Mercury methylation rates of biofilm and plankton microorganisms from a hydroelectric reservoir in French Guiana
The Petit-Saut ecosystem is a hydroelectric reservoir covering 365 km2 of flooded tropical forest. This reservoir and the Sinnamary Estuary downstream of the dam are subject to significant mercury methylation. The mercury methylation potential of plankton and biofilm microorganisms/components from different depths in the anoxic reservoir water column and from two different sites along the estuary was assessed. For this, reservoir water and samples of epiphytic biofilms from the trunk of a submerged tree in the anoxic water column and from submerged branches in the estuary were batch-incubated from 1 h to 3 months with a nominal 1000 ng/L spike of Hg(II) chloride enriched in 199Hg. Methylation rates were determined for different reservoir and estuarine communities under natural nutrient (reservoir water, estuary freshwater) and artificial nutrient (culture medium) conditions. Methylation rates in reservoir water incubations were the highest with plankton microorganisms sampled at − 9.5 m depth (0.5%/d) without addition of biofilm components. Mercury methylation rates of incubated biofilm components were strongly enhanced by nutrient addition. The results suggested that plankton microorganisms strongly contribute to the total Hg methylation in the Petit-Saut reservoir and in the Sinnamary Estuary. Moreover, specific methylation efficiencies (%Me199Hgnet/cell) suggested that plankton microorganisms could be more efficient methylating actors than biofilm consortia and that their methylation efficiency may be reduced in the presence of biofilm components. Extrapolation to the reservoir scale of the experimentally determined preliminary methylation efficiencies suggested that plankton microorganisms in the anoxic water column could produce up to 27 mol MeHg/year. Taking into account that (i) demethylation probably occurs in the reservoir and (ii) that the presence of biofilm components may limit the methylation efficiency of plankton microorganisms, this result is highly consistent with the annual net MeHg production estimated from mass balances (8.1 mol MeHg/year, Muresan et al., 2008a).
(Science of the Total Environment. vol. 408, n° 0048-9697, pp. 1338 - 1348, 01/02/2010)
LCPME, INC-CNRS, UL, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Serial analysis of gene expression in the skeletal muscles of zebrafish fed with a methylmercury-contaminated diet
Mercury (Hg) is a widespread environmental contaminant and its organic form, methylmercury (MeHg), has been known as a potent neurotoxic since the Minamata tragedy. In the Amazonian basin, gold mining leads to MeHg biomagnification all along the food web, culminating in piscivorous fish, ultimately responsible for contamination of human beings through fish consumption. In order to assess the biological impact of dietary MeHg on fish at the genome scale, we contaminated zebrafish with MeHg-contaminated food for 25 days (13.5 microg of Hg/g of food). A serial analysis of gene expression (SAGE) was conducted on the skeletal muscle because this tissue does not perform MeHg demethylation, and 19171 SAGE tags were sequenced from the control library versus 22 261 from the MeHg-contaminated library, corresponding to 5280 different transcripts. Among those identified, 60 genes appeared up-regulated and 15 down-regulated by more than 2 times. A net impact of MeHg was noticed on 14 ribosomal protein genes, indicating a perturbation of protein synthesis. Several genes involved in mitochondrial metabolism, the electron transport chain, endoplasmic reticulum (ER) function, detoxification, and general stress responses were differentially regulated, suggesting an onset of oxidative stress and ER stress. Several other genes for which expression varied with MeHg contamination could be clustered in various compartments of the cell's life, such as lipid metabolism, calcium homeostasis, iron metabolism, muscle contraction, and cell cycle regulation. This study reveals the effectiveness of the SAGE approach to acquire a better understanding of the MeHg global effects. Furthermore, this is the first time that the SAGE was used to characterize the effect of a toxicant at the genome scale in an aquatic organism.
