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Mohamed Laabir - One of the best experts on this subject based on the ideXlab platform.
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in silico prediction of the secretome from the invasive neurotoxic marine dinoflagellate Alexandrium catenella
Environmental Microbiology Reports, 2019Co-Authors: Cherif Chetouhi, Estelle Masseret, Mohamed Laabir, Natacha JeanAbstract:Alexandrium catenella, a marine dinoflagellate responsible for harmful algal blooms (HABs), proliferates with greater frequency, distribution and intensity, in disturbed marine coastal ecosystems. The proteins secreted into seawater may play a crucial role in maintaining this dinoflagellate in these ecosystems, but this possibility has never been investigated before. In this study, the A. catenella secretome was predicted from its transcriptome by combining several bioinformatics tools. Our results predict a secretome of 2 779 proteins, among which 79% contain less than 500 amino acids, suggesting that most secreted proteins are short in length. The predicted secretome includes 963 proteins (35%) with Pfam domains: 773 proteins with one Pfam domain and 190 proteins with two or more Pfam domains. Their functional annotation showed that they are mainly involved in (i) proteolysis, (ii) stress responses and (iii) primary metabolism. In addition, 47% of the secreted proteins appear to be enzymes, primarily peptidases, known to be biologically active in the extracellular medium during stress responses. Finally, this study provides a wealth of candidates of proteins secreted by A. catenella, which may interact with the marine environment and help this dinoflagellate develop in various environmental conditions.
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Exposure to the Paralytic Shellfish Toxin Producer Alexandrium catenella Increases the Susceptibility of the Oyster Crassostrea gigas to Pathogenic Vibrios
Toxins, 2016Co-Authors: Celina Abi-khalil, Carmen Lopez-joven, Véronique Savar, Zouher Amzil, Eric Abadie, Mohamed Laabir, Jean-luc RollandAbstract:The multifactorial etiology of massive Crassostrea gigas summer mortalities results from complex interactions between oysters, opportunistic pathogens and environmental factors. In a field survey conducted in 2014 in the Mediterranean Thau Lagoon (France), we evidenced that the development of the toxic dinoflagellate Alexandrium catenella, which produces paralytic shellfish toxins (PSTs), was concomitant with the accumulation of PSTs in oyster flesh and the occurrence of C. gigas mortalities. In order to investigate the possible role of toxic algae in this complex disease, we experimentally infected C. gigas oyster juveniles with Vibrio tasmaniensis strain LGP32, a strain associated with oyster summer mortalities, after oysters were exposed to Alexandrium catenella. Exposure of oysters to A. catenella significantly increased the susceptibility of oysters to V. tasmaniensis LGP32. On the contrary, exposure to the non-toxic dinoflagellate Alexandrium tamarense or to the haptophyte Tisochrysis lutea used as a foraging alga did not increase susceptibility to V. tasmaniensis LGP32. This study shows for the first time that A. catenella increases the susceptibility of Crassostrea gigas to pathogenic vibrios. Therefore, in addition to complex environmental factors explaining the mass mortalities of bivalve mollusks, feeding on neurotoxic dinoflagellates should now be considered as an environmental factor that potentially increases the severity of oyster mortality events.
