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The Roseobacter clade represents one of the most abundant groups of marine bacteria and plays important biogeochemical roles in marine environments. Roseobacter genomes commonly contain a conserved gene transfer agent (GTA) gene cluster. A major capsid protein-encoding GTA (g5) has been used as a genetic marker to estimate the diversity of marine roseobacters. Here, the diversity of roseobacters in the coastal seawater of Arctic Kongsfjorden and Antarctic Maxwell Bay was investigated based on g5 gene clone library analysis. Four g5 gene clone libraries were constructed from microbial assemblages representing Arctic and Antarctic regions. The genus Phaeobacter was exclusively detected in Arctic seawater, whereas the genera Jannaschia, Litoreibacter and Pacificibacter were only observed in Antarctic seawater. More diverse genera within the Roseobacter clade were observed in Antarctic clones than in Arctic clones. The genera Sulfitobacter, Loktanella and Yoonia were dominant (higher than 10% of total clones) in both Arctic and Antarctic samples, implying their roles in polar marine environments. The results not only indicated a bipolar or even global distribution of roseobacters in marine environments but also showed their endemic distribution either in the Arctic or Antarctic. Endemic phylotypes were more frequently observed in polar regions than cosmopolitan phylotypes. In addition, endemic phylotypes were more abundant in Arctic samples (84.8% of Arctic sequences) than in Antarctic samples (54.3% of Antarctic sequences). [ABSTRACT FROM AUTHOR]

Increased conformational flexibility is the prevailing explanation for the high catalytic efficiency of cold-adapted enzymes at low temperatures. However, less is known about the structural determinants of flexibility. We reported two novel cold-adapted zinc metalloproteases in the thermolysin family, vibriolysin MCP-02 from a deep sea bacterium and vibriolysin E495 from an Arctic sea ice bacterium, and compared them with their mesophilic homolog, pseudolysin from a terrestrial bacterium. Their catalytic efficiencies, kcat/K,n (10-40 °C), followed the order pseudolysin < MCP-02 < E495 with a ratio of -1:2:4. MCP-02 and E495 have the same optimal temperature (T[subopt], 57°C, 5°C lower than pseudolysin) and apparent melting temperature (Tm = 64 `C, ∼10°C lower than pseudolysin). Structural analysis showed that the slightly lower stabilities resulted from a decrease in the number of salt bridges. Fluorescence quenching experiments and molecular dynamics simulations showed that the flexibilities of the proteins were pseudolysin < MCP-02 < E495, suggesting that optimization of flexibility is a strategy for cold adaptation. Molecular dynamics results showed that the ordinal increase in flexibility from pseudolysin to MCP-02 and E495, especially the increase from MCP-02 to E495, mainly resulted from the decrease of hydrogen-bond stability in the dynamic structure, which was due to the increase in asparagine, serine, and threonine residues. Finally, a model for the cold adaptation of MCP-02 and E495 was proposed. This is the first report of the optimization of hydrogen-bonding dynamics as a strategy for cold adaptation and provides new insights into the structural basis underlying conformational flexibility. [ABSTRACT FROM AUTHOR]

Two Gram-stain-negative, aerobic, rod-shaped, non-endospore-forming and motile bacterial strains, designated IT1137 T and S025 T , were isolated from an intertidal sediment sample collected from the Fildes Peninsula (King George Island, Maritime Antarctica) and a soil sample under red snow in the Ny-Ålesund region (Svalbard, High Arctic), respectively. The 16S rRNA gene sequence similarity values grouped them in the genus Pseudomonas . The two strains were characterized phenotypically using API 20E, API 20NE, API ZYM and Biolog GENIII tests and chemotaxonomically by their fatty acid contents, polar lipids and respiratory quinones. Multilocus sequence analysis (concatenated 16S rRNA, gyrB , rpoB and rpoD sequences), together with genome comparisons by average nucleotide identity and digital DNA-DNA hybridization, were performed. The results showed that the similarity values of the two isolates with the type strains of related Pseudomonas species were below the recognized thresholds for species definition. Based on polyphasic taxonomy analysis, it can be concluded that strains IT1137 T and S025 T represent two novel species of the genus Pseudomonas , for which the names Pseudomonas paeninsulae sp. nov. (type strain IT1137 T =PMCC 100533 T =CCTCC AB 2023226 T =JCM 36637 T ) and Pseudomonas svalbardensis sp. nov. (type strain S025 T =PMCC 200367 T = CCTCC AB 2023225 T =JCM 36638 T ) are proposed.

