Copepods Boost the Production but Reduce the Carbon Export Efficiency by Diatoms

The fraction of net primary production that is exported from the euphotic zone as sinking particulate organic carbon (POC) varies notably through time and from region to region. Phytoplankton containing biominerals, such as silicified diatoms have long been associated with high export fluxes. However, recent reviews point out that the magnitude of export is not controlled by diatoms alone, but determined by the whole plankton community structure. The combined effect of phytoplankton community composition and zooplankton abundance on export flux dynamics, were explored using a set of 12 large outdoor mesocosms. All mesocosms received a daily addition of minor amounts of nitrate and phosphate, while only 6 mesocosms received silicic acid (dSi). This resulted in a dominance of diatoms and dinoflagellate in the +Si mesocosms and a dominance of dinoflagellate in the -Si mesocosms. Simultaneously, half of the mesocosms had decreased mesozooplankton populations whereas the other half were supplemented with additional zooplankton. In all mesocosms, POC fluxes were positively correlated to Si/C ratios measured in the surface community and additions of dSi globally increased the export fluxes in all treatments highlighting the role of diatoms in C export. The presence of additional copepods resulted in higher standing stocks of POC, most probably through trophic cascades. However it only resulted in higher export fluxes for the +Si mesocosms. In the +Si with copepod addition (+Si +Cops) export was dominated by large diatoms with higher Si/C ratios in sinking material than in standing stocks. During non-bloom situations, the grazing activity of copepods decrease the export efficiency in diatom dominated systems by changing the structure of the phytoplankton community and/or preventing their aggregation. However, in flagellate-dominated system, the copepods increased phytoplankton growth, aggregation and fecal pellet production, with overall higher net export not always visible in term of export efficiency

Etude des vésicules extracellulaires endothéliales et autres marqueurs de toxicité du Benzo[a]pyrène : influence d’extraits de microalgues d’origine marine

Polycyclic aromatic hydrocarbons (PAHs), such as benzo[a]pyrene (B[a]P), are environmental pollutants associated with cancers and cardiovascular diseases. The aims of the present thesis have been : (1) to identify biomarkers of a risk of developing these pathologies due to PAHs, and (2) to test the preventing effects of natural products on HMEC-1 endothelial cells. In this context, extracellular vesicles (EV) : exosomes (EXO) and microvesicles (MV), accessible in biological fluids, seem to be promising non-invasive biomarkers. EV composition and production depend on the type and physiopathological state of the cell. Our results demonstrate that some PAHs stimulate in vitro and in vivo EV production and modify their content. We have further shown that the overproduction of EXO depends on the aromatic hydrocarbon receptor (AhR) unlike the MV. We have studied the influence of two extracts of microalgae, O. tauri and P. tricornutum, rich in omega-3 and pigments, on the toxicity of B[a]P. We have observed that O. tauri extract can influence the toxicity of B[a]P. Indeed, apoptosis and EV production were decreased likely through reduction of the expression of CYP1A1, a B[a]P bioactivation enzyme. In addition, the B[a]P-induced expression of the inflammatory cytokines IL-8 and IL1-β was reduced. The P. tricornutum extract only inhibited the expression of the B[a]P-induced cytokine IL-8 expression. Overall, this thesis suggests a potential application of EVs as biomarkers of PAH toxicity, and the possible use of O. tauri extract in the prevention of PAHs-mediated pathologies.Les hydrocarbures aromatiques polycycliques (HAP), e.g. benzo[a]pyrène (B[a]P), sont des polluants environnementaux associés aux cancers et aux maladies cardiovasculaires. Les objectifs de cette thèse ont été: (1) d’'identifier des biomarqueurs d’'un risque de développement de ces maladies dues aux HAP et (2) de tester des produits naturels en prévention, sur les cellules endothéliales HMEC-1. Dans ce contexte, les vésicules extracellulaires (VE) : exosomes (EXO) et microvésicules (MV), accessibles dans les fluides biologiques, semblent être des biomarqueurs prometteurs non invasifs. La composition et la production des VE dépendent du type et de l’'état physiopathologique de la cellule. Nos résultats démontrent que certains HAP stimulent in vitro et in vivo la production de VE et modifient leur contenu. Nous avons montré que la surproduction d’'EXO dépend du récepteur aux hydrocarbures aromatiques (AhR) contrairement aux MV. Nous avons étudié l’'influence de deux extraits de microalgues, O. tauri et P. tricornutum, riches en oméga-3 et en pigments sur la toxicité du B[a]P. Nous avons observé que l'extrait d’'O. tauri peut influencer la toxicité du B[a]P. En effet, l'apoptose et la production de VE ont diminué probablement par réduction de l'expression du CYP1A1, une enzyme de bioactivation du B[a]P. En outre, l'expression des cytokines inflammatoires induite par le B[a]P a été réduite. L'extrait de P. tricornutum n'a inhibé que l'expression de la cytokine IL-8 induite par le B[a]P. Ces travaux de thèse suggèrent une application potentielle des VE comme biomarqueurs de toxicité des HAP et la possible utilisation d'O. tauri dans la prévention de pathologies médiées par les HAP

