Publishing type：Research paper (scientific journal)   Publisher：The Oceanographic Society of Japan  

DOI： 10.5928/kaiyou.30.5_179

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Publishing type：Research paper (scientific journal)   Publisher：The Oceanographic Society of Japan  

DOI： 10.5928/kaiyou.30.5_199

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Oceanographic Society of Japan  

The future direction of Japanese oceanographic research in the next decade is discussed, mainly from a coastal oceanographic perspective. Coastal oceans serve two functions: (1) as a filter-reactor region connecting the open ocean and land, and (2) as a biologically rich and diverse region where environmental changes have a direct impact on society. Therefore, understanding the material cycle within the coastal region is important not only scientifically but also to preserve and maintain the ocean. Process studies are needed, with close collaboration between physical, chemical, and biological science communities. Coastal oceans continue to lack observations to understand and resolve the small spatial and time-scale events that govern the region. However, advances in observational instruments/techniques, satellite measurements, and unmanned aerial vehicles are starting to provide high temporal spatial data than ever before. In addition to long-term monitoring, we discuss the research infrastructure and numerical models needed for future studies.

DOI： 10.5928/kaiyou.30.5_87

CiNii Books

CiNii Research

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Publishing type：Research paper (scientific journal)  

Seasonal and vertical variations in photosynthetic–irradiance (P–E) parameters and primary production were examined in offshore Suruga Bay, where both the subtropical warm Kuroshio Water and eutrophic coastal water were influential. The maximum light-utilization coefficient, α*, did not show significant variation between the surface and subsurface layers in both the warm and cold periods. Vertical differences in the maximum photosynthetic rate, Pmax∗, and the light-saturation parameter,Ek, were small even during the warm period. Seasonal variations in the P–E parameters were not significantly related to dissolved inorganic nitrogen (DIN) at the surface layer. These results suggest that low-nutrient and high-light stresses were not serious at the surface layer, even in the stratified season, because of the continuous inflow of high-nutrient river water. Seasonal variations in Pmax∗ and α* were suggested to be regulated by both the Ek-dependent (photo-acclimation of phytoplankton) and Ek-independent (response to nutrient and growth conditions) mechanisms from the correlation analyses. The subsurface chlorophyll maximum (SCM) formation was less obvious, and a major part of the primary production occurred in the upper half of the euphotic zone. The water-column primary production, ΣPP (total), tended to be overestimated by ignoring vertical variations in the P–E parameters and chlorophyll a, especially during the warm period. These features of primary production appeared to be similar to those reported in coastal waters rather than in subtropical waters, playing an essential role in the fishing ground formation in the bay.

DOI： 10.1007/s10872-021-00610-9

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Zoological Society of Japan  

The exumbrellar surfaces of six pelagic cnidarians from three classes were ultra-structurally compared to reveal their structural diversity in relation to their gelatinous, transparent bodies. We examined two hydrozoans (Diphyes chamissonis and Colobonema sericeum), a cubozoan (Chironex yamaguchii), and three scyphozoans (Atolla vanhöffeni, Aurelia coerulea, and Mastigias papua). The exumbrellar surfaces of the mesoglea in D. chamissonis, Ch. yamaguchii, Au. coerulea, and M. papua were covered with a simple epidermis; the shapes of the epidermal cells were remarkably different among the species. The epidermal cells of Ch. yamaguchii and M. papua possessed an array of microvilli on the apical side. The array possibly reduced light reflectance and provided some other surface properties, as seen for the cuticular nipple array in tunicates, considering the length, width, and pitch of the microvilli. The reduction of light reflectance on the array of microvilli was supported by the simulation with rigorous coupled wave analysis (RCWA). Microvilli were sparse and did not form an array in metephyrae of Au. coerulea. The mesoglea matrix beneath the basal side of the epidermis was loose in all of the species. The exumbrellar side of the mesoglea was exposed only in the mesopelagic species, At. vanhöffeni and Co. sericeum, and electron-dense layer(s) covered the surface of the mesoglea. It is uncertain whether the exumbrellar epidermis is absent in these species or the epidermal cells are completely exfoliated during the sampling and handling processes. In the latter case, the electron-dense layer(s) on the mesoglea surface might originally underlie the epidermis.

