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Yoshihiko Sako - One of the best experts on this subject based on the ideXlab platform.

  • analysis of the mitochondrial genome transcripts and electron transport activity in the dinoflagellate alexandrium Catenella gonyaulacales dinophyceae
    Phycological Research, 2009
    Co-Authors: Ryoma Kamikawa, Hiroshi Nishimura, Yoshihiko Sako
    Abstract:

    SUMMARY The mitochondrial (mt) genomes of dinoflagellates are not completely sequenced due to frequent recombination events resulting in a shortage of information about the dinoflagellate mt genome. To obtain a large amount of information, we characterized 14 polymerase chain reaction (PCR) fragments of more than 27 kb of the mt genome of the toxic dinoflagellate Alexandrium Catenella Whedon et Kofoid (Balech) using the cob and cox1 genes, the only identified functional mt genes of A. Catenella excluding rRNA fragments. The mt PCR clones encode multiple copies of cytochrome b (cob) and cytochrome c oxidase subunit 1 (cox1) bearing several types of 5′ or 3′ sequences, and two rRNA fragments showing sequence similarity with a large subunit (LSU) rRNA D fragment and LSU RNA2 of apicomplexa. Each mt PCR clone showed different gene arrangements and intergenic sequences suggesting multiple contexts in the mt genome of A. Catenella and frequent homologous recombinations. Reverse transcription PCR analysis suggested some types of the multiple copies of cob and cox1 genes are likely non-transcriptional. Further, A. Catenella mt mRNAs lacked in-frame termination codons and a canonical initiation codon, excluding an ‘atg’ codon in cob mRNA. However, we successfully detected the activity of the electron transport proteins suggesting mt translation requires no canonical initiation and termination codons.

  • fragmentation of mitochondrial large subunit rrna in the dinoflagellate alexandrium Catenella and the evolution of rrna structure in alveolate mitochondria
    Protist, 2007
    Co-Authors: Ryoma Kamikawa, Yuji Inagaki, Yoshihiko Sako
    Abstract:

    Extensive investigations on apicomplexan mitochondria, such as those of Plasmodium falciparum, revealed that ribosomal RNAs (rRNAs) are fragmented into multiple short pieces. In this study, we isolated three mitochondrial large subunit rRNA (mtLSU rRNA) fragments from the dinoflagellate Alexandrium Catenella. A piece of mtLSU rRNA that possesses high sequence similarity to the P. falciparum LSU rRNA E fragment was identified in a 1.7-kbp mitochondrial (mt) DNA clone. We further confirmed that the A. Catenella “E-like” fragment is indeed transcriptionally active and that the transcript could form appropriate RNA secondary structures. In addition, we identified expression of two additional rRNA fragments with sequence similarities to P. falciparum F and G fragments. Notably, the 1.7-kbp mt DNA clone contains only one of the three rRNA fragments identified in this study, suggesting that the rRNA fragments are separately encoded in the A. Catenella mt genome. Given the sister relationship between apicomplexa and dinoflagellates in eukaryote phylogeny, it is most parsimonious to assume that the mt rRNA fragmentation was established prior to the separation of the two protist groups. However, current sequence data on dinoflagellate mitochondria are insufficient to reject the alternative scenario, in which the rRNA fragmentation evolved independently in apicomplexan and dinoflagellate mitochondria.

  • application of real time pcr assay for detection and quantification of alexandrium tamarense and alexandrium Catenella cysts from marine sediments
    Harmful Algae, 2007
    Co-Authors: Ryoma Kamikawa, Satoshi Nagai, Shoko Hosoitanabe, Shigeru Itakura, Mineo Yamaguchi, Yoshitaka Uchida, Toshinori Baba, Yoshihiko Sako
    Abstract:

    Abstract The dinoflagellates Alexandrium tamarense (Lebor) Balech and Alexandrium Catenella (Whedon and Kofoid) Balech (Dinophyceae) are believed to be the main species responsible for paralytic shellfish poisoning (PSP) all over the world. It is necessary to identify A. tamarense and A. Catenella cysts and to monitor their distribution in sediment in order to minimize the damages caused by PSP to the economy and food quality because cysts are the seed population for blooms caused by motile vegetative cells. In this study, we developed an efficient DNA extraction method from the natural cysts present in marine sediments after they were size fractionated with a plankton net (mesh size of 20–150 μm). The 10–3000 cysts were added to the sediments collected from the Ariake Sea, and for which the primuline-staining method did not reveal any cysts. DNA was then extracted from each sample, and linear standard curves for A. tamarense and A. Catenella cysts were obtained from the correlation between the Ct values by real-time PCR and the log of the initial densities of cysts. We monitored the A. tamarense and A. Catenella cyst densities in the environmental samples. This assay was demonstrated to be a powerful tool for the identification, detection, and quantification of the cysts of the toxic dinoflagellates.

