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Because Allee effects have major impacts on the dynamics of small populations, they are routinely included in demographic models for the evaluation of extinction risks. However, the structure of most common models implies that other demographic parameters (like the maximum growth rate) are modified by the inclusion of an Allee effect, which also affects in return the extinction risk of the population. Whether such correlations between demographic traits occur in natural populations or merely reflect a practical constraint related to model formalism is of primary importance to understand better the dynamics of small populations. We investigated this question using 20 populations of Trichogramma wasps raised under similar conditions, of which 3 were subject to an Allee effect. We showed that these 3 populations were also characterized by lower maximum growth rate and lower carrying capacity, and that their extinction probability was higher than for non-Allee populations. These results provide the first empirical demonstration of a correlation between the presence of positive density-dependence and impaired demographic performance, which increases the extinction risk of population, especially during the establishment phase.

International audience; Nowadays, trace metal contamination of soils is a worldwide concern. In the soil, the trace metals are distributed within different mineralogical fractions, which influence the transfers and the bioavailability, then the associated toxic risk. This study aims to investigate how the development of selected fungal mycelium influences the mineralogical speciation of cadmium. In a microcosm experiment with an industrial soil contaminated by various metal, including Cd, bioaugmentation experiments with the fungus Abisdia cylindrospora were conducted. A. cylindrospora showed a good development in the microcosm. Sequential extraction procedure highlighted the decrease of the potentially available fraction (5%) after 20 days of incubation. Most of the variations occur in the reducible and the oxidable fractions.

The freshwater lakes of southwestern France are subject to the development of invasive macrophytes which are associated with mercury (Hg) contamination of the food web. The aim of this study was to determine the bioavailability of methylmercury (MeHg) produced by plant roots in aquatic ecosystems. A microcosm experiment was performed using isotopically enriched inorganic Hg at environmental concentrations (1 &micro, g 199IHg&middot, L&minus, 1). For all conditions, total Hg in fish as well as Hg species associated with different compartments (water, sediments, plant roots, fish) were analyzed by gas chromatography-inductively coupled plasma-mass spectrometry (GC-ICP-MS). In addition, sediment, plants, and fish gut microbiota were studied by MiSEQ sequencing. Some strains were isolated and tested for their ability to methylate Hg. The results revealed 199MeHg production in plant roots and the presence of this form in fish (tissues and gut), highlighting a MeHg trophic transfer. Moreover, methylator bacteria were identified from the gut contents of the fish when they were in the presence of plants. Some of them were related to bacteria found in the plant roots. On the basis of these results, the transfer of MeHg and bacteria from plants to fish is highlighted, in addition, Hg methylation is strongly suspected in the fish gut, potentially increasing the Hg bioaccumulation.

In temperate oceans, yearly transitions from winter to spring are accompanied by a phytoplanktonic bloom. Phytoplankton, at the basis of the food chain in the oceans, plays an essential role in biogeochemical cycles as it generates 50\% of the global primary production. A time series established in 2007 at SOLA, a coastal site in the North Western Mediterranean Sea, monitors environmental and biological parameters. In the first chapter, we demonstrated that several microbial amplicon sequence variants (ASVs) displayed yearly rhythmicity, despite stochastic environmental perturbations, inherent to coastal ecosystems. Network analyses, described in the second chapter, revealed that salinity and temperature deeply impacted the microbial community structure. Subnetworks highlighted that persistent ASVs switched their first neighbors depending on environmental perturbations. These observations suggest the existence of functional redundancy in marine microbial communities. In the third chapter, microcosms confirmed that temperature fluctuations strongly affected natural microbial community structure. Picophytoplankton dominated the incubated communities at low temperature, whereas diatoms prevailed at higher temperatures. These results help explain Bathycoccus prasinos peak of abundance every year at the temperature minimum at SOLA. By integrating results from a time series, cell culture and microcosms experiments, this manuscript helps unravel the impact of anthropologically driven climate change on marine microbial communities.; Dans les océans tempérés, les transitions printanières annuelles sont accompagnées de blooms phytoplanctoniques. Le phytoplancton joue un rôle essentiel dans les cycles biogéochimiques et produit la moitié de la production primaire globale. Une série temporelle établie en 2007 à SOLA, un site côtier dans le Nord-Ouest méditerranéen, surveille les paramètres environnementaux et biologiques. Dans le premier chapitre, plusieurs « amplicon sequence variants » (ASVs) microbiens avaient des motifs annuels récurrents, malgré les perturbations environnementales caractéristiques des zones côtières. L’analyse de réseaux, décrite dans le deuxième chapitre, a révélé que la salinité et la température impactaient la structure des communautés microbiennes. Des sous-réseaux ont montré que des ASVs persistant changeaient de partenaires en fonction des perturbations environnementales. Ces observations suggèrent l’existence de redondance fonctionnelle dans les communautés microbiennes marines. Dans le troisième chapitre, des expériences microcosmes ont confirmé que des variations de température affectaient la structure des communautés microbiennes naturelles. À basse température, les picophytoplanctons étaient dominants, tandis que les diatomées prévalaient aux températures plus fortes. Ces résultats permettent d’expliquer le maximum d’abondance de Bathycoccus prasinos tous les ans au minimum de température à SOLA. Ce manuscrit, intégrant à la fois les résultats d’une série temporelle, de cultures cellulaires et de microcosmes, a permis d’éclaircir l’impact anthropologique sur les communautés microbiennes marines.

In temperate oceans, yearly transitions from winter to spring are accompanied by a phytoplanktonic bloom. Phytoplankton, at the basis of the food chain in the oceans, plays an essential role in biogeochemical cycles as it generates 50\% of the global primary production. A time series established in 2007 at SOLA, a coastal site in the North Western Mediterranean Sea, monitors environmental and biological parameters. In the first chapter, we demonstrated that several microbial amplicon sequence variants (ASVs) displayed yearly rhythmicity, despite stochastic environmental perturbations, inherent to coastal ecosystems. Network analyses, described in the second chapter, revealed that salinity and temperature deeply impacted the microbial community structure. Subnetworks highlighted that persistent ASVs switched their first neighbors depending on environmental perturbations. These observations suggest the existence of functional redundancy in marine microbial communities. In the third chapter, microcosms confirmed that temperature fluctuations strongly affected natural microbial community structure. Picophytoplankton dominated the incubated communities at low temperature, whereas diatoms prevailed at higher temperatures. These results help explain Bathycoccus prasinos peak of abundance every year at the temperature minimum at SOLA. By integrating results from a time series, cell culture and microcosms experiments, this manuscript helps unravel the impact of anthropologically driven climate change on marine microbial communities., Dans les océans tempérés, les transitions printanières annuelles sont accompagnées de blooms phytoplanctoniques. Le phytoplancton joue un rôle essentiel dans les cycles biogéochimiques et produit la moitié de la production primaire globale. Une série temporelle établie en 2007 à SOLA, un site côtier dans le Nord-Ouest méditerranéen, surveille les paramètres environnementaux et biologiques. Dans le premier chapitre, plusieurs « amplicon sequence variants » (ASVs) microbiens avaient des motifs annuels récurrents, malgré les perturbations environnementales caractéristiques des zones côtières. L’analyse de réseaux, décrite dans le deuxième chapitre, a révélé que la salinité et la température impactaient la structure des communautés microbiennes. Des sous-réseaux ont montré que des ASVs persistant changeaient de partenaires en fonction des perturbations environnementales. Ces observations suggèrent l’existence de redondance fonctionnelle dans les communautés microbiennes marines. Dans le troisième chapitre, des expériences microcosmes ont confirmé que des variations de température affectaient la structure des communautés microbiennes naturelles. À basse température, les picophytoplanctons étaient dominants, tandis que les diatomées prévalaient aux températures plus fortes. Ces résultats permettent d’expliquer le maximum d’abondance de Bathycoccus prasinos tous les ans au minimum de température à SOLA. Ce manuscrit, intégrant à la fois les résultats d’une série temporelle, de cultures cellulaires et de microcosmes, a permis d’éclaircir l’impact anthropologique sur les communautés microbiennes marines.