DOI： 10.2108/zs200111

PubMed

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Publishing type：Research paper (scientific journal)   Publisher：Japanese Society of Microbial Ecology  

DOI： 10.1264/jsme2.me20150

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Publishing type：Research paper (scientific journal)   Publisher：Frontiers Media SA  

DOI： 10.3389/fmicb.2020.01764

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Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1007/s11084-020-09593-x

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Other Link： http://link.springer.com/article/10.1007/s11084-020-09593-x/fulltext.html

Publishing type：Research paper (scientific journal)   Publisher：The Plankton Society of Japan/The Japanese Association of Benthology  

DOI： 10.3800/pbr.14.276

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japanese Society of Fish Pathology  

Miamiensis avidus is the causative agent of scuticociliatosis in various marine fish species. The virulence factors of the parasite have not been identified, so far. In this study, we examined M. avidus extracellular proteinases (ECPs) as potential virulence factors, using culture supernatants as an ECPs source. We investigated the substrate specificity of ECPs using artificial peptides, and the cytotoxicity of the ECPs was examined using CHSE-214 cells. To elucidate the role of ECPs in ciliate growth, M. avidus was cultured on CHSE-214 cells in the presence of proteinase inhibitors. We detected proteinase activities from the supernatant of M. avidus. Viable CHSE-214 cells decreased significantly in number, when incubated in a medium supplemented with the culture supernatant of M. avidus. The growth of ciliates on CHSE-214 cells was delayed in the presence of PMSF (serine proteinase inhibitor) and E-64 (cysteine proteinase inhibitor). These results suggested that the culture supernatant contained ECPs showing cytotoxicity, and the proteinases facilitated nutrient uptake by the ciliates. Thus, ECPs may be responsible for virulence factors of M. avidus.

DOI： 10.3147/jsfp.53.1

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：FRONTIERS MEDIA SA  

Microbial extracellular hydrolytic enzymes that degrade organic matter in aquatic ecosystems play key roles in the biogeochemical carbon cycle. To provide linkages between hydrolytic enzyme activities and genomic or metabolomic studies in aquatic environments, reliable measurements are required for many samples at one time. Extracellular proteases are one of the most important classes of enzymes in aquatic microbial ecosystems, and protease activities in seawater are commonly measured using fluorogenic model substrates. Here, we examined several concerns for measurements of extracellular protease activities (aminopeptidases, and trypsin-type, and chymotrypsin-type activities) in seawater. Using a fluorometric microplate reader with low protein binding, 96-well microplates produced reliable enzymatic activity readings, while use of regular polystyrene microplates produced readings that showed significant underestimation, especially for trypsin-type proteases. From the results of kinetic experiments, this underestimation was thought to be attributable to the adsorption of both enzymes and substrates onto the microplate. We also examined solvent type and concentration in the working solution of oligopeptide-analog fluorogenic substrates using dimethyl sulfoxide (DMSO) and 2-methoxyethanol (MTXE). The results showed that both 2% (final concentration of solvent in the mixture of seawater sample and substrate working solution) DMSO and 2% MTXE provide similarly reliable data for most of the tested substrates, except for some substrates which did not dissolve completely in these assay conditions. Sample containers are also important to maintain the level of enzyme activity in natural seawater samples. In a small polypropylene containers (e.g., standard 50-mL centrifugal tube), protease activities in seawater sample rapidly decreased, and it caused underestimation of natural activities, especially for trypsin-type and chymotrypsin-type proteases. In conclusion, the materials and method for measurements should be carefully selected in order to accurately determine the activities of microbial extracellular hydrolytic enzymes in aquatic ecosystems; especially, low protein binding materials should be chosen to use at overall processes of the measurement.

DOI： 10.3389/fmicb.2017.01952

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPANESE SOC MICROBIAL ECOLOGY, DEPT BIORESOURCE SCIENCE  

Extracellular DNA (exDNA) is released from bacterial cells through various processes. The antibiotic resistance genes (ARGs) coded on exDNA may be horizontally transferred among bacterial communities by natural transformation. We quantitated the released/leaked tetracycline resistance gene, tet(M) over time under grazing stress by ciliates and heterotrophic nanoflagellates (HNFs), and found that extracellular tet(M) (ex-tetM) increased with bacterial grazing. Separate microcosms containing tet(M)-possessing bacteria with ciliates or HNFs were prepared. The copy number of ex-tetM in seawater in the ciliate microcosm rapidly increased until 3 d after the incubation, whereas that in the HNF microcosm showed a slower increase until 20 d. The copy number of ex-tetM was stable in both cases throughout the incubation period, suggesting that extracellular ARGs are preserved in the environment, even in the presence of grazers. Additionally, ARGs in bacterial cells were constant in the presence of grazers. These results suggest that ARGs are not rapidly extinguished in a marine environment under grazing stress.