(Environmental Science and Technology. vol. 44, n° 0013-936X, pp. 469-475, 01/01/2010)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Sublethal effects of waterborne uranium exposures on the zebrafish brain: transcriptional responses and alterations of the olfactory bulb ultrastructure
The toxic action modes of uranium (U) in fish are still scarcely known. U is known to modify the acetylcholinesterase activity in the fish brain. To gain further insight into U neurotoxicity in fish, we examined transcriptional responses in the brain of the zebrafish, Danio rerio, exposed to 15 μg L−1 and 100 μg L−1 of waterborne U for 3 and 10 days. In parallel, an ultrastructure analysis of the neuropil of the olfactory bulb, an area in the brain of fish sensitive to metal contamination, was performed after 10 days of U exposure. This combined transcriptomic and histological study is the first report performed in the brain and specifically the olfactory bulb of fish exposed to U. We found that 56 transcripts responded to the metal exposure, and the anatomical structure of the olfactory bulb was damaged. The greatest gene response occurred at the lower U concentration and the numbers of responding genes common to any two U exposures were much smaller than those unique to each exposure. These data showed that the intensity of gene response may not correlate positively with toxicant concentrations according to our experimental design. Instead, different patterns of gene expression are expected for each exposure. Gene responses were categorized into eight functional classes, and the transcriptional responses of genes involved in the olfactory system were significantly affected. Collectively, the data suggest that genes in the olfactory region may be ecologically relevant and sensitive transcriptional biomarkers of U waterborne exposure.
(Environmental Science and Technology. vol. 44, n° 0013-936X, pp. 1438-1443, 01/01/2010)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Serial analysis of gene expression in the skeletal muscles of zebrafish fed with a methylmercury-contaminated diet
Mercury (Hg) is a widespread environmental contaminant and its organic form, methylmercury (MeHg), has been known as a potent neurotoxic since the Minamata tragedy. In the Amazonian basin, gold mining leads to MeHg biomagnification all along the food web, culminating in piscivorous fish, ultimately responsible for contamination of human beings through fish consumption. In order to assess the biological impact of dietary MeHg on fish at the genome scale, we contaminated zebrafish with MeHg-contaminated food for 25 days (13.5 microg of Hg/g of food). A serial analysis of gene expression (SAGE) was conducted on the skeletal muscle because this tissue does not perform MeHg demethylation, and 19171 SAGE tags were sequenced from the control library versus 22 261 from the MeHg-contaminated library, corresponding to 5280 different transcripts. Among those identified, 60 genes appeared up-regulated and 15 down-regulated by more than 2 times. A net impact of MeHg was noticed on 14 ribosomal protein genes, indicating a perturbation of protein synthesis. Several genes involved in mitochondrial metabolism, the electron transport chain, endoplasmic reticulum (ER) function, detoxification, and general stress responses were differentially regulated, suggesting an onset of oxidative stress and ER stress. Several other genes for which expression varied with MeHg contamination could be clustered in various compartments of the cell's life, such as lipid metabolism, calcium homeostasis, iron metabolism, muscle contraction, and cell cycle regulation. This study reveals the effectiveness of the SAGE approach to acquire a better understanding of the MeHg global effects. Furthermore, this is the first time that the SAGE was used to characterize the effect of a toxicant at the genome scale in an aquatic organism.
(Environmental Science and Technology. vol. 44, n° 0013-936X, pp. 469-475, 01/01/2010)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LMBA, UBS, UBO EPE, CNRS
Seasonal progression of diatom assemblages in surface waters of Ryder Bay, Antarctica
Phytoplankton assemblages from seasonally sea-ice covered Ryder Bay (Adelaide Island, Antarctica) were studied over three austral summers (2004-2007), to link sea-ice variability and environmental conditions with algal speciation. Typical of near-shore Antarctic waters, biomass was dominated by large diatoms, although the prymnesiophyte Phaeocystis antarctica was numerically dominant. Although there was considerable interannual variability between main diatom species, high biomass of certain species or species groups corresponded consistently to certain phases of seasonal progression. We present the first documentation of an extensive bloom of the late-season diatom Proboscia inermis in February 2006, accounting for over 90% of diatom biomass. At this time, water column stratification and nutrient drawdown were high relative to other periods of the study, although carbon export was relatively low. Melt water flux in this region promotes well-stratified surface waters and high chlorophyll levels, but not necessarily concurrent increases in export production relative to seasons with lower freshwater inputs.
(Polar Biology. vol. 33, n° 0722-4060, pp. 13-29, 01/01/2010)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, BAS, NERC
What drives the millennial and orbital variations of δ18Oatm?
