection via low-level endotoxin assays and molecular detection via gas chromatography-mass spectrometry were used to test the effectiveness of the decontamination protocol for sampling of glacial ice with a coring device and for sampling of sediments with a rover scoop during deployment at Arctic Mars-analog sites in Svalbard, Norway. Our results indicate that the protocols and detection technique sufficiently remove and detect low levels of molecular constituents necessary for life-detection tests.

Bacterial diversity in the snow over Tibetan Plateau Glaciers

Bacterial diversity and cell abundance in the snow of the four glaciers (Guoqu, Zadang, East Rongbuk and Palong No. 4) located in different climatic zones of the Tibetan Plateau were investigated through culture-independent molecular analysis of 16S rRNA gene clone library and flow cytometry approaches. Cell abundance ranged from 0.68 x 10(3) to 720 x 10(3) cells mL(-1), with higher values in the northern glaciers than in the southern ones. Bacterial diversity was unexpectedly high in the snow habitats of the world's highest plateau, with 15 common genera distributed widely among the glaciers. The bacterial diversity in the snow at different glaciers was related to the surrounding environments. The Guoqu Glacier, to the north near the desert zone and with the lowest temperature, preserved more bacteria closely related to a cold environment and soil than the other glaciers. However, in the Palong No. 4 Glacier located in the south warm region around vegetation, most bacteria were phylogenetically related to plant-associated bacteria.

Macromolecular synthesis by yeasts under frozen conditions

Although viable fungi have been recovered from a wide variety of icy environments, their metabolic capabilities under frozen conditions are still largely unknown. We investigated basidiomycetous yeasts isolated from an Antarctic ice core and showed that after freezing at a relatively slow rate (0.8 degrees C min(-1)), the cells are excluded into veins of liquid at the triple junctions of ice crystals. These strains were capable of reproductive growth at -5 degrees C under liquid conditions. Under frozen conditions, metabolic activity was assessed by measuring rates of [(3)H]leucine incorporation into the acid-insoluble macromolecular fraction, which decreased exponentially at temperatures between 15 degrees C and -15 degrees C and was inhibited by the protein synthesis inhibitor cycloheximide. Experiments at -5 degrees C under frozen and liquid conditions revealed 2-3 orders of magnitude lower rates of endogenous metabolism in ice, likely due to the high salinity in the liquid fraction of the ice (equivalent of approximately 1.4 mol l(-1) of NaCl at -5 degrees C). The mesophile Saccharomyces cerevisae also incorporated [(3)H]leucine at -5 degrees C and -15 degrees C, indicating that this activity is not exclusive to cold-adapted microorganisms. The ability of yeast cells to incorporate amino acid substrates into macromolecules and remain metabolically active under these conditions has implications for understanding the survival of Eukarya in icy environments.

Critical review of mercury fates and contamination in the Arctic tundra ecosystem

Mercury (Hg) contamination in tundra region has raised substantial concerns, especially since the first report of atmospheric mercury depletion events (AMDEs) in the Polar Regions. During the past decade, steady progress has been made in the research of Hg cycling in the Polar Regions. This has generated a unique opportunity to survey the whole Arctic in respect to Hg issue and to find out new discoveries. However, there are still considerable knowledge gaps and debates on the fate of Hg in the Arctic and Antarctica, especially regarding the importance and significance of AMDEs vs. net Hg loadings and other processes that burden Hg in the Arctic. Some studies argued that climate warming since the last century has exerted profound effects on the limnology of High Arctic lakes, including substantial increases in autochthonous primary productivity which increased in sedimentary Hg, whereas some others pointed out the importance of the formation and postdeposition crystallographic history of the snow and ice crystals in determining the fate and concentration of mercury in the cryosphere in addition to AMDEs. Is mercury re-emitted back to the atmosphere after AMDEs? Is Hg methylation effective in the Arctic tundra? Where the sources of MeHg are? What is its fate? Is this stimulated by human made? This paper presents a critical review about the fate of Hg in the Arctic tundra, such as pathways and process of Hg delivery into the Arctic ecosystem; Hg concentrations in freshwater and marine ecosystems; Hg concentrations in terrestrial biota; trophic transfer of Hg and bioaccumulation of Hg through food chain. This critical review of mercury fates and contamination in the Arctic tundra ecosystem is assessing the impacts and potential risks of Hg contamination on the health of Arctic people and the global northern environment by highlighting and "perspectiving" the various mercury processes and concentrations found in the Arctic tundra.