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This study analyzes the molecular composition of dissolved organic matter (DOM) in Prydz Bay by Fourier Transform Ion Cyclotron Resonance mass spectrometry to probe the carbon sequestration capacity in the continental shelf system. Concentrations of particulate organic carbon (POC), particulate nitrogen and dissolved organic carbon (DOC) with water depth show that POC could be mainly decomposed into DOC and/or microbially degraded. Highly labile DOC is further degraded and remineralized by microorganisms within the upper 200 m, as evidenced by a downward enrichment of 13CPOC and increases in the average molecular weight, oxygen atom number (O) and double bond equivalents of DOM molecules, indicating that biodegradation is the main driver for particulate organic matter and DOM evolution with water depth. Semi‐quantitative calculation demonstrates that ∼83% of POC was transformed to DOC as well as dissolved inorganic carbon (DIC), and ∼30% of DOC further to DIC via microbial degradation within the upper 200 m in summer, resulting in a relatively low total organic carbon content in sediments of Prydz Bay. The newly transformed DIC and residue DOC can be preserved in the deep layer due to the formation of well stratified and stable water body in summer of Prydz Bay, ultimately entering the regional circulation system instead of being released back into the atmosphere. This could be one of the most important processes determining the atmosphere CO2 uptake in the continental shelf system of Southern Ocean. Plain Language Summary: The continental shelf system in the Southern Ocean, especially with the development of polynyas, plays a critical role in the global carbon cycle and disproportionally accounts for almost half of the anthropogenic CO2 uptake by the biological pump, with ensuing deep‐sea sequestration by the form of particulate and dissolved organic carbon, and even CO2 due to microbial degradation of primary productivity. However, complex interactions between physical, chemical and biological processes significantly affect the fate of organic carbon through the water column, resulting in an uncertainty of vertical carbon export. In this study, we conduct an investigation on the dissolved organic matter sources and evolution with water depth in summer of Prydz Bay, a typical polynya‐developed continental shelf system in the East Antarctica. The results clearly show that biodegradation is the main factor controlling organic carbon mineralization and mainly occurs within the upper 200 m of water column, with a transformation into dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC). Integrated with regional circulation system and hydrological characteristics, our study further indicates that newly formed DIC and DOC can be preserved in the deep layer of Prydz Bay, then into the regional circulation system rather back to the atmosphere. Key Points: Novel evidence at molecular level shows the vital role of biodegradation during carbon sink in Prydz BayThe conversion of POC into DOC/DIC mainly occurs within the upper 200 m of water columnHighlighting regional circulation's contribution to carbon transport and sequestration in the Southern Ocean [ABSTRACT FROM AUTHOR]

Metallothioneins (MTs) are low-molecular weight sulfur-rich proteins, widely distributed in nature. They play a homeostatic role in the control and detoxification of metal ions. Previous studies indicated that MTs also have the capacity to scavenge reactive oxygen species. This study aimed to investigate the evolution of the protein in the notothenioid fish, evolved under the selective pressure of relatively high oxygen partial pressures, characteristics of cold Antarctic seawaters, and relatively high concentrations of metal ions, Cd and Cu in particular. The cDNA sequences of MT isoforms were characterized in members of the Nototheniidae, Bathydraconidae, Artedidraconidae, and Channichthyidae families. The phylogenetic relationships of MTs from these families and other teleosts were inferred by using Maximum Likelihood and Bayesian methods. The analysis of coding region and untranslated (UTR) sequences indicated the presence of two MT clades, each containing one of the two MT isoforms, MT-1 and MT-2. Our results indicated, for the first time for these proteins, that the evolution of MT genes has been characterized by strong purifying selection, whereas it did not observe any evidence of positive selection. In addition, phylogenetic analysis of the UTRs suggested that functional changes, in particular related to the MT-1 gene expression, had accompanied the duplication event. [ABSTRACT FROM AUTHOR]

Although carbonic anhydrase is a ubiquitous enzyme involved in a variety of physiological processes, the information on its evolution and cold adaptation among Antarctic fish is still limited: the only Antarctic fish carbonic anhydrase characterized up-to-date is from Chionodraco hamatus, a member of the Channichthyidae family. In this work, we characterized orthologous genes within two other fish families: Nototheniidae ( Trematomus eulepidotus, Trematomus lepidorhinus, Trematomus bernacchii) and Bathydraconidae ( Cygnodraco mawsoni). The cDNAs of epithelial gill carbonic anhydrases were cloned and sequenced. Both coding and deduced amino acid sequences were used in phylogenetic analyses. The group of enzymes preferentially expressed in fish erythrocytes (CAIIb) represented the most conserved variant. This result suggests that, although the two variants derived from the same ancestor, CAIIc genes have a more complex evolutionary history than CAIIb. The peculiar distribution of Antarctic CAs among fish CAIIcs suggests that the CAIIc gene appeared at different times through independent duplication events, even after the speciation that led to the differentiation of Antarctic fish families. Using the new CA sequences, we built homology models to trace the expected consequences of sequence variability at the protein structure level. From these analyses, we inferred that sequence variability in Antarctic fish CAs affect important physicochemical properties of these proteins and consequentially influence their reactivity. Furthermore, we searched and tested the validity of various potential molecular trademarks for cold adaptation: significant features that can be related to cold adaptation in fish CAs include reduction of positively charged solvent accessible surfaces and an increased flexibility of N-terminal and C-terminal regions. [ABSTRACT FROM AUTHOR]