  • Genetic differentiation in the marine dinoflagellates Alexandrium tamarense and Alexandrium Catenella based on DNA-DNA hybridization
    Plankton and Benthos Research, 2006
    Co-Authors: Shoko Hosoi-tanabe, Yoshihiko Sako
    Abstract:

    The genetic relationship between the toxic marine dinoflagellates Alexandrium tamarense and Alexandrium Catenella, which share similar morphological characteristics and are clustered as a sister group on the phylogenetic tree based on 28S rDNA analysis was examined by DNA–DNA hybridization. This method has contributed to the information on relative comparisons of total sequences in the field of microbiology; however limited DNA–DNA hybridization studies have been carried out on microalgae, including dinoflagellates. The intragroup homology of DNA–DNA hybridization within the A. tamarense and A. Catenella groups, that was identified on the basis of morphotypes, was 85.0%–99.8% in both cases, whereas the intergroup homology between these two groups was 62.5%–70.3%, which was lower than the intragroup homology. These percentages revealed that not only the rDNA sequences but also the total sequence reflects slight morphological differences between A. tamarense and A. Catenella, indicating the possibility that strains identified as these two species could be differentiated as distinct groups based on the percentage obtained using DNA–DNA hybridization. The homology of A. tamarense with other Alexandrium species was low—37.1%–45.2% with A. tamiyavanichii, 41.0%–45.5% with A. affine, and 24.8%–35.8% with A. ostenfeldii. The relatedness between A. Catenella and other Alexandrium strains tested (e.g. between A. Catenella and A. tamiyavanichii was 39.0%–51.2%) was also lower than that between A. tamarense and A. Catenella. Further, these percentages were consistent with the rDNA phylogenetic analysis, indicating that DNA–DNA hybridization might be a useful tool to understand the relatedness among Alexandrium species.

  • species specific detection and quantification of toxic marine dinoflagellates alexandrium tamarense and a Catenella by real time pcr assay
    Marine Biotechnology, 2005
    Co-Authors: Shoko Hosoitanabe, Yoshihiko Sako
    Abstract:

    A Real-time polymerase chain reaction (PCR) assay was designed and evaluated for rapid detection and quantification of the toxic dinoflagellates Alexandrium Catenella and A. tamarense, which cause paralytic shellfish poisoning. Two sets of PCR primers and fluorogenic probes targeting these two species were derived from the sequence of 28S ribosomal DNA. PCR specificity was examined in closely related Alexandrium spp. and many other microalgae. A. Catenella–specific primers and probe detected the PCR amplification only from A. Catenella strains, and nonspecific signals were not detected from any microalgae. Also, A. tamarense–specific primers and probe also detected the targeted species, suggesting the strict species specificity of each PCR. This assay could detect one cell of each species, showing its high sensitivity. Moreover, using the developed standard curves, A. tamarense and A. Catenella could be quantified in agreement with the quantification by optical microscopy. The performance characteristics of species specificity, sensitivity, and rapidity suggest that this method is applicable to the monitoring of the toxic A. tamarense and A. Catenella.

Yves Collos - One of the best experts on this subject based on the ideXlab platform.

  • comparing diatom and alexandrium Catenella tamarense blooms in thau lagoon importance of dissolved organic nitrogen in seasonally n limited systems
    Harmful Algae, 2014
    Co-Authors: Yves Collos, Cecile Jauzein, Eric Abadie, Philippe Souchu, Widya Ratmaya, Andre Vaquer
    Abstract:

    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.

  • A comparative analysis of Alexandrium Catenella/tamarense blooms in Annaba Bay (Algeria) and Thau lagoon (France); phosphorus limitation as a trigger.
    Comptes Rendus Biologies, 2014
    Co-Authors: Imene Hadjadji, Eric Abadie, Hocine Frehi, Lembarek Ayada, Yves Collos
    Abstract:

    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.

