Molecular diversity of microbial eukaryotes in sea water from Fildes Peninsula, King George Island, Antarctica

Metagenomic insights into the antibiotic resistome in freshwater and seawater from an Antarctic ice-free area

The comprehensive profiles of antibiotic resistance genes (ARGs) in the Antarctic water environments and their potential health risks are not well understood. The present study characterized the bacterial community compositions and ARG profiles of freshwater (11 samples) and seawater (28 samples) around the Fildes Region (an ice-free area in Antarctica) using a shotgun metagenomic sequencing approach for the first time. There were significant differences in the compositions of the bacterial community and ARG profiles between freshwater and seawater. In the 39 water samples, 114 ARG subtypes belonging to 15 ARG types were detectable. In freshwater, the dominant ARGs were related to multidrug and rifamycin resistance. In seawater, the dominant ARGs were related to peptide, multidrug, and beta-lactam resistance. Both the bacterial community compositions and ARG profiles were significantly related to certain physicochemical properties (e.g., pH, salinity, NO₃^-). Procrustes analysis revealed a significant correlation between the bacterial community compositions and ARG profiles of freshwater and seawater samples. A total of 31 metagenome-assembled genomes (MAGs) carrying 35 ARG subtypes were obtained and identified. The results will contribute to a better evaluation of the ARG contamination in relation to human health in the Antarctic aquatic environments.

Spatiotemporal Variations in Antarctic Protistan Communities Highlight Phytoplankton Diversity and Seasonal Dominance by a Novel Cryptophyte Lineage

The Andvord fjord in the West Antarctic Peninsula (WAP) is known for its productivity and abundant megafauna. Nevertheless, seasonal patterns of the molecular diversity and abundance of protistan community members underpinning WAP productivity remain poorly resolved. We performed spring and fall expeditions pursuing protistan diversity, abundance of photosynthetic taxa, and the connection to changing conditions. 18S rRNA amplicon sequence variant (ASV) profiles revealed diverse predatory protists spanning multiple eukaryotic supergroups, alongside enigmatic heterotrophs like the Picozoa. Among photosynthetic protists, cryptophyte contributions were notable. Analysis of plastid-derived 16S rRNA ASVs supported 18S ASV results, including a dichotomy between cryptophytes and diatom contributions previously reported in other Antarctic regions. We demonstrate that stramenopile and cryptophyte community structures have distinct attributes. Photosynthetic stramenopiles exhibit high diversity, with the polar diatom Fragilariopsis cylindrus, unidentified Chaetoceros species, and others being prominent. Conversely, ASV analyses followed by environmental full-length rRNA gene sequencing, electron microscopy, and flow cytometry revealed that a novel alga dominates the cryptophytes. Phylogenetic analyses established that TPG clade VII, as named here, is evolutionarily distinct from cultivated cryptophyte lineages. Additionally, cryptophyte cell abundance correlated with increased water temperature. Analyses of global data sets showed that clade VII dominates cryptophyte ASVs at Southern Ocean sites and appears to be endemic, whereas in the Arctic and elsewhere, Teleaulax amphioxeia and Plagioselmis prolonga dominate, although both were undetected in Antarctic waters. Collectively, our studies provide baseline data against which future change can be assessed, identify different diversification patterns between stramenopiles and cryptophytes, and highlight an evolutionarily distinct cryptophyte clade that thrives under conditions enhanced by warming.

The pico-sized Mamiellophyceae and a novel Bathycoccus clade from the summer plankton of Russian Arctic Seas and adjacent waters

Global climate changes and anthropogenic activity greatly impact Arctic marine biodiversity including phytoplankton which contribute greatly to atmospheric oxygen production. Thus the study of microalgae has rising topicality. Class Mamiellophyceae is an important component of phototrophic picoplankton. To gain more knowledge about Mamiellophyceae distribution and diversity special studies were performed in such remote areas as the Russian Arctic seas. A metabarcoding of pico-sized Mamiellophyceae was undertaken by high-throughput sequencing of the 18S rRNA gene sequence V4 region from samples collected in July-September 2017 in the Barents, Kara and Laptev seas, and in the adjacent waters of the Norwegian Sea. Our study is the first to show that Mamiellophyceae among the summer picoplankton of Russian Arctic seas are diverse and represented by 16 algae species/phylotypes. We discovered a new candidate species of Bathycoccus assigned to a new Bathycoccus clade A-uncultured Bathycoccus Kara 2017. It was found that several Micromonas species can co-exist, with Micromonas polaris dominating north of 72°N. The presence of Ostreococcus tauri, Ostreococcus lucimarinus and Ostreococcus mediterraneus at high latitudes beyond 65°N was documented for the first time, similar to findings for some other taxa. Our results will be important for obtaining a global view of Mamiellophyceae community dynamics.