Study of endothelial extracellular vesicles and other toxicity markers of Benzo[a]pyrene : influence of marine microalgal extracts

Les hydrocarbures aromatiques polycycliques (HAP), e.g. benzo[a]pyrène (B[a]P), sont des polluants environnementaux associés aux cancers et aux maladies cardiovasculaires. Les objectifs de cette thèse ont été: (1) d’'identifier des biomarqueurs d’'un risque de développement de ces maladies dues aux HAP et (2) de tester des produits naturels en prévention, sur les cellules endothéliales HMEC-1. Dans ce contexte, les vésicules extracellulaires (VE) : exosomes (EXO) et microvésicules (MV), accessibles dans les fluides biologiques, semblent être des biomarqueurs prometteurs non invasifs. La composition et la production des VE dépendent du type et de l’'état physiopathologique de la cellule. Nos résultats démontrent que certains HAP stimulent in vitro et in vivo la production de VE et modifient leur contenu. Nous avons montré que la surproduction d’'EXO dépend du récepteur aux hydrocarbures aromatiques (AhR) contrairement aux MV. Nous avons étudié l’'influence de deux extraits de microalgues, O. tauri et P. tricornutum, riches en oméga-3 et en pigments sur la toxicité du B[a]P. Nous avons observé que l'extrait d’'O. tauri peut influencer la toxicité du B[a]P. En effet, l'apoptose et la production de VE ont diminué probablement par réduction de l'expression du CYP1A1, une enzyme de bioactivation du B[a]P. En outre, l'expression des cytokines inflammatoires induite par le B[a]P a été réduite. L'extrait de P. tricornutum n'a inhibé que l'expression de la cytokine IL-8 induite par le B[a]P. Ces travaux de thèse suggèrent une application potentielle des VE comme biomarqueurs de toxicité des HAP et la possible utilisation d’'O. tauri dans la prévention de pathologies médiées par les HAP.Polycyclic aromatic hydrocarbons (PAHs), such as benzo[a]pyrene (B[a]P), are environmental pollutants associated with cancers and cardiovascular diseases. The aims of the present thesis have been : (1) to identify biomarkers of a risk of developing these pathologies due to PAHs, and (2) to test the preventing effects of natural products on HMEC-1 endothelial cells. In this context, extracellular vesicles (EV) : exosomes (EXO) and microvesicles (MV), accessible in biological fluids, seem to be promising non-invasive biomarkers. EV composition and production depend on the type and physiopathological state of the cell. Our results demonstrate that some PAHs stimulate in vitro and in vivo EV production and modify their content. We have further shown that the overproduction of EXO depends on the aromatic hydrocarbon receptor (AhR) unlike the MV. We have studied the influence of two extracts of microalgae, O. tauri and P. tricornutum, rich in omega-3 and pigments, on the toxicity of B[a]P. We have observed that O. tauri extract can influence the toxicity of B[a]P. Indeed, apoptosis and EV production were decreased likely through reduction of the expression of CYP1A1, a B[a]P bioactivation enzyme. In addition, the B[a]P-induced expression of the inflammatory cytokines IL-8 and IL1-β was reduced. The P. tricornutum extract only inhibited the expression of the B[a]P-induced cytokine IL-8 expression. Overall, this thesis suggests a potential application of EVs as biomarkers of PAH toxicity, and the possible use of O. tauri extract in the prevention of PAHs-mediated pathologies