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influence of environmental factors on the paralytic shellfish toxin content and profile of Alexandrium catenella dinophyceae isolated from the mediterranean sea
Marine Drugs, 2013Co-Authors: Mohamed Laabir, Véronique Savar, Eric Abadie, Estelle Masseret, Daniel Grzebyk, Yves Collos, Manoella Sibat, Zouher AmzilAbstract:Laboratory experiments were designed to study the toxin content and profile of the Alexandrium catenella strain ACT03 (isolated from Thau Lagoon, French Mediterranean) in response to abiotic environmental factors under nutrient-replete conditions. This dinoflagellate can produce various paralytic shellfish toxins with concentrations ranging from 2.9 to 50.3 fmol/cell. The toxin profile was characterized by carbamate toxins (GTX3, GTX4 and GTX5) and N-sulfocarbamoyl toxins (C1, C2, C3 and C4). C2 dominated at 12-18 ° C, but only for salinities ranging from 10 to 25 psu, whereas GTX5 became dominant at temperatures ranging from 21 to 30 ° C at almost all salinities. There was no significant variation in the cellular toxin amount from 18 ° C to 27 ° C for salinities ranging between 30 and 40 psu. At salinities of 10 to 25 psu, the toxin concentrations always remained below 20 fmol/cell. Toxin content was stable for irradiance ranging from 10 to 70 μmol photons/m 2 /s then slightly increased. Overall, the toxin profile
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influences of sedimentation and hydrodynamics on the spatial distribution of Alexandrium catenella tamarense resting cysts in a shellfish farming lagoon impacted by toxic blooms
Harmful Algae, 2013Co-Authors: Benjamin Genovesi, Annie Fiandrino, Thierry Laugier, Andre Vaquer, Mohamed Laabir, David Mouillot, Daniel GrzebykAbstract:Abstract Since resting cysts are a potential seeding source for blooms, the presence of these cysts in sediments is a marker of an established population for a number of harmful algal species. The spatial patterns of cyst density in relation to sediment characteristics and hydrodynamics are still largely misunderstood. This study investigated the spatial distribution of resting cysts belonging to the Alexandrium tamarense species complex (Dinophyceae) in sediments of a Mediterranean coastal lagoon (Thau Lagoon, France). This lagoon, hosting shellfish farming, is regularly impacted by toxic Alexandrium catenella blooms. The average cyst density across the whole lagoon was rather low,
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Influences of sedimentation and hydrodynamics on the spatial distribution of Alexandrium catenella/tamarense resting cysts in a shellfish farming lagoon impacted by toxic blooms
Harmful Algae, 2013Co-Authors: Benjamin Genovesi, Annie Fiandrino, Thierry Laugier, Andre Vaquer, Mohamed Laabir, David Mouillot, Daniel GrzebykAbstract:Abstract Since resting cysts are a potential seeding source for blooms, the presence of these cysts in sediments is a marker of an established population for a number of harmful algal species. The spatial patterns of cyst density in relation to sediment characteristics and hydrodynamics are still largely misunderstood. This study investigated the spatial distribution of resting cysts belonging to the Alexandrium tamarense species complex (Dinophyceae) in sediments of a Mediterranean coastal lagoon (Thau Lagoon, France). This lagoon, hosting shellfish farming, is regularly impacted by toxic Alexandrium catenella blooms. The average cyst density across the whole lagoon was rather low,
Yves Collos - One of the best experts on this subject based on the ideXlab platform.
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comparing diatom and Alexandrium catenella tamarense blooms in thau lagoon importance of dissolved organic nitrogen in seasonally n limited systems
Harmful Algae, 2014Co-Authors: Yves Collos, Widya Ratmaya, Cecile Jauzein, Philippe Souchu, Eric Abadie, Andre VaquerAbstract:Abstract Diatom blooms in Thau lagoon are always related to rain events leading to inputs of inorganic nutrients such as phosphate, ammonium and nitrate through the watershed with time lags of about 1 week. In contrast, blooms of Alexandrium catenella/tamarense can occur following periods of 3 weeks without precipitation and no significant input of conventional nutrients such as nitrate and phosphate. Field results also indicate a significant drop (from 22–25 to 15–16 μM over 3 days) in dissolved organic nitrogen (DON) at the bloom peak, as well as a significant inverse relationship between A. catenella/tamarense cell density and DON concentrations that is not apparent for diatom blooms. Such dinoflagellate blooms are also associated with elevated (6–9 μM) ammonium concentrations, a curious feature also observed by other investigators, possibly the results of ammonium excretion by this organism during urea or other organic nitrogen assimilation. The potential use of DON by this organism represents short cuts in the nitrogen cycle between plants and nutrients and requires a new model for phytoplankton growth that is different from the classical diatom bloom model. In contrast to such diatom blooms that are due to conventional (nitrate, phosphate) nutrient pulses, Alexandrium catenella/tamarense blooms on the monthly time scale are due to organic nutrient enrichment, a feature that allows net growth rates of about 1.3 d −1 , a value higher than that generally attributed to such organisms.