  • discrepancies between net particulate carbon production and 13 c labelled bicarbonate uptake by alexandrium Catenella dinophyceae grazing controls the balance between autotrophic and non autotrophic carbon acquisition 1
    Journal of Phycology, 2013
    Co-Authors: Yves Collos, Cecile Jauzein, Mohamed Laabir, Andre Vaquer
    Abstract:

    Inorganic carbon uptake by Alexandrium Catenella estimated from incorporation of 13C labelled bicarbonate (an estimate of carbon gain by autotrophy) was compared to increases in particulate carbon (PC) that integrate all processes leading to carbon gain by cells (autotrophy, heterotrophy, mixotrophy). During blooms of A. Catenella in the field, the 13C tracer technique could account for only 47% (range 29%–59%) of the increase in PC in conventional 24 h incubations. From dilution experiments, the ratio of PC increases to bicarbonate uptake was related significantly and positively to the grazing rate, indicating that dissolved organic carbon contributes to growth as a direct function of grazing activity. In addition, as grazing rate increases, the contribution of dissolved inorganic carbon uptake to carbon-based growth decreases in a linear way (from 56% to 33% of total C acquisition) and the contribution of non autotrophic processes increases (from 54% to 67%). Thus, grazing appears to closely control the balance between autotrophic and non autotrophic processes leading to carbon acquisition by natural populations of A. Catenella.

  • dark metabolism and carbon nitrogen uncoupling in the toxic dinoflagellate alexandrium Catenella dinophyceae
    Harmful Algae, 2011
    Co-Authors: Cecile Jauzein, Yves Collos, Mohamed Laabir, Andre Vaquer
    Abstract:

    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.

  • growth and phosphorus uptake by the toxic dinoflagellate alexandrium Catenella dinophyceae in response to phosphate limitation
    Journal of Phycology, 2010
    Co-Authors: Cecile Jauzein, Claire Labry, Agnes Youenou, Julien Quere, Daniel Delmas, Yves Collos
    Abstract:

    Alexandrium Catenella (Whedon et Kof.) Balech has exhibited seasonal recurrent blooms in the Thau lagoon (South of France) since first reported in 1995. Its appearance followed a strong decrease (90%) in phosphate (PO(4)3-) concentrations in this environment over the 1970-1995 period. To determine if this dinoflagellate species has a competitive advantage in PO(4)3--limited conditions in terms of nutrient acquisition, semicontinuous cultures were carried out to characterize phosphorus (P) uptake by A. Catenella cells along a P-limitation gradient using different dilution rates (DRs). Use of both inorganic and organic P was investigated from measurements of 33PO(4)3- uptake and alkaline phosphatase activity (APA), respectively. P status was estimated from cellular P and carbon contents (Q(P) and Q(C)). Shifts in trends of Q(P)/Q(C) and Q(P) per cell (Q(P center dot cell-1)) along the DR gradient allowed the definition of successive P-stress thresholds for A. Catenella cells. The maximal uptake rate of 33PO(4)3- increased strongly with the decrease in DR and the decrease in Q(P)/Q(C), displaying physiological acclimations to PO(4)3- limitation. Concerning maximal APA per cell, the observation of an all-or-nothing pattern along the dilution gradient suggests that synthesis of AP was induced and maximized at the cellular scale as soon as PO(4)3- limitation set in. APA variations revealed that the synthesis of AP was repressed over a PO(4)3- threshold between 0.4 and 1 mu M. As lower PO(4)3- concentrations are regularly observed during A. Catenella blooms in Thau lagoon, a significant portion of P uptake by A. Catenella cells in the field may come from organic compounds.

Donald M Anderson - One of the best experts on this subject based on the ideXlab platform.

  • evaluation of sxta and rdna qpcr assays through monitoring of an inshore bloom of alexandrium Catenella group 1
    Scientific Reports, 2019
    Co-Authors: Shauna A Murray, Donald M Anderson, Rendy Ruvindy, Gurjeet S Kohli, Michael L Brosnahan
    Abstract:

    Alexandrium Catenella (formerly A. tamarense Group 1, or A. fundyense) is the leading cause of Paralytic Shellfish Poisoning in North and South America, Europe, Africa, Australia and Asia. The quantification of A.Catenella via sxtA, a gene involved in Paralytic Shellfish Toxin synthesis, may be a promising approach, but has not been evaluated in situ on blooms of A. Catenella, in which cell abundances may vary from not detectable to in the order of 106 cells L−1. In this study, we compared sxtA assay performance to a qPCR assay targeted to a species-specific region of ribosomal DNA (rDNA) and an established fluorescent in situ hybridization (FISH) microscopy method. Passing-Bablok regression analyses revealed the sxtA assay to overestimate abundances when <5 cell equivalents A. Catenella DNA were analysed, but otherwise was closer to microscopy estimates than the rDNA assay, which overestimated abundance across the full range of concentrations analysed, indicative of a copy number difference between the bloom population and a culture used for assay calibration a priori. In contrast, the sxtA assay performed more consistently, indicating less copy number variation. The sxtA assay was generally reliable, fast and effective in quantifying A. Catenella and was predictive of PST contamination of shellfish.

