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The antifreeze protein gene (Cn-AFP) from the Antarctic marine diatom, Chaetoceros neogracile was cloned and characterized. The full-length Cn-AFP cDNA contained an open reading frame of 849 bp and the deduced 282 amino acid peptide chain encodes a 29.2 kDa protein, which includes a signal peptide of 30 amino acids at the N terminus. Both the Cn-AFP coding region with and without the signal sequence were cloned and expressed in Escherichia coli. Recombinant Cn-AFPs were shown to display antifreeze activities based on measuring the thermal hysteresis and modified morphology of single ice crystals. Recombinant mature Cn-AFP showed 16-fold higher thermal hysteresis activity than that of pre-mature Cn-AFP at the same concentration. The ice crystal shape changed to an elongated hexagonal shape in the presence of the recombinant mature Cn-AFP, while single ice crystal showed a circular disk shape in absence of Cn-AFP. Northern analysis demonstrated a dramatic accumulation of Cn-AFP transcripts when the cells were subjected to freezing stress. This rapid response to freeze stress, and the antifreeze activity of recombinant Cn-AFPs, indicates that Cn-AFP plays an important role in low temperature adaptation.

Statistical experimental designs; involving (i) a fractional factorial design (FFD) and (ii) a central composite design (CCD) were applied to optimize the culture medium constituents for production of a unique antifreeze protein by the Antartic microalgae Chaetoceros neogracile. The results of the FFD suggested that NaCl, KCl, MgCl2, and Na2SiO3 were significant variables that highly influenced the growth rate and biomass production. The optimum culture medium for the production of an antifreeze protein from C. neogracile was found to be Kalleampersandrsquor;s artificial seawater, pH of 7.0ampersandplusmn;0.5, consisting of 28.566 g/l of NaCl, 3.887 g/l of MgCl2, 1.787 g/l of MgSO4, 1.308 g/l of CaSO4, 0.832 g/l of K2SO4, 0.124 g/l of CaCO3, 0.103 g/l of KBr, 0.0288 g/l of SrSO4, and 0.0282 g/l of H3BO3. The antifreeze activity significantly increased after cells were treated with cold shock (at -5oC) for 14 h. To the best of our knowledge, this is the first report demonstrating an antifreeze-like protein of C. neogracile.

To better understand the gene expression of the cold-adapted polar diatom, we conducted a survey of the Chaetoceros neogracile transcriptome by cDNA sequencing and expression of interested cDNAs from the Antarctic diatom. A non-normalized cDNA library was constructed from the C. neogracile, and a total of 2,500 cDNAs were sequenced to generate 1,881 high-quality expressed sequence tags (ESTs) (accession numbers EL620615-EL622495). Based on their clustering, we identified 154 unique clusters comprising 342 ESTs. The remaining 1,540 ESTs did not cluster. The number of unique genes identified in the data set is thus estimated to be 1,694. Taking advantage of various tools and databases, putative functions were assigned to 939 (55.4%) of these genes. Of the remaining 540 (31.9%) unknown sequences, 215 (12.7%) appeared to be C. neogracile-specific since they lacked any significant sequence similarity to any sequence available in the public databases. C. neogracile consisted of a relatively high percentage of genes involved in metabolism, genetic information processing, cellular processes, defense or stress resistance, photosynthesis, structure, and signal transduction. From the ESTs, the expression of these putative C. neogracile genes was investigated: fucoxanthin chlorophyll (chl) a,c-binding protein (FCP), ascorbate peroxidase (ASP), and heat-shock protein 90 (HSP90). The abundance of ASP and HSP90 changed substantially in response to different culture conditions, indicating the possible regulation of these genes in C. neogracile.

To understand the community structure and the functional dynamics of phytoplankton over the long term, it is essential to identify rapid changes in the properties of Antarctic phytoplankton communities in relation to ongoing changes in environmental factors due to climate change. This study investigated short-term variability in the phytoplankton biomass and its composition over the summer of 2010 when the sea surface temperature was lowest and chlorophyll-a (chl-a) concentrations were the highest, relative to a 15-year monitoring period (1996–2011). We assessed the intraseasonal variability of the phytoplankton assemblage structure and its synchrony with changes in the main environmental variables in Marian Cove of King George Island, Antarctica. Chlorophyll-a concentrations in summer 2010 (January–February) were significantly higher (up to 24 μg L−1) when the high phytoplankton carbon biomass (603 μg C L−1) was dominated by the sympagic diatom Navicula glaciei, the benthic diatoms Licmophora belgicae and Fragilaria striatula, the planktonic diatoms Thalassiosira antarctica and Thalassiosira spp. (cell size < 10 μm), and the Haptophyceae nanoplanktonic cells of Phaeocystis antarctica. Intraseasonal processes such as easterly winds direction on Maxwell Bay appeared to be the main factors affecting the advection of cold, nutrient-rich waters, and water stability that enhanced phytoplankton growth in Marian Cove. [ABSTRACT FROM AUTHOR]

Here we report morphological and molecular characteristics of dominant freshwater diatoms in summer Arctic reservoirs of Svalbard (Norway), using four culture isolates, when we collected the samples in the field on 15 August 2005. Analyses of morphology and BLAST searches with 18S rDNA sequences identified them to Diatoma tenue (HYNP006, HYNP013), Navicula pelliculosa (HYNP021), and Fragilaria vaucheriae (HYNP022), respectively. Comparative studies of morphology revealed that the body shapes of the three polar diatoms were nearly identical to the known morphology of each species; however, they were considerably shorter in body length than previously described identical species from other locations. The 18S rDNA sequences of the diatoms were nearly identical to the same species from temperate and other regions. Phylogenetic analysis showed that the polar diatoms each formed a clade with their identical species and genera according to their taxonomic positions. This suggests that the polar diatoms may possess little or no genetic or morphological variation compared to more temperate strains. [ABSTRACT FROM AUTHOR]