Planktonic microbial eukaryotes in polar surface waters: recent advances in high-throughput sequencing

Marine microbial eukaryotes are important primary producers and play critical roles in key biogeochemical cycles. Recent advances in sequencing technology have focused attention on the extent of microbial biodiversity, revealing a huge, previously underestimated phylogenetic diversity with many new lineages. This technology has now become the most important tool to understand the ecological significance of this huge and novel diversity in polar oceans. In particular, high-throughput sequencing technologies have been successfully applied to enumerate and compare marine microbial diversity in polar environments. Here, a brief overview of polar microbial eukaryote diversity, as revealed by in-situ surveys of the high-throughput sequencing on 18S rRNA gene, is presented. Using these 'omic' approaches, further attention still needs to be focused on differences between specific locations and/or entire polar oceans and on bipolar comparisons of diversity and distribution.

Annual phytoplankton dynamics in coastal waters from Fildes Bay, Western Antarctic Peninsula

Year-round reports of phytoplankton dynamics in the West Antarctic Peninsula are rare and mainly limited to microscopy and/or pigment-based studies. We analyzed the phytoplankton community from coastal waters of Fildes Bay in the West Antarctic Peninsula between January 2014 and 2015 using metabarcoding of the nuclear and plastidial 18/16S rRNA gene from both size-fractionated and flow cytometry sorted samples. Overall 14 classes of photosynthetic eukaryotes were present in our samples with the following dominating: Bacillariophyta (diatoms), Pelagophyceae and Dictyochophyceae for division Ochrophyta, Mamiellophyceae and Pyramimonadophyceae for division Chlorophyta, Haptophyta and Cryptophyta. Each metabarcoding approach yielded a different image of the phytoplankton community with for example Prymnesiophyceae more prevalent in plastidial metabarcodes and Mamiellophyceae in nuclear ones. Diatoms were dominant in the larger size fractions and during summer, while Prymnesiophyceae and Cryptophyceae were dominant in colder seasons. Pelagophyceae were particularly abundant towards the end of autumn (May). In addition of Micromonas polaris and Micromonas sp. clade B3, both previously reported in Arctic waters, we detected a new Micromonas 18S rRNA sequence signature, close to, but clearly distinct from M. polaris, which potentially represents a new clade specific of the Antarctic. These results highlight the need for complementary strategies as well as the importance of year-round monitoring for a comprehensive description of phytoplankton communities in Antarctic coastal waters.

Application of microbial network analysis to discriminate environmental heterogeneity in Fildes Peninsula, Antarctica

In order to determine the practicability of developing a protocol for bioassessing polar marine environment based on network analysis, microplankton communities and co-occurrence patterns at Ardley Cove and Great Wall Cove (King George Island, Antarctica) were studied in January 2016 through high-through sequencing. The spatial patterns and significant differences between community structures in two coves clearly reflect those in environmental heterogeneity. Moreover, both coves had their discriminated network structure and keystones. Then multivariate analyses to quantify the relationship between environmental variation and planktonic microbes response, give further evidence that nitrate and temperature, alone or in combination with other several parameters, structuring the communities respectively indeed. This study presents the first detailed description on co-occurrence networks between microbes and local environmental parameters in Antarctic coastal water. These findings suggest that co-occurrence networks based on planktonic microbes have the robust potential to assess environmental heterogeneity in polar marine ecosystem.

Detection of the phycotoxin pectenotoxin-2 in waters around King George Island, Antarctica

In order to set a base line for the observation of planktonic community changes due to global change, protistan plankton sampling in combination with phycotoxin measurements and solid phase adsorption toxin tracking (SPATT) was performed in two bays of King George Island (KGI) in January 2013 and 2014. In addition, SPATT sampling was performed in Potter Cove during a one-year period from January 2014 until January 2015. Known toxigenic taxa were not firmly identified in plankton samples but there was microscopical evidence for background level presence of Dinophysis spp. in the area. This was consistent with environmental conditions during the sampling periods, especially strong mixing of the water column and low water temperatures that do not favor dinoflagellate proliferations. Due to the lack of significant abundance of thecate toxigenic dinoflagellate species in microplankton samples, no phycotoxins were found in net tow samples. In contrast, SPATT sampling revealed the presence of dissolved pectenotoxin-2 (PTX-2) and its hydrolyzed form PTX-2 seco acid in both bays and during the entire one-year sampling period. The presence of dissolved PTX in coastal waters of KGI is strong new evidence for the presence of PTX-producing species, i.e., dinoflagellates of the genus Dinophysis in the area. The presence of phycotoxins and their respective producers, even at the low background concentrations found in this study, may be the seed of possible proliferations of these species under changing environmental conditions. Furthermore, phycotoxins can be used as chemotaxonomic markers for a very specific group of plankton thus allowing to track the presence of this group over time.