International audience; Many scientific disciplines are currently experiencing a 'reproducibility crisis' because numerous scientific findings cannot be repeated consistently. A novel but controversial hypothesis postulates that stringent levels of environmental and biotic standardization in experimental studies reduce reproducibility by amplifying the impacts of laboratory-specific environmental factors not accounted for in study designs. A corollary to this hypothesis is that a deliberate introduction of controlled systematic variability (CSV) in experimental designs may lead to increased reproducibility. To test this hypothesis, we had 14 European laboratories run a simple microcosm experiment using grass (Brachypodium distachyon L.) monocultures and grass and legume (Medicago truncatula Gaertn.) mixtures. Each laboratory introduced environmental and genotypic CSV within and among replicated microcosms established in either growth chambers (with stringent control of environmental conditions) or glasshouses (with more variable environmental conditions). The introduction of genotypic CSV led to 18% lower among-laboratory variability in growth chambers, indicating increased reproducibility, but had no significant effect in glasshouses where reproducibility was generally lower. Environmental CSV had little effect on reproducibility. Although there are multiple causes for the 'reproducibility crisis', deliberately including genetic variability may be a simple solution for increasing the reproducibility of ecological studies performed under stringently controlled environmental conditions.

UB BIOmE EA SUPDAT; International audience; Understanding how Listeria monocytogenes, the causative agent of listeriosis, adapts to the environment is crucial. Adaptation to new matrices requires regulation of gene expression. To determine how the pathogen adapts to lagoon effluent and soil, two matrices where L. monocytogenes has been isolated, we compared the transcriptomes of L. monocytogenes CIP 110868 20 min and 24 h after its transfer to effluent and soil extract. Results showed major variations in the transcriptome of L. monocytogenes in the lagoon effluent but only minor modifications in the soil. In both the lagoon effluent and in the soil, genes involved in mobility and chemotaxis and in the transport of carbohydrates were the most frequently represented in the set of genes with higher transcript levels, and genes with phage-related functions were the most represented in the set of genes with lower transcript levels. A modification of the cell envelop was only found in the lagoon environment. Finally, the differential analysis included a large proportion of regulators, regulons, and ncRNAs.

Chloromethane (CH3Cl) is a volatile organic compound responsible for over 15% of stratospheric ozone degradation due to chlorinated compounds. It is mainly produced by living and decaying plants. Bacteria utilizing CH3Cl as sole carbon and energy source for growth were shown to be involved in the filtering of CH3Cl emissions to the atmosphere. This biological process remains to be quantified in the environment, especially for forest soil, a major CH3Cl sink. The cmuA gene is used as a biomarker of bacterial CH3Cl degradation in environmental studies. It encodes a CH3Cl methyltransferase essential for bacterial growth by the cmu (chloromethane utilization) pathway for growth with CH3Cl and the only one characterized so far. My thesis project had a double aim: i) In depth studies of CH3Cl adaptation of a model methylotrophic bacterium, Methylobacterium extorquens strain CM4; ii) Exploration of bacterial CH3Cl-utilizers in forest. An RNAseq study of strain CM4 has shown that growth with CH3Cl leads to a difference of transcription of 137 genes in its 6.2 Mb genome compared to growth with methanol (CH3OH). Among those, genes of the cmu pathway and other genes involved in the metabolism of essential cofactors for CH3Cl utilization by this pathway, are all plasmid pCMU01-encoded. Paralogous genes located on the chromosome were not differentially expressed. On the other hand, other chromosomal genes potentially involved in extruding protons generated during CH3Cl deshalogenation (hppA), NADP+ regeneration (pnt), or in the cofactor tetrahydrofolate metabolism (gcvPHT) were differentially expressed. The diversity of CH3Cl-degrading bacteria in forest soil of the German natural park of Steigerwald was studied in microcosms using stable isotope probing. Microorganisms able to assimilate labeled [13C]- CH3Cl incorporate this heavy carbon isotope in their DNA. Sequence analysis of the PCR-amplified 16S RNA encoding gene from [13C]-DNA fractions uncovered phylotypes of the genus Methylovirgula and of the order of the Actinomycetales, which were not associated with bacterial CH3Cl degradation so far. In contrast, PCR-amplified sequences of cmuA and other genes of methylotrophic metabolism were closely related to known CH3Cl-degrading isolates. These results suggest that bacteria containing genes of the cmu pathway acquired by horizontal gene transfer as well as bacteria lacking the cmu pathway contribute to biological filtering of CH3Cl in forest soil. Future experiments coupling molecular and culture methods will aim to discover new CH3Cl-degrading pathways and to characterize the abundance and diversity of CH3Cl-degradation metabolism in soil and other environmental compartments., Le chlorométhane (CH3Cl) est un composé organique volatile responsable de plus de 15 % de la dégradation de l’ozone stratosphérique due aux composés chlorés. Il est produit majoritairement par les plantes vivantes ou en décomposition. Les bactéries capables d’utiliser le CH3Cl comme source de carbone pour leur croissance peuvent jouer un rôle de filtre dans les émissions de CH3Cl vers l'atmosphère. Ce processus biologique reste à quantifier dans l'environnement, notamment pour les sols forestiers considérés comme un puits majeur de ce composé.Dans les études environnementales, le gène cmu A est utilisé comme biomarqueur de la dégradation bactérienne du CH3Cl. Il code une chlorométhane méthyltransférase essentielle à la croissance bactérienne avec le CH3Cl parla voie cmu (pour chloromethane utilisation), la seule caractérisée à ce jour. Mon projet de thèse avait un double objectif : i) l’approfondissement des connaissances de l’adaptation au CH3Cl chez une bactérie méthylotrophe modèle, Methylobacterium extorquens CM4; ii) l’exploration de la diversité des bactéries CH3Cl-dégradantes de sols forestiers. L’étude RNAseq chez la souche CM4 a montré que la croissance avec le CH3Cl s'accompagne de différences dans la transcription de 137 gènes de son génome (6.2 Mb) par rapport à sa croissance sur le méthanol (CH3OH). Les gènes de la voie cmu, ainsi que d’autres gènes impliqués dans le métabolisme de cofacteurs essentiels à l’utilisation du CH3Cl par cette voie et eux aussi portés par le plasmide pCMU01 de la souche, en font partie. Les paralogues de ces gènes localisés sur le chromosome ne sont quant à eux pas différentiellement exprimés. En revanche, d’autres gènes du chromosome, potentiellement impliqués dans l’excrétion de protons produits lors de la déshalogénation (hppA), la régénération du NADP+ (pnt), ou le métabolisme du cofacteur tétrahydrofolate(gènes gcvPHT), le sont. L’étude de la diversité des bactéries CH3Cl-dégradantes de sol forestier de la réserve naturelle de Steigerwald (Allemagne) a été réalisée sur des microcosmes par une approche de « Stable Isotope Probing ». Les microorganismes capables d’assimiler le CH3Cl marqué au [13C] incorporent cet isotope lourd du carbone dans leur ADN. L'analyse des séquences amplifiées par PCR des gènes codant l’ARN 16S des fractions d'ADN enrichies en [13C] a permis de mettre en évidence de nouveaux phylotypes, du genre Methylovirgula et de l’ordre des Actinomycetales, distincts de ceux auxquelles les souches dégradant le CH3Cl isolées jusqu'ici sont affiliées. En revanche, les séquences du gène cmuA et d’autres gènes du métabolisme méthylotrophe obtenues par PCR à partir de l'ADN enrichi en [13C] sont très proches de celles des souches CH3Cl-dégradantes connues. Les résultats obtenus suggèrent ainsi que des bactéries ayant acquis par transfert horizontal les gènes de dégradation de la voie cmu ou ne possédant pas de gène cmuA contribuent au filtrage biologique du CH3Cl des sols forestiers. A l'avenir, le couplage de différentes méthodes moléculaires et des approches culturales visera à découvrir de nouvelles voies microbiennes de l’utilisation du CH3Cl, et à caractériser l’abondance et la diversité des métabolismes impliqués dans la dégradation du CH3Cl dans les sols et d'autres compartiments environnementaux.