(Quaternary Science Reviews. vol. 29, n° 0277-3791, pp. 235-246, 01/01/2010)
LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, GLACCIOS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UNIBE, ITU
Abrupt climate changes of the last deglaciation detected in a Western Mediterranean forest record
Abrupt changes in Western Mediterranean climate during the last deglaciation (20 to 6 cal ka BP) are detected in marine core MD95-2043 (Alboran Sea) through the investigation of high-resolution pollen data and pollen-based climate reconstructions by the modern analogue technique (MAT) for annual precipitation (Pann) and mean temperatures of the coldest and warmest months (MTCO and MTWA). Changes in temperate Mediterranean forest development and composition and MAT reconstructions indicate major climatic shifts with parallel temperature and precipitation changes at the onsets of Heinrich stadial 1 (equivalent to the Oldest Dryas), the Bölling-Allerød (BA), and the Younger Dryas (YD). Multi-centennial-scale oscillations in forest development occurred throughout the BA, YD, and early Holocene. Shifts in vegetation composition and (Pann reconstructions indicate that forest declines occurred during dry, and generally cool, episodes centred at 14.0, 13.3, 12.9, 11.8, 10.7, 10.1, 9.2, 8.3 and 7.4 cal ka BP. The forest record also suggests multiple, low-amplitude Preboreal (PB) climate oscillations, and a marked increase in moisture availability for forest development at the end of the PB at 10.6 cal ka BP. Dry atmospheric conditions in the Western Mediterranean occurred in phase with Lateglacial events of high-latitude cooling including GI-1d (Older Dryas), GI-1b (Intra-Allerød Cold Period) and GS-1 (YD), and during Holocene events associated with high-latitude cooling, meltwater pulses and N. Atlantic ice-rafting. A possible climatic mechanism for the recurrence of dry intervals and an opposed regional precipitation pattern with respect to Western-central Europe relates to the dynamics of the westerlies and the prevalence of atmospheric blocking highs. Comparison of radiocarbon and ice-core ages for well-defined climatic transitions in the forest record suggests possible enhancement of marine reservoir ages in the Alboran Sea by 200 years (surface water age 600 years) during the Lateglacial.
(Climate of the Past. vol. 6, n° 1814-9324, pp. 245-264, 27/08/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, EPHE, PSL, LCE, CNRS, UMLP, UBFC
Deciphering of six blocks of Gondwanan origin within Eastern Indonesia (South East Asia)
The French Indonesian research programs, both conducted on land and offshore in the Banda Sea basins area, have led us to formulate a new interpretation of the East Indonesian geological components. In this area we distinguish, within the three main tectonic plates (Eurasian, Indo-Australian and Philippine-Pacific), seven blocks. Six blocks are deciphered as issued from the north-eastern Gondwanan margin and only one (the Halmahera block) issued from the Pacific plate. Among the Gondwanan blocks, two of them, namely Timor (probably originates from "Greater India") and Kolonodale (or the Argo block) came from the north-west Australian margin. The Lucipara, Seram and Banggai-Sula blocks originated from the western extension of the Papua-New Guinea Island while the Irian Jaya block is still linked to the North Australian margin. The last one, the Halmahera block, originated from the Pacific plate, moved westward along the North Papua-New-Guinea margin up to its present position in the northern part of the Banda Sea area. Our interpretation is mainly based on the lithostratigraphic succession, the geological evolution and the Early Mesozoic paleoposition of these blocks with respect to the climatic environment deduced from micropaleontological studies. According to previous studies, the Timor and Kolonodale blocks were detached from Gondwana during the Jurassic whereas the Lucipara, Seram and Banggai-Sula blocks were detached from Papua-New Guinea Island during the Neogene period. All these Gondwanan blocks collided with the Eurasian active margin, in the vicinity of Sulawesi Island: Timor and Kolonodale had joined the Eurasian margin by the end of the Paleogene, while Lucipara, Seram and Banggai-Sula collided with Sulawesi Island between the Middle Miocene to Middle Pliocene. After the collisions the last three blocks together with the Kolonodale block did not move again but suffered the opening of North and South Banda back-arc basins, by the Late Miocene. On the contrary, part of the Timor block moved south together with the southern margin of the south Banda basin and, later on during the middle Pliocene, collided with the northern Australian margin. The detachment of these blocks from the Gondwana margin, and their amalgamation with the Eurasian margin, are discussed and illustrated through palaeogeographic maps.