Distribution of aerophilous diatom communities associated with terrestrial green macroalgae in the South Shetland Islands, Maritime Antarctica

The establishment of diatom communities depends on environmental factors such as the type of substrate and geographic conditions that influence the dispersal processes of these organisms. The main goal of this study was to evaluate the similarity between diatom communities associated with the macroalgae Prasiola crispa (Lightfoot) Kützing in relation to spatial distance from six sampled sites located in the South Shetland Islands, Maritime Antarctica. The diatom flora associated with Prasiola crispa was represented by 23 species distributed in 15 genera. Pinnularia australoschoenfelderi Zidarova, Kopalová & Van de Vijver, Luticola austroatlantica Van de Vijver, Kopalová, S.A.Spaulding & Esposito, Luticola amoena Van der Vijver, Kopalová, Zidarova & Levkov, Pinnularia austroshetlandica (Carlson) Cleve-Euler and Psammothidium papilio (D.E. Kellogg et al.) Kopalová & Zidarova were the most abundant species in our samples, together they represented 68% of the total number of individuals collected. There was great similarity and abundance of the diatom communites among the sampled points, which resulted in the absence of a linear relationship pattern with distance between sampling points. We conclude that distance was not a factor of differentiation of Antarctic diatom communities associated with terrestrial green macroalgae. This suggests that Antarctic environments may have unique characteristics with homogeneous abiotic factors, at least in relation to this substrate.

The disappearing periglacial ecosystem atop Mt. Kilimanjaro supports both cosmopolitan and endemic microbial communities

Microbial communities have not been studied using molecular approaches at high elevations on the African continent. Here we describe the diversity of microbial communities from ice and periglacial soils from near the summit of Mt. Kilimanjaro by using both Illumina and Sanger sequencing of 16S and 18S rRNA genes. Ice and periglacial soils contain unexpectedly diverse and rich assemblages of Bacteria and Eukarya indicating that there may be high rates of dispersal to the top of this tropical mountain and/or that the habitat is more conducive to microbial life than was previously thought. Most bacterial OTUs are cosmopolitan and an analysis of isolation by geographic distance patterns of the genus Polaromonas emphasized the importance of global Aeolian transport in the assembly of bacterial communities on Kilimanjaro. The eukaryotic communities were less diverse than the bacterial communities and showed more evidence of dispersal limitations and apparent endemism. Cercozoa dominated the 18S communities, including a high abundance of testate amoebae and a high diversity of endemic OTUs within the Vampyrellida. These results argue for more intense study of this unique high-elevation "island of the cryosphere" before the glaciers of Kilimanjaro disappear forever.

Challenging Dogma Concerning Biogeographic Patterns of Antarctica and the Southern Ocean

Antarctica is enormous, cold, remote, and particularly sensitive to climate change. Most biological research below 60°S has focused on the isolated nature of the biota and how organisms have adapted to the cold and ice. However, biogeographic patterns in Antarctica and the Southern Ocean, and the processes explaining how those patterns came about, still await adequate explanation. Both terrestrial and marine organisms have been influenced by climatic change (e.g., glaciation), physical phenomena (e.g., oceanic currents), and/or potential barriers to gene flow (e.g., steep thermal gradients). Whereas the Antarctic region contains diverse and complex marine communities, terrestrial systems tend to be comparatively simple with limited diversity. Here, we challenge the current dogma used to explain the diversity and biogeographic patterns present in the Antarctic. We assert that relatively modern processes within the last few million years, rather than geo-logical events that occurred in the Eocene and Miocene, account for present patterns of biodiversity in the region. Additionally, reproductive life history stages appear to have little influence in structuring genetic patterns in the Antarctic, as currents and glacial patterns are noted to be more important drivers of organismal patterns of distribution. Finally, we highlight the need for additional sampling, high-throughput genomic approaches, and broad, multinational cooperation for addressing outstanding questions of Antarctic biogeography and biodiversity.

Pelagic and benthic communities of the Antarctic ecosystem of Potter Cove: Genomics and ecological implications

Molecular technologies are more frequently applied in Antarctic ecosystem research and the growing amount of sequence-based information available in databases adds a new dimension to understanding the response of Antarctic organisms and communities to environmental change. We apply molecular techniques, including fingerprinting, and amplicon and metagenome sequencing, to understand biodiversity and phylogeography to resolve adaptive processes in an Antarctic coastal ecosystem from microbial to macrobenthic organisms and communities. Interpretation of the molecular data is not only achieved by their combination with classical methods (pigment analyses or microscopy), but furthermore by combining molecular with environmental data (e.g., sediment characteristics, biogeochemistry or oceanography) in space and over time. The studies form part of a long-term ecosystem investigation in Potter Cove on King-George Island, Antarctica, in which we follow the effects of rapid retreat of the local glacier on the cove ecosystem. We formulate and encourage new approaches to integrate molecular tools into Antarctic ecosystem research, environmental conservation actions, and polar ocean observatories.