DOI： 10.1264/jsme2.ME17042

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

The biodegradation of proteins in seawater requires various proteases which are commonly thought to be mainly derived from heterotrophic bacteria. We, however, found that protists showed a high protease activity and continuously produced trypsin-type enzymes. The free-living marine heterotrophic ciliate Paranophrys marina together with an associated bacterium was isolated and used for microcosm incubation with different concentrations of killed bacteria as food for 10 days. The results showed that the coexistence of the ciliate with its associated bacterium produced a significant protease activity in both cell-associated and cell-free fractions while that in the associated bacterium only microcosm was negligible. The protease profiles are different between cell-associated and cell-free fractions, and a trypsin-type enzyme hydrolyzing Boc-Val-Leu-Lys-MCA was detected throughout the period in the presence of ciliates. This suggests that ciliates release proteases into the surrounding environment which could play a role in protein digestion outside cells. It has been previously suggested that bacteria are the major transformers in seawater. We here present additional data which indicates that protists, or at least ciliates with their specific enzymes, are a potential player in organic matter degradation in water columns. (C) 2015 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.marenvres.2015.06.011

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Language：English   Publisher：THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES  

A wide variety of organic compounds have been found in space, and their relevance to the origin of life is discussed. Interplanetary dust particles (IDPs) are most promising carriers of extraterrestrial organic compounds, but presence of bioorganic compounds are controversial since they are so small and were collected in the terrestrial biosphere. In addition, IDPs are directly exposed to cosmic and solar radiation. Thus, it is important to evaluate the stability of organics in IDPs in space environment. We are planning a novel astrobiology mission named <i>Tanpopo </i>by utilizing the Exposed Facility of Japan Experimental Module (JEM/EF) of the International Space Station (ISS). Two types of experiments will be done: Capture experiments and exposure experiments. In the exposure experiments, organics and microbes will be exposed to the space environments to examine possible alteration of organic compounds and survivability of microbes. Selected targets for the exposure experiments of organic compounds are as follows: Amino acids (glycine and isovaline), their possible precursors (hydantoin and 5-ethyl-5-methyl hydantoin) and complex precursors "CAW" synthesized from a mixture of carbon monoxide, ammonia and water by proton irradiation. In addition to them, powder of the Murchison meteorite will be exposed to examine possible alteration of meteoritic organics in space. We will show the results of preparatory experiments on ground by using a UV lamp, a ⁶⁰Co source, synchrotron facilities, and a heavy ion irradiation facility.

DOI： 10.2322/tastj.12.Pp_1

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Frontiers Media S. A  

Proteins constitute the major portion of labile substances in the marine environment and are an important source of organic matter supporting marine ecosystems. However, previous studies have revealed that specific bacterial membrane proteins are refractory in the oceans. We here show by kinetic analyses of protease degradation activity using inactivated Pseudomonas aeruginosa (Pa) cells as a proteinaceous substrate that bacterial proteases are insufficient to completely hydrolyze proteins, which may partially cause the protein accumulation in seawater. Protease activity was monitored simultaneously in 8 microcosms subjected to differing conditions. Some Pa proteins were retained for 30 days in the presence of bacteria without protists, whereas the Pa proteins were completely disappeared in the presence of both, indicating that these proteins were substantially incorporated into protist biomass. Our result suggests that protists play an important role in the transformation of bacterial proteins in seawater. Our experiments also imply that the functional/taxonomic diversity should be taken into account when considering decomposition activity in marine environments.

DOI： 10.3389/fmars.2014.00069

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Language：English   Publishing type：Research paper (scientific journal)  

Abstract Titan, the largest satellite of Saturn, has a thick atmosphere containing nitrogen and methane. A variety of organic compounds have been detected in the atmosphere, most likely produced when atmospheric gases are exposed to ultraviolet light, electrons captured by the magnetosphere of Saturn and cosmic rays. The Cassini/Huygens probe showed that the average temperature on the surface of Titan is 93.7 K, with lakes of liquid ethane and methane. Sub-surface mixtures of liquid ammonia and water may also be present. We have synthesized complex organic compounds (tholins) by exposing a mixture of nitrogen and methane to plasma discharges, and investigated their interactions with several different liquids that simulate Titan's liquidosphere. We found that coacervates formed when tholins were extracted in non-polar solvents followed by exposure to aqueous ammonia solutions. The results suggest that coacervates can self-assemble in Titan's liquidosphere which have the potential to undergo further chemical evolution. Similar processes are likely to occur in the early evolution of habitable planets when tholin-like compounds undergo phase separation into microscopic structures dispersed in a suitable aqueous environment. Copyright © Cambridge University Press 2013Â.