Abstract: Only two vascular plants, Deschampsia antarctica Desv. (Poaceae) and Colobanthus quitensis Kunth. Bartl. (Caryophyllaceae), inhabit the Antarctic. To clarify the taxonomic position, phylogeographic origin, genetic heterogeneity, and population dynamics of D. antarctica, we comparatively analyzed the ITS1 and ITS2 sequences for several populations from two geographically distant regions of the maritime Antarctic (the South Shetland Islands and the Argentine archipelago). All accessions of D. antarctica formed a strongly supported clade in the phylogenetic dendrograms constructed. Despite the high degree of sequence similarity at ITS1–ITS2 (97%–100%), the populations of D. antarctica in Tierra del Fuego, Falkland Islands and Antarctic can be discriminated at the molecular level. Our data indicate that the majority of D. antarctica populations originated from South America. Different populations may have invaded Antarctic at different times. Genetically distinct plants may coexist within the same or adjacent populations on Antarctic islands. [ABSTRACT FROM AUTHOR]

Aim The evolutionary speed hypothesis (ESH) attempts to explain global patterns of species richness on the basis that rates of molecular evolution and speciation in warmer climates have led to a greater accumulation of taxa at lower latitudes. A substantial alternative hypothesis to the ESH is the tropical conservatism hypothesis (TCH). However, recent tests of the TCH, using amphibians as the model taxon, have relied on the assumption that rates of molecular evolution are stable across latitudes and elevations. Here, we test for the first time for systematic variation in rates of molecular evolution across latitude and elevation among amphibians. Location The dataset is geographically diverse with samples from all continents except Antarctica and also from many of the earth's major tropical–warm temperate archipelagos. Methods We tested for substitution rate heterogeneity across climatically varying habitats with the mitochondrial RNA genes 12S and 16S. Thus, we report here on our findings for amphibians – a taxon whose phylogenetic and trophic contexts are remote from those previously tested – using genes that have also not been examined before. The study utilized paired contrasts of sister species (188 species across 18 families, including both caudates and anurans) that are spatially separated in either latitudinal or elevational dimensions. Results We found substantially faster substitution rates for species living in warmer habitats ( P= 0.001–0.002) at both lower latitudes ( P < 0.02) and lower elevations ( P < 0.01). Main conclusions The consistency of these results with the previous studies that used quite different organisms – and in this instance also using different genes – suggests that this is a ubiquitous pattern in nature consistent with the predictions of the ESH. Recent tests of the TCH that, in estimating diversification rates, have relied on the assumption that DNA evolution occurs at a constant rate across latitudes and elevations, require reconsideration in light of the findings presented here. Our results indicate that greater caution is required when estimating dates of divergence using DNA sequence data. [ABSTRACT FROM AUTHOR]

Abstract: Notothenioid teleosts underwent major modifications of their genome to adapt to the cooling of the Antarctic environment. In order to identify specific features of the Antarctic teleost immunoglobulin, transcripts encoding the constant region of the IgM heavy chain from 13 Antarctic and non-Antarctic notothenioid species were sequenced. The primary mRNA splicing for the membrane form was found to be atypical in the majority of Antarctic species, because it led to exclusion of two entire constant exons, and to inclusion of 39-nucleotide exons encoding an unusually long Extracellular Membrane-Proximal Domain (EMPD). Genomic DNA analysis revealed that each 39-nucleotide exon fell within a long sequence that was the reverse complement of an upstream region. Deduced amino acid sequence analysis lead to the identification of cysteine encoding codons in the 39-nucleotide exons, but not in the respective sequence counterpart, suggesting that these residues might play an important role in the folding of the EMPD. [Copyright &y& Elsevier]

Trematomus species (suborder Notothenioidei; family Nototheniidae) are widely distributed in the southern oceans near Antarctica. There are 11 recognized species in the genus Trematomus, and notothenioids are known to have high chromosomal diversity (2n = 24–58) because of relatively recent and rapid adaptive radiation. Herein, we report the chromosomal-level genome assembly of T. loennbergii, the first characterized genome representative of the genus Trematomus. The final genome assembly of T. loennbergii was obtained using a Pacific Biosciences long-read sequencing platform and high-throughput chromosome conformation capture technology. Twenty-three chromosomal-level scaffolds were assembled to 940 Mb in total size, with a longest contig size of 48.5 Mb and contig N50 length of 24.7 Mb. The genome contained 42.03% repeat sequences, and a total of 24,525 protein-coding genes were annotated. We produced a high-quality genome assembly of T. loennbergii. Our results provide a first reference genome for the genus Trematomus and will serve as a basis for studying the molecular taxonomy and evolution of Antarctic fish. [ABSTRACT FROM AUTHOR]

