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208. An assessment of phytoplankton primary productivity in the Arctic Ocean from satellite ocean color/in situ chlorophyll‐a based models

Author

Lee, Younjoo J., primary, Matrai, Patricia A., additional, Friedrichs, Marjorie A. M., additional, Saba, Vincent S., additional, Antoine, David, additional, Ardyna, Mathieu, additional, Asanuma, Ichio, additional, Babin, Marcel, additional, Bélanger, Simon, additional, Benoît‐Gagné, Maxime, additional, Devred, Emmanuel, additional, Fernández‐Méndez, Mar, additional, Gentili, Bernard, additional, Hirawake, Toru, additional, Kang, Sung‐Ho, additional, Kameda, Takahiko, additional, Katlein, Christian, additional, Lee, Sang H., additional, Lee, Zhongping, additional, Mélin, Frédéric, additional, Scardi, Michele, additional, Smyth, Tim J., additional, Tang, Shilin, additional, Turpie, Kevin R., additional, Waters, Kirk J., additional, and Westberry, Toby K., additional

Published
2015
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219. Enzyme activities of phytoplankton in the South Shetland Islands (Antarctica) in relation to nutrients and primary production

Author

IRIARTE, JOSÉ L, GONZÁLEZ, RODRIGO R, QUIÑONES, RENATO A, KANG, SUNG-HO, SHIM, JAE H, and VALENZUELA, CYNTHIA P

Subjects
primary productivity, nitrate reductase, clorofila, Antártica, fosfatasa alcalina, Antarctica, nitrato reductasa, chlorophyll, alkaline phosphatase, producción primaria
Abstract

Given the potential significance of enzyme activities as a link between internal metabolic pathways and environmental nutrients, we investigated the relationships of nitrate reductase (NR) and alkaline phosphatase (AP) with primary production and inorganic nutrients in South Shetland Islands, Antarctica. Enzymatic activities of the phytoplankton (0.7-210 µm), primary productivity, autotrophic biomass and inorganic nutrients were studied in the upper 100 m depth at nine stations during a cruise in the northwestern area of South Shetland Islands (Antarctica), during late austral spring (December 2000). NR activities fluctuated between 0 and 42.8 nmol L-1 h-1 (mean = 10.08 nmol L-1 h-1, SD = 10.42 nmol L-1 h-1), AP activities between 0.81 and 5.67 nmol L-1 h-1 (mean = 2.68 nmol L-1 h-1, SD = 0.95 nmol L-1 h-1). Stations with primary productivity (PP) and chlorophyll a greater than 2 mg C m-3 h-1 and 0.75 mg chlorophyll a L-1, respectively, presented higher enzymatic activities of nitrate reductase, alkaline phosphatase than those stations characterized by primary productivity and chlorophyll a less than 2 mg C m-3 h-1 and 0.17 mg chlorophyll a L-1, respectively. The AP specific activity was negatively correlated with orthophosphate concentrations lower than 2.0 µM, which indicates that the microplankton were under phosphate deficient environment condition. Our results indicated that NR specific activity was positively associated with autotrophic biomass and primary productivity estimates, giving evidence of the use of nitrate by phytoplankton as external nitrogen source in surface waters. In addition, high NR activities were positively correlated with NO3-, suggesting the occurrence of nitrate respiration in the well oxygenated surface waters of Antarctica Dada la potencial importancia de la actividad enzimática de ensambles fitoplanctónicos, como indicador de su metabolismo interno dominante respecto de los nutrientes, este estudio investigó las relaciones entre la nitrato reductasa (NR) y la fosfatasa alcalina (FA) con la producción primaria y nutrientes inorgánicos en las Islas Shetland del Sur, Antártica. Las variables de actividad enzimática del fitoplancton (0,7-210 µm), producción primaria, biomasa autotrófica y nutrientes inorgánicos fueron analizadas en nueve estaciones en los primeros 100 m de profundidad durante un crucero oceanográfico en el área noroeste de las Islas Shetland del Sur (Antártica), durante la primavera austral (diciembre 2000). Las actividades enzimáticas de NR fluctuaron entre 0 y 42,8 nmol L-1 h-1 (promedio = 10,08 nmol L-1 h-1, DE = 10,42 nmol L-1 h-1) y de FA entre 0,81 y 5,67 nmol L-1 h-1 (promedio = 2,68 nmol L-1 h-1, DE = 0,95 nmol L-1 h-1). Aquellas estaciones con estimaciones de productividad primaria (PP) y clorofila a mayores que mg C m-3 h-1 y 0,75 mg clorofila a L-1, respectivamente, presentaron mayores actividades enzimáticas de nitrato reductasa y fosfatasa alcalina que aquellas estaciones caracterizadas por estimaciones de producción primaria y clorofila a menores que 2 mg C m-3 h-1 y 0,17 mg clorofila a L-1, respectivamente. La actividad específica de FA fue negativamente correlacionada con ortofosfato a concentraciones menores que 2,0 µM, lo que sugiere que el fitoplancton se encontraba en condiciones ambientales de deficiencia de fosfato. Nuestros resultados indican que la actividad específica de NR estuvo positivamente asociada a la biomasa autotrófica y producción primaria en la zona fótica, lo que evidencia el uso de nitrato como nutriente nitrogenado por el fitoplancton en aguas superficiales. Además, altas actividades de NR fueron positivamente correlacionadas con NO3-, lo que sugiere la ocurrencia del proceso de respiración de nitrato en aguas superficiales bien oxigenadas de la Antártica