  • Evaluation of sxtA and rDNA qPCR assays through monitoring of an inshore bloom of Alexandrium Catenella Group 1
    Scientific Reports, 2019
    Co-Authors: Shauna A Murray, Donald M Anderson, Rendy Ruvindy, Gurjeet S Kohli, Michael L Brosnahan
    Abstract:

    Alexandrium Catenella (formerly A. tamarense Group 1, or A. fundyense) is the leading cause of Paralytic Shellfish Poisoning in North and South America, Europe, Africa, Australia and Asia. The quantification of A.Catenella via sxtA, a gene involved in Paralytic Shellfish Toxin synthesis, may be a promising approach, but has not been evaluated in situ on blooms of A. Catenella, in which cell abundances may vary from not detectable to in the order of 106 cells L−1. In this study, we compared sxtA assay performance to a qPCR assay targeted to a species-specific region of ribosomal DNA (rDNA) and an established fluorescent in situ hybridization (FISH) microscopy method. Passing-Bablok regression analyses revealed the sxtA assay to overestimate abundances when

  • spatiotemporal genetic structure of regional scale alexandrium Catenella dinoflagellate blooms explained by extensive dispersal and environmental selection
    Harmful Algae, 2019
    Co-Authors: Ingrid Sassenhagen, Mindy L Richlen, Donald M Anderson, Jennifer L Martin, Deana L Erdner
    Abstract:

    Abstract Paralytic Shellfish Poisoning (PSP) caused by the dinoflagellate Alexandrium Catenella is a well-known global syndrome that negatively impacts human health and fishery economies. Understanding the population dynamics and ecology of this species is thus important for identifying determinants of blooms and associated PSP toxicity. Given reports of extensive genetic heterogeneity in the toxicity and physiology of Alexandrium species, knowledge of genetic population structure in harmful algal species such as A. Catenella can also facilitate the understanding of toxic bloom development and ecological adaptation. In this study we employed microsatellite markers to analyze multiple A. Catenella strains isolated from several sub-regions in the Gulf of Maine (GoM) during summer blooms, to gain insights into the sources and dynamics of this economically important phytoplankton species. At least three genetically distinct clusters of A. Catenella were identified in the GoM. Each cluster contained representatives from different sub-regions, highlighting the extent of connectivity and dispersal throughout the region. This shared diversity could result from cyst beds created by previous coastal blooms, thereby preserving the overall diversity of the regional A. Catenella population. Rapid spatiotemporal genetic differentiation of A. Catenella populations was observed in local blooms, likely driven by natural selection through environmental conditions such as silicate and nitrate/nitrite concentrations, emphasizing the role of short-term water mass intrusions and biotic processes in determining the diversity and dynamics of marine phytoplankton populations. Given the wide-spread intraspecific diversity of A. Catenella in GoM and potentially elsewhere, harmful algal blooms will likely persist in many regions despite global warming and changing environmental conditions in the future. Selection of different genetic lineages through variable hydrological conditions might impact toxin production and profiles of future blooms, challenging HAB control and prediction of PSP risk in the future.

  • bloom termination of the toxic dinoflagellate alexandrium Catenella vertical migration behavior sediment infiltration and benthic cyst yield
    Limnology and Oceanography, 2017
    Co-Authors: Michael L Brosnahan, David K Ralston, Alexis D Fischer, Andrew R Solow, Donald M Anderson
    Abstract:

    New resting cyst production is crucial for the survival of many microbial eukaryotes including phytoplankton that cause harmful algal blooms. Production in situ has previously been estimated through sediment trap deployments, but here was instead assessed through estimation of the total number of planktonic cells and new resting cysts produced by a localized, inshore bloom of Alexandrium Catenella, a dinoflagellate that is a globally important cause of paralytic shellfish poisoning. Our approach utilizes high frequency, automated water monitoring, weekly observation of new cyst production, and pre- and post-bloom spatial surveys of total resting cyst abundance. Through this approach, new cyst recruitment within the study area was shown to account for at least 10.9% ± 2.6% (SE) of the bloom's decline, ∼ 5× greater than reported from comparable, sediment trap based studies. The observed distribution and timing of new cyst recruitment indicate that: (1) planozygotes, the immediate precursor to cysts in the life cycle, migrate nearer to the water surface than other planktonic stages and (2) encystment occurs after planozygote settlement on bottom sediments. Near surface localization by planozygotes explains the ephemerality of red surface water discoloration by A. Catenella blooms, and also enhances the dispersal of new cysts. Following settlement, bioturbation and perhaps active swimming promote sediment infiltration by planozygotes, reducing the extent of cyst redistribution between blooms. The concerted nature of bloom sexual induction, especially in the context of an observed upper limit to A. Catenella bloom intensities and heightened susceptibility of planozygotes to the parasite Amoebophrya, is also discussed.

  • 2302 proposal to reject the name gonyaulax Catenella alexandrium Catenella dinophyceae
    Taxon, 2014
    Co-Authors: Uwe John, Shauna A Murray, Michael L Brosnahan, Wayne Litaker, Marina Montresor, Donald M Anderson
    Abstract:

    The dinoflagellate species Alexandrium Catenella (Whedon & Kof.) Balech (in Anderson & al., Toxic Dinoflagellates: 37. 1985), first published as Gonyaulax Catenella Whedon & Kof., was described from marine waters off San Francisco, California, U.S.A. The protologue included the species diagnosis, a detailed description and seven drawings in which the thecal plate pattern in apical, antapical, dorsal and ventral view was provided, as well as a sketch of four cells joined in a chain and two drawings showing the shape and position of the nucleus. The species name was published according to the International Code of Zoological Nomenclature and did not include a Latin diagnosis). The type material for the name, however, was not designated. Gonyaulax Catenella was subsequently transferred to the genus Alexandrium by Balech (l.c. 1985), but no lectotype was designated. Alexandrium Catenella, together with A. tamarense (M. Lebour) Balech and A. fundyense Balech, comprise the A. tamarense species complex, one of the most studied marine dinoflagellate groups due to their ecological, toxicological and economic importance. Several members of this complex produce saxitoxins, potent neurotoxins that cause paralytic shellfish poisoning. Identification of thecate dinoflagellates such as Alexandrium is largely based on the number, shape and arrangement of the thecal plates that surround vegetative cells. The three morpho-species grouped in the A. tamarense species complex are morphologically very similar, share the same plate pattern and have been distinguished based on the combination of two main characters: the ability to form chains and the presence/absence of a ventral pore between plates 1 and 4 (Balech, l.c. 1985; Genus Alexandrium. 1995). John & al. (in Protist, in review) critically reviewed the taxonomic status of the species grouped into the Alexandrium tamarense species complex. This analysis included a broad range of information on cell morphology, sequences of multiple regions in the rDNA operon, mating compatibility, ITS/5.8S genetic distances, ITS2 compensatory base changes, toxicity and presence of the gene sxtA published over the last several decades. As already shown by various independent studies (for a complete list of references, see John & al., l.c. in review) morphological characters used to identify the three species are not consistent and/or distinctive. Moreover, phylogenies based on multiple rDNA regions (SSU, LSU, ITS) indicate that the sequences from morphologically indistinguishable isolates consistently partition into five clades, designated Groups I–V (John & al. in Molec. Biol. Evol. 20: 1015–1027. 2003; Lilly & al. in J. Phycol. 43: 1329–1338. 2007). The preponderance of evidence supports each of these groups as distinct species (John & al., l.c. in review). A majority of the Group I sequences currently come from isolates in regions adjacent to the type locality for A. fundyense (Bay of Fundy, Canada). Similarly the Group III sequences come primarily from isolates obtained in regions adjacent to the type locality for A. tamarense (Tamar River Estuary, England). Given that these two genetically distinct species are morphologically indistinguishable, it was logical to designate Group I as A. fundyense and Group III as A. tamarense (John & al., l.c. in review). Since most of the published studies on A. fundyense and A. tamarense encompass Group I and Group III sequences, respectively, these revised species designations cause a minimum of confusion with regard to the current literature. The same, however, is not true for A. Catenella. Alexandrium Catenella cells were originally described as being slightly broader than long and to form chains. Based on these morphological criteria, a majority of the strains isolated in various sites in the Pacific Ocean were reported as A. Catenella (see the recent reviews Anderson & al. in Harmful Algae 14: 10–35. 2012; in Annual Rev. Mar. Sci. 4: 143–176. 2012). However, the molecular analysis of these “morphologically” identified strains primarily fell into either Clade I (primarily eastern Pacific along coasts of North, Central and South America) or Clade IV (primarily western Pacific). The isolates sequenced to date from the A. Catenella type locality (California) belong to Group I (Ruiz Sebastian & al. in Phycologia 44: 49–60. 2005; Jester & al. in Mar. Biol. 156: 493–504. 2010; Garneau & al. in Appl. Environm. Microbiol. 77: 7669–7680. 2011). These observations indicate that the Group I morphology is more variable than originally described and that the A. Catenella species description was incorrectlybased on a population of A. fundyense cells exhibiting chain formation and the shape slightly broader than long (i.e., A. Catenella simply represents one of the distinct morphological variants of A. fundyense). Therefore based on Art. 56.1 of the ICN (McNeill & al. in Regnum Veg. 154. 2012) we propose rejection of the basionym of Alexandrium Catenella (Whedon & Kof.) Balech for the following reasons: (1) The identity of the type material on which this species was based remains unclear. No type was designated by the author and strains isolated from the region from which the material most likely originated that was the basis of the species description belong to a different species (A. fundyense). (2) Alexandrium Catenella could in principle supplant the name A. fundyense and be applied to all Group I strains, because its original description (Whedon & Kofoid, l.c.) predates that of A. fundyense (Balech, l.c. 1985). However, a large number of studies on Group I strains have been published using the name A. fundyense and making this nomenclatural change would cause considerable confusion in the research community. As an alternative, John & al. (l.c. in review) proposed in their revision of the A. tamarense species complex that A. fundyense be retained as an accepted species name. This required formally designating a lectotype and epitype for A. fundyense. (3) Retention of A. Catenella would foster continued confusion in the literature concerning whether the data in a given study pertains to Group I or Group IV species. To rectify the existing taxonomic confusion in this group, John & al. (l.c. in review) formally proposed Group I isolates as A. fundyense, Group III isolates as A. tamarense and Group IV isolates as a new species, Alexandrium pacificum Litaker (in John & al., l.c. in review). The designation of Alexandrium pacificum as distinct from A. fundyense will allow the confusion caused by the A. Catenella species designation having been simultaneously applied to Group I and IV to be more easily addressed.

