Consulta: creatorFacets:"Le Gac, Mickael"
Registros recuperados: 15
Data/hora: 02/06/2024 04:32:05

Uptake of Inorganic and Organic Nitrogen Sources by Dinophysis acuminata and D. acuta
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: García-portela, Maria; Reguera, Beatriz; Gago, Jesus; Le Gac, Mickael; Rodríguez, Francisco.
Dinoflagellate species of Dinophysis are obligate mixotrophs that require light, nutrients, and prey for sustained growth. Information about their nitrogenous nutrient preferences and their uptake kinetics are scarce. This study aimed to determine the preferred nitrogen sources in cultures of D. acuminata and D. acuta strains from the Galician Rías Baixas (NW Spain) and to compare their uptake kinetics. Well-fed versus starved cultures of D. acuminata and D. acuta were supplied with N15 labeled inorganic (nitrate, ammonium) and organic (urea) nutrients. Both species showed a preference for ammonium and urea whereas uptake of nitrate was negligible. Uptake rates by well-fed cells of D. acuminata and D. acuta were 200% and 50% higher, respectively, than by...
Tipo: Text
Palavras-chave: Dinophysis; Nitrate; Ammonium; Urea; Uptake rates; N-15 incubations; Antibiotic treatment.
Ano: 2020
URL: https://archimer.ifremer.fr/doc/00606/71770/70250.pdf

Differential influence of life cycle on growth and toxin production of three   Pseudo-nitzschia   species (Bacillariophyceae)
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Sauvey, Aurore; Claquin, Pascal; Le Roy, Bertrand; Le Gac, Mickael; Fauchot, Juliette.
We used a multi‐strain approach to study the intra‐ and interspecific variability of the growth rates of three Pseudo‐nitzschia species – P. australis, P. fraudulenta, and P. pungens – and of their domoic acid (DA) production. We carried out mating and batch experiments to investigate the respective effects of strain age and cell size, and thus the influence of their life cycle on the physiology of these species. The cell size ‐ life cycle relationship was characteristic of each species. The influence of age and cell size on the intraspecific variability of growth rates suggests that these characteristics should be considered cautiously for the strains used in physiological studies on Pseudo‐nitzschia species. The results from all three species do not...
Tipo: Text
Palavras-chave: Cell size; Domoic acid; Growth; Life cycle; Pseudo-nitzschia strains.
Ano: 2019
URL: https://archimer.ifremer.fr/doc/00505/61679/65622.pdf

Inter and intra-specific growth and domoic acid production in relation to nutrient ratios and concentrations in Pseudo-nitzschia : phosphate an important factor
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Lema, Anais Kimberley; Latimier, Marie; Nezan, Elisabeth; Fauchot, Juliette; Le Gac, Mickael.
The factors responsible for inducing the synthesis of toxins and responses from toxic phytoplankton blooms remain unclear. In this study we compare the influence of genotypic (at both the intra and interspecific levels) and environmental factors (nutrient concentration and ratio) on growth (in terms of cell densities) and domoic acid (DA) production in three Pseudo-nitzschia species: P. australis, P.pungens and P.fradulenta. A strong phosphate effect was detected. More precisely, a low initial concentration in phosphate, even at high initial nitrogen and silicate concentrations, induced the highest DA concentrations and the lowest cell densities in all strains/species studied. In contrast, a low initial concentration of nitrogen and silicate combined, with...
Tipo: Text
Palavras-chave: Pseudo-nitzschia strains; Domoic acid; Ratio; Phosphate; Nitrogen.
Ano: 2017
URL: http://archimer.ifremer.fr/doc/00377/48849/49397.pdf

Contrasting effects of historical contingency on phenotypic and genomic trajectories during a two-step evolution experiment with bacteria
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Plucain, Jessica; Suau, Antonia; Cruveiller, Stephane; Medigue, Claudine; Schneider, Dominique; Le Gac, Mickael.
Background  The impact of historical contingency, i.e. the past evolutionary history of a population, on further adaptation is mostly unknown at both the phenotypic and genomic levels. We addressed this question using a two-step evolution experiment. First, replicate populations of Escherichia coli were propagated in four different environmental conditions for 1000 generations. Then, all replicate populations were transferred and propagated for further 1000 generations to a single new environment. Results  Using this two-step experimental evolution strategy, we investigated, at both the phenotypic and genomic levels, whether and how adaptation in the initial historical environments impacted evolutionary trajectories in a new environment. We showed that...
Tipo: Text
Palavras-chave: Experimental evolution; Escherichia coli; Adaptation; Historical contingency; Epistasis.
Ano: 2016
URL: http://archimer.ifremer.fr/doc/00333/44447/44118.pdf