Contamination of coastal environments is often due to a complex mixture of pollutants, sometimes in trace levels, that may have significant effects on diversity and function of organisms. The aim of this study was to evaluate the short-term dynamics of bacterioplankton exposed to natural and artificial mixtures of contaminants. Bacterial communities from a southwestern Mediterranean ecosystem, lagoon and the bay (offshore) of Bizerte were exposed to i) elutriate from resuspension of contaminated sediment, and ii) an artificial mixture of metals and herbicides mimicking the contamination observed during sediment resuspension. Elutriate incubation as well as artificial spiking induced strong enrichments in nutrients (up to 18 times), metals (up to six times) and herbicides (up to 20 times) relative to the in situ concentrations in the offshore station, whereas the increases in contaminants were less marked in the lagoon station. In the offshore waters, the artificial mixture of pollutants provoked a strong inhibition of bacterial abundance, production and respiration and significant modifications of the potential functional diversity of bacterioplankton with a strong decrease of the carbohydrate utilization. In contrast, incubation with elutriate resulted in a stimulation of bacterial activities and abundances, suggesting that the toxic effects of pollutants were modified by the increase in nutrient and DOM concentrations due to the sediment resuspension. The effects of elutriate and the artificial mixture of pollutants on bacterial dynamics and the functional diversity were less marked in the lagoon waters, than in offshore waters, suggesting a relative tolerance of lagoon bacteria against contaminants.

International audience

These experiments are part of the actual problematic of understanding the poorknown effects of pesticides mixtures in soil ecosystem. The herbicidal commercial formulations of S-metolachlor (Dual Gold Safeneur®), mesotrione (Callisto®) and nicosulfuron (Milagro®) were applied in mixtures at the recommended field rate. Formulated compounds are more toxic than active ingredients alone (Microtox®) and no synergistic or antagonistic effects were recorded. However, these mixtures impaired rapidly and transitory the Limagne soil microbial communities, without modifying the global parameters of structure and abundance. Effects were also recorded on sensitive communities, such as phototrophic, nitrifying and denitrifying communities. A comparison of mixtures effects on phototrophic communities from two soils underlined the high toxicity of Dual Gold Safeneur® and challenged its use from an ecotoxicological point of view.., Ces travaux s’inscrivent dans une problématique actuelle de compréhension des effets, encore peu connus, des mélanges de pesticides dans le sol. Les formulations d’herbicides S-métolachlore (Dual Gold Safeneur®), mésotrione (Callisto®) et nicosulfuron (Milagro®) ont été appliquées en mélanges et à la dose agronomique recommandée. Les molécules formulées sont plus toxiques que les molécules actives seules (Microtox®) et aucun effet synergique ou antagoniste des mélanges n’a été observé. Cependant, ces mélanges impactent transitoirement et à court terme les communautés microbiennes du sol de Limagne, sans modifier les paramètres généraux de structure et d’abondance. Toutefois, des effets ont été mis en évidence sur des communautés sensibles telles que les phototrophes ou celles impliquées dans les processus de nitrification et de dénitrification. De plus, une comparaison des effets des mélanges sur les communautés phototrophes de deux sols souligne l’importante toxicité du Dual Gold Safeneur® et remet en cause son utilisation d’un point de vue écotoxicologique.

International audience; The roles of species richness, resource use, and resource availability are central to many hypotheses explaining the diversityinvasion phenomenon but are generally not investigated together. Here, we created a large diversity gradient of soil microbial communities by either assembling communities of pure bacterial strains or removing the diversity of a natural soil. Using data on the resource-use capacities of the soil communities and an invader that were gathered from 71 carbon sources, we quantified the niches available to both constituents by using the metrics community niche and remaining niche available to the invader. A strong positive relationship between species richness and community niche across both experiments indicated the presence of resource complementarity. Moreover, community niche and the remaining niche available to the invader predicted invader abundance well. This suggested that increased competition in communities of higher diversity limits community invasibility and underscored the importance of resource availability as a key mechanism through which diversity hinders invasions. As a proof of principle, we subjected selected invaded communities to a resource pulse, which progressively uncoupled the link between soil microbial diversity and invasion and allowed the invader to rebound after nearly being eliminated in some communities. Our results thus show that (1) resource competition suppresses invasion, (2) biodiversity increases resource competition and decreases invasion through niche preemption, and (3) resource pulses that cannot be fully used, even by diverse communities, are favorable to invasion.

Polycyclic aromatic hydrocarbons (PAHs) are persistent organic pollutants (POP) emitted mainly by human activities due to the incomplete combustion of organic matter (industry, heating, traffic ...). Because of their low rate of degradation, their toxicity and their bioaccumulation, PAHs are main of concern in ecological studies. In this context, the objectives of this thesis were to assess the impact of PAHs on the benthic microflora and meiofauna and apply different techniques of bioremediation (biostimulation, bioaugmentation and combination of both treatments) in order to degrade PAHs, using experimental approach with microcosms.Our results showed that PAHs are toxic for microflora but also for meiofauna of Bizerta lagoon. The toxic effects of these contaminants were demonstrated by the inhibition of bacterial activity in the sediment/water interface and by profound changes in the structure of bacterial communities. PAHs provoked significant changes on meiofaunal community with the selection of nematode species that could be proposed as bioindicators of PAH pollution. Thus, Spirinia parasitifera which significantly (p

International audience; Purpose: The main goals of this study were to investigate (1) the behavior of microbial communities in response to low-dose bioavailable anthracene addition in lightly contaminated sediment from Bizerte Lagoon and (2) the effects of bioremediation treatments on microbial biomass, activity, and community structure. Methods: Sediment microcosms amended with 1 ppm anthracene were incubated in triplicate during 30 days. Biostimulation (addition of nitrogen and phosphorus fertilizer) and bioaugmentation (inoculation of a hydrocarbonoclastic bacterium) were used as bioremediation treatments. Bacterial biomass was estimated using flow cytometry. Sediment oxygen consumption was measured with oxygen microelectrodes. Bacterial community structure was assessed by molecular fingerprints (terminal restriction fragment length polymorphism; T-RFLP) analysis. Results: Anthracene contamination resulted in a significant reduction of bacterial abundance with an impact on cell integrity. Concomitantly, sediment oxygen consumption was strongly inhibited. Correspondence analysis on T-RFLP data indicated that bacterial community structures from anthracene-contaminated microcosms were different from that of the control. Interestingly, the changes observed in microbial biomass, structure, and activities as a result of anthracene contamination were not alleviated even with the use of biostimulation and combination of biostimulation and bioaugmentation strategy for anthracene bioremediation. Nevertheless, both treatment methods resulted in different community structures relative to the contaminated and control microcosms with the appearance of distinct populations. Conclusion: Anthracene spiking severely affected microbial communities, suggesting dominance of nontolerant populations in this lightly-contaminated sediment. Although biostimulation and/or bioaugmentation treatments did not alleviate the anthracene toxic effects, the changes observed in microbial population and structure suggest that the proposed treatments might be promising to promote bacterial growth. Further works are still required to propose a more efficient strategy to stimulate biodegradation that takes into account the complex interactions between species for resource access. © 2012 Springer-Verlag.