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A comparative analysis of Alexandrium catenella/tamarense blooms in Annaba Bay (Algeria) and Thau lagoon (France); phosphorus limitation as a trigger.
Comptes Rendus Biologies, 2014Co-Authors: Imene Hadjadji, Hocine Frehi, Lembarek Ayada, Eric Abadie, Yves CollosAbstract:Environmental conditions ultimately leading to blooms of the toxic dinoflagellate Alexandrium catenella/tamarense were investigated at two Mediterranean sites (Annaba Bay, Algeria and Thau lagoon, France). Three years were examined in details: 1992 (a pre-Alexandrium period), 2002 (a year with the first bloom in Annaba) and 2010 (a year with a major bloom in Annaba). Most conditions were similar, but ammonium concentrations were much higher in Annaba (up to 100 μM) than in Thau (up to 10 μM). First records of A. catenella/tamarense were in 1995 for Thau and 2002 for Annaba, and coincided with soluble reactive phosphorus (SRP) decreasing below a concentration of about 1 μM. No other environmental variable could be related to those blooms. Thus, it is likely that the large reductions in SRP at both sites led to phosphorus limitation of a certain number of phytoplankton species and favored the development of A. catenella/tamarense.
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a comparative analysis of Alexandrium catenella tamarense blooms in annaba bay algeria and thau lagoon france phosphorus limitation as a trigger
Comptes Rendus Biologies, 2014Co-Authors: Imene Hadjadji, Hocine Frehi, Lembarek Ayada, Eric Abadie, Yves CollosAbstract:Environmental conditions ultimately leading to blooms of the toxic dinoflagellate Alexandrium catenella/tamarense were investigated at two Mediterranean sites (Annaba Bay, Algeria and Thau lagoon, France). Three years were examined in details: 1992 (a pre-Alexandrium period), 2002 (a year with the first bloom in Annaba) and 2010 (a year with a major bloom in Annaba). Most conditions were similar, but ammonium concentrations were much higher in Annaba (up to 100 μM) than in Thau (up to 10 μM). First records of A. catenella/tamarense were in 1995 for Thau and 2002 for Annaba, and coincided with soluble reactive phosphorus (SRP) decreasing below a concentration of about 1 μM. No other environmental variable could be related to those blooms. Thus, it is likely that the large reductions in SRP at both sites led to phosphorus limitation of a certain number of phytoplankton species and favored the development of A. catenella/tamarense.
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Comparing diatom and Alexandrium catenella/tamarense blooms in Thau lagoon: Importance of dissolved organic nitrogen in seasonally N-limited systems
Harmful Algae, 2014Co-Authors: Yves Collos, Widya Ratmaya, Cecile Jauzein, Philippe Souchu, Eric Abadie, Andre VaquerAbstract:Abstract Diatom blooms in Thau lagoon are always related to rain events leading to inputs of inorganic nutrients such as phosphate, ammonium and nitrate through the watershed with time lags of about 1 week. In contrast, blooms of Alexandrium catenella/tamarense can occur following periods of 3 weeks without precipitation and no significant input of conventional nutrients such as nitrate and phosphate. Field results also indicate a significant drop (from 22–25 to 15–16 μM over 3 days) in dissolved organic nitrogen (DON) at the bloom peak, as well as a significant inverse relationship between A. catenella/tamarense cell density and DON concentrations that is not apparent for diatom blooms. Such dinoflagellate blooms are also associated with elevated (6–9 μM) ammonium concentrations, a curious feature also observed by other investigators, possibly the results of ammonium excretion by this organism during urea or other organic nitrogen assimilation. The potential use of DON by this organism represents short cuts in the nitrogen cycle between plants and nutrients and requires a new model for phytoplankton growth that is different from the classical diatom bloom model. In contrast to such diatom blooms that are due to conventional (nitrate, phosphate) nutrient pulses, Alexandrium catenella/tamarense blooms on the monthly time scale are due to organic nutrient enrichment, a feature that allows net growth rates of about 1.3 d −1 , a value higher than that generally attributed to such organisms.
