140 research outputs found
Water column gradients beneath the summer ice of a High Arctic freshwater lake as indicators of sensitivity to climate change
Ice cover persists throughout summer over many lakes at extreme polar latitudes but is likely to become increasingly rare with ongoing climate change. Here we addressed the question of how summer ice-cover affects the underlying water column of Ward Hunt Lake, a freshwater lake in the Canadian High Arctic, with attention to its vertical gradients in limnological properties that would be disrupted by ice loss. Profiling in the deepest part of the lake under thick mid-summer ice revealed a high degree of vertical structure, with gradients in temperature, conductivity and dissolved gases. Dissolved oxygen, nitrous oxide, carbon dioxide and methane rose with depth to concentrations well above air-equilibrium, with oxygen values at >150% saturation in a mid water column layer of potential convective mixing. Fatty acid signatures of the seston also varied with depth. Benthic microbial mats were the dominant phototrophs, growing under a dim green light regime controlled by the ice cover, water itself and weakly colored dissolved organic matter that was mostly autochthonous in origin. In this and other polar lakes, future loss of mid-summer ice will completely change many water column properties and benthic light conditions, resulting in a markedly different ecosystem regime
A Technology Selection Process for the Optimal Capture of Design Information
There is currently a lack of good practice guidance and commonly accepted standards for empirical design researchers in terms of a) the amount of information to capture and b) the appropriateness (what is captured, and in what form). For example, it is common for researchers to default to video capture. This is often costly to implement and generates large datasets that are difficult and time consuming to analyse. This paper thus attempts to provide practical guidance to the researcher on what technologies are optimal for capturing various common design situations
Next-generation sequencing (NGS) in the microbiological world : how to make the most of your money
The Sanger sequencing method produces relatively long DNA sequences of unmatched quality and has been considered for long time as the gold standard for sequencing DNA. Many improvements of the Sanger method that culminated with fluorescent dyes coupled with automated capillary electrophoresis enabled the sequencing of the first genomes. Nevertheless, using this technology to sequence whole genomes was costly, laborious and time consuming even for genomes that are relatively small in size. A major technological advance was the introduction of next-generation sequencing (NGS) pioneered by 454 Life Sciences in the early part of the 21th century. NGS allowed scientists to sequence thousands to millions of DNA molecules in a single machine run. Since then, new NGS technologies have emerged and existing NGS platforms have been improved, enabling the production of genome sequences at an unprecedented rate as well as broadening the spectrum of NGS applications. The current affordability of generating genomic information, especially with microbial samples, has resulted in a false sense of simplicity that belies the fact that many researchers still consider these technologies a black box. In this review, our objective is to identify and discuss four steps that we consider crucial to the success of any NGS-related project. These steps are: (1) the definition of the research objectives beyond sequencing and appropriate experimental planning, (2) library preparation, (3) sequencing and (4) data analysis. The goal of this review is to give an overview of the process, from sample to analysis, and discuss how to optimize your resources to achieve the most from your NGS-based research. Regardless of the evolution and improvement of the sequencing technologies, these four steps will remain relevant
Chlorovirus and myovirus diversity in permafrost thaw ponds
Permafrost thaw ponds occur in high abundance across the northern landscape of Canada and are sites of intense microbial activity, resulting
in carbon dioxide and methane emissions to the atmosphere. In this study, we focused on viruses as largely unstudied agents of top-down control in
these high-latitude microbial ecosystems. Specifically, we compared the diversity of myovirus, chlorovirus and host microbial communities in an
organic soil palsa valley pond and a mineral soil lithalsa valley pond. These 2 subarctic permafrost landscapes are both common in northern Québec,
Canada. Sequence analysis of ribosomal small subunit RNA genes showed that the community structure of bacteria and microbial eukaryotes
differed significantly between the 2 ponds, which both differed from microbial communities in a rock-basin lake (whose formation was not related
to permafrost thawing and which we used as a reference pond) in the same region. The viral assemblages included 439 OTUs in the uncultured
Myoviridae category and 41 OTUs in the family Phycodnaviridae. Phylogenetic analysis of the latter based on an amino acid sequence alignment
revealed a single large clade related to chloroviruses, consistent with the abundant presence of chlorophytes in these waters. As there was for the
bacterial and eukaryotic communi-ties, there were also significant differences in the community structure of these viral groups among the 3 ponds.
These results suggest that host community composition is influenced by environmental filtering, which in turn contributes to driving viral diversity
across landscape types
Genomic evidence for sulfur intermediates as new biogeochemical hubs in a model aquatic microbial ecosystem
Background: The sulfur cycle encompasses a series of complex aerobic and anaerobic transformations of S-containing
molecules and plays a fundamental role in cellular and ecosystem-level processes, influencing biological carbon transfers and
other biogeochemical cycles. Despite their importance, the microbial communities and metabolic pathways involved in
these transformations remain poorly understood, especially for inorganic sulfur compounds of intermediate oxidation states
(thiosulfate, tetrathionate, sulfite, polysulfides). Isolated and highly stratified, the extreme geochemical and environmental
features of meromictic ice-capped Lake A, in the Canadian High Arctic, provided an ideal model ecosystem to resolve the
distribution and metabolism of aquatic sulfur cycling microorganisms along redox and salinity gradients.