Mohamed Laabir - One of the best experts on this subject based on the ideXlab platform.

  • Exposure to the Paralytic Shellfish Toxin Producer Alexandrium Catenella Increases the Susceptibility of the Oyster Crassostrea gigas to Pathogenic Vibrios
    Toxins, 2016
    Co-Authors: Celina Abi-khalil, Mohamed Laabir, Carmen Lopez-joven, Eric Abadie, Véronique Savar, Zouher Amzil, Jean-luc Rolland
    Abstract:

    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.

  • Alexandrium Catenella increases the susceptibility of Crassostrea gigas to pathogenic vibrios: possible implications in oyster mass mortalities in the Mediterranean Thau lagoon
    2015
    Co-Authors: Celina Abi-khalil, Mohamed Laabir, Carmen Lopez-joven, Eric Abadie, Véronique Savar, Zouher Amzil, Jean-luc Rolland
    Abstract:

    Since several years an alarming worldwide expansion of Harmful Algae Bloom (HAB) was observed in coastal and / or confined waters. Alexandrium Catenella, a paralytic shellfish poisoning (PSP) producer, is now regularly found in Thau lagoon (south of France) at concentrations up to 15x106 cellules. l-1. In the same periods, events of oyster’s mortality are also observed causing huge economic losses. The purpose of this study is to investigate the relationship between these toxic events and mortality phenomenon. For that, we conducted a field work to evaluate the presence of the toxic A. Catenella in Thau lagoon during the years 2013 and 2014 in which high mortality of oysters spats were observed in spring. At the same time, we experimentally infected spats with the pathogenic bacterium V. tasmaniensis LGP32 and kept them unfed or previously fed either with the toxic alga A. Catenella or with nontoxic algae, Alexandrium tamarense or Tisochrysis lutea. Results showed that the toxic alga was present in the lagoon when spats' mortalities occurred suggesting A. Catenella could be involved in these events. Moreover, our laboratory experiment showed that the exposure to A. Catenella increases the susceptibility of spats to one of its pathogens, V. tasmaniensis LGP32. Those results both together suggest for the first time that, in the environment, toxic algae could be implicated in oysters’ mortality. Further studies should be conducted to determine the main factors of this alga implicated in weakening oysters and their immune system against their pathogen which lead to these large scale mortalities