DOI： 10.1017/S1473550413000116

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

Aqueous solutions of 5-substituted hydantoins were irradiated with ultraviolet (UV) light, to investigate their structural stability against UV radiation as well as the possible photolysis products. The photolysis products were identified and the degree of photolysis was measured using reversed-phase and ion-exchange high-performance liquid chromatography. Hydantoin (2,4-imidazolidinedione) was dominantly detected as a photolysis product of 5-substituted hydantoins. With hydrolysis of UV-irradiated 5-substituted hydantoins, glycine and alanine were dominantly detected. These experimental results are important for the prebiotic photochemistry of 5-substituted hydantoins in the formation of hydantoin since they have been detected in Solar System materials. (C) 2013 COSPAR. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.asr.2013.01.029

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

Experimental simulations have previously shown that tholins (complex solid organics) can be abundantly formed in Titan's atmosphere and that they contain precursors of amino acids. In this study, we investigated their relevance to possible chemical evolution toward the generation of life in various potential Titan environments (liquidospheres), using tholins synthesized by plasma discharge at low pressure (LP, 26 Pa) and high pressure (HP, 133 Pa). We focused our study on composition of amino acids recovered from LP and HP tholins, as well as on the solubility of these tholins in solvents such as hexane, acetonitrile, ethanol, methanol, water, and ammonia water. Both hydrolyzed extracts of LP and HP tholins were composed of a wide variety of amino acids. Tholins were dissolved more easily in polar solvents than in nonpolar ones: Ammonia water, simulating a potential Titan subsurface ocean, could dissolve tholins quite efficiently. These results show thus the possibility of starting chemical evolution toward life's origin in Titan's environment.

DOI： 10.1246/cl.130101

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

We tested the stability and reaction of several amino acids using hydrothermal system simulators: an autoclave and two kinds of flow reactors at 200-250 A degrees C. This study generally showed that there is a variation in the individual amino acids survivability in the simulators. This is mainly attributed to the following factors; heat time, cold quenching exposure, metal ions and also silica. We observed that, in a rapid heating flow reactor, high aggregation and/or condensation of amino acids could occur even during a heat exposure of 2 min. We also monitored their stability in a reflow-type of simulator for 120 min at 20 min intervals. The non-hydrolyzed and hydrolyzed samples for this system showed a similar degradation only in the absence of metal ions.

DOI： 10.1007/s11084-013-9330-9

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：INTER-RESEARCH  

Protein biodegradation in the marine environment is caused by proteases derived from various organisms, including bacteria, which are considered to be a major source of these enzymes. We investigated the succession of bacterial proteases in seawater to determine the variation in protease activity over time. The potential activities of proteolytic enzymes in stored seawater and isolated bacteria were studied using 19 different synthetic oligopeptide substrates for aminopeptidase, trypsin, chymotrypsin and elastase. In time-course experiments carried out over 112 d, aminopeptidase activity increased, whereas trypsin activity decreased over time. Amino peptidase activity was mainly found in unfiltered seawater containing bacterial cells, whereas trypsin activity was mainly found in 0.2 mu m seawater filtrates. Individual bacterial isolates showed different proteolytic properties but all exhibited aminopeptidase activity. Members of the Gammaproteobacteria and Bacteroidetes showed high trypsin and chymotrypsin activities. Based on these results, we conclude that protein degradation in seawater occurs via the combined action of various bacterial proteases.

DOI： 10.3354/ame01618

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Language：English  

Although abiotic polymerization of amino acids is an important step in origin of life study, it has often eluded that their formation could be limited in the hydrothermal systems. To show this we heated an aqueous solution of several amino acids in a simulated hydrothermal environment to assess the possible formation of peptides among the heated products. Peptide concentrations estimated by the Lowry method were significantly higher when the mixture was heated at 300℃ than those at lower temperatures, despite having more than 80% of the initial amino acids decomposed. We also revealed that the peptides measured here were only part of the bonds in the heated products. The major heat products were non-peptide amino acid condensates (NPACs) that only possess partial peptide bonds. The role of NPACs should be examined though they were often ignored in the classical chemical evolution scenario so far.

