Samples of surface water and ice bottom samples were collected at 23 stations surrounding Cornwallis Island, in Lancaster Sound, Wellington Channel and adjacent channels, between The sampling was carried out between May 4 and 18, , which corresponded to the period of the ice algal bloom. Three cores, used for biomass measurements and DNA analyses, were pooled together and melted with the addition of 0.
This procedure was performed to dilute the thick microbial mats found at the bottom of the cores and maintain osmotic pressure in the samples to be filtered for DNA extraction. The three other cores, used for chemical analyses, were placed in a sterile bag and melted without the addition of filtered seawater.
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Sterile gloves were always worn when manipulating the cores. At the time of sampling, snow thickness and ice thickness were measured at 5 sites near core collection. The map was generated using Google Earth version 7. Bacterial abundance was measured by flow cytometry as detailed in Belzile et al.
Additional details on the methods can be found in Michel and Niemi Volumes of reagents were tripled in comparison to the original protocol to ensure full submersion of filters. Following UPGMA cluster analysis of the samples based on the 16S rRNA gene dataset not shown , representative samples of major clusters were selected for metagenomic sequencing.
Barcoded libraries were pooled in an equimolar ratio three by three. A total of 3. Sequencing of the pooled libraries was performed using the PGM system with the Ion Sequencing kit and chips. Sequences were analyzed through our internal rRNA short amplicon analysis pipeline as previously described 19 , This normalized OTU table was used for downstream analysis and for computing alpha and beta diversity metrics. Sequencing statistics are presented in Supplementary Table S1. Paired and non-paired t-tests were performed using the t.
NA: not applicable.
The microbial communities associated with the sea ice were more spatially variable than the microbial communities in seawater average weighted UniFrac distance between samples of 0. Seawater samples were significantly richer Chao 1 richness: Principal coordinate ordinations of a UniFrac distances calculated from 16S rRNA gene, b Bray-Curtis distances calculated from relative abundance of species in metagenomic datasets and c Bray-Curtis distances calculated from relative abundance of functions in metagenomic datasets.
Similar differences between the sea ice and seawater samples were visible in the metagenomic dataset, both for the species-level taxonomic table Fig. Although the differences between sea ice and seawater samples were visually less clear for the function-level ordination Fig. The seawater samples showed less variability than the sea ice for both the taxonomic and function tables average Bray-Curtis distance between samples of 0.
The differences observed between sea ice and seawater samples were also visible at relatively high taxonomic levels phylum-class Fig.
Seawater samples were significantly enriched in Thaumarcheota, Euryarchaeota, Actinobacteria, Cyanobacteria, Fimicutes, Planctomycetes, Betaproteobacteria, Deltaproteobacteria , and Verrucomicrobia and significantly depleted in Bacteroidetes, Alphaproteobacteria and Gammaproteobacteria when compared to sea ice samples. Some of these trends were also visible in the metagenomic datasets Fig.
As expected in view of the biases associated with PCR amplification, the relative abundance of some phyla varied considerably between 16S rRNA gene and metagenomic datasets Fig. The numbers on the x-axis represent the sampling station number as shown in Fig. The 15 most abundant OTUs depicted in Fig. These differences were particularly visible in photosynthesis-related genes Fig.
Given the expected significant differences between sea ice and seawater constituents, the two sample types were treated separately during the analyses. The effect of environmental variables on the microbial community structure was tested by CCA with forward selection of variables to be included in the model. Many OTUs showed significant correlations with environmental variables.
In the seawater 16S rRNA gene dataset, Spearman correlations were significant positive, negative. Si OH 4 was the factor having the highest number of positive 23 and negative 37 correlations. In the present study, we compared seawater and the immediately overlying sea ice at 23 locations around Cornwallis Island in the Canadian high Arctic. It is one of the first studies to simultaneously look at linked seawater and sea ice samples using shotgun metagenomics and 16S rRNA gene sequencing and to relate this genomic data to potential environmental drivers.
As expected, seawater and sea ice exhibited large differences in terms of chemistry, community composition and functional gene content. A key difference between the two sample types was the dominance of algae in sea ice samples, as visualized by the higher relative abundance of algae and photosynthesis-related genes in the shotgun metagenomic datasets and the high sea ice chl a concentrations. Metagenomic datasets from this study showed that these algae were mainly diatoms, confirming visual observations during sampling and corresponding with ice algal taxonomic studies near the study area Indeed, primary producers, such as algae, are responsible for the increased availability of labile carbon 28 , benefiting heterotrophs, such as Gammaproteobacteria , and this taxon was significantly more abundant in sea ice as compared to seawater.
A symbiotic relationship was proposed to exist between algae and bacteria by production of vitamin B12 29 , and algae exuded exopolymeric substances 30 , 31 , acting as osmo- and cryoprotectants, probably allowing for the survival of bacteria that are not necessarily cold-adapted 32 , 33 , However, in our metagenomic dataset, the relative abundance of genes related to the biosynthesis of vitamin B12 was significantly higher in the seawater, while the relative abundance of genes related to osmoregulation varied greatly from sample to sample, with no significant differences between sea ice and seawater.
The mean values and range for the physico-chemical indicators are similar to values previously reported for surface water in the Northwest Passage Among these indicators, salinity and nutrients were shown to be correlated with the abundance of various microbial taxa, even though variability in environmental parameters was small Interestingly, in the present study, the number of sea ice OTUs and functions that had significant negative correlations with environmental parameters was much higher than the number of OTUs and functions having significantly positive correlations.