This work aims to study the effects of a few pesticides and one adjuvant on marine organisms, representatives of four trophic levels : micro-algae, echinoderm, bivalves and fish. Analysis of the pollu-sensitivity was based on the utilisation of existing bio-assays or adapted to this study.Phytotoxic assessments were conducted on three phytoplanktonic species (Chaetoceros calcitrans, Isochrysis aff. Galbana et Tetraselmis suecica) using the fungicide epoxiconazole and the adjuvant nonylphenol. Sensitivity to these toxicants of C. calcitrans and I. aff. Galbana was high. Thus, when C. calcitrans was grown in a medium simulating pre-winter conditions in Gabès Gulf, EC50 values were respectively, 2.31 mg/L and 2.9 μg/L for epoxiconazole active ingredient and epoxiconazole-formulated. These results questioned the use of ecotoxicological data obtained solely using active molecules of pesticides rather the complete formulation and show that non-target micro-algae may be affected by a triazole fungicide.Moreover, cell age, light and nutrient composition induced changes in epoxiconazole sensitivity, suggesting that cellular density is an important parameter in toxicity tests.Analysis of a few physiological parameters show that contaminants used in this study induce an increase of pigment content, ATP synthesis, and rates of oxygen exchanges while the cell volume enlarges. Consequently, the toxicants might reduce the growth rate, by a prolongation of the cell cycle without affecting the production of new material for the construction of new cells.Bioassays were conducted using microcosms during a bloom of the toxic algae Karenia selliformis in the Gulf of Gabès. The different toxicants (epoxiconazole, chlorpyrifos-éthyl, nonyphenol) produced drastic changes in the phytoplankton communities, depending on the type and concentration of the contaminant.Phytotoxic assessments were conducted on marine animal models, using different developmental stages: embryo-larval development (sea urchin, oyster, and clam), metamorphosis larvae (clam) and larvae survival (turbot). Results show that turbot larvae are most sensitive to the action of contaminants with EC50 values ranging from 2.78 to 492 μg/L depending on the toxic and that the metamorphosis is the stage the most sensitive of the three stages of development of clam studied.The pollutants produced developmental and embryonic abnormalities that might induce a reduction in the natural production by acting i) directly on the development of the marine organisms and ii) indirectly on the quality and bioavailability of food through the variation of phytoplankton biomass.These results underline the need to study pollutant effects on marine organisms having different organizations to evaluate their full impact.; L’objectif de ce travail de thèse vise à analyser les effets de quelques pesticides et d’un adjuvant sur des organismes marins, représentatifs de quatre niveaux trophiques, à savoir des micro-algues, un échinoderme, des bivalves et un poisson. L’analyse de la pollu-sensibilité est basée sur l’utilisation de différents bio-essais existants ou adaptés au contexte de cette étude.Les tests de toxicité ont permis d’évaluer la sensibilité de trois espèces phytoplanctoniques (Chaetoceros calcitrans, Isochrysis aff. Galbana et Tetraselmis suecica) vis-à-vis d’un fongicide l’époxiconazole (pur et en formulation commerciale Opus) et de l’adjuvant nonylphénol. D’une manière générale, la croissance de C. calcitrans et I. aff. Galbana s’avère plus sensible à l’action des contaminants étudiés. Ainsi, en utilisant pour C. calcitrans un milieu reproduisant les conditions naturelles du Golfe de Gabès, des valeurs de CE50 de 2 ,31 mg/L et 2,9 μg/l sont obtenues respectivement avec la substance active époxiconazole, et le produit formulé. Ces résultats montrent l’importance des adjuvants dans la toxicité et que les micro-algues peuvent être sensibles aux effets non-cibles d’un fongicide triazole.En outre, l’âge des cellules, les conditions d’éclairement et de composition des milieux de culture induisent des changements de sensibilité au fongicide, suggérant que la densité cellulaire est un paramètre important dans les tests de toxicité.L’analyse de quelques paramètres physiologiques montre que les contaminants utilisés induisent une augmentation du volume cellulaire, des échanges gazeux, de la teneur en pigments et en ATP. Il apparaît ainsi que les toxiques utilisés réduisent la vitesse de croissance, prolongeant le cycle cellulaire, sans affecter la production de nouveaux matériaux, nécessaires à la construction de nouvelles cellules.Par ailleurs, une étude réalisée en microcosmes lors d’un bloom de l’algue toxique Karenia selliformis dans le golfe de Gabès, montre que les différents contaminants chimiques (époxiconazole, chlorpyriphos-éthyl, nonylphénol) produisent des modifications drastiques de la structure des communautés phytoplanctoniques, fonction de la nature et de la concentration du contaminant.La toxicité des différents contaminants a été étudiée sur des animaux marins, aux stades embryo-larvaire (oursin, huître, palourde), métamorphose des larves (palourde) et survie des larves (turbot). Les résultats montrent que les larves du turbot sont les plus sensibles à l’action des contaminants avec des CE50 allant de 2,78 à 492 μg/L selon le toxique et que chez la palourde, la métamorphose est le stade le plus sensible parmi les trois stades de développement étudiés. Les contaminants utilisés produisent des anomalies du développement et des malformations embryonnaires qui peuvent induire une réduction de la production naturelle en agissant i) directement sur le développement embryo-larvaire et ii) indirectement sur la qualité et la biodisponibilité de l’aliment à travers la variation de la biomasse phytoplanctonique. Ces résultats soulignent la nécessité d’appliquer les toxiques à différents organismes marins présentant des organisations différentes pour apprécier pleinement leur impact.

This work aims to study the effects of a few pesticides and one adjuvant on marine organisms, representatives of four trophic levels : micro-algae, echinoderm, bivalves and fish. Analysis of the pollu-sensitivity was based on the utilisation of existing bio-assays or adapted to this study.Phytotoxic assessments were conducted on three phytoplanktonic species (Chaetoceros calcitrans, Isochrysis aff. Galbana et Tetraselmis suecica) using the fungicide epoxiconazole and the adjuvant nonylphenol. Sensitivity to these toxicants of C. calcitrans and I. aff. Galbana was high. Thus, when C. calcitrans was grown in a medium simulating pre-winter conditions in Gabès Gulf, EC50 values were respectively, 2.31 mg/L and 2.9 μg/L for epoxiconazole active ingredient and epoxiconazole-formulated. These results questioned the use of ecotoxicological data obtained solely using active molecules of pesticides rather the complete formulation and show that non-target micro-algae may be affected by a triazole fungicide.Moreover, cell age, light and nutrient composition induced changes in epoxiconazole sensitivity, suggesting that cellular density is an important parameter in toxicity tests.Analysis of a few physiological parameters show that contaminants used in this study induce an increase of pigment content, ATP synthesis, and rates of oxygen exchanges while the cell volume enlarges. Consequently, the toxicants might reduce the growth rate, by a prolongation of the cell cycle without affecting the production of new material for the construction of new cells.Bioassays were conducted using microcosms during a bloom of the toxic algae Karenia selliformis in the Gulf of Gabès. The different toxicants (epoxiconazole, chlorpyrifos-éthyl, nonyphenol) produced drastic changes in the phytoplankton communities, depending on the type and concentration of the contaminant.Phytotoxic assessments were conducted on marine animal models, using different developmental stages: embryo-larval development (sea urchin, oyster, and clam), metamorphosis larvae (clam) and larvae survival (turbot). Results show that turbot larvae are most sensitive to the action of contaminants with EC50 values ranging from 2.78 to 492 μg/L depending on the toxic and that the metamorphosis is the stage the most sensitive of the three stages of development of clam studied.The pollutants produced developmental and embryonic abnormalities that might induce a reduction in the natural production by acting i) directly on the development of the marine organisms and ii) indirectly on the quality and bioavailability of food through the variation of phytoplankton biomass.These results underline the need to study pollutant effects on marine organisms having different organizations to evaluate their full impact., L’objectif de ce travail de thèse vise à analyser les effets de quelques pesticides et d’un adjuvant sur des organismes marins, représentatifs de quatre niveaux trophiques, à savoir des micro-algues, un échinoderme, des bivalves et un poisson. L’analyse de la pollu-sensibilité est basée sur l’utilisation de différents bio-essais existants ou adaptés au contexte de cette étude.Les tests de toxicité ont permis d’évaluer la sensibilité de trois espèces phytoplanctoniques (Chaetoceros calcitrans, Isochrysis aff. Galbana et Tetraselmis suecica) vis-à-vis d’un fongicide l’époxiconazole (pur et en formulation commerciale Opus) et de l’adjuvant nonylphénol. D’une manière générale, la croissance de C. calcitrans et I. aff. Galbana s’avère plus sensible à l’action des contaminants étudiés. Ainsi, en utilisant pour C. calcitrans un milieu reproduisant les conditions naturelles du Golfe de Gabès, des valeurs de CE50 de 2 ,31 mg/L et 2,9 μg/l sont obtenues respectivement avec la substance active époxiconazole, et le produit formulé. Ces résultats montrent l’importance des adjuvants dans la toxicité et que les micro-algues peuvent être sensibles aux effets non-cibles d’un fongicide triazole.En outre, l’âge des cellules, les conditions d’éclairement et de composition des milieux de culture induisent des changements de sensibilité au fongicide, suggérant que la densité cellulaire est un paramètre important dans les tests de toxicité.L’analyse de quelques paramètres physiologiques montre que les contaminants utilisés induisent une augmentation du volume cellulaire, des échanges gazeux, de la teneur en pigments et en ATP. Il apparaît ainsi que les toxiques utilisés réduisent la vitesse de croissance, prolongeant le cycle cellulaire, sans affecter la production de nouveaux matériaux, nécessaires à la construction de nouvelles cellules.Par ailleurs, une étude réalisée en microcosmes lors d’un bloom de l’algue toxique Karenia selliformis dans le golfe de Gabès, montre que les différents contaminants chimiques (époxiconazole, chlorpyriphos-éthyl, nonylphénol) produisent des modifications drastiques de la structure des communautés phytoplanctoniques, fonction de la nature et de la concentration du contaminant.La toxicité des différents contaminants a été étudiée sur des animaux marins, aux stades embryo-larvaire (oursin, huître, palourde), métamorphose des larves (palourde) et survie des larves (turbot). Les résultats montrent que les larves du turbot sont les plus sensibles à l’action des contaminants avec des CE50 allant de 2,78 à 492 μg/L selon le toxique et que chez la palourde, la métamorphose est le stade le plus sensible parmi les trois stades de développement étudiés. Les contaminants utilisés produisent des anomalies du développement et des malformations embryonnaires qui peuvent induire une réduction de la production naturelle en agissant i) directement sur le développement embryo-larvaire et ii) indirectement sur la qualité et la biodisponibilité de l’aliment à travers la variation de la biomasse phytoplanctonique. Ces résultats soulignent la nécessité d’appliquer les toxiques à différents organismes marins présentant des organisations différentes pour apprécier pleinement leur impact.