Published
2006

220. Porphyrin Sensitizers with Donor Structural Engineering for Superior Performance Dye-Sensitized Solar Cells and Tandem Solar Cells for Water Splitting Applications.

Author

Kang, Sung Ho, Jeong, Myung Jin, Eom, Yu Kyung, Choi, In Taek, Kwon, Seung Mo, Yoo, Youngjun, Kim, Jeongho, Kwon, Jeong, Park, Jong Hyeok, and Kim, Hwan Kyu

Subjects
*DYE-sensitized solar cells, *PORPHYRINS, *PHOTOSENSITIZERS, *STRUCTURAL engineering, *WATER electrolysis
Abstract

Zn(II)-porphyrin sensitizers, coded as SGT-020 and SGT-021, are designed and synthesized through donor structural engineering. The photovoltaic (PV) performances of SGT sensitizer-based dye-sensitized solar cells (DSSCs) are systematically evaluated in a thorough SM315 as a reference sensitizer. The effect of the donor ability and the donor bulkiness on photovoltaic performances is investigated for establishing the structure-performance relationship in the platform of porphyrin-triple bond-benzothiadiazole-acceptor sensitizers. By introducing a more bulky fluorene unit to the amine group in the SM315, the power conversion efficiency (PCE) is enhanced with the increased short-circuit current ( Jsc) and open-circuit voltage ( Voc), due to the improved light-harvesting ability and the efficient prevention of charge recombination, respectively. As a consequence, a maximum PCE of 12.11% is obtained for SGT-021, whose PCE is much higher than the 11.70% PCE for SM315. To further improve their maximum efficiency, the first parallel tandem DSSCs employing cobalt electrolyte in the top and bottom cells are demonstrated and an extremely high efficiency of 14% is achieved, which is currently the highest reported value for tandem DSSCs. The series tandem DSSCs give a remarkably high Voc value of >1.83 V. From this DSSC tandem configuration, 7.4% applied bias photon-to-current efficiency is achieved for solar water splitting. [ABSTRACT FROM AUTHOR]

Published
2017
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221. Enzymatic modification by point mutation and functional analysis of an omega-6 fatty acid desaturase from Arctic Chlamydomonas sp.

Author

Jung, Woongsic, Kim, Eun Jae, Han, Se Jong, Kang, Sung-Ho, Choi, Han-Gu, and Kim, Sanghee

Subjects
FUNCTIONAL analysis, FATTY acids, DESATURASES, CHLAMYDOMONAS, HISTIDINE
Abstract

ArcticChlamydomonassp. is a dominant microalgal strain in cold or frozen freshwater in the Arctic region. The full-length open reading frame of the omega-6 fatty acid desaturase gene (AChFAD6) was obtained from the transcriptomic database of ArcticChlamydomonassp. from the KOPRI culture collection of polar micro-organisms. Amino acid sequence analysis indicated the presence of three conserved histidine-rich segments as unique characteristics of omega-6 fatty acid desaturases, and three transmembrane regions transported to plastidic membranes by chloroplast transit peptides in the N-terminal region. The AChFAD6 desaturase activity was examined by expressing wild-type and V254A mutant (Mut-AChFAD6) heterologous recombinant proteins. Quantitative gas chromatography indicated that the concentration of linoleic acids inAChFAD6-transformed cells increased more than 3-fold [6.73 ± 0.13 mg g−1dry cell weight (DCW)] compared with cells transformed with vector alone. In contrast, transformation with Mut-AChFAD6increased the concentration of oleic acid to 9.23 ± 0.18 mg g−1DCW, indicating a change in enzymatic activity to mimic that of stearoyl-CoA desaturase. These results demonstrate that AChFAD6 of ArcticChlamydomonassp. increases membrane fluidity by enhancing denaturation of C18 fatty acids and facilitates production of large quantities of linoleic fatty acids in prokaryotic expression systems. [ABSTRACT FROM PUBLISHER]