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influence of environmental factors on the paralytic shellfish toxin content and profile of Alexandrium catenella dinophyceae isolated from the mediterranean sea
Marine Drugs, 2013Co-Authors: Mohamed Laabir, Véronique Savar, Eric Abadie, Estelle Masseret, Daniel Grzebyk, Yves Collos, Manoella Sibat, Zouher AmzilAbstract:Laboratory experiments were designed to study the toxin content and profile of the Alexandrium catenella strain ACT03 (isolated from Thau Lagoon, French Mediterranean) in response to abiotic environmental factors under nutrient-replete conditions. This dinoflagellate can produce various paralytic shellfish toxins with concentrations ranging from 2.9 to 50.3 fmol/cell. The toxin profile was characterized by carbamate toxins (GTX3, GTX4 and GTX5) and N-sulfocarbamoyl toxins (C1, C2, C3 and C4). C2 dominated at 12-18 ° C, but only for salinities ranging from 10 to 25 psu, whereas GTX5 became dominant at temperatures ranging from 21 to 30 ° C at almost all salinities. There was no significant variation in the cellular toxin amount from 18 ° C to 27 ° C for salinities ranging between 30 and 40 psu. At salinities of 10 to 25 psu, the toxin concentrations always remained below 20 fmol/cell. Toxin content was stable for irradiance ranging from 10 to 70 μmol photons/m 2 /s then slightly increased. Overall, the toxin profile
Andre Vaquer - One of the best experts on this subject based on the ideXlab platform.
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comparing diatom and Alexandrium catenella tamarense blooms in thau lagoon importance of dissolved organic nitrogen in seasonally n limited systems
Harmful Algae, 2014Co-Authors: Yves Collos, Widya Ratmaya, Cecile Jauzein, Philippe Souchu, Eric Abadie, Andre VaquerAbstract:Abstract Diatom blooms in Thau lagoon are always related to rain events leading to inputs of inorganic nutrients such as phosphate, ammonium and nitrate through the watershed with time lags of about 1 week. In contrast, blooms of Alexandrium catenella/tamarense can occur following periods of 3 weeks without precipitation and no significant input of conventional nutrients such as nitrate and phosphate. Field results also indicate a significant drop (from 22–25 to 15–16 μM over 3 days) in dissolved organic nitrogen (DON) at the bloom peak, as well as a significant inverse relationship between A. catenella/tamarense cell density and DON concentrations that is not apparent for diatom blooms. Such dinoflagellate blooms are also associated with elevated (6–9 μM) ammonium concentrations, a curious feature also observed by other investigators, possibly the results of ammonium excretion by this organism during urea or other organic nitrogen assimilation. The potential use of DON by this organism represents short cuts in the nitrogen cycle between plants and nutrients and requires a new model for phytoplankton growth that is different from the classical diatom bloom model. In contrast to such diatom blooms that are due to conventional (nitrate, phosphate) nutrient pulses, Alexandrium catenella/tamarense blooms on the monthly time scale are due to organic nutrient enrichment, a feature that allows net growth rates of about 1.3 d −1 , a value higher than that generally attributed to such organisms.
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Comparing diatom and Alexandrium catenella/tamarense blooms in Thau lagoon: Importance of dissolved organic nitrogen in seasonally N-limited systems
Harmful Algae, 2014Co-Authors: Yves Collos, Widya Ratmaya, Cecile Jauzein, Philippe Souchu, Eric Abadie, Andre VaquerAbstract:Abstract Diatom blooms in Thau lagoon are always related to rain events leading to inputs of inorganic nutrients such as phosphate, ammonium and nitrate through the watershed with time lags of about 1 week. In contrast, blooms of Alexandrium catenella/tamarense can occur following periods of 3 weeks without precipitation and no significant input of conventional nutrients such as nitrate and phosphate. Field results also indicate a significant drop (from 22–25 to 15–16 μM over 3 days) in dissolved organic nitrogen (DON) at the bloom peak, as well as a significant inverse relationship between A. catenella/tamarense cell density and DON concentrations that is not apparent for diatom blooms. Such dinoflagellate blooms are also associated with elevated (6–9 μM) ammonium concentrations, a curious feature also observed by other investigators, possibly the results of ammonium excretion by this organism during urea or other organic nitrogen assimilation. The potential use of DON by this organism represents short cuts in the nitrogen cycle between plants and nutrients and requires a new model for phytoplankton growth that is different from the classical diatom bloom model. In contrast to such diatom blooms that are due to conventional (nitrate, phosphate) nutrient pulses, Alexandrium catenella/tamarense blooms on the monthly time scale are due to organic nutrient enrichment, a feature that allows net growth rates of about 1.3 d −1 , a value higher than that generally attributed to such organisms.