  • discrepancies between net particulate carbon production and 13 c labelled bicarbonate uptake by alexandrium Catenella dinophyceae grazing controls the balance between autotrophic and non autotrophic carbon acquisition 1
    Journal of Phycology, 2013
    Co-Authors: Yves Collos, Cecile Jauzein, Mohamed Laabir, Andre Vaquer
    Abstract:

    Inorganic carbon uptake by Alexandrium Catenella estimated from incorporation of 13C labelled bicarbonate (an estimate of carbon gain by autotrophy) was compared to increases in particulate carbon (PC) that integrate all processes leading to carbon gain by cells (autotrophy, heterotrophy, mixotrophy). During blooms of A. Catenella in the field, the 13C tracer technique could account for only 47% (range 29%–59%) of the increase in PC in conventional 24 h incubations. From dilution experiments, the ratio of PC increases to bicarbonate uptake was related significantly and positively to the grazing rate, indicating that dissolved organic carbon contributes to growth as a direct function of grazing activity. In addition, as grazing rate increases, the contribution of dissolved inorganic carbon uptake to carbon-based growth decreases in a linear way (from 56% to 33% of total C acquisition) and the contribution of non autotrophic processes increases (from 54% to 67%). Thus, grazing appears to closely control the balance between autotrophic and non autotrophic processes leading to carbon acquisition by natural populations of A. Catenella.

  • paralytic toxins accumulation and tissue expression of α amylase and lipase genes in the pacific oyster crassostrea gigas fed with the neurotoxic dinoflagellate alexandrium Catenella
    Marine Drugs, 2012
    Co-Authors: Jean-luc Rolland, Estelle Masseret, Véronique Savar, Zouher Amzil, Kevin Pelletier, Fabien Rieuvilleneuve, Adrien Santini, Mohamed Laabir
    Abstract:

    The pacific oyster Crassostrea gigas was experimentally exposed to the neurotoxic Alexandrium Catenella and a non-producer of PSTs, Alexandrium tamarense (control algae), at concentrations corresponding to those observed during the blooming period. At fixed time intervals, from 0 to 48 h, we determined the clearance rate, the total filtered cells, the composition of the fecal ribbons, the profile of the PSP toxins and the variation of the expression of two α-amylase and triacylglecerol lipase precursor (TLP) genes through semi-quantitative RT-PCR. The results showed a significant decrease of the clearance rate of C. gigas fed with both Alexandrium species. However, from 29 to 48 h, the clearance rate and cell filtration activity increased only in oysters fed with A. tamarense. The toxin concentrations in the digestive gland rose above the sanitary threshold in less than 48 h of exposure and GTX6, a compound absent in A. Catenella cells, accumulated. The α-amylase B gene expression level increased significantly in the time interval from 6 to 48 h in the digestive gland of oysters fed with A. tamarense, whereas the TLP gene transcript was significantly up-regulated in the digestive gland of oysters fed with the neurotoxic A. Catenella. All together, these results suggest that the digestion capacity could be affected by PSP toxins.

  • dark metabolism and carbon nitrogen uncoupling in the toxic dinoflagellate alexandrium Catenella dinophyceae
    Harmful Algae, 2011
    Co-Authors: Cecile Jauzein, Yves Collos, Mohamed Laabir, Andre Vaquer
    Abstract:

    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.

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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, 2014
    Co-Authors: Yves Collos, Cecile Jauzein, Eric Abadie, Philippe Souchu, Widya Ratmaya, Andre Vaquer
    Abstract:

    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.

