Biotic communities and ecosystem dynamics in terrestrial Antarctica are limited by an array of extreme conditions including low temperatures, moisture and organic matter availability, high salinity, and a paucity of biodiversity to facilitate key ecological processes. Recent studies have discovered that the prokaryotic communities in these extreme systems are highly diverse with patchy distributions. Investigating the physical and biological controls over the distribution and activity of microbial biodiversity in Victoria Land is essential to understanding ecological functioning in this region. Currently, little information on the distribution, structure and activity of soil communities anywhere in Victoria Land are available, and their sensitivity to potential climate change remains largely unknown. We investigated soil microbial communities from low- and high-productivity habitats in an isolated Antarctic location to determine how the soil environment impacts microbial community composition and structure. The microbial communities in Luther Vale, Northern Victoria Land were analysed using bacterial 16S rRNA gene clone libraries and were related to soil geochemical parameters and classical morphological analysis of soil metazoan invertebrate communities. A total of 323 16S rRNA gene sequences analysed from four soils spanning a productivity gradient indicated a high diversity (Shannon-Weaver values > 3) of phylotypes within the clone libraries and distinct differences in community structure between the two soil productivity habitats linked to water and nutrient availability. In particular, members of the Deinococcus/Thermus lineage were found exclusively in the drier, low-productivity soils, while Gammaproteobacteria of the genus Xanthomonas were found exclusively in high-productivity soils. However, rarefaction curves indicated that these microbial habitats remain under-sampled. Our results add to the recent literature suggesting that there is a higher biodiversity within Antarctic soils than previously expected.

The abundance and structure of archaeal and bacterial communities from the active layer and the associated permafrost of a moderately acidic (pH < 5.0) High Arctic wetland (Axel Heiberg Island, Nunavut, Canada) were investigated using culture-and molecular-based methods. Aerobic viable cell counts from the active layer were ∼100-fold greater than those from the permafrost (2.5 × 10 5 CFU·(g soil dry mass) -1 ); however, a greater diversity of isolates were cultured from permafrost, as determined by 16S rRNA gene sequencing. Isolates from both layers demonstrated growth characteristics of a psychrotolerant, halotolerant, and acidotolerant community. Archaea constituted 0.1% of the total 16S rRNA gene copy number and, in the 16S rRNA gene clone library, predominantly (71% and 95%) consisted of Crenarchaeota related to Group I. 1b. In contrast, bacterial communities were diverse (Shannon's diversity index, H = ∼4), with Acidobacteria constituting the largest division of active layer clones (30%) and Actinobacteria most abundant in permafrost (28%). Direct comparisons of 16S rRNA gene sequence data highlighted significant differences between the bacterial communities of each layer, with the greatest differences occurring within Actinobacteria. Comparisons of 16S rRNA gene sequences with those from other Arctic permafrost and cold-temperature wetlands revealed commonly occurring taxa within the phyla Chloroflexi, Acidobacteria, and Actinobacteria (families Intrasporangiaceae and Rubrobacteraceae).Key words: active layer, permafrost, wetland, Arctic, microbial diversity, 16S rRNA gene library.Résumé : L'abondance et la structure des communautés d'archées et de bactéries de la couche active et du pergélisol d'un milieu humide modérément acide (pH < 5,0) du Grand Nord (Île de Axel Heiberg, Nunavut, Canada) ont été étudiées à l'aide de méthodes en culture et moléculaires. La numération des cellules aérobies viables de la couche active était~100 fois supérieure à celle du pergélisol (2,5 × 10 5 UFC·(g ps de sol) -1 ); cependant, une diversité plus élevée d'isolats a été cultivée à partir du pergélisol, tel que déterminé par le séquençage génique de l'ARNr 16S. Les isolats des deux couches montraient les caractéristiques de croissance d'une communauté psychotrophe, halotolérante et acidotolérante. Les archées constituaient 0.1% du nombre de copies de gènes d'ARNr 16S total et, dans la banque de clones de gènes d'ARNr 16S, comprenaient de façon prédominante (71 % et 95 %) le groupe I. 1b relié aux Crenarchaeota. Par contre, les communautés bactériennes étaient diversifiées (indice de diversité de Shannon, H = ∼4), les Acidobacteria constituant la division la plus large des clones de la couche active (30 %), et les Actinobacteria étant les plus abondantes dans le pergélisol (28 %). Des comparaisons directes des données du séquençage génique de l'ARNr 16S ont mis en évidence des différences significatives entre les communautés bactériennes de chaque couche, les différences les plus importantes apparaissant au sein d...

Eolian transport of biomass from ephemerally wetted soils, associated with summer glacial meltwater runoffs and lake edges, to low‐productivity areas of the Antarctic Dry Valleys (DV) has been postulated to be an important source of organic matter (fixed nitrogen and fixed carbon) to the entire DV ecosystem. However, descriptions and identification of the microbial members responsible for N2 fixation within these wetted sites are limited. In this study, N2 fixers from wetted soils were identified by direct nifH gene sequencing and their in situ N2 fixation activities documented via acetylene reduction and RNA‐based quantitative PCR assays. Shannon‐index nifH diversity levels ranged between 1.8 and 2.6 and included the expected cyanobacterial signatures and a large number of phylotypes related to the gamma‐, beta‐, alpha‐, and delta‐proteobacteria. N2 fixation rates ranged between approximately 0.5 and 6 nmol N cm−3 h−1 with measurements indicating that approximately 50% of this activity was linked with sulfate reduction at some sites. Comparisons with proximal dry soils also suggested that these communities are not ubiquitously distributed, and conditions unrelated to moisture content may define the composition, diversity, or habitat suitability of the microbial communities within wetted soils of the DVs.

We report the first microbiological characterization of a terrestrial methane seep in a cryoenvironment in the form of an Arctic hypersaline (B24% salinity), subzero (À5 1C), perennial spring, arising through thick permafrost in an area with an average annual air temperature of À15 1C. Bacterial and archaeal 16S rRNA gene clone libraries indicated a relatively low diversity of phylotypes within the spring sediment (Shannon index values of 1.65 and 1.39, respectively). Bacterial phylotypes were related to microorganisms such as Loktanella, Gillisia, Halomonas and Marinobacter spp. previously recovered from cold, saline habitats. A proportion of the bacterial phylotypes were cultured, including Marinobacter and Halomonas, with all isolates capable of growth at the in situ temperature (À5 1C). Archaeal phylotypes were related to signatures from hypersaline deep-sea methane-seep sediments and were dominated by the anaerobic methane group 1a (ANME-1a) clade of anaerobic methane oxidizing archaea. CARD-FISH analyses indicated that cells within the spring sediment consisted of B84.0% bacterial and 3.8% archaeal cells with ANME-1 cells accounting for most of the archaeal cells. The major gas discharging from the spring was methane (B50%) with the low CH 4 /C 2 þ ratio and hydrogen and carbon isotope signatures consistent with a thermogenic origin of the methane. Overall, this hypersaline, subzero environment supports a viable microbial community capable of activity at in situ temperature and where methane may behave as an energy and carbon source for sustaining anaerobic oxidation of methane-based microbial metabolism. This site also provides a model of how a methane seep can form in a cryoenvironment as well as a mechanism for the hypothesized Martian methane plumes.