A cadmium-binding protein was purified from the digestive gland of the Antarctic scallop, Adamussium colbecki, and biochemically characterized. Purification procedures included gel permeation and anion exchange chromatography, followed by preparative polyacrylamide gel electrophoresis. Our results demonstrate that the A. colbecki cadmium-binding protein has the general properties of metallothioneins: low molecular weight of about 10 kDa, spectroscopic features typical of cadmium thiolate clusters and high metal (cadmium) content. Analysis of amino acid composition reveals the absence of aromatic amino acids, histidine, methionine and arginine. Asparagine and glutamine are also absent. The A. colbecki metallothionein shows high levels of glycine (14%), aspartic acid (14%), glutamic acid (11%) and a low lysine content (4%); the A. colbecki metallothionein shows a lower cysteine content (12%) compared to other metallothioneins (17–30%) purified from both vertebrate and invertebrate organisms. The presence of a metallothionein in the digestive gland of A. colbecki suggests that in cold-ocean-adapted molluscs the heavy metal homeostasis mechanisms may have evolved similarly to those of organisms living in temperate marine environments, although the A. colbecki cadmium-binding protein shows a typical amino acidic composition that might reflect a peculiar physiological role. [ABSTRACT FROM AUTHOR]

Antarctic ecosystems are dominated by micro-organisms, and viruses play particularly important roles in the food webs. Since the first report in 2009 (López-Bueno et al. ), 'omic'-based studies have greatly enlightened our understanding of Antarctic aquatic microbial diversity and ecosystem function (Wilkins et al. ; Cavicchioli ). This has included the discovery of many new eukaryotic viruses (López-Bueno et al. ), virophage predators of algal viruses (Yau et al. ), bacteria with resistance to phage (Lauro et al. ) and mechanisms of haloarchaeal evasion, defence and adaptation to viruses (Tschitschko et al. ). In this issue of Molecular Ecology, López-Bueno et al. () report the first discovery of RNA viruses from an Antarctic aquatic environment. High sequence coverage enabled genome variation to be assessed for four positive-sense single-stranded RNA viruses from the order Picornavirales. By examining the populations present in the water column and in the lake's catchment area, populations of 'quasispecies' were able to be linked to local environmental factors. In view of the importance of viruses in Antarctic ecosystems but lack of data describing them, this study represents a significant advance in the field. [ABSTRACT FROM AUTHOR]

In the present study, we describe the purification and molecular characterization of Cu,Zn superoxide dismutase (SOD) from Chionodraco hamatus, an Antarctic teleost widely distributed in many areas of the Ross Sea that plays a pivotal role in the Antarctic food chain. The primary sequence was obtained using biochemical and molecular biology approaches and compared with Cu,Zn SODs from other organisms. Multiple sequence alignment using the amino acid sequence revealed that Cu,Zn SOD showed considerable sequence similarity with its orthologues from various vertebrate species, but also some specific substitutions directly linked to cold adaptation. Phylogenetic analyses presented the monophyletic status of Antartic Teleostei among the Perciformes, confirming the erratic differentiation of these proteins and concurring with the theory of the "unclock-like" behavior of Cu,Zn SOD evolution. Expression of C. hamatus Cu,Zn SOD at both the mRNA and protein levels were analyzed in various tissues, highlighting the regulation of gene expression related to environmental stress conditions and also animal physiology. The data presented are the first on the antioxidant enzymes of a fish belonging to the Channichthyidae family and represent an important starting point in understanding the antioxidant systems of these organisms that are subject to constant risk of oxidative stress. [ABSTRACT FROM AUTHOR]

In the present study we describe the molecular characterization of the two paralogous mitochondrial peroxiredoxins from Trematomus bernacchii , a teleost that plays a pivotal role in the Antarctic food chain. The two putative amino acid sequences were compared with orthologs from other fish, highlighting a high percentage of identity and similarity with the respective variant, in particular for the residues that are essential for the characteristic peroxidase activity of these enzymes. The temporal expression of Prdx3 and Prdx5 mRNAs in response to short-term thermal stress showed a general upregulation of prdx3 , suggesting that this isoform is the most affected by temperature increase. These data, together with the peculiar differences between the molecular structures of the two mitochondrial Prdxs in T. bernacchii as well as in the tropical species Stegastes partitus , suggest an adaptation that allowed these poikilothermic aquatic vertebrates to colonize very different environments, characterized by different temperature ranges. Unlabelled Image • Two new mitochondrial peroxiredoxin genes have been identified in Trematomus bernacchii. • Phylogenetic analyses indicate that of both Prdx3s and Prdx5s probably evolved under purifying selection effect. • Both Prdx3 and Prdx5 are not "cold-adapted" enzymes. • The Antarctic emerald rockcode performs rapid and specific responses to wormer temperature. [ABSTRACT FROM AUTHOR]