CiNii Books

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Other Link： http://dl.ndl.go.jp/info:ndljp/pid/10488558

Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

It is generally thought that the terrestrial atmosphere at the time of the origin of life was CO2-rich and that organic compounds such as amino acids would not have been efficiently formed abiotically under such conditions. It has been pointed out, however, that the previously reported low yields of amino acids may have been partially due to oxidation by nitrite/nitrate during acid hydrolysis. Specifically, the yield of amino acids was found to have increased significantly (by a factor of several hundred) after acid hydrolysis with ascorbic acid as an oxidation inhibitor. However, it has not been shown that CO2 was the carbon source for the formation of the amino acids detected after acid hydrolysis with ascorbic acid. We therefore reinvestigated the prebiotic synthesis of amino acids in a CO2-rich atmosphere using an isotope labeling experiment. Herein, we report that ascorbic acid does not behave as an appropriate oxidation inhibitor, because it contributes amino acid contaminants as a consequence of its reactions with the nitrogen containing species and formic acid produced during the spark discharge experiment. Thus, amino acids are not efficiently formed from a CO2-rich atmosphere under the conditions studied.

DOI： 10.1007/s11084-012-9296-z

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

Submarine hydrothermal systems (SHSs) have been thought of as a suitable environment for the origin of life subsequent to the abiotic synthesis of organic molecules. However, it has been pointed out that bioorganic molecules, such as amino acids, are easily degraded at a high temperature, and thus not likely to survive for the next step of chemical evolution in a SHS environment. On the other hand, it has been suggested that the main compounds generated abiotically at the first stage of chemical evolution are not "free" amino acid monomers but amino acid precursors with high molecular weights, i.e., complex combined amino acids. In this study, we tested the stability of complex combined amino acids, which were abiotically synthesized from a simulated primitive Earth atmosphere with proton irradiation, in a high-temperature and high-pressure environment compared with that of monomeric amino acids. Complex combined amino acids preserved more amino acids (including amino acid precursors that give amino acids after acid hydrolysis) than free amino acids after heating in simulated SHS environments. Our results suggest the possibility that complex organics prebiotically synthesized by cosmic rays could serve as primitive materials of chemical evolution at hydrothermal systems on primitive Earth.

DOI： 10.1246/bcsj.20110349

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

We observed formation of organic aggregates from a solution of complex organics which were abiotically synthesized from a simulated primitive earth atmosphere with high-energy protons. The structure of the complex organics was partly altered under hydrothermal conditions to form organic aggregates. The aggregates possessed properties of combined amino acids, which had high tolerance against heating. Formation of this kind of organic aggregates might have been an important step in the chemical evolution leading to the origin of life.

DOI： 10.1246/cl.2012.441

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MDPI AG  

Aqueous solutions of isovaline and its precursor molecule, 5-ethyl-5-methylhydantoin, were irradiated with ultraviolet and gamma-ray photons, to evaluate their structural stability against space radiation. The degree of photolysis was measured and irradiation products were identified using chiral, reversed-phase and ion-exchange high-performance liquid chromatography. The experimental results show that the degree of photolysis of 5-ethyl-5-methylhydantoin is more significant than that of isovaline under ultraviolet light irradiation, while the results under gamma-ray irradiation are the opposite. As the products of isovaline photolysis, aspartic acid, serine, glutamic acid and alanine were dominantly detected.

DOI： 10.3390/ijms13011006

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Language：English   Publishing type：Research paper (scientific journal)  

Aqueous solutions of isovaline and its precursor molecule, 5-ethyl-5-methylhydantoin, were irradiated with ultraviolet and γ-ray photons, to evaluate their structural stability against space radiation. The degree of photolysis was measured and irradiation products were identified using chiral, reversed-phase and ion-exchange high-performance liquid chromatography. The experimental results show that the degree of photolysis of 5-ethyl-5-methylhydantoin is more significant than that of isovaline under ultraviolet light irradiation, while the results under γ-ray irradiation are the opposite. As the products of isovaline photolysis, aspartic acid, serine, glutamic acid and alanine were dominantly detected. © 2012 by the authors
licensee MDPI, Basel, Switzerland.