Species specific gene expression dynamics during harmful algal blooms
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Metegnier, Gabriel; Paulino, Sauvann; Ramond, Pierre; Siano, Raffaele; Sourisseau, Marc; Destombe, Christophe; Le Gac, Mickael.
Harmful algal blooms are caused by specific members of microbial communities. Understanding the dynamics of these events requires comparing the strategies developed by the problematic species to cope with environmental fluctuations to the ones developed by the other members of the community. During three consecutive years, the meta-transcriptome of micro-eukaryote communities was sequenced during blooms of the toxic dinoflagellate Alexandrium minutum. The dataset was analyzed to investigate species specific gene expression dynamics. Major shifts in gene expression were explained by the succession of different species within the community. Although expression patterns were strongly correlated with fluctuation of the abiotic environment, and more...
Tipo: Text
Ano: 2020
URL: https://archimer.ifremer.fr/doc/00622/73390/72602.pdf

The Bay of Brest (France), a new risky site for toxic Alexandrium minutum blooms and PSP shellfish contamination
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Chapelle, Annie; Le Gac, Mickael; Labry, Claire; Siano, Raffaele; Quere, Julien; Caradec, Florian; Le Bec, Claude; Nezan, Elisabeth; Doner, Anne; Gouriou, Jeremie.
Tipo: Text
Ano: 2015
URL: http://archimer.ifremer.fr/doc/00278/38921/37461.pdf

From the sxtA4 Gene to Saxitoxin Production: What Controls the Variability Among Alexandrium minutum and Alexandrium pacificum Strains?
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Geffroy, Solene; Lechat, Marc-marie; Le Gac, Mickael; Rovillon, Georges-augustin; Marie, Dominique; Bigeard, Estelle; Malo, Florent; Amzil, Zouher; Guillou, Laure; Caruana, Amandine.
Paralytic shellfish poisoning (PSP) is a human foodborne syndrome caused by the consumption of shellfish that accumulate paralytic shellfish toxins (PSTs, saxitoxin group). In PST-producing dinoflagellates such as Alexandrium spp., toxin synthesis is encoded in the nuclear genome via a gene cluster (sxt). Toxin production is supposedly associated with the presence of a 4th domain in the sxtA gene (sxtA4), one of the core genes of the PST gene cluster. It is postulated that gene expression in dinoflagellates is partially constitutive, with both transcriptional and post-transcriptional processes potentially co-occurring. Therefore, gene structure and expression mode are two important features to explore in order to fully understand toxin production processes...
Tipo: Text
Palavras-chave: Alexandrium; Saxitoxins; SxtA4; Copy number variation; SxtA; Expression; Isoform.
Ano: 2021
URL: https://archimer.ifremer.fr/doc/00682/79402/81944.pdf

Evolutionary history and genetic parallelism affect correlated responses to evolution
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Le Gac, Mickael; Cooper, Tim F.; Cruveiller, Stephane; Edigue, Claudine M.; Schneider, Dominique.
We investigated the relationship between genomic and phenotypic evolution among replicate populations of Escherichia coli evolved for 1000 generations in four different environments. By resequencing evolved genomes, we identified parallel changes in genes encoding transcription regulators within and between environments. Depending on both the environment and the altered gene, genetic parallelism at the gene level involved mutations that affected identical codons, protein domains or were widely distributed across the gene. Evolved clones were characterized by parallel phenotypic changes in their respective evolution environments but also in the three alternative environments. Phenotypic parallelism was high for clones that evolved in the same environment,...
Tipo: Text
Palavras-chave: Adaptation; Epistasis; Experimental evolution; Genome sequencing; Parallelism.
Ano: 2013
URL: https://archimer.ifremer.fr/doc/00148/25928/24096.pdf