International audience; Purpose: The main goals of this study were (1) to examine the effects of zinc on the microbial community structure of anthropogenically impacted sediments in a tropical coastal ecosystem and (2) to determine whether these microbial benthic communities may enhance the adsorption of zinc. Methods: The interactions between zinc and bacteria in tropical sediments were studied in sediment microcosms amended with 2.5 mg L-1 of Zn in the water phase and incubated for 8 days under different environmental conditions, oxic/anoxic and glucose addition. At the end of incubation, microbial structure was assessed by molecular fingerprints (T-RFLP) analysis and Zn speciation in the sediment was determined by sequential extraction. Results: In the three studied sediments, Zn spiking resulted in only slight changes in bacterial community structure. In contrast, the addition of low concentrations of glucose (5 mM) strongly modified the bacterial community structure

An increasing number of chemicals are produced worldwide and a large part of them are plant protection products (PPPs). France is the first European consumer of PPPs and the third on the global level. The aim of our research was to investigate the fate and the effects of pesticides in the environment, particularly in the agrosystem, with the use of a bioindicator model, the snail Helix aspersa. We chose to characterize the exposure, the transfer and the effects on snails of 8 commercial herbicide and fungicide formulations (Roundup® and Bypass® = glyphosate; Basta® = glufosinate; Valiant® Flash = folpet + cymoxanil + fosetyl-Al; Corail® = tebuconazole; Cabrio® Top = pyraclostrobin + metiram-Zn; Thiovit® = sulphur; Bordeaux mixture = copper salts), commonly employed in vineyards. A field study in real conditions of pesticide application allowed the quantification of the spray deposits on soil in the parcel and in its surroundings showing the PPP drift deposits. At the same time, few effects were demonstrated on the survival and growth of juvenile snails exposed in microcosms to the different treatments, except for growth inhibition after Roundup® exposure, probably in relation to heavy spray deposits on the soil, accumulation and metabolisation of the active ingredient in the tissues. A soil extraction and analysis method involving two herbicides (glyphosate, glufosinate) was developed allowing the determination of exposure concentrations along the experiments and their persistence in a vineyard soil. The effects of Bypass® and Basta® were studied on the whole life cycle of snails in laboratory conditions. No significant effects were shown on survival and growth although an accumulation of glyphosate was revealed in snails (6 mg kg-1) exposed continuously to contaminated food (30 mg kg-1). However, we found that exposure of snails to glyphosate during their embryonic development tended to disrupt reproduction in the resulting adult snail (by decreasing fertility) due to a delayed effect of the herbicide. The potential targets affected at the level of neuro-endocrine control are discussed. All pesticides inhibited egg hatching success at lower concentrations than those applied in the field and the influence of soil characteristics on the toxicity of the pesticides was demonstrated. These effects were showcased by laboratory experiments that led to the development of embryotoxicity bioassays. This work has contributed to current understanding of the in- and on-soil fate and effects on snails (transfer and toxicity) of various pesticides applied to the vineyard. It allowed the development of tools (laboratory bioassays and field exposure device) that could help improving pesticide risk assessment proceedings in a terrestrial environment. The analysis methods designed for use in complex matrixes (soil and animal tissues) make an original contribution to environmental and human health risk assessment. Extensive analytic difficulties were encountered and it was not possible to finalize the analytical methods for all of the substances studied. Thus, the determination of pesticide residues in animal tissues still represents an essential challenge for current environmental concerns.; De plus en plus de substances chimiques sont produites dans le monde et une grande partie d'entre elles entrent dans la composition des produits phytosanitaires. La France en est le premier consommateur européen et le troisième au niveau mondial. L'objectif de nos recherches est de comprendre le devenir et les effets de ces molécules dans l'environnement, notamment agricole, grâce à l'utilisation d'un invertébré bioindicateur, l'escargot Helix aspersa. Nous avons choisi de caractériser l'exposition, le transfert et les effets sur l'escargot de 8 formulations commerciales de fongicides et d'herbicides (Roundup® et Bypass® = glyphosate; Basta® = glufosinate; Valiant® Flash = folpel + cymoxanil + fosétyl-Al; Corail® = tébuconazole; Cabrio® Top = pyraclostrobine + métirame-Zn; Thiovit® = soufre; Bouillie bordelaise = cuivre), communément utilisées en viticulture. Une étude réalisée en conditions in situ a permis de quantifier les retombées au sol des pesticides appliqués sur la vigne, dans la parcelle et en périphérie mettant en évidence les dépôts suite à la dérive des substances. En parallèle, peu d'effets ont été démontrés sur la survie et la croissance d'escargots juvéniles placés en microcosmes et soumis aux différents traitements de pesticides, mis à part un effet inhibiteur du Roundup® sur la masse des organismes, probablement en relation avec d'importants dépôts au sol, l'accumulation et la métabolisation de la substance active dans les tissus. Une méthode d'extraction et d'analyse de deux herbicides (glyphosate et glufosinate) dans le sol a été développée afin de pouvoir mesurer les concentrations d'exposition pour diverses expériences et de caractériser leur persistance dans ce sol de vigne. Les effets du Bypass® et du Basta® ont été étudiés sur l'ensemble du cycle de vie de l'escargot en conditions contrôlées. Aucun effet significatif sur la survie et la croissance n'a été démontré bien qu'une accumulation de glyphosate ait été quantifiée chez des escargots (6 mg kg-1) nourris continuellement par de l'aliment contaminé (à 30 mg kg-1). Cependant, une exposition au glyphosate des escargots durant le développement embryonnaire semble perturber leur reproduction (diminution de la fertilité) du fait d'un effet différé de cet herbicide. Les cibles potentiellement affectées au niveau du contrôle neuroendocrine sont discutées. Tous les pesticides inhibent l'éclosion des œufs de l'escargot à des concentrations inférieures à celles appliquées au champ et l'influence des caractéristiques du sol sur leur toxicité a été démontrée. Ces effets ont été mis en évidence lors d'expériences réalisées en laboratoire dans le cadre d'un développement de bioessais d'embryotoxicité. Ces travaux de thèse ont apporté des connaissances sur le comportement, en surface et dans le sol, ainsi que dans l'escargot (transfert, toxicité), de plusieurs pesticides appliqués sur la vigne. Ils ont également permis de développer plusieurs outils (bioessais de laboratoire, dispositif d'exposition sur le terrain) visant à améliorer les procédures d'évaluation du risque des pesticides dans l'environnement terrestre. Les techniques d'analyse de ces composés mises au point pour des matrices complexes (sols, tissus animaux), constituent un apport original pour l'évaluation du risque environnemental et sanitaire. D'importantes difficultés analytiques ont été rencontrées et il n'a pas été possible de finaliser les méthodes de dosage pour la totalité des substances. Ainsi, la mesure des résidus de pesticides dans les tissus d'origine animale reste un challenge fort et qui plus est, au cœur des préoccupations environnementales actuelles.

