Mercury and methylmercury concentrations, sources and distribution in submarine canyon sediments (Capbreton, SW France): Implications for the net methylmercury production

International audienceSubmarine canyons are important stocks of commercial interest fish, whose consumption is one of the main monomethymercury (MeHg) exposure to humans. Currently, biogeochemistry of mercury in those biologically productive system is unknown. In this work, inorganic mercury (Hg(II)) and organic mercury (MeHg) distributions were measured in sedimentary accumulative zones (slopes and terraces) against adjacent continental shelf sediments. Hg compound concentrations in these sediments show a huge range of concentrations (Hg(II) ranging from 18 to 973 ng g−1 and MeHg ranging from 0.07 to 2.03 ng g−1) exhibiting factors 50 and 20 fold, respectively. Higher values of mercury compounds were observed in canyon locations suggesting a high accumulation of mercury associated with higher values of clay fraction and organic matter content. The reactivity of mercury was investigated in sediment of three locations along Capbreton submarine canyon axis using slurry incubations experiments and isotopic tracers. Specific methylation and demethylation rate constants (kM and kD) were calculated. Results clearly showed that MeHg concentrations in these sediments are controlled by competing and simultaneous methylation and demethylation reactions mainly mediated by biotic process. Mercury reactivity was found higher in coastal stations compared to the offshore station due to more labile organic matter which may stimulate microbial activities. However, higher net MeHg production was estimated for the offshore station due to high Hg(II) concentrations suggesting a potential MeHg source for such marine environments

Combination of high throughput cultivation and dsrA sequencing for assessment of sulfate-reducing bacteria diversity in sediments

International audienceImproving the knowledge on sulfate-reducing bacteria (SRB) diversity and ecophysiology will permit a better understanding on their key roles in aquatic ecosystems. Therefore, their diversity was evaluated in estuarine sediments by a polyphasic approach including dsrA gene cloning and sequencing (156 clones) and high-throughput isolations in 384-well microplates (177 strains). Using the related thresholds of 95% (DsrA amino acid sequences) and 97% (16S rRNA gene sequences) for sequence similarity, SRB were grouped into 60 and 22 operational taxonomic units, respectively. Both approaches poorly overlapped and rather complemented each other. The clone library was dominated by sequences related to the Desulfobacteraceae, while only one isolate belonged to this family. Most of the strains were affiliated to the genera Desulfopila and Desulfotalea within the Desulfobulbaceae. Desulfopila-related strains exhibited a high phylogenetic microdiversity and represented numerically significant populations. In contrast, Desulfovibrio isolates were less abundant but displayed a high phylogenetic diversity. Three hundred and eighty-four-well microplate isolations enhanced significantly the number of isolates handled. As a consequence, 15 new taxa sharing less than 98% sequence similarity (16S rRNA gene) with their closest relatives were obtained. This polyphasic approach allowed to obtain a high phylogenetic diversity and thus a better view of sulfate-reducing communities in intertidal sediments. © 2012 Federation of European Microbiological Societies

Draft genome sequence of desulfovibrio BerOc1, a mercury-methylating Strain

Desulfovibrio BerOc1 is a sulfate-reducing bacterium isolated from the Berre lagoon (French Mediterranean coast). BerOc1 is able to methylate and demethylate mercury. The genome size is 4,081,579 bp assembled into five contigs. We identified the hgcA and hgcB genes involved in mercury methylation, but not those responsible for mercury demethylation

Priority and emerging micropollutants distribution from coastal to continental slope sediments: A case study of Capbreton Submarine Canyon (North Atlantic Ocean)

International audienceIncising continental margins, submarine canyons are key issue for understanding shelf/deep sea exchange of particulate pollutant, impact on marine ecosystem and global geochemical cycling. The occurrence and distribution of 100 priority and emerging micropollutants were investigated in sediments within the first 25 km of the Capbreton submarine area. The most predominant compounds were polycyclic aromatic hydrocarbons (PAHs), trace metals and metalloid (TMs) (e.g. mercury, lead and arsenic), synthetical musks (e.g. musk ketone, galaxolide), UV filters (e.g. octocrylene and 2-ethylhexyl 4-methoxycinnamate, EHMC) as well as some pharmaceuticals (e.g. azithromycin, acetaminophen). Highest concentrations were measured in submarine canyon sediments, distant from the coast and were correlated with both organic carbon and fine fraction contents, where PAHs, EHMC and musk ketone concentrations up to 7116, 32 and 7 ng g−1 dry weight, respectively. Those results likely demonstrate, that atmospheric inputs of pyrogenic PAHs, and both trapping and transporting of polluted particles along the continuum shore/deep sea by the Capbreton Canyon, might lead to an accumulation of anthropogenic micropollutants. The ecological risk assessment indicates that priority pollutants raise a potentially high risk for benthic organisms (e.g. PAHs, TMs). This might raised a specific concern about how the human can impact this ecosystem

Impact of Bioaugmentation on the Bioremediation of Saline-Produced Waters Supplemented with Anaerobic Digestate