A Gram-negative, non-motile, non-spore-forming, psychrotolerant and halotolerant bacterium designated BSw21516B(T), was obtained from seawater in Kongsfjorden, a glacial fjord in the Arctic Svalbard and subjected to taxonomic analysis using a polyphasic approach. This bacterium was observed to optimally grow at 25-29 °C; between at 4 and 34 °C, but not at >35 °C; and in the presence of 0-8 % (w/v) NaCl at an optimum concentration of 2-5 % (w/v) NaCl. Strain BSw21516B(T) was found to contain Ubiquinone-8 (Q-8) as a predominant respiratory lipoquinone and C18:1 ω9c and summed feature 3 (C16:1 ω7c and/or iso-C15:0 2-OH) as predominant cellular fatty acids. Phylogenetic analysis of 16S rRNA and gyrB gene sequences showed that this isolate belongs to the genus Psychrobacter and is closely related to Psychrobacter fozii LMG 21280(T), which was isolated from a sediment sample in Antarctica. DNA hybridization experiments revealed a low level of DNA-DNA relatedness (less than 58.6 %) between strain BSw21516B(T) and its closest relatives. Based on these results a new species Psychrobacter fjordensis sp. nov. is proposed (type strain BSw21516B(T) = KCTC 42279(T) = CCTCC AB 2014020(T)).

Fjords and open oceans are two typical marine ecosystems in the Arctic region, where glacial meltwater and sea ice meltwater have great effects on the bacterioplankton community structure during the summer season. This study aimed to determine the differences in bacterioplankton communities between these two ecosystems in the Arctic region. We conducted a detailed census of microbial communities in Kongsfjorden (Spitsbergen) and the Chukchi Borderland using high-throughput pyrosequencing of the 16S rRNA gene. Gammaproteobacteria and Bacteroidetes were the dominant members of the bacterioplankton community in Kongsfjorden. By contrast, the most abundant bacterial groups in the surface seawater samples from the Chukchi Borderland were Alphaproteobacteria and Actinobacteria. Differences in bacterial communities were found between the surface and subsurface waters in the investigation area of the Chukchi Borderland, and significant differences in bacterial community structure were also observed in the subsurface water between the shelf and deep basin areas. These results suggest the effect of hydrogeographic conditions on bacterial communities. Ubiquitous phylotypes found in all the investigated samples belonged to a few bacterial groups that dominate marine bacterioplankton communities. The sequence data suggested that changes in environmental conditions result in abundant rare phylotypes and reduced amounts of other phylotypes.

A novel psychrotolerant bacterial strain, BCw111(T), was isolated from seawater samples from the Chukchi Sea in the Arctic Ocean. Cells of strain BCw111(T) were Gram-negative, motile, facultatively anaerobic, curved rods and were able to grow at 0-30 °C (optimum 23-25 °C). Strain BCw111(T) had Q-8 as the major respiratory quinone and contained iso-C(15 : 0) 2-OH and/or C(16 : 1)ω7c (28.13 %), C(16 : 0) (13.28 %) and C(17 : 1) (12.90 %) as the major cellular fatty acids. The genomic DNA G+C content was 41.3 mol%. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain BCw11(T) formed a distinct lineage within the genus Colwellia and exhibited the highest 16S rRNA gene sequence similarity with Colwellia polaris 537(T) (97.8 %) and Colwellia aestuarii SMK-10(T) (97.1 %). Based on phenotypic characteristics, phylogenetic analysis and DNA-DNA relatedness, a novel species, Colwellia chukchiensis sp. nov., is proposed. The type strain is BCw111(T) ( = CGMCC 1.9127(T)  = LMG 25329(T)  = DSM 22576(T)).

Increased conformational flexibility is the prevailing explanation for the high catalytic efficiency of cold-adapted enzymes at low temperatures. However, less is known about the structural determinants of flexibility. We reported two novel cold-adapted zinc metalloproteases in the thermolysin family, vibriolysin MCP-02 from a deep sea bacterium and vibriolysin E495 from an Arctic sea ice bacterium, and compared them with their mesophilic homolog, pseudolysin from a terrestrial bacterium. Their catalytic efficiencies, k(cat)/K(m) (10-40 degrees C), followed the order pseudolysin < MCP-02 < E495 with a ratio of approximately 1:2:4. MCP-02 and E495 have the same optimal temperature (T(opt), 57 degrees C, 5 degrees C lower than pseudolysin) and apparent melting temperature (T(m) = 64 degrees C, approximately 10 degrees C lower than pseudolysin). Structural analysis showed that the slightly lower stabilities resulted from a decrease in the number of salt bridges. Fluorescence quenching experiments and molecular dynamics simulations showed that the flexibilities of the proteins were pseudolysin < MCP-02 < E495, suggesting that optimization of flexibility is a strategy for cold adaptation. Molecular dynamics results showed that the ordinal increase in flexibility from pseudolysin to MCP-02 and E495, especially the increase from MCP-02 to E495, mainly resulted from the decrease of hydrogen-bond stability in the dynamic structure, which was due to the increase in asparagine, serine, and threonine residues. Finally, a model for the cold adaptation of MCP-02 and E495 was proposed. This is the first report of the optimization of hydrogen-bonding dynamics as a strategy for cold adaptation and provides new insights into the structural basis underlying conformational flexibility.