Published
2017
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230. Marine ice sheets of Pleistocene age on the East Siberian Continental Margin

Author

Niessen, Frank, Hong, Jong Kuk, Hegewald, Anne, Matthiessen, Jens, Stein, Rüdiger, Kim, Hyoungjun, Kim, Sookwan, Jensen, Laura, Jokat, Wilfried, Nam, Seung-Ill, Kang, Sung-Ho, Niessen, Frank, Hong, Jong Kuk, Hegewald, Anne, Matthiessen, Jens, Stein, Rüdiger, Kim, Hyoungjun, Kim, Sookwan, Jensen, Laura, Jokat, Wilfried, Nam, Seung-Ill, and Kang, Sung-Ho

Abstract

Based on swath bathymetry, sediment echosounding, seismic profiling and sediment coring we present results of the RV „Polarstern“ cruise ARK-XIII/3 (2008) and RV "Araon" cruise ARA02B (2012), which investigated an area between the Chukchi Borderland and the East Siberian Sea between 165°W and 170°E. At the southern end of the Mendeleev Ridge, close to the Chukchi and East Siberian shelves, evidence is found for the existence of Pleistocene ice sheets/ice shelves, which have grounded several times in up to 1200 m present water depth. We found mega-scale glacial lineations associated with deposition of glaciogenic wedges and debris-flow deposits indicative of sub-glacial erosion and deposition close to the former grounding lines. Glacially lineated areas are associated with large-scale erosion, accentuated by a conspicuous truncation of pre-glacial strata typically capped with mostly thin layers of diamicton draped by pelagic sediments. Our tentative age model suggests that the youngest and shallowest grounding event of an ice sheet should be within Marine Isotope Stage (MIS) 3. The oldest and deepest event predates MIS 6. According to our results, ice sheets of more than one km in thickness continued onto, and likely centered over, the East Siberian Shelf. They were possibly linked to previously suggested ice sheets on the Chukchi Borderland and the New Siberian Islands. We propose that the ice sheets extended northward as thick ice shelves, which grounded on the Mendeleev Ridge to an area up to 78°N within MIS 5 and/or earlier. These results have important implication for the former distribution of thick ice masses in the Arctic Ocean during the Pleistocene. They are relevant for global sea-level variations, albedo, ocean-atmosphere heat exchange, freshwater export from the Arctic Ocean at glacial terminations and the formation of submarine permafrost. The existence of km-thick Pleistocene ice sheets in the western Arctic Ocean during glacial times predating that of

Published
2013

231. Repeated Pleistocene glaciation of the East Siberian continental margin

Author

Niessen, Frank, Hong, Jong Kuk, Hegewald, Anne, Matthiessen, Jens, Stein, Rüdiger, Kim, Hyoungjun, Kim, Sookwan, Jensen, Laura, Jokat, Wilfried, Nam, Seung-Il, Kang, Sung-Ho, Niessen, Frank, Hong, Jong Kuk, Hegewald, Anne, Matthiessen, Jens, Stein, Rüdiger, Kim, Hyoungjun, Kim, Sookwan, Jensen, Laura, Jokat, Wilfried, Nam, Seung-Il, and Kang, Sung-Ho

Abstract

During the Pleistocene glaciations, Arctic ice sheets onwestern Eurasia, Greenland and North America terminated at their continental margins1–4. In contrast, the exposed continental shelves in the Beringian region of Siberia are thought to have been covered by a tundra landscape5–7. Evidence of grounded ice on seafloor ridges and plateaux off the coast of the Beringian margin, at depths of up to 1,000 m, have generally been attributed to ice shelves or giant icebergs that spread oceanwards during glacial maxima8–12. Here we identify marine glaciogenic landforms visible in seismic profiles and detailed bathymetric maps along the East Siberian continental margin. We interpret these features, which occur in present water depths of up to 1,200 m, as traces from grounding events of ice sheets and ice shelves. We conclude that the Siberian Shelf edge and parts of the Arctic Ocean were covered by ice sheets of about 1 km in thickness during several Pleistocene glaciations before the most recent glacial period, which must have had a significant influence on albedo and oceanic and atmospheric circulation.