DOI： 10.3390/ijms13011006

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PubMed

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Language：English  

We present laboratory studies examining the photolysis products of isovaline (Ival) and its precursor molecule, 5-ethyl-5-methylhydantoin (EM-Hyd) against continuous ultraviolet (UV), monochromatic UV, and γ-ray photons. The irradiation experiments were performed with Ival and EM-Hyd in aqueous state. In both UV and γ-ray irradiation experiments, Ival produced serine and alanine as common photolysis products. On the other hand, hydantoin and 5-methylhydantoin were detected as photolysis products of irradiated EM-Hyd. This experimental result may point out the potential importance of the prebiotic photochemistry of Ival and EM-Hyd in Solar System materials.

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Other Link： http://dl.ndl.go.jp/info:ndljp/pid/10488493

Language：English   Publisher：THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES  

A wide variety of organic compounds have been detected in such extraterrestrial bodies as carbonaceous chondrites and comets. Amino acids have been confirmed in extracts from carbonaceous chondrites and cometary dusts. It was suggested that these organics were formed in quite cold environments. We irradiated possible interstellar media, such as a frozen mixture of methanol, ammonia and water, with high-energy particles. Amino acid precursors with high molecular weights were detected in the irradiated products. Such complex amino acid precursors are much more stable than free amino acids against radiation, and heat. It is suggested that interplanetary dust particles (IDPs) brought much more organics than meteorites and comets. However, characteristics of organic compounds in IDPs are little known, since they have been collected only in terrestrial biosphere. We are planning the Tanpopo Mission, where IDPs would be collected in aerogel equipped on the Exposure Facility of the International Space Station. In addition, amino acids and their relating compounds would be exposed to space environments to see their possible alteration processes.

DOI： 10.2322/tastj.10.Tp_7

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CiNii Books

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Other Link： http://iyokan.lib.ehime-u.ac.jp/dspace/handle/iyokan/1365

Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

Microbial degradation and utilization of proteins derived from bacterial detritus were investigated in a microcosm experiment using Pseudomonas aeruginosa detritus as a substrate. To assess the effects of natural marine microbial communities on degradation and utilization of protein derived from P. aeruginosa cells, four microcosms were prepared: natural seawater (containing the natural microbial community) with P. aeruginosa detritus (N+Pa), autoclaved seawater with P. aeruginosa detritus (A+Pa), natural seawater (N) and autoclaved seawater (A) without adding anything as a control. The numbers of total and growing bacterial cells, protease activity, and transition of P. aeruginosa proteins were monitored in the four microcosms. Changes in the numbers of total and growing bacterial cells and protease activities indicated that bacterial detritus significantly stimulated the microbial community in the microcosms. Both the surviving P. aeruginosa in A+Pa and natural microbial community in N+Pa microcosms were able to degrade and utilize P. aeruginosa detritus; however, the community in N+Pa including various microbes maintained high activity longer, indicating that diversity is an important factor in keeping the community active. Even under the very high protease activity in N+Pa, 39-kDa and 48-kDa proteins from P. aeruginosa remained in the microcosm during the entire experiment (150 days). Immunoblotting suggested the 48-kDa protein was an intact molecule of OprP, which had been detected from the dissolved fraction of natural seawater in previous studies. This result suggests that the protein molecules that had been detected from natural seawater actually had a high tolerance to microbial degradation.

DOI： 10.1007/s10872-010-0043-7

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DOI： 10.2174/187445080903010083

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

In aquatic environments extracellular enzymes are bound to microbial cells or exist in a free and adsorbed state. Various filters have been used to fractionate these enzymatic activities, but enzymes may be readily adsorbed onto some materials, and such adsorption can induce errors in the estimation of enzymatic activity. In this study we examined three filters to determine the most suitable filter for fractionation when estimating proteolytic enzyme activity in seawater. We found that the polycarbonate Nuclepore membrane, widely used for size fractionation because of its pore-size accuracy, was the most favorable for this purpose, even though it adsorbed slightly more enzymes than the low-protein-binding polyethersulfone membrane. We also found that trypsin- and chymotrypsin-type enzymes were more easily adsorbed than aminopeptidases.