Using PCR-DGGE (denaturing gradient gel electrophoresis) methods, bacterial phylogenetic diversity in three Pacific Arctic sediment samples were investigated, taken from different depths in the range of 47 m to 3850 m. DGGE profiles of different layers in the same sediment sample are not completely same. 16S rDNA sequences corresponding to 50 excised bands from three sediment samples were analyzed and fell into seven lineages of the domain Bacteria: alpha- beta-, gamma-, delta-, epsilon- Proteobacteria, the Cytophaga-Flavobacterium-Bacteroides (CFB) group and Actinobacteria. However, the composition of bacterial phylotypes in three sediments is different. Fourteen sequences obtained from sediment B78 collected from the Canadian Basin belong to beta-, gamma- Proteobacteria, Comamonadaceae and Acidobacteria. Bacterial phylotypes in submarine plateau sediment P24 are alpha-, gamma-, delta-Proteobacteria; While seventeen sequences from sediment S11 colleted from continental slop in the Chukchi Sea are grouped into alpha-, gamma-, delta-, epsilon-Proteobacteria, the Cytophaga-Flavobacterium-Bacteroides (CFB) group and Actinobacteria. It is suggested the different characteristics of three sediments may cause the difference in the composition of bacterial phylotypes. 16S rDNA sequences from members of gamma-Proteobacteria dominated three sediments samples. The majority of the sequences were most closely related to uncultured marine environmental sequences, especially marine sediment environmental sequences (88% - 100%).

The phylogenetic diversity of culturable psychrophilic bacteria associated with sea ice from high latitude sea (77 degrees 30'N - 81 degrees 12'N), Canadian Basin and Greenland sea Arctic, was investigated. A total of 37 psychrophilic strains were isolated using three different methods of ( i ) spread plate method: 100 microL of each dilution ice-melt sample was spreaded onto the surface of Marine 2216 agar (DIFCO laboratories, Detroit, MI) and incubated for 2 to 6 weeks at 4 degrees C; ( ii ) bath culture and spread plate method: 1 mL of sample was added to 9mL of NSW (unamended natural seawater, 0.2 microm prefiltered and autoclaved) and incubated for 1 months at - 1 degrees C, then spread plate method was used to isolate bacterial strains from the pre-cultured samples; ( iii ) cold shock, bath culture and spread plate method: samples were exposed to - 20 degrees C for 24h, then bacterial strains isolated by bath culture and spread plate method under aerobic conditions. Nearly half of psychrophilic strains are isolated by using method iii . 16S rDNA nearly full-length sequence analysis reveal that psychrophilic strains fall in two phylogenetic divisions, gamma-proteobacteria (in the genera Colwellia, Marinobacter, Shewanella, Thalassomonas, Glaciecola, Marinomonas and Pseudoalteromonas) and Cytophaga-Flexibacter-Bacteroides (in the genera Flavobacterium and Psychroflexus). Nine of bacterial isolates (BSi20007, BSi20497, BSi20517, BSi20537, BSi20170, BSi20001, BSi20002, BSi20675 and BSi20101) quite likely represent novel species (16S rDNA sequence similarity below 97%). One of strains (BSi20002) from Canadian Basin shows 100% sequence similarity to the Antarctic Weddell sea ice isolate Marinobacter sp. ANT8277, suggesting bacteria may have a bipolar distribution at the species level. AF283859 sequences were submitted to the BLAST search program of the National Center for Biotechnology Information website (NCBI, http://www. ncbi. nlm.nih. gov). Twenty sequences showing 100% similarity each other are retrieved from the database, eleven from Antarctic seawater bacteria, three from Antarctic sea-ice bacteria, one from Spitzbergen sea-ice bacteria, two from Chukchi Sea sea-ice bacteria, two from Canadian Basin sea-ice bacteria (in this study) and one from uncultured bacterium clone PDA-OTU11 associated with the coral Pocillopora damicornis from the Great Barrier Reef. These may indicate that the physiological and geographic barriers appear to be permeable and some bacterial species can survive in different environment. The majority of the bacterial strains are able to secrete diversity cold-adaptive hydrolytic enzymes into the medium at 4 degrees C. The isolates that are able to degrade Tween-80, glutin, and starch account for, respectively, 62.6%, 51.4% and 40.5%.