In the seawater datasets, the number of positive and negative significant correlations was more balanced, suggesting different ecological strategies or susceptibilities to environmental drivers between the microbial communities inhabiting seawater and overlying sea ice. Most results showed higher variability in microbial communities in sea ice samples as compared to seawater. Sea ice is highly variable in terms of physiochemical properties, especially within its microenvironments 36 , as well as snow cover depth, resulting in an uneven distribution e.
Accordingly, we observed variability in physical and chemical characteristics of sea ice samples, which resulted in higher variability in microbial communities when compared to the more homogeneous seawater samples. Still, the water mass in the Canadian Arctic archipelago is quite variable regarding dynamics and nutrient content Although previous studies used different PCR primers 7 , 40 , sampled multi-year ice as compared to first-year ice here 12 , 33 , 41 , 42 and sampled later in summer as compared to our springtime sampling in the midst of the algal bloom 11 , the community composition of the surface water and bottom layer of the sea ice samples of this study were comparable to previous studies of Arctic and Antarctic sea ice and surface water.
The Gammaproteobacteria and Bacteroidetes were abundant in sea ice samples, similar to multi-year ice sampled near the geographic North Pole 12 and in first-year ice from a Norwegian Fjord study Other taxa that were present, but at lower abundances, were Actinobacteria, Alpha - and Betaproteobacteria , which are also common to other first-year and multi-year sea ice samples As in the sea ice, both Proteobacteria and Bacteroidetes were relatively abundant in seawater samples, similar to previous reports from Antarctic and Arctic seawater 8 , 12 , 35 , In conclusion, our study has shown that the microbial communities and their associated functional genes present around Cornwallis Island in the Canadian high Arctic are very different between sea ice and seawater, even though they were quite variable between sampling sites.
The functional differences observed could be at the root of the different capacities of sea ice and seawater to degrade hydrocarbon, as recently shown using samples from the same area How to cite this article: Yergeau, E. Metagenomic survey of the taxonomic and functional microbial communities of seawater and sea ice from the Canadian Arctic.
Publisher's note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. The authors declare no conflict of interest. The authors declare no competing financial interests. Author Contributions J.
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National Center for Biotechnology Information , U. Sci Rep. Published online Feb 8. Greer a, 3. Thomas L. Charles W. Author information Article notes Copyright and License information Disclaimer.
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Received Nov 2; Accepted Jan 3. This work is licensed under a Creative Commons Attribution 4. This article has been cited by other articles in PMC. Abstract Climate change has resulted in an accelerated decline of Arctic sea ice since resulting in primary production increases and prolongation of the ice-free season within the Northwest Passage. Material and Methods Sample collection Samples of surface water and ice bottom samples were collected at 23 stations surrounding Cornwallis Island, in Lancaster Sound, Wellington Channel and adjacent channels, between Open in a separate window.
Figure 1. Location of sampling stations in the Canadian Arctic Archipelago Nunavut. Metagenomic sequencing Following UPGMA cluster analysis of the samples based on the 16S rRNA gene dataset not shown , representative samples of major clusters were selected for metagenomic sequencing.
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Table 1 Physico-chemical characterization of the surface waters and sea ice bottom samples. Figure 2. Figure 3. Figure 4. Figure 5. Figure 6. Discussion In the present study, we compared seawater and the immediately overlying sea ice at 23 locations around Cornwallis Island in the Canadian high Arctic. Additional Information How to cite this article: Yergeau, E.
At the Mirny coastal station it is only minus Even less precipitation remains lying on the inland ice: 20 grams of ice per square centimetre and year, or 5 to 50 millimetres of water equivalent. At the Russian Vostok research station in East Antarctica, at a height of 3, metres, a world cold record of minus In contrast to the North Pole, at the South Pole there is thick inland ice reaching heights of up to 4, metres above sea level.
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Thus the average height of the Antarctic is 2, metres, while the average height of the other continents is only some metres. Beside the East Antarctic Shield the ice holds together the archipelago of West Antarctica, from which only a few individual mountain ranges break through the ice nunataks and only a few of the coasts are free of ice. But even just the 2 to 3 percent of periglacial regions, which lie without ice cover at the periphery of the glaciers, when taken together amount to a territory that is larger than Germany.
Despite the inhospitable living conditions for humans, the coasts and oceans are an ecologically rich habitat for adapted species such as whales, seals, penguins, fish, krill and others. In the deep Antarctic seas, especially in the Pacific sector, rich fields of manganese nodules have been proved at a depth of 1, to 5, metres beneath the sea. The inland ice is the most important fresh water repository in the Earth's water supply. Technical developments in this direction have already been discussed and experiments have been carried out. Research and Conservation Today the Antarctic is the subject of research programmes in international cooperation.
For the duration of the treaty, military uses are banned and claims of sovereignty are frozen. A provisional agreement on raw materials exploration with a view to environmental protection was signed in In a Protocol to the Antarctic Treaty in , all activities relating to mineral resources are prohibited for the time being except for scientific purposes, and the status of the Antarctic as a nature reserve is stipulated, initially for a period of 50 years. Following the disastrous and irresponsible whaling campaigns that began in the Arctic in the 17th century and in the Antarctic in the 19th century, the International Whaling Commission IWC was set up in with the purpose of regulating the stocks of the marine mammals by means of conservative catch quotas.