Bioremediation of produced waters has been widely investigated in the last decades. More recently, microalgae-based treatments have been developed to produce biomass. The objective of this study was to determine, at lab scale, the remediation efficiency of three origin of microorganisms: a consortium of three halotolerant and halophilic microalgae and their associated bacteria, bacteria from liquid digestate, and aromatic-degrading bacteria selected to perform bioaugmentation. The medium was composed of artificial oil-produced water and seawater, and contained nutrients from liquid digestate. In order to identify what plays a role in nitrogen, chemical oxygen demand, and aromatics compounds elimination, and to determine the effectiveness of bioaugmentation to treat this mix of waters, 16S rRNA analyses were performed. Combination of microorganisms from different origins with the selected aromatic-degrading bacteria were also realized, to determine the effectiveness of bioaugmentation to treat these waters. Each population of microorganisms achieved similar percentage of removal during the biological treatment, with 43–76%, 59–77%, and 86–93% of elimination for ammonium, chemical oxygen demand, and aromatic compounds (with 50% of volatilization), respectively, after 7 days, and up to with 100%, 77%, and 99% after 23 days, demonstrating that in the case of this produced water, bioaugmentation with the specialized aromatic-degrading bacteria had no significant impact on the treatment. Regarding in detail the populations present and active during the tests, those from genus Marinobacter always appeared among the most active microorganisms, with some strains of this genus being known to degrade aromatic compounds

Distribution of sulfate-reducing communities from estuarine to marine bay waters

Estuaries are highly dynamic ecosystems in which freshwater and seawater mix together. Depending on tide and river inflows, particles originating from rivers or from the remobilization of sediments accumulate in the water column. Due to the salinity gradient and the high heterotrophic activity in the estuarine plume, hypoxic and anoxic microniches may form in oxygenated waters, sustaining favorable conditions for resuspended anaerobic microorganisms. In this context, we tested the hypothesis that anaerobic sulfate-reducing prokaryotes may occur in the water column of the Adour River. Using 16S ribosomal RNA (rRNA) and dsrAB-based terminal restriction fragment length polymorphism (T-RFLP) techniques, we characterized total prokaryotic and sulfate-reducing communities along a gradient from estuarine to marine bay waters.[br/] Sulfate-reducing prokaryotes were further characterized by the description of dsrB genes and the cultivation of sulfidogenic anaerobic microorganisms. As a result, physical-chemical parameters had a significant effect on water bacterial diversity and community structure along the studied gradient. The concentration of cultured sulfidogenic microorganisms ranged from 1 to 60 x 10(3) cells l(-1) in the water column. Sulfate-reducing prokaryotes occurring in estuarine waters were closely related to microorganisms previously detected in freshwater sediments, suggesting an estuarine origin, mainly by the remobilization of the sediments. In the marine bay station, sediment-derived sulfate-reducing prokaryotes were not cultured anymore, probably due to freshwater dilution, increasing salinity and extended oxic stress.[br/] Nevertheless, isolates related to the type strain Desulfovibrio oceani were cultured from the diluted plume and deep marine waters, indicating the occurrence of autochthonous sulfate-reducing bacteri

Ecotoxicology of silver nanoparticles and their derivatives introduced in soil with or without sewage sludge: A review of effects on microorganisms, plants and animals

International audienceSilver nanoparticles (AgNPs) are widely incorporated in many products, partly due to their antimicrobial properties. The subsequent discharge of this form of silver into wastewater leads to an accumulation of silver species (AgNPs and derivatives resulting from their chemical transformation), in sewage sludge. As a result of the land application of sewage sludge for agricultural or remediation purposes, soils are the primary receiver media of silver contamination. Research on the long-term impact of AgNPs on the environment is ongoing, and this paper is the first review that summarizes the existing state of scientific knowledge on the potential impact of silver species introduced into the soil via sewage sludge, from microorganisms to earthworms and plants. Silver species can easily enter cells through biological membranes and affect the physiology of organisms, resulting in toxic effects. In soils, exposure to AgNPs may change microbial biomass and diversity, decrease plant growth and inhibit soil invertebrate reproduction. Physiological, biochemical and molecular effects have been documented in various soil organisms and microorganisms. Negative effects on organisms of the dominant form of silver in sewage sludge, silver sulfide (Ag2S), have been observed, although these effects are attenuated compared to the effects of metallic AgNPs. However, silver toxicity is complex to evaluate and much remains unknown about the ecotoxicology of silver species in soils, especially with respect to the possibility of transfer along the trophic chain via accumulation in plant and animal tissues. Critical points related to the hazards associated with the presence of silver species in the environment are described, and important issues concerning the ecotoxicity of sewage sludge applied to soil are discussed to highlight gaps in existing scientific knowledge and essential research directions for improving risk assessment