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influences of sedimentation and hydrodynamics on the spatial distribution of Alexandrium catenella tamarense resting cysts in a shellfish farming lagoon impacted by toxic blooms
Harmful Algae, 2013Co-Authors: Benjamin Genovesi, Annie Fiandrino, Thierry Laugier, Andre Vaquer, Mohamed Laabir, David Mouillot, Daniel GrzebykAbstract:Abstract Since resting cysts are a potential seeding source for blooms, the presence of these cysts in sediments is a marker of an established population for a number of harmful algal species. The spatial patterns of cyst density in relation to sediment characteristics and hydrodynamics are still largely misunderstood. This study investigated the spatial distribution of resting cysts belonging to the Alexandrium tamarense species complex (Dinophyceae) in sediments of a Mediterranean coastal lagoon (Thau Lagoon, France). This lagoon, hosting shellfish farming, is regularly impacted by toxic Alexandrium catenella blooms. The average cyst density across the whole lagoon was rather low,
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Influences of sedimentation and hydrodynamics on the spatial distribution of Alexandrium catenella/tamarense resting cysts in a shellfish farming lagoon impacted by toxic blooms
Harmful Algae, 2013Co-Authors: Benjamin Genovesi, Annie Fiandrino, Thierry Laugier, Andre Vaquer, Mohamed Laabir, David Mouillot, Daniel GrzebykAbstract:Abstract Since resting cysts are a potential seeding source for blooms, the presence of these cysts in sediments is a marker of an established population for a number of harmful algal species. The spatial patterns of cyst density in relation to sediment characteristics and hydrodynamics are still largely misunderstood. This study investigated the spatial distribution of resting cysts belonging to the Alexandrium tamarense species complex (Dinophyceae) in sediments of a Mediterranean coastal lagoon (Thau Lagoon, France). This lagoon, hosting shellfish farming, is regularly impacted by toxic Alexandrium catenella blooms. The average cyst density across the whole lagoon was rather low,
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dark metabolism and carbon nitrogen uncoupling in the toxic dinoflagellate Alexandrium catenella dinophyceae
Harmful Algae, 2011Co-Authors: Cecile Jauzein, Yves Collos, Mohamed Laabir, Andre VaquerAbstract:Uptake rates of three potential N-sources (ammonium, nitrate and N-urea) and two potential C-sources (HCO(3)(-) and C-urea) were estimated during growth of Alexandrium catenella in both light and dark phases. According to the variations observed in (13)C-isotopic ratio, A. catenella cells were not able to use C-urea. Furthermore, decreases in (13)C cell content during darkness revealed a probably high involvement of C recently fixed in dark respiration. Dark N-uptake capacities of A. catenella were characterized by dark/light uptake ratio of 27%, 43% and 65% for NO(3)(-), NH(4)(+) and N-urea, respectively. An accumulation of C-rich compounds during the light period was highlighted through strong diel variations in C:N ratio and would provide C and energy for these dark uptake processes indicating an uncoupling between N and C metabolism. Total costs in terms of C associated with dark N-uptake and assimilation were estimated and revealed that the main part of those costs may be associated with maintenance metabolism in A. catenella cells. The relatively low C-costs of biosynthesis in darkness suggest that dark uptake and C-storage strategies correspond to a benefit in terms of competitiveness for A. catenella, optimized by the migrating abilities of this species. (C) 2011 Elsevier B.V. All rights reserved.