International audience; Aggregates derived from senescent phytoplankton populations and associated microbial assemblages were incubated aerobically in the dark to assess the compositional changes in lipids during the degradation of artificial marine snow. The prevalence of saturated over unsaturated fatty acids indicated that aggregates were already degraded when incubation started. Nonetheless, the lipids in the artificial aggregates were quickly further degraded as indicated by a depletion in short-chain (20) saturated fatty acids fluctuated, suggesting that some of these lipids could have been produced in situ by marine microorganisms rather than deriving from higher plant debris. In addition, a bacterial branched monounsaturated fatty acid (11-methyloctadecenoic acid), which has not been found previously in marine particles was present in artificial aggregates. Molecular (16S rRNA gene) analyses indicate that the bacterial community attached to aggregates is dominated by (predominantly uncultured) alpha-Proteobacteria. gamma-Proteobacteria and Planctomycetes. Of these, a Roseobacter sp. which was present in artificial aggregates analysed in a parallel study (Balzano et al. 2009, Aquatic Microbial Ecology 54:291-303), can contain 11-methyloctadecenoic acid, and other bacteria present in artificial aggregates have the potential to produce long-chain saturated fatty acids. Thus, the fatty acid assemblage appears to reflect both organic matter degradation, including selective preservation, but also changes in the microbial assemblage. (C) 2010 Elsevier B.V. All rights reserved.

International audience; The aim of this study was to clarify the potential of soil enzyme activities as indicators of pesticide contamination, and to compare this to using the functional diversity of bacterial communities via Biolog (R) Ecoplates. The individual effects of the pure active ingredients (i.e. not the commercial formulations) of ten pesticides on various soil enzyme activities were recorded under laboratory conditions at different incubation times (i.e. 0, 2, 6 and 12 months). Results clearly showed that response patterns of soil enzyme activities differed in their sensitivities to pesticide addition over time (i.e. stimulation, inhibition or no effect). Results suggested that phenol oxidase activity could be used as an early indicator of pesticide contamination, and arylamidase and beta-glucosidase could be used to evaluate soil resilience after pesticide disturbances. We concluded that the functional diversity of bacterial communities was less efficient than soil enzyme activities as an indicator of pesticide contamination. (C) 2011 Published by Elsevier Masson SAS.

International audience

International audience; Marine nematodes from subtidal tropical sediments of Cienfuegos Bay were subjected to organic enrichment in a microcosm experiment for 32 days. Nematode abundance and diversity decreased, and the taxonomic and trophic structure was altered. The results suggested that the nematodes were not food limited in the microcosms or in their natural environment. Chemical stressors such as ammonia and hydrogen sulfide derived from reduced conditions in sediments may be important factors affecting the assemblages. Hypoxic conditions occurred in all experimental units, as well as in the field, suggesting a nematode assemblage adapted to naturally enriched sediments. However, tolerant species showed a grade of sensitivity to reduced conditions. In agreement with the model by Pearson and Rosenberg (1978), we predict that further organic enrichment in sediments from Cienfuegos Bay may cause a phase shift into a strongly depleted benthic fauna and reduced conditions in water and sediments.

International audience; The long-term physical persistence and biological activity of transplastomic plant DNA (transgenes contained in the chloroplast genome) either purified and added to soil or naturally released by decaying tobacco leaves in soil was determined. Soil microcosms were amended with transplastomic tobacco leaves or purified plant DNA and incubated for up to 4 years. Total DNA was extracted from soil and the number of transgenes (aadA, which confers resistance to both spectinomycin and streptomycin) was quantified by quantitative PCR. The biological activity of these transgenes was assessed by transformation in the bacterial strain Acinetobacter sp. BD413(pBAB2) in vitro. While the proportion of transgenes recovered increased with the increasing amount of transplastomic DNA added, plant DNA was rapidly degraded over time. The number of transgenes recovered decreased about 10,000 fold within 2 weeks. Data reveal, however, that a small fraction of the plant DNA escaped degradation. Transgene sequences were still detected after 4 years and transformation assays showed that extracted DNA remained biologically active and could still transform competent cells of Acinetobacter sp. BD413(pBAB2). The approach presented here quantified the number of transgenes (based on quantitative PCR of 50% of the gene) released and persisting in the environment over time and provided new insights into the fate of transgenic plant DNA in soil. (C) 2010 Elsevier Masson SAS. All rights reserved.

This study aims at developing a depollution system for vineyard sediments and passing water. Glyphosate, diuron and 3,4-dichloroaniline (3,4-DCA) have been chosen, taking a copper load into account. Strategical choices are increased pollutant hydraulic retention time and the use of bioaugmentation together with phytoextraction. Each item of this « sorbent-bacterial inoculum-plant » triplet has been beforehand selected in the laboratory and implemented in microcosm experiments under semi-controlled conditions. Sorbent material selection in different liquid matrices with pollutants alone or in combination shows that material sorption capacities change with the type of pollutant. It has also been shown that these capacities vary with formulation (alone or in combination) and liquid matrix chosen. Sediment is awarded the best sorbent for glyphosate, sand the best sorbent for diuron and 3,4-DCA. Dissipation performances from isolated colonies are strongly related to the nature of the compound. Elected consortium degrades glyphosate, diuron and 3,4-dichloroaniline (3,4-DCA) in liquid culture as well as it complexes copper. Microcosm experiments show that hydraulic retention time weighs on pollutant concentration in water at the system outlet. Sorbents prove to be efficient. Dissipation performances are satisfactory. Bioaugmentation does not impact on glyphosate and 3,4-DCA dissipation performances significantly, but enhances diuron dissipation in average. Suitable process efficiency requires increased action time within the solid matrix.; Cette étude vise à développer un système de dépollution d'eau et de sédiments viticoles. Le glyphosate, diuron et 3,4-dichloroaniline (3,4-DCA) sont considérés, en tenant compte de la charge en cuivre. L'augmentation du temps de séjour des polluants dans le système et le choix de la bioaugmentation couplée à la phytoremédiation est la stratégie retenue. Chaque composante d'un triplet « sorbant-inoculum bactérien-plante » a été sélectionnée en laboratoire et le triplet mis en œuvre en microcosmes en conditions partiellement contrôlées. La sélection de matériaux sorbants dans différentes matrices liquides en présence des polluants seuls ou en mélange montre que les capacités de sorption des différents matériaux testés varient selon le polluant, sa formulation (seul ou en mélange) et la matrice liquide. Le sédiment se révèle être le meilleur sorbant pour le glyphosate ; le sable pour le diuron et le 3,4-DCA. Les performances de dissipation des colonies tolérantes isolées varient fortement selon le polluant. Le consortium sélectionné pour le procédé dissipe le glyphosate, le diuron et le 3,4-DCA en milieu liquide et complexe par ailleurs le cuivre. L'expérience en microcosmes montre que le temps de rétention hydraulique influe sur l'efficacité du système et que les matériaux sorbants sont efficaces. De plus les performances de dissipation atteintes sont bonnes. L'effet de la bioaugmentation sur les performances de dissipation n'est pas significatif pour le glyphosate et le 3,4-DCA, mais améliore en moyenne la dissipation du diuron. Un temps d'action prolongé dans la matrice solide s'avère nécessaire pour obtenir une bonne efficacité du procédé.