  • discrepancies between net particulate carbon production and 13 c labelled bicarbonate uptake by alexandrium Catenella dinophyceae grazing controls the balance between autotrophic and non autotrophic carbon acquisition 1
    Journal of Phycology, 2013
    Co-Authors: Yves Collos, Cecile Jauzein, Mohamed Laabir, Andre Vaquer
    Abstract:

    Inorganic carbon uptake by Alexandrium Catenella estimated from incorporation of 13C labelled bicarbonate (an estimate of carbon gain by autotrophy) was compared to increases in particulate carbon (PC) that integrate all processes leading to carbon gain by cells (autotrophy, heterotrophy, mixotrophy). During blooms of A. Catenella in the field, the 13C tracer technique could account for only 47% (range 29%–59%) of the increase in PC in conventional 24 h incubations. From dilution experiments, the ratio of PC increases to bicarbonate uptake was related significantly and positively to the grazing rate, indicating that dissolved organic carbon contributes to growth as a direct function of grazing activity. In addition, as grazing rate increases, the contribution of dissolved inorganic carbon uptake to carbon-based growth decreases in a linear way (from 56% to 33% of total C acquisition) and the contribution of non autotrophic processes increases (from 54% to 67%). Thus, grazing appears to closely control the balance between autotrophic and non autotrophic processes leading to carbon acquisition by natural populations of A. Catenella.

  • dark metabolism and carbon nitrogen uncoupling in the toxic dinoflagellate alexandrium Catenella dinophyceae
    Harmful Algae, 2011
    Co-Authors: Cecile Jauzein, Yves Collos, Mohamed Laabir, Andre Vaquer
    Abstract:

    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.

  • unexpected genetic diversity among and within populations of the toxic dinoflagellate alexandrium Catenella as revealed by nuclear microsatellite markers
    Applied and Environmental Microbiology, 2009
    Co-Authors: Estelle Masseret, Satoshi Nagai, Yves Collos, Mohamed Laabir, Andre Vaquer, Daniel Grzebyk, Benjamin Genovesi, Bernard Lasserre, Patrick Berrebi
    Abstract:

    Since 1998, blooms of Alexandrium Catenella associated with paralytic shellfish poisoning have been repeatedly reported for Thau Lagoon (French Mediterranean coast). Based on data obtained for rRNA gene markers, it has been suggested that the strains involved could be closely related to the Japanese temperate Asian ribotype of the temperate Asian clade. In order to gain more insight into the origin of these organisms, we carried out a genetic analysis of 61 Mediterranean and 23 Japanese strains using both ribosomal and microsatellite markers. Whereas the phylogeny based on ribosomal markers tended to confirm the previous findings, the analysis of microsatellite sequences revealed an unexpected distinction between the French and Japanese populations. This analysis also highlighted great intraspecific diversity that was not detected with the classical rRNA gene markers. The Japanese strains are divided into two differentiated A. Catenella lineages: the Sea of Japan lineage and the east coast lineage, which includes populations from the Inland Sea and the Pacific Ocean. A. Catenella strains isolated from Thau Lagoon belong to another lineage. These findings indicate that microsatellite markers are probably better suited to investigations of the population genetics of this species that is distributed worldwide. Finally, application of the population genetics concepts available for macroorganisms could support new paradigms for speciation and migration in phytoplankton assemblages.

  • contribution of several nitrogen sources to growth of alexandrium Catenella during blooms in thau lagoon southern france
    Harmful Algae, 2007
    Co-Authors: Yves Collos, Mohamed Laabir, Andre Vaquer, Eric Abadie, Thierry Laugier, Annie Pastoureaud, Philippe Souchu
    Abstract:

    A monitoring program with a weekly sampling frequency over a 15-month period indicates that urea concentrations above a certain threshold level may trigger the blooms of Alexandrium Catenella in Thau lagoon. However, urea concentrations were also sometimes related to ammonium and dissolved organic nitrogen concentrations, indicating that the role of urea may not be a direct one. An original approach is used to assess the relative contribution of several nitrogen sources (nitrate, nitrite, ammonium, urea) to growth of A. Catenella by comparing nitrogen uptake rates to nitrogen-based growth rates estimated from dilution experiments during four blooms over a 4-year period (2001–2004) in Thau lagoon. Nitrate and nitrite contributed 0.1–14% and 0.1–5% respectively of growth requirements. Ammonium and urea were the main N sources fueling growth of A. Catenella (30–100% and 2–59%, respectively). Indirect estimates indicated that an unidentified N source could also contribute significantly to growth at specific times. Concerning ammonium and urea uptake kinetics, half-saturation constants varied between 0.2 and 20 μgat N L −1 for ammonium and between 0.1 and 44 μgat N L −1 over the 4-year period, indicating that A. Catenella can have a competitive advantage over other members of the phytoplankton even under low concentrations of ammonium and urea. However, the observed large changes in ammonium and urea uptake kinetics on a short time scale (days) during blooms preclude more precise estimates of those contributions to growth and require further investigation.