Daniel Grzebyk - One of the best experts on this subject based on the ideXlab platform.
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influence of environmental factors on the paralytic shellfish toxin content and profile of Alexandrium catenella dinophyceae isolated from the mediterranean sea
Marine Drugs, 2013Co-Authors: Mohamed Laabir, Véronique Savar, Eric Abadie, Estelle Masseret, Daniel Grzebyk, Yves Collos, Manoella Sibat, Zouher AmzilAbstract:Laboratory experiments were designed to study the toxin content and profile of the Alexandrium catenella strain ACT03 (isolated from Thau Lagoon, French Mediterranean) in response to abiotic environmental factors under nutrient-replete conditions. This dinoflagellate can produce various paralytic shellfish toxins with concentrations ranging from 2.9 to 50.3 fmol/cell. The toxin profile was characterized by carbamate toxins (GTX3, GTX4 and GTX5) and N-sulfocarbamoyl toxins (C1, C2, C3 and C4). C2 dominated at 12-18 ° C, but only for salinities ranging from 10 to 25 psu, whereas GTX5 became dominant at temperatures ranging from 21 to 30 ° C at almost all salinities. There was no significant variation in the cellular toxin amount from 18 ° C to 27 ° C for salinities ranging between 30 and 40 psu. At salinities of 10 to 25 psu, the toxin concentrations always remained below 20 fmol/cell. Toxin content was stable for irradiance ranging from 10 to 70 μmol photons/m 2 /s then slightly increased. Overall, the toxin profile
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influences of sedimentation and hydrodynamics on the spatial distribution of Alexandrium catenella tamarense resting cysts in a shellfish farming lagoon impacted by toxic blooms
Harmful Algae, 2013Co-Authors: Benjamin Genovesi, Annie Fiandrino, Thierry Laugier, Andre Vaquer, Mohamed Laabir, David Mouillot, Daniel GrzebykAbstract:Abstract Since resting cysts are a potential seeding source for blooms, the presence of these cysts in sediments is a marker of an established population for a number of harmful algal species. The spatial patterns of cyst density in relation to sediment characteristics and hydrodynamics are still largely misunderstood. This study investigated the spatial distribution of resting cysts belonging to the Alexandrium tamarense species complex (Dinophyceae) in sediments of a Mediterranean coastal lagoon (Thau Lagoon, France). This lagoon, hosting shellfish farming, is regularly impacted by toxic Alexandrium catenella blooms. The average cyst density across the whole lagoon was rather low,
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Influences of sedimentation and hydrodynamics on the spatial distribution of Alexandrium catenella/tamarense resting cysts in a shellfish farming lagoon impacted by toxic blooms
Harmful Algae, 2013Co-Authors: Benjamin Genovesi, Annie Fiandrino, Thierry Laugier, Andre Vaquer, Mohamed Laabir, David Mouillot, Daniel GrzebykAbstract:Abstract Since resting cysts are a potential seeding source for blooms, the presence of these cysts in sediments is a marker of an established population for a number of harmful algal species. The spatial patterns of cyst density in relation to sediment characteristics and hydrodynamics are still largely misunderstood. This study investigated the spatial distribution of resting cysts belonging to the Alexandrium tamarense species complex (Dinophyceae) in sediments of a Mediterranean coastal lagoon (Thau Lagoon, France). This lagoon, hosting shellfish farming, is regularly impacted by toxic Alexandrium catenella blooms. The average cyst density across the whole lagoon was rather low,
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gene expression in proliferating cells of the dinoflagellate Alexandrium catenella dinophyceae
Applied and Environmental Microbiology, 2010Co-Authors: Eve Toulza, Yves Collos, Mohamed Laabir, Misun Shin, Guillaume Blanc, Stephane Audic, Jeanmichel Claverie, Daniel GrzebykAbstract:Understanding the conditions leading to harmful algal blooms, especially those produced by toxic dinoflagellate species, is important for environmental and health safety. In addition to investigations into the environmental conditions necessary for the formation of toxic blooms, we postulate that investigating gene expression in proliferating cells is essential for understanding bloom dynamics. Expressed sequence tags were produced from cultured cells of the toxic dinoflagellate Alexandrium catenella sampled during the initiation phase of growth using Sanger's method and by 454 pyrosequencing. A significant proportion of identified genes (ca. 25%) represented enzymes and proteins that participate in a variety of cellular regulatory mechanisms that may characterize proliferating cells, e.g., control of the cell cycle and division, regulation of transcription, translation and posttranslational protein modifications, signaling, intracellular trafficking, and transport. All of the several genes selected for gene expression assays due to their involvement in metabolism and the cell cycle were overexpressed during exponential growth. These data will be useful for investigating the mechanisms underlying growth and toxin production in toxic Alexandrium species and for studying and monitoring the development of toxic blooms.
