Plouzané, France
Plouzané, France

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Lelong A.,LEMAR UMR 6539 | Hegaret H.,LEMAR UMR 6539 | Soudant P.,LEMAR UMR 6539 | Bates S.S.,Gulf
Phycologia | Year: 2012

Pseudo-nitzschia is a globally distributed diatom genus, some species of which produce domoic acid (DA), the neurotoxin that causes amnesic shellfish poisoning. This toxin killed at least three humans in 1987, launching numerous studies concerning the identification, distribution, ecology and physiology of Pseudo-nitzschia spp. Since previous reviews in 1998, knowledge has been gained about the fate of DA, including its accumulation by marine animals and its degradation by light and bacteria. Molecular techniques and more precise microscopy have enabled the description of new Pseudo-nitzschia species, 15 since 2002, including ones that are cryptic and pseudo-cryptic. An increasing number of the 37 identified species, including oceanic and coastal species, have been studied in laboratory culture. The sexual reproduction of 14 species has been documented. Fourteen species have now been shown to be toxigenic, although some strains are not always toxic under the testing conditions. The biotic and abiotic factors that modify DA production are reviewed, with a focus on how new discoveries have changed our original hypotheses about control mechanisms. Recent studies confirm that silicate and phosphate limitation trigger DA production. However, stress by low concentrations of iron or high concentrations of copper are newly discovered triggers, suggesting a trace-metal chelation role for DA. Organic sources of nitrogen (urea and glutamine), as well as changes in pH, CO 2, salinity and bacterial concentration, also enhance DA production. Laboratory and field studies sometimes give divergent results for conditions that are conducive to toxin production. Gaps in knowledge include further information about the whole genome of Pseudonitzschia (including sexual stages), mechanisms of DA production and decline, presence or absence of a resting stage, heterotrophic ability, impact of viruses and fungi, and a more complete description of the ecological and physiological roles of DA.

Queroue F.,University of Tasmania | Queroue F.,University of Western Brittany | Townsend A.,University of Tasmania | Van Der Merwe P.,University of Tasmania | And 4 more authors.
Analytical Methods | Year: 2014

Trace metals are fundamental components of various biochemical reactions for phytoplankton. They serve as micronutrients and therefore play a key role in marine biogeochemical cycles. International programs such as GEOTRACES require fast, sensitive and reliable methods for the simultaneous analysis of multiple trace elements in seawater. This paper reports the development of a simplified, automated, low cost, portable, off-line extraction method with high sample throughput. The extraction uses the chelating resin Nobias-chelate PA1 offering an extraction factor of 18 from 27 mL of seawater. This solid phase extraction has been coupled with Sector Field-Inductively Coupled Plasma-Mass Spectrometry (SF-ICP-MS) for analysing dissolved manganese (dMn), cobalt (dCo), nickel (dNi), copper (dCu), cadmium (dCd) and lead (dPb). An optimum pH of 6.2 was selected allowing quantitative recovery of most elements of interest, offering stable Cu and minimum molybdenum (Mo) recoveries, limiting interferences of Cd determination. Picomolar or subpicomolar trace metal blank concentrations and detection limits were obtained suitable for open ocean sample measurements. Regular analysis of reference seawater samples (SAFe, GEOTRACES and in-house seawater) showed excellent short-term and medium-term precision (1-8% RSD) and accuracy of the method. Twenty four samples, 3 blanks, 6 standard addition calibration samples, 3 replicates of in-house seawater and 2 reference seawater samples were extracted daily. The method has been successfully applied to the analysis of seawater samples from the Southern and Pacific Oceans. © The Royal Society of Chemistry 2014.

Giraud M.,LEMAR UMR 6539 | Boye M.,LEMAR UMR 6539 | Garcon V.,LEGOS UMR 5566 | Donval A.,LEMAR UMR 6539 | de la Broise D.,LEMAR UMR 6539
Journal of Experimental Marine Biology and Ecology | Year: 2016

The inflow of deep seawater in the surface layer by an Ocean Thermal Energy Conversion (OTEC) plant will generate artificial upwelling. In order to study the potential impact on biogeochemical processes that could result, in situ microcosms were designed to simulate seawater plant discharge and these were deployed off the Caribbean coast of Martinique. Seawater was collected in ultra-clean conditions at maximum chlorophyll a concentrations (45 m depth). The water was then mixed with either 2% or 10% deep seawater (1100 m depth) and put in 2.3 L polycarbonate bottles. These microcosms were immersed for 6 days at 45 m depth on a 220 m mooring. Samples from the surrounding environment and from the microcosms were analyzed by pigment quantification, counting of picophytoplankton groups and macronutrient analyses. Similar trends in the evolutions of the phytoplankton populations were observed over time between the control microcosms (without addition of deep seawater) and the surrounding environment, suggesting that these microcosms can be used as a realistic representation of the natural surrounding waters over a 6-day incubation period. Microcosm enrichment with 10% deep seawater induced a shift in the phytoplankton assemblage towards the development of diatoms, haptophytes, and Prochlorococcus, whereas 2% enrichment only led to an increase in the Prochlorococcus population. © 2015 Elsevier B.V.

PubMed | LEMAR UMR 6539 and University Pierre and Marie Curie
Type: | Journal: Frontiers in microbiology | Year: 2015

Successive disease outbreaks in oyster (Crassostrea gigas) beds in France have resulted in dramatic losses in production, and subsequent decline in the oyster-farming industry. Deaths of juvenile oysters have been associated with the presence of a herpes virus (OsHV-1 var) and bacterial populations of the genus Vibrio. Although the pathogenicity of OsHV-1 var, as well as several strains of Vibrio has been demonstrated by experimental infections, our understanding of the complexity of infections occurring in the natural environment remains limited. In the present study, we use specific-pathogen-free (SPF) oysters infected in an estuarine environment to study the diversity and dynamics of cultured microbial populations during disease expression. We observe that rapid Vibrio colonization followed by viral replication precedes oyster death. No correlation was found between the vibrio concentration and viral load in co-infected animals. We show that the quantity of viral DNA is a predictor of mortality, however, in the absence of bacteria, a high load of herpes virus is not sufficient to induce the full expression of the disease. In addition, we demonstrate that juvenile mortalities can occur in the absence of herpes virus, indicating that the herpes virus appears neither essential nor sufficient to cause juvenile deaths; whereas bacteria are necessary for the disease. Finally, we demonstrate that oysters are a reservoir of putative pathogens, and that the geographic origin, age, and cultivation method of oysters influence disease expression.

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