(Gondwana Research. vol. 18, n° 1342-937X, pp. 420-437, 27/08/2026)
FRE 2761, CNRS, UNIGE, LDO, INSU - CNRS, UBO EPE, CNRS, PEPS, UCBL, INSU - CNRS, CNRS, CEREGE, IRD, INRA, AMU, CdF (institution), INSU - CNRS, CNRS, Unhas, ISTO, INSU - CNRS, UO, UT, NEOLAiA, CNRS, iSTeP, UPMC, CNRS, LPGN, UN, CNRS
How life history contributes to stress response in the Manila clam Ruditapes philippinarum
Introduction Within the last decade, numerous studies have investigated the role of environmental history on tolerance to stress of many organisms. This study aims to assess if Manila clams Ruditapes philippinarum may react differently to cadmium exposure and trematode parasite infection (Himasthla elongata) depending on their origin and environmental history in Arcachon Bay (France). Materials and methods Clams were exposed to Cd (15 µg L−1) and parasites (25 cercariae per clam), alone or in combination, at 15°C under controlled laboratory conditions for 7 days. Metal accumulation and success of parasite infestation were examined, also physiological parameters such as metallothionein response and hemocyte counts and activities (phagocytosis, oxidative burst, viability, and adhesion). Results and Discussion Sensitivity of Manila clams to both stressors differed from one site to another, suggesting local adaptation of populations. Clams from the more parasitized site presented better resistance to trematodes than the others in terms of first line defense, i.e., avoidance of infection. On the other hand, clams that adapted to chronic Cd contamination showed better detoxification mechanisms, both in a faster transfer of metal from gills to visceral mass and in a higher metallothionein baseline, than clams which had never experienced Cd contamination. Finally, hemocyte concentration and viability differed between clam origin site, highlighting the fact that populations living in different environments may adapt their physiological and biochemical responses to environmental stressors. Conclusion It is therefore important to be cautious when extrapolating results from field studies of one species and one site, if the life history of the organisms is not taken into account.
(Environmental Science and Pollution Research. vol. 17, n° 0944-1344, pp. 987-998, 27/08/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LEMAR, IRD, IFREMER, UBO EPE, CNRS
Post-depositional redistribution of trace metals in reservoir sediments of a mining/smelting-impacted watershed (the Lot River, SW France)
Mining/smelting wastes and reservoir sediment cores from the Lot River watershed were studied using mineralogical (XRD, SEM-EDS, EMPA) and geochemical (redox dynamics, selective extractions) approaches to characterize the main carrier phases of trace metals. These two approaches permitted determining the role of post-depositional redistribution processes in sediments and their effects on the fate and mobility of trace metals. The mining/smelting wastes showed heterogeneous mineral compositions with highly variable contents of trace metals. The main trace metal-bearing phases include spinels affected by secondary processes, silicates and sulfates. The results indicate a clear change in the chemical partitioning of trace metals between the reservoir sediments upstream and downstream of the mining/smelting activities, with the downstream sediments showing a 2-fold to 5-fold greater contribution of the oxidizable fraction. This increase was ascribed to stronger post-depositional redistribution of trace metals related to intense early diagenetic processes, including dissolution of trace metal-bearing phases and precipitation of authigenic sulfide phases through organic matter (OM) mineralization. This redistribution is due to high inputs (derived from mining/smelting waste weathering) at the water-sediment interface of (i) dissolved SO4 promoting more efficient OM mineralization, and (ii) highly reactive trace metal-bearing particles. As a result, the main trace metal-bearing phases in the downstream sediments are represented by Zn- and Fe-sulfides, with minor occurrence of detrital zincian spinels, sulfates and Fe oxyhydroxides. Sequestration of trace metals in sulfides at depth in reservoir sediments does not represent long term sequestration owing to possible resuspension of anoxic sediments by natural (floods) and/or anthropogenic (dredging, dam flush) events that might promote trace metal mobilization through sulfide oxidation. It is estimated that, during a major flood event, about 870 t of Zn, 18 t of Cd, 25 t of Pb and 17 t of Cu could be mobilized from the downstream reservoir sediments along the Lot River by resuspension-induced oxidation of sulfide phases. These amounts are equivalent to 13-fold (Cd), not, vert, similar6-fold (Zn), 4-fold (Pb) the mean annual inputs of the respective dissolved trace metals into the Gironde estuary.
(Applied Geochemistry. vol. 25, n° 0883-2927, pp. 778-794, 27/08/2026)
LMTG, UT3, Comue de Toulouse, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, GRESE, UNILIM, ISTO, INSU - CNRS, UO, UT, NEOLAiA, CNRS, UWr, UWr