This study aims at developing a depollution system for vineyard sediments and passing water. Glyphosate, diuron and 3,4-dichloroaniline (3,4-DCA) have been chosen, taking a copper load into account. Strategical choices are increased pollutant hydraulic retention time and the use of bioaugmentation together with phytoextraction. Each item of this « sorbent-bacterial inoculum-plant » triplet has been beforehand selected in the laboratory and implemented in microcosm experiments under semi-controlled conditions. Sorbent material selection in different liquid matrices with pollutants alone or in combination shows that material sorption capacities change with the type of pollutant. It has also been shown that these capacities vary with formulation (alone or in combination) and liquid matrix chosen. Sediment is awarded the best sorbent for glyphosate, sand the best sorbent for diuron and 3,4-DCA. Dissipation performances from isolated colonies are strongly related to the nature of the compound. Elected consortium degrades glyphosate, diuron and 3,4-dichloroaniline (3,4-DCA) in liquid culture as well as it complexes copper. Microcosm experiments show that hydraulic retention time weighs on pollutant concentration in water at the system outlet. Sorbents prove to be efficient. Dissipation performances are satisfactory. Bioaugmentation does not impact on glyphosate and 3,4-DCA dissipation performances significantly, but enhances diuron dissipation in average. Suitable process efficiency requires increased action time within the solid matrix.; Cette étude vise à développer un système de dépollution d'eau et de sédiments viticoles. Le glyphosate, diuron et 3,4-dichloroaniline (3,4-DCA) sont considérés, en tenant compte de la charge en cuivre. L'augmentation du temps de séjour des polluants dans le système et le choix de la bioaugmentation couplée à la phytoremédiation est la stratégie retenue. Chaque composante d'un triplet « sorbant-inoculum bactérien-plante » a été sélectionnée en laboratoire et le triplet mis en œuvre en microcosmes en conditions partiellement contrôlées. La sélection de matériaux sorbants dans différentes matrices liquides en présence des polluants seuls ou en mélange montre que les capacités de sorption des différents matériaux testés varient selon le polluant, sa formulation (seul ou en mélange) et la matrice liquide. Le sédiment se révèle être le meilleur sorbant pour le glyphosate ; le sable pour le diuron et le 3,4-DCA. Les performances de dissipation des colonies tolérantes isolées varient fortement selon le polluant. Le consortium sélectionné pour le procédé dissipe le glyphosate, le diuron et le 3,4-DCA en milieu liquide et complexe par ailleurs le cuivre. L'expérience en microcosmes montre que le temps de rétention hydraulique influe sur l'efficacité du système et que les matériaux sorbants sont efficaces. De plus les performances de dissipation atteintes sont bonnes. L'effet de la bioaugmentation sur les performances de dissipation n'est pas significatif pour le glyphosate et le 3,4-DCA, mais améliore en moyenne la dissipation du diuron. Un temps d'action prolongé dans la matrice solide s'avère nécessaire pour obtenir une bonne efficacité du procédé.

International audience; Fluidized bed combustion ash (FBC) is a by-product from coal-fired power stations used for many decades in concrete, cement and brick manufacturing and more recently for trace metal immobilization and pesticide retention in soils. Moreover FBC ash has been recommended by some authors as a soil amendment in agriculture for its nutrient supply. In this study silico-aluminous (SiAl) and sulfo-calcic (SCa) fly ashes have been added to a fluvisol (calcaric) sampled in the Rhine River plain (Germany) in order to investigate the physical, chemical and physico-chemical possible modifications of the amended soil. Earthworms were introduced into microcosms hydrated with a solution of water and CaCl2 (3.7 10− 4 mg/L; pH = 6.2) and stabilized during 7 and 14 weeks. Batch leaching tests were performed during 6 weeks on the amended soil in order to obtain data on the mobilization potential of major elements (NH4+, Na+, K+, Mg2+, Cl−, Ca2+, NO3−, SO42−, PO43−, H4SiO4) and trace elements (Sr, Ba, V, Zn, Cu, Co, As, Ni, Mo, Cr, Cd, Pb) during ash–soil–water interactions. The main modification is an increase in pH (≈ 12) of soil water in soil amended with sulfo-calcic ash, whereas soil pH only slightly changes in the other soil as compared to control soil. This alkaline pH causes a strong mortality of the macrofauna and a higher mobility of Co, Ni and V on the contrary to Cr, Cu, Pb and Zn which are less mobile and more strongly retained by soil. Soil physico-chemical properties remain generally similar to control soil in soil amended with silico-aluminous ash (SiAl) but show major differences in the case of soil amended with sulfo-calcic ash (SCa). The sulfo-calcic ash therefore seems less adapted to integration in soils from an agricultural and farming point of view, contrary to the silico-aluminous ash which increases the cation exchange capacity, thus improving the nutrient and water reserve for plants.

The present study was undertaken to assess the impact of a candidate mosquito larvicide, spinosad (8, 17 and 33 μg L−1) on a field population of Daphnia magna under natural variations of water temperature and salinity, using Bti (0.16 and 0.50 μL L−1) as the reference larvicide. Microcosms (125 L) were placed in a shallow temporary marsh where D. magna was naturally present. The peak of salinity observed during the 21-day observation period may have been partly responsible for the decrease of daphnid population density in all the microcosms. It is also probably responsible for the absence of recovery in the microcosms treated with spinosad which caused a sharp decrease of D. magna abundance within the first two days following treatment whereas Bti had no effect. These results suggest that it may be difficult for a field population of daphnids to cope simultaneously with natural (water salinity and temperature) and anthropogenic (larvicides) stressors. Significant interaction between salinity and spinosad exposure impairs the recovery of a natural population of Daphnia magna

International audience; Seasonal variation in the response of riverine microbial communities to an environmentally relevant exposure to glyphosate (about 10 microgl(-1)) was assessed on natural communities collected in spring and summer, using two 14-day microcosm studies. The two experiments showed no major effect of glyphosate on algal biomass (chlorophyll a concentrations), bacterial activity ([(3)H]thymidine incorporation), or bacterial community diversity (16S PCR-TTGE detection). Effects on algal community composition (genus-level taxonomic identification) and eukaryotic community diversity (18S PCR-DGGE on

Tank-bromeliads are discrete habitats which contain distinct aquatic communities, and which commonly occur in the neotropics. Because they span a broad range of ecological gradients in terms of habitat structure and amount of resources, researchers study the associations between the biodiversity of communities and these gradients in rainforests, where the very high species richness and densities within other continuous habitats makes it difficult to quantify animal communities. We analysed the diversity of aquatic insect communities in relation to different tank-bromeliad species in a primary rainforest (French Guiana) using artificial intelligence and complex optimization techniques to classify communities and model their determinants. First, the self-organizing map (neural network) was used to classify 158 bromeliads according to the quantitative structure of the insect communities. Catopsis berteroniana and Guzmania lingulata formed separate clusters of plants on the virtual map, while Vriesea splendens, Vriesea pleiosticha and Aechmea melinonii were grouped together in the remaining clusters. Some insect taxa occurred in all bromeliads, while other taxa were specific to a given species. Second, general linear modelling allowed us to specify the influence of the bromeliad species; water volume and volume of fine particulate organic matter inside of the tank; elevation above the ground; and sampling site on taxonomic richness and insect abundance. The number of taxa and individuals per plant increased with greater water volume, but the slope of the relationships depended on the bromeliad species. The significant influence of bromeliad species suggested that at similar water volumes different plant species had different taxon richness and insect abundance. Greater amounts of fine particulate organic matter were detrimental to community diversity in the tanks, probably because they decreased available space by clogging it and/or affected oxygen concentrations. The influence of tank-bromeliad species on the aquatic insect community was primarily related to their physical (and probably chemical) features rather than to species-specific associations sensu stricto. The classification of bromeliads with respect to animal species is likely to provide referential schemes for those biodiversity patterns to be expected under certain conditions, and may help to target model communities for subsequent experimental research.