Comparison of methods for DMSP measurements in dinoflagellate cultures

International audienceA comparison of three analytical methods (the indirect GC‐FPD and MIMS, and direct LC‐MS/MS) for dimethylsulfoniopropionate (DMSP) measurements was conducted to assess their accuracy and reliability. The three methods showed a linear response but are distinguished by their linearity range, the largest being for MIMS. All three methods showed good precision on Alexandrium minutum samples (2–12%). The variability between the three methods when comparing analyses of A. minutum replicates was 11%, with the DMSP measurements by LC‐MS/MS being the highest. This result also confirms that indirect DMSP measurement after hydrolysis for GC or MIMS methods does not lead to an overestimation of DMSP values in A. minutum . A special focus was made on the more recent LC‐MS/MS method including further assays in sample preparation and storage from cultures of the dinoflagellate A. minutum . Dinoflagellate cells should be harvested by gentle filtration (< 5 cm Hg) or slow centrifugation (500 × g ) to retrieve the largest DMSP pool. For the LC‐MS/MS method, MeOH used for cell extraction should be added prior to freezing (to prevent DMSP degradation). Samples will then be stable in frozen storage for at least 2 months. Finally, direct and indirect methods are complementary for identifying the exact DMSP fraction among dimethylsulfide‐producing compounds that compose total and particulate DMSP pools issued from newly screened organisms or environmental samples

Seasonal and diurnal variability in carbon respiration, calcification and excretion rates of the abalone Haliotis tuberculata L.

WOS:000462532100012International audienceAbalone (Haliotis spp.) are commercially important marine shellfish species worldwide. Knowledge about the physiology of abalone that impacts life-history traits is important for a better understanding of the biology of the species and the impact of stressful husbandry procedures at different seasons. The present study quantified the seasonal and diurnal variations in four physiological parameters of the European species Haliotis tuberculata, i.e. carbon aerial and aquatic respiration, calcification and excretion rates, and the effect of prolonged aerial exposure upon abalone aerial respiration. We also investigated the effect of individual size upon these physiological parameters. Aquatic respiration and calcification rates showed an allometric relationship with biomass. All parameters showed lower rates in cool season and higher rates in warmer season. Temperature was assumed to be the primary driver of the reported seasonal variability in physiological parameters, although reproductive needs and nutrition may also contribute to the observed patterns. Importantly, abalone did not stop calcifying in winter, and calcified more at night than during the day. Abalone did not respire more underwater at night-time than at daytime, however they excreted more overnight. The low air:aquatic ratio (0.2) is likely to be an energy-saving strategy for emerged H. tuberculata individuals. This study highlights the temporal heterogeneity in physiological rates of H. tuberculata, which constitutes a species recently domesticated in Europe

Identification of the origin of faecal contamination in estuarine oysters using Bacteroidales and F-specific RNA bacteriophage markers

Aims: The aim of this study was to identify the origin of faecal pollution impacting the Elorn estuary (Brittany, France) by applying microbial source tracking (MST) markers in both oysters and estuarine waters. Methods and Results: The MST markers used were as follows: (i) human-, ruminant- and pig-associated Bacteroidales markers by real-time PCR and (ii) human genogroup II and animal genogroup I of F-specific RNA bacteriophages (FRNAPH) by culture/genotyping and by direct real-time reverse-transcriptase PCR. The higher occurrence of the human genogroup II of F-specific RNA bacteriophages using a culture/genotyping method, and human-associated Bacteroidales marker by real-time PCR, allowed the identification of human faecal contamination as the predominant source of contamination in oysters (total of 18 oyster batches tested) and waters (total of 24 water samples tested). The importance of using the intravalvular liquids instead of digestive tissues, when applying host-associated Bacteroidales markers in oysters, was also revealed. Conclusions: This study has shown that the application of a MST toolbox of diverse bacterial and viral methods can provide multiple lines of evidence to identify the predominant source of faecal contamination in shellfish from an estuarine environment. Significance and Impact of the Study: Application of this MST toolbox is a useful approach to understand the origin of faecal contamination in shellfish harvesting areas in an estuarine setting