Inter and intra-specific transcriptional and phenotypic responses of   Pseudo-nitzschia   under different nutrient conditions
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Lema, Anais Kimberley; Metegnier, Gabriel; Quéré, Julien; Latimier, Marie; Youenou, Agnes; Lambert, Christophe; Fauchot, Juliette; Le Gac, Mickael.
Untangling the functional basis of divergence between closely related species is a step towards understanding species dynamics within communities at both the evolutionary and ecological scales. We investigated cellular (i.e: growth, domoic acid production, nutrient consumption) and molecular (transcriptomic analyses) responses to varying nutrient concentrations across several strains belonging to three species of the toxic diatom genus Pseudo-nitzschia. Three main results were obtained. First, strains from the same species displayed similar transcriptomic, but not necessarily cellular, responses to the experimental conditions. It showed the importance of considering intra-specific diversity to investigate functional divergence between species. Second, a...
Tipo: Text
Palavras-chave: Phenotype; Transcriptomics; Pseudo-nitzschia; Divergence; Nutrients.
Ano: 2019
URL: https://archimer.ifremer.fr/doc/00482/59392/62157.pdf

Cophylogeny of the anther smut fungi and their caryophyllaceous hosts: Prevalence of host shifts and importance of delimiting parasite species for inferring cospeciation
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Refregier, Guislaine; Le Gac, Mickael; Jabbour, Florian; Widmer, Alex; Shykoff, Jacqui A.; Yockteng, Roxana; Hood, Michael E.; Giraud, Tatiana.
Background: Using phylogenetic approaches, the expectation that parallel cladogenesis should occur between parasites and hosts has been validated in some studies, but most others provided evidence for frequent host shifts. Here we examine the evolutionary history of the association between Microbotryum fungi that cause anther smut disease and their Caryophyllaceous hosts. We investigated the congruence between host and parasite phylogenies, inferred cospeciation events and host shifts, and assessed whether geography or plant ecology could have facilitated the putative host shifts identified. For cophylogeny analyses on microorganisms, parasite strains isolated from different host species are generally considered to represent independent evolutionary...
Tipo: Text
Ano: 2008
URL: http://archimer.ifremer.fr/doc/00176/28694/27138.pdf

Etude sur la prolifération de la micro algue Alexandrium minutum en rade de Brest. Projet Daoulex. Rapport d’avancement n° 1 : Novembre 2013
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Chapelle, Annie; Le Bec, Claude; Le Gac, Mickael; Labry, Claire; Amzil, Zouher; Guillou, Laure; Dreanno, Catherine; Pineau-guillou, Lucia.
Suite à l’événement de grande ampleur d’efflorescence d’Alexandrium minutum et des toxicités associées en Rade de Brest en 2012, un projet a été monté avec la Région dans le cadre du développement du port de Brest. De juillet à août 2013, l’Ifremer a organisé un échantillonnage serré dans l’estuaire de Daoulas, zone la plus touchée en 2012. De ce suivi et des mesures réalisées au laboratoire à ce jour, ainsi que des résultats du réseau Rephy et Velyger, il ressort que : * Alexandrium minutum s’est développé à nouveau en rade de Brest en 2013 mais à des teneurs inférieures à 2012. * l’épisode de bloom et de toxicité supérieur aux seuils légaux s’est déroulé plus tard qu’en 2012, du 1er juillet jusqu’à 5 août. * les efflorescences et la toxicité ont touché...
Tipo: Text
Ano: 2013
URL: https://archimer.ifremer.fr/doc/00191/30230/28644.pdf

Influence of gametogenesis pattern and sex on paralytic shellfish toxin levels in triploid Pacific oyster Crassostrea gigas exposed to a natural bloom of Alexandrium minutum
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Hermabessiere, Ludovic; Fabioux, C.; Lassudrie, Malwenn; Boullot, F.; Long, Marc; Lambert, Christophe; Le Goic, N.; Gouriou, Jeremie; Le Gac, Mickael; Chapelle, Annie; Soudant, P.; Hegaret, Helene.
This study investigated the effect of gametogenesis pattern and sex on levels of paralytic shellfish toxins (PST) accumulated by triploid oysters Crassostrea gigas exposed to a natural bloom of the toxic dinoflagellate Alexandrium minutum in the Bay of Brest (Western Brittany, France), over the summer 2014. Toxin accumulation in oysters was proposed to be influenced by the proportion of energy allocated to reproduction versus other metabolisms, as proposed by Haberkorn et al. (2010). Thus, we hypothesized that triploid oysters with different gametogenesis patterns (α or β, producing respectively numerous gametes or rare gametes) could result in differences in toxin accumulation. Toxin level could also be different according to the gender of the oysters. To...
Tipo: Text
Palavras-chave: Crassostrea gigas; Alexandrium minutum; Harmful algal bloom (HAB); Paralytic shellfish toxin (PST); Gametogenesis pattern; Triploid.
Ano: 2016
URL: https://archimer.ifremer.fr/doc/00307/41801/41010.pdf