Published
2013

232. Comparative study of edge-functionalized graphene nanoplatelets as metal-free counter electrodes for highly efficient dye-sensitized solar cells

Author

Kim, Chang Ki, Kim, Hong Mo, Aftabuzzaman, M., Jeon, In-Yup, Kang, Sung Ho, Eom, Yu Kyung, Baek, Jong Beom, and Kim, Hwan Kyu

Abstract

Edge-functionalized graphene nanoplatelets (GnPs) were synthesized by a simple ball-milling process of graphite in the presence of halogen (F, I), metalloids (Se, Te and Sb) and subsequently applied to dye-sensitized solar cells (DSSCs) as counter electrodes (CEs). In our previous works, a series of edge-functionalized GnPs were thoroughly studied and successfully utilized as CEs in DSSCs, with the aim of finding possible alternatives to the noble and expensive Pt metal as CE. However, in each study, the GnP-CEs were not only fabricated with different dyes and electrolytes but were also evaluated on different occasions, and thus, it was difficult to identify which type of edge-functionalized GnPs was the best. Herein, DSSCs with different edge-functionalized GnP-CEs were fabricated under the same environmental conditions, photovoltaic performances were then evaluated employing both I−/I3−and Co(bpy)32+/3+(bpy = 2,2′-bipyridine) redox couples with three different sensitizers to assess the electrocatalytic activity of the different GnP-CEs. Photovoltaic performances of edge-halogenated GnP-CEs with N719dye employing the I−/I3−redox couple were lower than those of the metalloid-doped GnP-CEs and were even inferior to Pt-CE, which was consistent with the Rctvalues. Conversely, among the metalloid-doped GnP-CEs, SbGnP-CE exhibited a higher Rctvalue and lower power conversion efficiency (PCE) value of 8.70% and 6.60% with N719and SGT-130dyes, respectively. However, when the devices were fabricated with the Co(bpy)32+/3+redox couple, the opposite occurred and SbGnPs displayed the highest PCE of 10.42% with SGT-130dye and 12.08% with SGT-021dye. Furthermore, SeGnP-CE and TeGnP-CE showed superior compared to the Pt-CE with both I−/I3−and Co(bpy)32+/3+electrolyte solutions.

Published
2018
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238. Induction of beta defensin 2 by NTHi requires TLR2 mediated MyD88 and IRAK-TRAF6-p38MAPK signaling pathway in human middle ear epithelial cells.

Author

Lee, Haa-Yung, Lee, Haa-Yung, Takeshita, Tamotsu, Shimada, Jun, Akopyan, Arsen, Woo, Jeong-Im, Pan, Huiqi, Moon, Sung K, Andalibi, Ali, Park, Rae-Kil, Kang, Sung-Ho, Kang, Shin-Seok, Gellibolian, Robert, Lim, David J, Lee, Haa-Yung, Lee, Haa-Yung, Takeshita, Tamotsu, Shimada, Jun, Akopyan, Arsen, Woo, Jeong-Im, Pan, Huiqi, Moon, Sung K, Andalibi, Ali, Park, Rae-Kil, Kang, Sung-Ho, Kang, Shin-Seok, Gellibolian, Robert, and Lim, David J

Abstract

BackgroundAll mucosal epithelia, including those of the tubotympanium, are secreting a variety of antimicrobial innate immune molecules (AIIMs). In our previous study, we showed the bactericidal/bacteriostatic functions of AIIMs against various otitis media pathogens. Among the AIIMs, human beta-defensin 2 is the most potent molecule and is inducible by exposure to inflammatory stimuli such as bacterial components or proinflammatory cytokines. Even though the beta-defensin 2 is an important AIIM, the induction mechanism of this molecule has not been clearly established. We believe that this report is the first attempt to elucidate NTHi induced beta-defensin expression in airway mucosa, which includes the middle ear.MethodsMonoclonal antibody blocking method was employed in monitoring the TLR-dependent NTHi response. Two gene knock down methods - dominant negative (DN) plasmid and small interfering RNA (siRNA) - were employed to detect and confirm the involvement of several key genes in the signaling cascade resulting from the NTHi stimulated beta-defensin 2 expression in human middle ear epithelial cell (HMEEC-1). The student's t-test was used for the statistical analysis of the data.ResultsThe experimental results showed that the major NTHi-specific receptor in HMEEC-1 is the Toll-like receptor 2 (TLR2). Furthermore, recognition of NTHi component(s)/ligand(s) by TLR2, activated the Toll/IL-1 receptor (TIR)-MyD88-IRAK1-TRAF6-MKK3/6-p38 MAPK signal transduction pathway, ultimately leading to the induction of beta-defensin 2.ConclusionThis study found that the induction of beta-defensin 2 is highest in whole cell lysate (WCL) preparations of NTHi, suggesting that the ligand(s) responsible for this up-regulation may be soluble macromolecule(s). We also found that this induction takes place through the TLR2 dependent MyD88-IRAK1-TRAF6-p38 MAPK pathway, with the primary response occurring within the first hour of stimulation. In combination with our previous studies show

Published
2008

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