Microalgal carotenoids and phytosterols regulate biochemical mechanisms involved in human health and disease prevention

International audienceMicroalgae are photosynthetic microorganisms that produce numerous bioactive molecules that can be used as food supplement to prevent chronic disease installation. Indeed, they produce phycobiliproteins, polysaccharides, lipids, carotenoids and sterolic compounds. The use of microalgae in human nutrition provide a mixture of these molecules with synergistic effect. The aim of this review is to present the specific roles played by the xanthophylls, and specifically astaxanthin and fucoxanthin, two high added value carotenoids, and by microalgal phytosterols such as β-sitosterol, campesterol and stigmasterol on several cell mechanisms involved in the prevention of cardiometabolic diseases and cancers. This review explains how these microalgal molecules modulate cell signaling pathways involved in carbohydrate and lipid metabolisms, inflammation, apoptosis, invasion and metastasis. Xanthophylls and phytosterols are involved in the reduction of inflammatory markers in relation with the regulation of the c-Jun N-terminal kinases and nuclear factor-kappa B signaling pathways, and suppression of production of pro-inflammatory mediators. Xanthophylls act on glucose and lipid metabolisms via both the upregulation of peroxisome proliferator-activated receptors (PPARs) and glucose transporters and its effects on the expression of enzymes involved in fatty acid synthesis and cholesterol metabolism. Their anti-cancer effects are related to the induction of intrinsic apoptosis due to down-regulation of key regulatory kinases. The anti-angiogenesis, anti-proliferative and anti-invasive effects are correlated with decreased production of endothelial growth factors and of matrix metalloproteinases. Phytosterols have a major role on cholesterol absorption via modification of the activities of Niemann-Pick C1 like 1 and ATP-binding cassette transporters and on cholesterol esterification. Their action are also related with the modulation of PPARs and sterol regulatory element-binding protein-1 activities

Copepod grazing on diatom aggregates: Influences on particles size, sinking velocities and carbon export

International audienceWithin the marine field, zooplankton grazing may contribute to carbon export through faecal pellets emission or delay vertical sinking flux sinking phytoplankton aggregates. To assess this process, artificial monospecific aggregates of two diatom species (Chaetoceros neogracile and Skeletonema marinoi) and natural aggregates of Melosira sp. were incubated with different copepod species (Acartia clausi, Temora longicornis, Calanus helgolandicus, Euterpina acutifrons and Calanus hyperboreus). We measured a direct grazing on aggregates with ingestion rates ranging from 0.39 to 6.71 µg pigment ind-1 d-1. The relation between aggregates equivalent spherical diameters and sinking velocities have not changed, showing that copepods grazing do not affect their densities. Regarding the particle flux, we observed three main trends: 1) Fragmentation: copepods activities increase the number of particles and decrease sinking velocities, the case of incubation with T. longicornis, the number of aggregates per litter increased with significant decrease of aggregates sinking velocities; 2) Re-aggregation: copepods activities increase aggregates size spectra and consequently the sinking velocities, the average size spectra of C. neogracile aggregates significantly increased during incubation with A. clausi but not with E. acutifrons; 3) No impact, when S. marinoi aggregates were incubated with E. acutifrons or C. helgolandicus. Our results showed that copepod grazing could modulate biological pump of carbon through fragmenting or re-aggregating but not through change of aggregate density