Rapport de campagne HaPoGé 12-19 juillet 2017

The HaPoGé survey was planned due to a scientific opportunity tender for the HROV Ariane, it follows the test AtlantHrov campaign technique, which took place from May 26 to June 9, 2017. HaPoGé is the first scientific cruise of the HROV Ariane in Atlantic ocean, aboard a coastal vessel the “Côtes de la Manche”. It took place from July 12 to July 19, 2017. The HROV dives were located in the Capbreton canyon. This survey involved scientist from Ifremer, Bordeaux and Pau universities. It had several objectives: i) to know the morphology of rockfall and sediment areas, ii) to sample in situ the rocky outcrops and characterize the benthic communities and iii) to determine the nature, levels of concentrations and distribution of contaminants in sediments and the water column. A part of the samples for pollutants (water, sediment) will be analyzed in the MICROPOLIT project of the UPPA. Ifremer team was in charge of the biology data collection and pre-processing of video and photo pictures recorded from HROV Ariane. In the MSFD context, these data enhance knowledge for the southern Bay of Biscay where a knowledge deficit has been clearly identified.La campagne HaPoGé (Habitats, Polluants, Géologie du canyon de Capbreton) a été programmée suite à un appel d’offres scientifique d’opportunité relatif au HROV Ariane de la Commission Nationale de la Flotte Côtière. Elle fait suite à la campagne d’essai technique AtlantHrov qui s’est déroulée du 26 mai au 9 juin 2017. HaPoGé est la première campagne opérationnelle scientifique du HROV Ariane en Atlantique, à bord d’un navire côtier, le Côtes de la Manche. Elle s’est déroulée du 12 au 19 juillet 2017 au niveau du canyon de Capbreton. Cette campagne a associé les équipes de l’Ifremer Anglet, de l’université de Bordeaux et de l’université de Pau et des Pays de l’Adour (UPPA). Elle avait plusieurs objectifs : i) connaitre la morphologie des zones à tombants rocheux et à sédiment, ii) échantillonner in situ les affleurements rocheux et caractériser les communautés benthiques de macro/mégafaune et halieutiques associées et iii) déterminer la nature, les niveaux de concentrations et la distribution en contaminants dans les sédiments et la colonne d’eau. Le traitement d’une partie des prélèvements relatifs aux polluants (eau, sédiment) sera valorisé dans le cadre du projet MICROPOLIT de l’UPPA. L’Ifremer est intervenu pour la partie biologie/habitat. Le travail consistait à réaliser des enregistrements vidéo, photographies et des prélèvements de la faune benthique sur des zones sélectionnées par les géologues. Ces données constituent des éléments d’informations dans le cadre de la DCSMM où un déficit de connaissances a été clairement identifié pour le sud du golfe de Gascogne (dont le canyon de Capbreton)

Mercury methylation/demethylation and volatilization pathways in estuarine sediment slurries using species-specific enriched stable isotopes

cited By 85International audienceSpecies-specific enriched stable isotopes have been used to study mercury transformations (methylation, demethylation and volatilization) in estuarine sediments under different environmental conditions (both biotic and abiotic and oxic and anoxic). These experiments have demonstrated the potential for the isotopically enriched species in combination with highly sensitive measurement methods (ICP MS) to facilitate the study of mercury speciation and reactivity. Sediments (sterilized and nonsterilized) were spiked with both isotopically enriched inorganic (199Hg) and monomethylmercury (MM201Hg) at environmental levels to avoid perturbing the system and incubated under both aerobic and anaerobic conditions. The formation of MM199Hg and the degradation of MM201Hg were measured simultaneously during time series experiments by capillary gas chromatography-inductively coupled mass spectrometry. Specific methylation and demethylation rate constants (K m and Kd) were calculated. Results clearly showed that methylmercury levels in sediments are controlled by competing and simultaneous methylation and demethylation reactions. Operating conditions, likely to drastically modify the reactivity of the media, were of primary importance to assess the relative significance of each mechanism. In estuarine sediments, mercury methylation was enhanced under anaerobic nonsterile conditions, whereas other environmental conditions were either less favorable for monomethylmercury production or more effective for its degradation. The production of total gaseous mercury was found to be minimal, although it could be demonstrated that it was related to the fate and transformation of methylmercury. © 2004 Elsevier B.V. All rights reserved

Pseudodesulfovibrio hydrargyri sp. nov., a mercury-methylating bacterium isolated from a brackish sediment

International audienceThe strain BerOc1T was isolated from brackish sediments contaminated with hydrocarbons and heavy metals. This strain has been used as a model strain of sulfate-reducer to study the biomethylation of mercury. The cells are vibrio-shaped, motile and not sporulated. Phylogeny and physiological traits placed this strain within the genus Pseudodesulfovibrio. Optimal growth was obtained at 30 °C, 1.5 % NaCl and pH 6.0-7.4. The estimated G+C content of the genomic DNA was 62.6 mol%. BerOc1T used lactate, pyruvate, fumarate, ethanol and hydrogen. Terminal electron acceptors used were sulfate, sulfite, thiosulfate and DMSO. Only pyruvate could be used without a terminal electron acceptor. The major fatty acids were C18 : 0, anteiso-C15 : 0, C16 : 0 and C18 : 1ω7. The name Pseudodesulfovibrio hydrargyri sp. nov. is proposed for the type strain BerOc1T (DSM 10384T=JCM 31820T