Results: Applying complementary molecular approaches, we identified sharply contrasting microbial communities and
metabolic potentials among the markedly distinct water layers of Lake A, with similarities to diverse fresh, brackish and saline
water microbiomes. Sulfur cycling genes were abundant at all depths and covaried with bacterial abundance. Genes for
oxidative processes occurred in samples from the oxic freshwater layers, reductive reactions in the anoxic and sulfidic
bottom waters and genes for both transformations at the chemocline. Up to 154 different genomic bins with potential for
sulfur transformation were recovered, revealing a panoply of taxonomically diverse microorganisms with complex metabolic
pathways for biogeochemical sulfur reactions. Genes for the utilization of sulfur cycle intermediates were widespread
throughout the water column, co-occurring with sulfate reduction or sulfide oxidation pathways. The genomic bin
composition suggested that in addition to chemical oxidation, these intermediate sulfur compounds were likely produced
by the predominant sulfur chemo- and photo-oxidisers at the chemocline and by diverse microbial degraders of organic
sulfur molecules.
Conclusions: The Lake A microbial ecosystem provided an ideal opportunity to identify new features of the biogeochemical
sulfur cycle. Our detailed metagenomic analyses across the broad physico-chemical gradients of this permanently stratified
lake extend the known diversity of microorganisms involved in sulfur transformations over a wide range of environmental
conditions. The results indicate that sulfur cycle intermediates and organic sulfur molecules are major sources of electron
donors and acceptors for aquatic and sedimentary microbial communities in association with the classical sulfur cycl
The littoral zone of polar lakes : inshore-offshore contrasts in an ice-covered High Arctic lake
In ice-covered polar lakes, a narrow ice-free moat opens up in spring or early summer, and then
persists at the edge of the lake until complete ice loss or refreezing. In this study, we analyzed the
horizontal gradients in Ward Hunt Lake, located in the High Arctic, and addressed the hypothesis
that the transition from its nearshore open-water moat to offshore ice-covered waters is marked
by discontinuous shifts in limnological properties. Consistent with this hypothesis, we observed
an abrupt increase in below-ice concentrations of chlorophyll a beyond the ice margin, along with
a sharp decrease in temperature and light availability and pronounced changes in benthic algal
pigments and fatty acids. There were higher concentrations of rotifers and lower concentrations
of viruses at the ice-free sampling sites, and contrasts in zooplankton fatty acid profiles that
implied a greater importance of benthic phototrophs in their inshore diet. The observed patterns
underscore the structuring role of ice cover in polar lakes. These ecosystems do not conform to
the traditional definitions of littoral versus pelagic zones, but instead may have distinct moat, icemargin
and ice-covered zones. This zonation is likely to weaken with ongoing climate change
Arctic bacterial diversity and connectivity in the coastal margin of the Last Ice Area
Arctic climate change is leading to sea-ice attrition in the Last Ice Area along the northern coast of Canada and Greenland, but less attention has been given to the associated land-based ecosystems. Here we evaluated bacterial community structure in a hydrologically coupled cryo-ecosystem in the region: Thores Glacier, proglacial Thores Lake, and its outlet to the sea. Deep amplicon sequencing revealed that Polaromonas was ubiquitous, but differed genetically among diverse niches. Surface glacier-ice was dominated by Cyanobacteria, while the perennially ice-capped, well-mixed water column of Thores Lake had a unique assemblage of Chloroflexi, Actinobacteriota, and Planctomycetota. Species richness increased downstream, but glacier microbes were little detected in the lake, suggesting strong taxonomic sorting. Ongoing climate change and the retreat of Thores Glacier would lead to complete drainage and loss of the lake microbial ecosystem, indicating the extreme vulnerability of diverse cryohabitats and unique microbiomes in the Last Ice coastal margin
Extreme warming and regime shift toward amplified variability in a far northern lake
Mean annual air temperatures in the High Arctic are rising rapidly, with extreme warming events becoming increasingly common. Little is known, however, about the consequences of such events on the ice‐capped lakes that occur abundantly across this region. Here, we compared 2 years of high‐frequency monitoring data in Ward Hunt Lake in the Canadian High Arctic. One of the years included a period of anomalously warm conditions that allowed us to address the question of how loss of multi‐year ice cover affects the limnological properties of polar lakes. A mooring installed at the deepest point of the lake (9.7 m) recorded temperature, oxygen, chlorophyll a (Chl a ) fluorescence, and underwater irradiance from July 2016 to July 2018, and an automated camera documented changes in ice cover. The complete loss of ice cover in summer 2016 resulted in full wind exposure and complete mixing of the water column. This mixing caused ventilation of lake water heat to the atmosphere and 4°C lower water temperatures than under ice‐covered conditions. There were also high values of Chl a fluorescence, elevated turbidity levels and large oxygen fluctuations throughout fall and winter. During the subsequent summer, the lake retained its ice cover and the water column remained stratified, with lower Chl a fluorescence and anoxic bottom waters. Extreme warming events are likely to shift polar lakes that were formerly capped by continuous thick ice to a regime of irregular ice loss and unstable limnological conditions that vary greatly from year to year
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