Evolutionary processes and cellular functions underlying divergence in Alexandrium minutum
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Le Gac, Mickael; Metegnier, Gabriel; Chomerat, Nicolas; Malestroit, Pascale; Quere, Julien; Bouchez, Olivier; Siano, Raffaele; Destombe, Christophe; Guillou, Laure; Chapelle, Annie.
Understanding divergence in the highly dispersive and seemingly homogeneous pelagic environment for organisms living as free drifters in the water column remains a challenge. Here, we analyzed the transcriptome wide mRNA sequences, as well as the morphology of 18 strains of Alexandrium minutum, a dinoflagellate responsible for Harmful Algal Blooms worldwide, to investigate the functional bases of a divergence event. Analysis of the joint site frequency spectrum (JSFS) pointed toward an ancestral divergence in complete isolations followed by a secondary contact resulting in gene flow between the two diverging groups, but heterogeneous across sites. The sites displaying fixed SNPs were associated with a highly restricted gene flow and a strong...
Tipo: Text
Palavras-chave: Dinoflagellates; Harmful algal blooms; Populations Genomics; Pseudocryptic species; Speciation.
Ano: 2016
URL: http://archimer.ifremer.fr/doc/00347/45857/45529.pdf

Historical records from dated sediment cores reveal the multidecadal dynamic of the toxic dinoflagellate     Alexandrium minutum     in the Bay of Brest (France)
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Klouch, Khadidja; Schmidt, Sabine; Andrieux-loyer, Francoise; Le Gac, Mickael; Hervio-heath, Dominique; Qui-minet, Zujaila Nohemi; Quere, Julien; Bigeard, Estelle; Guillou, Laure; Siano, Raffaele.
The multiannual dynamic of the cyst-forming and toxic marine dinoflagellate Alexandrium minutum was studied over a time scale of about 150 years by a paleoecological approach based on ancient DNA (aDNA) quantification and cyst revivification data obtained from two dated sediment cores of the Bay of Brest (Brittany, France). The first genetic traces of the species presence in the study area dated back to 1873 ± 6. Specific aDNA could be quantified by a newly-developed real-time PCR assay in the upper core layers, in which the germination of the species (in up to 17–19 year-old sediments) was also obtained. In both cores studied, our quantitative paleogenetic data showed a statistically significant increasing trend in the abundance of A. minutum ITS1 rDNA...
Tipo: Text
Palavras-chave: Paleoecology; Ancient DNA; Real-time PCR; Harmful algal blooms (HAB); Dinoflagellates; Coastal ecology.
Ano: 2016
URL: http://archimer.ifremer.fr/doc/00334/44516/44212.pdf

Étude sur la prolifération de la micro algue Alexandrium minutum en rade de Brest
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Chapelle, Annie; Le Bec, Claude; Amzil, Zouher; Dreanno, Catherine; Guillou, Laure; Klouch, Khadidja; Labry, Claire; Le Gac, Mickael; Pineau-guillou, Lucia; Siano, Raffaele; Abernot, Chantal; Andrieux, Francoise; Caradec, Florian; Destombe, Christophe; Dia, A.; Doner, Anne; Duval, Julia; Gouriou, Jeremie; Lazure, Pascal; Le Brun, Luc; Le Gal, Dominique; Malestroit, Pascale; Petton, Sebastien; Plus, Martin; Quere, Julien; Savar, Veronique; Schmitt, Sophie; Terre, A.; Youenou, Agnes.
Suite à l’événement de grande ampleur d’efflorescence d’Alexandrium minutum et des toxicités associées en Rade de Brest en 2012, un projet a été élaboré avec la Région Bretagne dans le cadre du développement du port de Brest. L’Ifremer a organisé un échantillonnage dans l’estuaire de la rivière de Daoulas, zone la plus touchée en 2012, au cours des printemps-été 2013 et 2014. Un suivi de la présence d’A. minutum dans les sédiments a également été réalisé en hiver 2014. De ces suivis, des mesures réalisées au laboratoire à ce jour, des simulations du modèle Prévimer ainsi que des résultats du réseau Rephy et Velyger, il ressort que: * La rade de Brest peut aujourd’hui être considérée comme une zone à risque pour Alexandrium minutum. En effet, depuis 2012...
Tipo: Text
Ano: 2014
URL: http://archimer.ifremer.fr/doc/00254/36487/35029.pdf