The effect of re-dissolution solvents and HPLC columns on the analysis of mycosporine-like amino acids in the eulittoral macroalgae and

International audienceMany macroalgal species that are regularly exposed to high solar radiation such as the eulittoral green alga and the red alga synthesize and accumulate high concentrations of mycosporine-like amino acids (MAAs) as UV-sunscreen compounds. These substances are typically extracted with a widely used standard protocol following quantification by various high performance liquid chromatography (HPLC) techniques. However, further preparation steps prior to HPLC analysis as well as different HPLC column types have not been systematically checked regarding separation quality and reproducibility. Therefore pure methanol, distilled water and HPLC eluent were evaluated as re-dissolution solvent for dried and extracts, which were subsequently analyzed on three reversed-phase C8 and C18 HPLC columns. The data indicate that distilled water and the HPLC eluent gave almost identical peak patterns and MAA contents on the C8 and C18 columns. In contrast, the application of the widely used methanol led to double peaks or even the loss of specific peaks as well as to a strong decline in total MAA amounts ranging from about 35% of the maximum in to 80% of the maximum in . Consequently, methanol should be avoided as re-dissolution solvent for the HPLC sample preparation. An improved protocol for the MAA analysis in macroalgae in combination with a reliable C18 column is suggested

Spatiotemporal changes in surface sediment characteristics and benthic macrofauna composition off the Rhône River in relation to its hydrological regime

International audienceThe consequences of changes in the water flow of the Rhône River on surface sediment characteristics and benthic macrofauna composition were assessed within 3 distinct areas: (1) the delta front, (2) the prodelta, and (3) the distal zone. Five stations were sampled during or closely after: (1) an oceanic flood (April 2007), (2) a generalized flood (May 2008), (3) a Cevenol flood (December 2008), and (4) a dry period (July 2011). Measurements of sediment characteristics included granulometry (D0.5), bulk descriptors of sedimentary organics (OC, TN and THAA), descriptors of labile components of sedimentary organics (chloropigments, EHAA), and both descriptors of origin (Chl-b/Chl-a, C/N) and lability (Chl-a/(Chl-a+Phaeo-a), EHAA/THAA) of sedimentary organics. Sediment Profile Images were collected during April 2007, May 2008 and July 2011. Temporal changes in both sedimentary organics and benthic macrofauna were more important in the delta front and the prodelta than in the distal zone. Bulk characteristics of sedimentary organics presented decreasing inshore/offshore gradients during both April 2007 and July 2011 but not during May and December 2008. There were significant temporal changes in EHAA/THAA at all stations. Changes in benthic macrofauna composition differed between: (1) the delta front and the prodelta, and (2) the distal zone. In the former area, the dry period was associated with establishing a mature community characterized by high abundances and species richness. The best description of spatiotemporal changes in benthic macrofauna composition by surface sediment characteristics was obtained using D0.5, Chl-b/Chl-a, Chl-a/(Chl-a+Phaeo-a) and EHAA, which supports the role of the quality of sedimentary organics in controlling benthic macrofauna composition

Composition isotopique δ18O-δ13C des otolithes des populations de poissons récifaux de Taiaro (Tuamotu, Polynésie française) : implications isotopiques et biologiques

International audienceNuclei (larval stage) and outer parts (adult stage) of fish otoliths from the Taiaro closed lagoon (French Polynesia) and adjacent ocean have been analysed for the C–O isotopic compositions. δ18O values of the nuclei of both populations indicate that isotopic equilibrium is reached. This impliesthat the lagoonal fish population has done its complete biological cycle in the lagoon and represents an adaptation ina closed system. δ18O values of the outer parts show a slight isotopic disequilibrium (< 0.2‰) interpreted in term of vital effect. All the δ13C values exhibit a strong isotopic disequilibrium related to metabolic activityLes compositions isotopiques (O–C) des nucleus (stade larvaire) et des zones périphériques (stade adulte) d’otolithes de poissons du lagon fermé de Taiaro (Polynésie française) et de l’océan Pacifique adjacent ont été mesurées. Les valeurs de δ18O des nucleus des deux populations indiquent que l’équilibre isotopique est atteint. Par conséquent, la population de poissons du lagon a effectué son cycle biologique complet dans le lagon et représente une adaptation au milieu fermé. Les valeurs de δ18O des parties périphériques respectives montrent un léger déséquilibre (< 0,2 ‰), interprété comme un effet vital. Les valeurs de δ13C montrent un profond déséquilibre isotopique associé au métabolism

Bacterial–Fungal Interactions in the Kelp Endomicrobiota Drive Autoinducer-2 Quorum Sensing

International audienceBrown macroalgae are an essential component of temperate coastal ecosystems and a growing economic sector. They harbor diverse microbial communities that regulate algal development and health. This algal holobiont is dynamic and achieves equilibrium via a complex network of microbial and host interactions. We now report that bacterial and fungal endophytes associated with four brown algae (Ascophyllum nodosum, Pelvetia canaliculata, Laminaria digitata, and Saccharina latissima) produce metabolites that interfere with bacterial autoinducer-2 quorum sensing, a signaling system implicated in virulence and host colonization. Additionally, we performed co-culture experiments combined to a metabolomic approach and demonstrated that microbial interactions influence production of metabolites, including metabolites involved in quorum sensing. Collectively, the data highlight autoinducer-2 quorum sensing as a key metabolite in the complex network of interactions within the algal holobiont