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development of compound microsatellite markers in the toxic dinoflagellate Alexandrium catenella dinophyceae
Plankton and Benthos Research, 2007Co-Authors: Goh Nishitani, Nina Yasuda, C L Lian, Shigeru Itakura, Patrick Berrebi, Estelle Masseret, Daniel Grzebyk, Satoshi Nagai, S. Yamaguchi, Masashi SekinoAbstract:In this study, we identified 9 polymorphic compound microsatellite markers in the toxic dinoflagellate Alexandrium catenella, which was isolated from Thau lagoon (France, Mediterranean Sea), using the compound microsatellite marker technique. These new microsatellites were characterized by screening DNA templates from 43 A. catenella clonal strains, which were collected from a seawater sample from Inokushi Bay (Oita Prefecture, Japan). These loci provide one class of highly variable genetic marker: the number of alleles ranged from 3 to 8, and the estimate of gene diversity varied between 0.285 and 0.762. We also analyzed the same 43 DNA samples using microsatellite markers previously identified for A. catenella, comparing the PCR amplification success, the number of alleles and gene diversity. These three parameters were not significantly different, showing that the compound microsatellite markers have the same potential to reveal A. catenella genetic structure. This simple and efficient method reduces the costs for developing SSR markers and for analyzing the genetic structure of populations, therefore, suggesting the effectiveness of applying this method to other species.
Philippe Souchu - One of the best experts on this subject based on the ideXlab platform.
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comparing diatom and Alexandrium catenella tamarense blooms in thau lagoon importance of dissolved organic nitrogen in seasonally n limited systems
Harmful Algae, 2014Co-Authors: Yves Collos, Widya Ratmaya, Cecile Jauzein, Philippe Souchu, Eric Abadie, Andre VaquerAbstract:Abstract Diatom blooms in Thau lagoon are always related to rain events leading to inputs of inorganic nutrients such as phosphate, ammonium and nitrate through the watershed with time lags of about 1 week. In contrast, blooms of Alexandrium catenella/tamarense can occur following periods of 3 weeks without precipitation and no significant input of conventional nutrients such as nitrate and phosphate. Field results also indicate a significant drop (from 22–25 to 15–16 μM over 3 days) in dissolved organic nitrogen (DON) at the bloom peak, as well as a significant inverse relationship between A. catenella/tamarense cell density and DON concentrations that is not apparent for diatom blooms. Such dinoflagellate blooms are also associated with elevated (6–9 μM) ammonium concentrations, a curious feature also observed by other investigators, possibly the results of ammonium excretion by this organism during urea or other organic nitrogen assimilation. The potential use of DON by this organism represents short cuts in the nitrogen cycle between plants and nutrients and requires a new model for phytoplankton growth that is different from the classical diatom bloom model. In contrast to such diatom blooms that are due to conventional (nitrate, phosphate) nutrient pulses, Alexandrium catenella/tamarense blooms on the monthly time scale are due to organic nutrient enrichment, a feature that allows net growth rates of about 1.3 d −1 , a value higher than that generally attributed to such organisms.