DOI： 10.1007/s10872-008-0029-x

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：INTER-RESEARCH  

We analyzed potential activities of different proteolytic enzymes in size-fractionated seawater, and estimated the contribution of each size fraction (&lt; 0.2, 0.2-0.8, 0.8-5, and &gt; 5 mu m) to the bulk hydrolytic activity of each enzyme in the seawater. The activity of leucine-aminopeptidase was highly attributed to cell-associated size fractions, while the contribution of the dissolved fraction (&lt; 0.2 mu m) to the bulk activity was only 10 to 30 %. In contrast, the contribution of the dissolved fraction to the activities of the trypsin- and chymotrypsin-type endopeptidases was as high as 40 to 80 % of their bulk activities measured in unfiltered seawater. These results indicated the potential importance of free proteolytic enzymes in seawater, especially for endopeptidases. Significant enzymatic activity in the dissolved fraction was also detected from experiments with isolated bacteria, suggesting that direct secretion of proteases from marine bacteria into surrounding water could be at least one of the sources of the dissolved proteolytic enzymes in seawater. Generally, the natural bacterial community of seawater was able to hydrolyze all of the 16 tested substrates, but at different rates. Selected members of the community (3 bacterial isolates and Synechococcus) hydrolyzed only one or a few of the applied substrates, and the substrate preference varied among the strains. These results suggest that natural bacterial communities are composed of a great variety of bacterial species with different (specific) enzymatic properties, including dissolved endopeptidases and cell-associated aminopeptidase. The combined activities of these enzymes are responsible for an effective degradation and re-use of high molecular weight organic matter at the community level.

DOI： 10.3354/ame01169

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：INTER-RESEARCH  

Planktonic food webs are primarily dependent on organic matter derived from phytoplankton. In coastal areas, aquaculture has accelerated in recent decades, and attached algae and invertebrates proliferate on the farming cages. We hypothesized that the organic material on the farm structures is important to planktonic food webs and that the effects of aquaculture differ between fish (fertilized) and pearl oyster farms (not fertilized). To test these hypotheses, we examined the planktonic food webs at fish and pearl oyster farms using stable isotopes in the Uwa Sea, Japan. We collected zooplankton, particulate organic matter (POM, predominantly phytoplankton), attached algae, and macroinvertebrates in July 2005 and February 2006. Based on the isotope mixing model results, the attached microalgae contributed up to approximately 70% of the copepod food sources, and the contribution of attached microalgae to cyclopoid copepods was similar to their contribution to attached macroinvertebrates. Amphipods mainly fed on planktonic detritus from microalgae that had detached from the farm structures. The contribution of attached microalgae to copepod biomass was lower on the pearl oyster farm than on the fish farm. Our results show that attached microalgae from sea farms are important food sources for planktonic food webs in areas with fish farms and that the 2 food webs, attached and pelagic, are coupled through zooplankton grazing.

DOI： 10.3354/meps07202

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：INTER-RESEARCH  

A 'Kyucho' (an intrusion of warm surface water) occurs in the Bungo Channel, located in southwestern Japan. The abundances of Prochlorococcus and Synechococcus during a Kyucho, together with physical and chemical environmental factors, were investigated from the Kuroshio region to the Seto Inland Sea, via Bungo Channel, from 26 November to 5 December 2003. With the occurrence of the Kyucho, oceanic water intruded from the Kuroshio region into the middle of the Bungo Channel. The abundance of Prochlorococcus was the highest in the Kuroshio region and the southern part of the Bungo Channel (&gt; 25 x 10(3) cells ml(-1)), low in the northern part of the Bungo Channel (&lt; 1 x 10(3) cells ml(-1)), and below detection levels in the Seto Inland Sea. A relatively high abundance of Synechococcus cells (&gt; 15 x 10(3) cells ml(-1)) was detected in the Kuroshio region and in the southern part of the Bungo Channel, but the abundance (&lt; 6 x 10(3) cells ml(-1)) was low in other regions. In the Kuroshio region and the southern part of the Bungo Channel, high-phycourobilin (PUB)-type cells were dominant (&gt; 90%); at this location, most of the available light in the deeper layer (&gt; 25 m depth) was in the 450 to 500 nm range, corresponding to the peak absorbance of PUB. In contrast, the abundance of low-PUB-type cells accounted for &gt; 75% of the total in the northern part of the Bungo Channel and in the Seto Inland Sea, where most of the available light in the deeper layer (&gt; 10 m depth) was in the 480 to 560 nm range, including the peak absorbance of both PUB and phycoerythrobilin (PEB). These results indicate that Synechococcus cells of high-PUB type, which have a higher Ex 495:545 (&gt; 1.5; ratio of orange fluorescence intensity excited at 495 nm to that at 545 nm), as well as Prochlorococcus cells were advected to the Bungo Channel by the Kyucho. The co-occurrence of the 2 pigment types of Synechococcus in coastal waters is highly affected by a physical process, such as the Kyucho.