A seasonal survey of the food web in the Lapalme Lagoon (northwestern Mediterranean) assessed by carbon and nitrogen stable isotope analysis

International audienceWe used carbon and nitrogen stable isotope analysis to describe the food web of the Lapalme Lagoon, one of the best preserved coastal lagoons along the French Mediterranean coast. Three surveys, corresponding to contrasting situations both in terms of continental inputs and of connection between the lagoon and the open sea, were conducted in June and September 2004 and in February 2005. There were significant spatiotemporal changes in the isotopic ratios of both primary producers and consumers. Temporal changes were mostly linked to important C-13-depleted continental inputs caused by the long period of heavy rainfall before the June survey. Conversely, isotopic ratios were rather similar in September and February despite the opening of the connection of the lagoon with the sea between these two surveys. The interpretation of the results in terms of the structure of the trophic network differed between the June period and the two other ones. In September 2004 and February 2005, the food web was mostly based on SOM and lagoon POM pools with only a few consumers departing from this general trend. In June 2004, a significant proportion of consumers were conversely C-13-depleted probably due to the assimilation of significant amounts of continental inputs by grazers and filter-feeders. This stresses the necessity of carrying out seasonal surveys to get a sound idea of the structure of the food web in highly variable ecosystems such as coastal lagoons. Spatial changes in isotopic ratios were likely linked to: (1) the salinity/confinement gradient with a trend toward lower delta C-13 and delta N-15 values (i.e., higher continental influence) in the inner part of the main lagoon; and (2) the high delta N-15 values of primary producers and discretely motile consumers in a semi-confined site located downstream a vineyard receiving large amounts of fertilizers. We hypothesised that these inputs are quickly N-15-enriched through denitrification and ammonia volatilisation processes and then contribute to the N-15-enrichment of salt marsh plants and seagrass at this site. This interpretation is supported by the fact that such a 15 N-enrichment of primary producers only occurred in February (i.e., after the dispersion of the fertilizers). Conversely, discretely motile consumers were 15 N-enriched all year round, which suggests that they were mostly exploiting the detritic pool derived from 1 5 N-enriched salt marsh plants

Comparison of ecological quality indices based on benthic macrofauna and sediment profile images: A case study along an organic enrichment gradient off the Rhône River

International audienc

Dynamics of phytoplankton communities in eutrophying tropical shrimp ponds affected by vibriosis

Tropical shrimp aquaculture systems in New Caledonia regularly face major crises resulting from outbreaks of Vibrio infections. Ponds are highly dynamic and challenging environments and display a wide range of trophic conditions. In farms affected by vibriosis, phytoplankton biomass and composition are highly variable. These conditions may promote the development of harmful algae increasing shrimp susceptibility to bacterial infections. Phytoplankton compartment before and during mortality outbreaks was monitored at a shrimp farm that has been regularly and highly impacted by these diseases. Combining information from flow cytometry, microscopy, pigment and phylogenetic analysis, the presence of Picocyanobacteria, Prasinophyceae and Diatomophyceae were detected as dominant phytoplankton groups and Cryptophyceae, Prymnesiophyceae and Dinophyceae as minor components. At the onset of the first shrimp mortalities, Bacillariophyceae increased while Cyanobacteria, Prymnesiophyceae and Dinophyceae decreased in the water column, followed by proliferation of Prasinophyceae. Several taxa were identified as potential harmful algae (Cyanobacteria, dinoflagellates and Phaeocystis)

Transient Receptor Potential-Vanilloid (TRPV1-TRPV4) Channels in the Atlantic Salmon, Salmo salar. A Focus on the Pineal Gland and Melatonin Production

International audienceFish are ectotherm, which rely on the external temperature to regulate their internal body temperature, although some may perform partial endothermy. Together with photoperiod, temperature oscillations, contribute to synchronizing the daily and seasonal variations of fish metabolism, physiology and behavior. Recent studies are shedding light on the mechanisms of temperature sensing and behavioral thermoregulation in fish. In particular, the role of some members of the transient receptor potential channels (TRP) is being gradually unraveled. The present study in the migratory Atlantic salmon, Salmo salar , aims at identifying the tissue distribution and abundance in mRNA corresponding to the TRP of the vanilloid subfamilies, TRPV1 and TRPV4, and at characterizing their putative role in the control of the temperature-dependent modulation of melatonin production—the time-keeping hormone—by the pineal gland. In Salmo salar , TRPV1 and TRPV4 mRNA tissue distribution appeared ubiquitous; mRNA abundance varied as a function of the month investigated. In situ hybridization and immunohistochemistry indicated specific labeling located in the photoreceptor cells of the pineal gland and the retina. Additionally, TRPV analogs modulated the production of melatonin by isolated pineal glands in culture. The TRPV1 agonist induced an inhibitory response at high concentrations, while evoking a bell-shaped response (stimulatory at low, and inhibitory at high, concentrations) when added with an antagonist. The TRPV4 agonist was stimulatory at the highest concentration used. Altogether, the present results agree with the known widespread distribution and role of TRPV1 and TRPV4 channels, and with published data on trout ( Oncorhynchus mykiss ), leading to suggest these channels mediate the effects of temperature on S. salar pineal melatonin production. We discuss their involvement in controlling the timing of daily and seasonal events in this migratory species, in the context of an increasing warming of water temperatures