Copepod Grazing Influences Diatom Aggregation and Particle Dynamics

In marine ecosystems, carbon export is driven by particle flux which is modulated by aggregation, remineralization, and grazing processes. Zooplankton contribute to the sinking flux through the egestion of fast sinking fecal pellets but may also attenuate the flux by tearing apart phytoplankton aggregates into small pieces through swimming activity or direct ingestion. Freely suspended cells, artificial monospecific aggregates from two different diatom species (Chaetoceros neogracile and Skeletonema marinoi) and natural aggregates of Melosira sp. were independently incubated with five different copepod species (Acartia clausi, Temora longicornis, Calanus helgolandicus, Euterpina acutifrons, and Calanus hyperboreus). During the grazing experiments initiated with free diatoms, E. acutifrons feeding activity evidenced by ingestion rates of 157 ± 155 ng Chl a ind–1 d–1, induced a significant increase of S. marinoi aggregation. Transparent exopolymeric particles (TEP) production was only slightly boosted by the presence of grazers and turbulences created by swimming may be the main trigger of the aggregation processes. All copepods studied were able to graze on aggregates and quantitative estimates led to chlorophyll a ingestion rates (expressed in Chla a equivalent, i.e., the sum of chlorophyll a and pheopigments in their guts) ranging from 4 to 23 ng Chl aeq ind–1 d–1. The relation between equivalent spherical diameters (ESDs) and sinking velocities of the aggregates did not significantly change after grazing, suggesting that copepod grazing did not affect aggregate density as also shown by Si:C and C:N ratios. Three main trends in particle dynamics could be identified and further linked to the copepod feeding behavior and the size ratio between prey and predators: (1) Fragmentation of S. marinoi aggregates by the cruise feeder T. longicornis and of Melosira sp. aggregates by C. hyperboreus at prey to predator size ratios larger than 15; (2) no change of particle dynamics in the presence of the detritic cruise feeder E. acutifrons; and finally (3) re-aggregation of C. neogracile and S. marinoi aggregates when the two filter feeders A. clausi and C. helgolandicus were grazing on aggregate at prey to predator size ratios lower than 10. Aggregation of freely suspended cells or small aggregates was facilitated by turbulence resulting from active swimming of small copepods. However, stronger turbulence created by larger cruise feeders copepods prevent aggregate formation and even made them vulnerable to breakage

Spatio-temporal variability in benthic silica cycling in two macrotidal estuaries: causes and consequences for local to global studies

International audienceThe high heterogeneity of silica cycling in coastal margins and the lack of silica data (compared to nitrogen and phosphorus) prevent the estimation of global silica retention in estuaries. In this study, the spatial and temporal variability of pore water silicic acid (Si(OH)4) profiles - that integrate benthic transport and reaction processes - was investigated at different spatial (meter, longitudinal and cross-section, intra-estuary) and temporal (tidal, seasonal) scales in two macrotidal estuaries, very close geographically but differing essentially in their shape. Studying the spatial and temporal variability of Si(OH)4 concentrations in pore waters provided evidence for the importance of transport processes, e.g. bio-irrigation, tidal pumping, resuspension and any combination of these processes, in affecting Si(OH)4 concentrations and fluxes and hence, temporary or permanent retention along the land-ocean continuum. We confirm that aSiO2 transported by rivers and estuaries clearly deserves to be better characterized as it provides an important source of reactive aSiO2 to sediments. This study brings crucial information which allows to (1) deconvoluate spatial and temporal scales, although both are most often in complete interaction, (2) design the most appropriate sampling schemes to be representative of any given system and to extrapolate at the scale of the whole estuary, (3) quantify uncertainty associated to the estimations of Si(OH)4 stocks and fluxes in this type of ecosystem, essential for budget calculations. We showed that two adjacent small macrotidal estuaries, may exhibit different behaviors regarding Si retention. Temporary retention has been observed in the meanders of the Aulne Estuary and not along the more linear Elorn Estuary, demonstrating the importance of the morphology and hydrodynamism component of the estuarine filter. This effort needs to be pursued in other systems and climatic zones, but our study suggests that the typology should not only account for the different types of land-ocean continuum (fjord, delta, mangrove...), but also incorporate the physical or biological attributes of the estuarine filter