Correspondance: rai.kookana@csiro.au; International audience; The impact of pesticides, namely thiobencarb (TBC), molinate (MOL)and chlorpyrifos (CPF), on soilmicrobial processeswas studied in two Australian soils. Substrate induced respiration (SIR), substrate induced nitrification (SIN) and phosphatases and chitinase enzymatic activities were assessed during a 30-day microcosm study. The pesticides were applied to soils at recommended rates either alone, or as binary mixtures with TBC. Soil samples were sampled at 5, 15 and 30 days after pesticide treatments. Substrate induced respiration was only transiently affected by pesticides in both soils. In contrast, the process of indigenous nitrification was affected by the presence of pesticides in both soils, especially when the pesticides were applied as binary mixtures. Substrate induced nitrification increased with pesticides in the Griffith soil (except withMOL+TBC after 5 days) whereas SIN values were non-significantly different to the control on the Coleambally soil. The binary mixtures of pesticides with TBC resulted in a decrease in SIN in both soils, but the effects disappeared within 30 days. The enzymatic activities were not consistently affected by pesticides, and varied with the soil and pesticides studied. This study showed that, when applied at recommended application rates, TBC,MOL, and CPF (individually or as binary mixtures), had little or only transitory effects on the functional endpoints studied. However, further investigations are needed to assess the effect on microbial densities and community structure despite the low disturbance to the functions noted in this work.

The effects of pesticides on natural algal and bacterial communities from a French stream were investigated using an in situ approach, followed over two years, and using microcosms studies realized with the herbicides diuron and glyphosate (10 μg l-1). The predominance of herbicides in the stream affects algal biomass and diversity and leads to a selection of four major genus. Algal communities sensitivity to a particular pesticide varies according to physiological state and taxonomic composition. The quantitative (i.e. cellular density, heterotrophic production and activity) and qualitative (i.e. genetic diversity) impact of herbicides on bacterial communities is principally due to indirect effects. This impact is more pronounced in microcosms where bacteria are more dependent on algal production in experimental systems due to the lack of allochthonous organic inputs ., Les effets de pesticides sur les communautés algales et bactériennes d'un cours d'eau ont été appréciés en couplant des approches in situ, menée au cours de deux années, à des approches expérimentales en microcosmes, réalisées avec le diuron et le glyphosate (10 μg l-1). La prédominance des herbicides affecte la biomasse et la diversité algale et induit une sélection prononcée dans la rivière où quatre genres majoritaires sont recensés. La sensibilité des communautés algales à un même pesticide varie suivant leur état physiologique et leur composition taxonomique. L'impact des herbicides sur le compartiment bactérien au niveau quantitatif (sur la densité, la production hétérotrophe et l'activité respiratoire) et qualitatif (diversité génétique), est majoritairement induit par des effets indirects. Il est plus perceptible dans les dispositifs expérimentaux où les bactéries ne peuvent bénéficier d'apports organiques allochtones et sont fortement tributaires de la production algale.

The Macoma balthica community, which is widely distributed in intertidal soft sediments bordering the north Atlantic, is dominated by two functional groups with different sediment mixing modes: the biodiffusers M. balthica and Mya arenaria and the gallery-diffuser Nereis virens. To compare the effects of these two groups on sediment oxygen uptake rates, we used experimental microcosms with identical biovolumes to measure the influence of each species on oxygen uptake. The two biodiffusers had similar effects on oxygen uptake in spite of different space occupation and different feeding, ventilation and burrowing modes. Biodiffusers and gallery-diffusers had different effects on oxygen uptake. Periodic ventilation by the gallery-diffusers stimulated the oxygen uptake by the sediment more than the steady activities of the biodiffusers. Temporal variation in oxygen fluxes in bioturbated microcosms was linked to construction and maintenance of biogenic structures. The results confirm that the functional group approach to bioturbation is a useful tool for quantifying the effects of intertidal benthic communities on benthic fluxes.

International audience; As a means to study the fate of polycyclic aromatic hydrocarbons (PAHs) in freshwater sediments, pyrene mineralization was examined in microcosms spiked with [C-14]-pyrene. Some microcosms were planted with reeds (Phragmites australis) and/or inoculated with a pyrene-degrading strain, Mycobacterium sp. 6PY1. Mineralization rates recorded over a 61 d period showed that reeds promoted a significant enhancement of pyrene degradation, which possibly resulted from a root-mediated increase of oxygen diffusion into the sediment layer, as indicated by in situ redox measurements. In inoculated microcosms, mineralization reached a higher level in the absence (8.8%) than in the presence of plants (4.4%). Mineralization activity was accompanied by the release of water-soluble pyrene oxidation products, the most abundant of which was identified as 4,5-diphenanthroic acid. Pyrene was recovered from plant tissues, including stems and leaves, at concentrations ranging between 40 and 240 mu g/g of dry mass. Plants also accumulated labeled oxidation products likely derived from microbial degradation. Pyrene-degrading strains were 35-70-fold more abundant in inoculated than in noninoculated microcosms. Most of the pyrene-degrading isolates selected from the indigenous microflora were identified as Mycobacterium austroafricanum strains. Taken together, the results of this study show that plants or PAH-degrading bacteria enhance pollutant removal, but their effects are not necessarily cumulative.

International audience; A short-term microcosm experiment was carried out to determine whether acid-tolerant collembolans are able to colonise metal-polluted soil. Polystyrene boxes were divided into two compartments by a perforated wall allowing free passage of soil fauna and preventing physical contact between soil substrates. All compartments were filled either with an acid dysmoder (pH 4.4) collected in a beech forest from Belgian Ardennes (Willerzie, Belgium) or with one of three neutral polluted soils (P1-P3) collected in the Bois des Asturies, along a metal-pollution gradient downwind of a zinc smelter (Auby, France). Different combinations were established, with five replicates each, and were incubated for 3 weeks at 15 degreesC, in darkness. Afterwards, Collembola were extracted and determined to the species level. It appeared that populations from the acid soil colonised the neutral soil polluted by heavy metals. Within 3 weeks, the number of species increased in compartments filled with the most heavily polluted soils (P2, P3) when they were in contact with the acid soil. However, colonisation was effected by only a few individuals. At the species level, the onychiurid Protaphorura eichhorni and the isotomid Folsomia quadrioculata colonised the polluted soil. For Protaphorura eichhorni the migration rate was highest when the soil was the least polluted (P1), while Folsomia quadrioculata showed a higher rate of dispersion to heavily polluted soil (P2) compared with the least polluted soil (P1). This behaviour could be explained by the humus form which was a mull in P1, more compact than the mor observed in P2 and P3, the physical structure of which approaches that of the dysmoder. Our observations indicate that both species are more affected by soil structure than by pollution.

International audience; Solid carriers have been developed to inoculate Trametes versicolor and Cunninghamella elegans into manufactured gas plant site soils. Pelleted wheat bran carriers were very efficient in stimulating the growth of fungi in an industrial soil containing about 2800 mg kg(-1) PAHs. Fungal biomass and activity of extracellular laccases, enzymes produced by T. versicolor as markers of metabolic activity in the contaminated soil, both decreased after 2 weeks of incubation. Supplementing the soil with a mixture of carbon, nitrogen and phosphorus enhanced the fungal activity period. A 38% decrease of solvent extractable PAHs was observed in manufactured gas plant site soils when supplemented with T. versicolor, Glucidex 19(TM), ammonium nitrate, lime phosphate and Montanox 80(TM), after 20 weeks. Then, the degradation proceeded more slowly during the following 30 weeks, and reached 43% of initial extractable PAHs. Some factors governing a limited PAH biotransformation in the soil are discussed.