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Comparing diatom and Alexandrium catenella/tamarense blooms in Thau lagoon: Importance of dissolved organic nitrogen in seasonally N-limited systems
Harmful Algae, 2014Co-Authors: Yves Collos, Widya Ratmaya, Cecile Jauzein, Philippe Souchu, Eric Abadie, Andre VaquerAbstract:Abstract Diatom blooms in Thau lagoon are always related to rain events leading to inputs of inorganic nutrients such as phosphate, ammonium and nitrate through the watershed with time lags of about 1 week. In contrast, blooms of Alexandrium catenella/tamarense can occur following periods of 3 weeks without precipitation and no significant input of conventional nutrients such as nitrate and phosphate. Field results also indicate a significant drop (from 22–25 to 15–16 μM over 3 days) in dissolved organic nitrogen (DON) at the bloom peak, as well as a significant inverse relationship between A. catenella/tamarense cell density and DON concentrations that is not apparent for diatom blooms. Such dinoflagellate blooms are also associated with elevated (6–9 μM) ammonium concentrations, a curious feature also observed by other investigators, possibly the results of ammonium excretion by this organism during urea or other organic nitrogen assimilation. The potential use of DON by this organism represents short cuts in the nitrogen cycle between plants and nutrients and requires a new model for phytoplankton growth that is different from the classical diatom bloom model. In contrast to such diatom blooms that are due to conventional (nitrate, phosphate) nutrient pulses, Alexandrium catenella/tamarense blooms on the monthly time scale are due to organic nutrient enrichment, a feature that allows net growth rates of about 1.3 d −1 , a value higher than that generally attributed to such organisms.
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nitrogenous nutrition of Alexandrium catenella dinophyceae in cultures and in thau lagoon southern france
Journal of Phycology, 2004Co-Authors: Yves Collos, Celine Gagne, Philippe Cecchi, Andre Vaquer, Mohamed Laabir, Philippe SouchuAbstract:Alexandrium catenella (Whedon et Kofoid) Balech was isolated from Thau lagoon (northern Mediterranean) and its growth and uptake characteristics measured for nitrate, ammonium, and urea. Although affinity constants did not indicate a preference for ammonium over nitrate, there was a strong inhibition of nitrate uptake by ammonium when both nitrogen (N) sources were present. Nitrogen budgets during growth in cultures revealed major imbalances between decreases in dissolved N and increases in particulate N, indicating excretion of dissolved organic N during the early part of the growth phase and uptake during the later part. A quasi-unialgal bloom in November 2001 (4 × 10 6 cells . L - 1 ) allowed measurements of uptake of nitrate, nitrite, ammonium, and urea; net and gross growth rate of A. catenella; and grazing rates on this organism. The affinity constants indicate that it is not a strong competitor for the N nutrients tested when these are in low concentrations (<10 μgat N.L - 1 ), compared with other members of the phytoplankton community. Indirect evidence from cultures indicate that dissolved organic N compounds could be important in triggering those blooms. Finally, the strongly unbalanced growth observed in the field indicates that A. catenella exhibits a storage rather than a growth response to a nutrient pulse and is adapted to low frequency events such as the passage of frontal disturbances. The disappearance of A. catenella was due to grazing that balanced growth at the peak of the bloom.
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Nitrogenous nutrition of Alexandrium catenella (Dinophyceae) in cultures and in Thau Lagoon, southern France
Journal of Phycology, 2004Co-Authors: Yves Collos, Celine Gagne, Philippe Cecchi, Andre Vaquer, Mohamed Laabir, Philippe SouchuAbstract:Alexandrium catenella (Whedon et Kofoid) Balech was isolated from Thau lagoon (northern Mediterranean) and its growth and uptake characteristics measured for nitrate, ammonium, and urea. Although affinity constants did not indicate a preference for ammonium over nitrate, there was a strong inhibition of nitrate uptake by ammonium when both nitrogen (N) sources were present. Nitrogen budgets during growth in cultures revealed major imbalances between decreases in dissolved N and increases in particulate N, indicating excretion of dissolved organic N during the early part of the growth phase and uptake during the later part. A quasi-unialgal bloom in November 2001 (4 × 10 6 cells . L - 1 ) allowed measurements of uptake of nitrate, nitrite, ammonium, and urea; net and gross growth rate of A. catenella; and grazing rates on this organism. The affinity constants indicate that it is not a strong competitor for the N nutrients tested when these are in low concentrations (