DOI： 10.3354/ame046191

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Language：English  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER SOC LIMNOLOGY OCEANOGRAPHY  

We assayed proteolytic enzymes in coastal surface seawater using 16 types of fluorogenic substrates, including those for aminopeptidase, trypsin, elastase, and chymotrypsin. Hydrolysis rates were similar or higher for substrates of trypsin and chymotrypsin than for those of aminopeptidase. Substrates for elastase were hardly hydrolyzed. The results strongly suggest trypsin-type and chymotrypsin-type endopeptidases and aminopeptidases were present in the seawater. In most previous studies of proteolytic enzymes in aquatic environments, leucine-aminopeptidase activity measured using a fluorogenic substrate has been used as a model of proteolytic activity. From the results of this study using various peptide analog fluorogenic substrates, the significance of endopeptidases, which could play a key role in downsizing of dissolved proteins and polypeptides to oligopeptides prior to microbial respiration, was confirmed.

DOI： 10.4319/lo.2005.50.2.0722

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Pigment-based growth rates of phytoplankton and mortality rates due to microzooplankton grazing were estimated using a dilution method combined with high-performance liquid chromatography (HPLC) pigment analysis in the northwestern North Pacific in autumn 1998. The dilution experiments were conducted at different hydrographic stations in both colder and warmer water masses. No significant difference was found between the growth rate of the phytoplankton community (0.38-0.70 day(-1); estimated by chlorophyll a) at the colder and warmer water stations, while the mortality rate (0.15-0.88 day(-1); estimated by chlorophyll a) tended to be higher at warmer water stations. The combination of estimates of daily chlorophyll a production and particulate organic carbon (POC) production enabled us to assess the carbon to chlorophyll a ratio (C/chl a) of "new" organic matter produced by living phytoplankton. The method provided an implicit value of the C/chl a of in situ living phytoplankton. The rate estimates from taxon-specific pigments suggested a possibility that chlorophyll b-containing green algae were grazed preferentially by microzooplankton during their active growth, and the standing stock of green algae was more strictly controlled by micrograzer than other algal groups such as diatoms. This result is one possible explanation for the fact that blooms of green algae have not been reported in the open ocean, in contrast with diatoms. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0022-0981(02)00365-9

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Particulate matter in surface waters of the northern North Pacific and the southern Bering Sea was analyzed for the spatial and temporal distribution of chlorophyll and carotenoid pigment compositions by high-performance liquid chromatography (HPLC). Samples were collected during 11 ship of opportunity cruises between Canada and Japan from April 1995 to June 1996. The cruises each took 13 days and were conducted every six weeks. Seasonal variability of the concentration of chlorophyll a showed different features among the three areas studied: the Alaskan Gyre (eastern part of the subarctic North Pacific), southern Baring Sea, and the area off the Kuril Islands (western part of the subarctic North Pacific). In the Alaskan Gyre, the concentrations of chlorophyll a were around 0.2-0.4 mug/l without any remarkable seasonal variation, consistent with previous studies. In the Bering Sea and the area off the Kuril Islands, a drastic change in chlorophyll a biomass was observed from spring to early summer, with extremely high levels, &gt; 2 mug/l being found. The composition of the phytoplankton community was estimated by multiple regression analysis. A high concentration of chlorophyll a exceeding 1 mug/l was always accompanied by a high contribution of fucoxanthin-containing diatoms constituting up to 90% of the total chlorophyll a biomass, Chlorophyll b-containing green algae were one of the important algal groups in the northern North Pacific throughout the year as were fucoxanthin-containing diatoms and 19'-hexanoyloxyfucoxanthin-containing prymnesiophytes. The results give new insights into the phytoplankton community structure of the subarctic North Pacific, namely, an ubiquitous basic structure made up of rather diverse algal groups, and a flourishing diatom population limited by area and season and superimposed on the basic structure. These two structures are thought to pray their respective roles in the biogeochemical cycle in the surface of the northern North Pacific. (C) 2000 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0967-0637(00)00036-4

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Language：English  

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