Environmental Concentrations of Copper, Alone or in Mixture With Arsenic, Can Impact River Sediment Microbial Community Structure and Functions

In many aquatic ecosystems, sediments are an essential compartment, which supports high levels of specific and functional biodiversity thus contributing to ecological functioning. Sediments are exposed to inputs from ground or surface waters and from surrounding watershed that can lead to the accumulation of toxic and persistent contaminants potentially harmful for benthic sediment-living communities, including microbial assemblages. As benthic microbial communities play crucial roles in ecological processes such as organic matter recycling and biomass production, we performed a 21-day laboratory channel experiment to assess the structural and functional impact of metals on natural microbial communities chronically exposed to sediments spiked with copper (Cu) and/or arsenic (As) alone or mixed at environmentally relevant concentrations (40 mg kg-1 for each metal). Heterotrophic microbial community responses to metals were evaluated both in terms of genetic structure (using ARISA analysis) and functional potential (using exoenzymatic, metabolic and functional genes analyses). Exposure to Cu had rapid marked effects on the structure and most of the functions of the exposed communities. Exposure to As had almost undetectable effects, possibly due to both lack of As bioavailability or toxicity toward the exposed communities. However, when the two metals were combined, certain functional responses suggested a possible interaction between Cu and As toxicity on heterotrophic communities. We also observed temporal dynamics in the functional response of sediment communities to chronic Cu exposure, alone or in mixture, with some functions being resilient and others being impacted throughout the experiment or only after several weeks of exposure. Taken together, these findings reveal that metal contamination of sediment could impact both the genetic structure and the functional potential of chronically exposed microbial communities. Given their functional role in aquatic ecosystems, it poses an ecological risk as it may impact ecosystem functioning

Changes in sediment microbial diversity following chronic copper-exposure induce community copper-tolerance without increasing sensitivity to arsenic

International audienceSediment microbial communities were exposed for 21 days to an environmental concentration of copper to assess Cu-induced composition changes and resulting effects on microbial sensitivity to acute Cu and As toxicity. Chronic Cu exposure reduced the diversity of the bacterial and archaeal communities from Day 0 to Day 21. The pollution-induced community tolerance concept (PICT) predicts that loss of the most sensitive taxa and gain of more tolerant ones should increase the capacity of Cu-exposed communities to tolerate acute Cu toxicity. Although diversity loss and functional costs of adaptation could have increased their sensitivity to subsequent toxic stress, no increased sensitivity to As was observed. PICT responses varied according to heterotrophic activity, selected as the functional endpoint for toxicity testing, with different results for Cu and As. This suggests that induced tolerance to Cu and As was supported by different species with different metabolic capacities. Ecological risk assessment of contaminants would gain accuracy from further research on the relative contribution of tolerance acquisition and co-tolerance processes on the functional response of microbial communitie

Réponse structurelle et fonctionnelle de communautés microbiennes de sédiments de rivières à une exposition réaliste de cuivre et d'arsenic, seuls et en mélange

International audienceSediments are an essential component of aquatic ecosystems both in terms of biodiversity and of ecological functioning. They receive direct or indirect inputs from the water column or from the watershed including some toxic and persistent contaminants (e.g. trace metals and PCBs) which can accumulate over time and impact exposed organisms. Among benthic organisms, microbial communities are major players in various key ecological processes such as organic matter recycling, greenhouse gas production and biomass production contributing to benthic food webs. However, knowledge about the effects of accumulated contaminants on the structure and functions of sediment microbial communities is scarce. In this context, the main aim of this work was to evaluate the structural and functional impact of chronic exposure to environmental concentrations of copper and arsenic (alone or mixed) on river sediment microbial communities. Natural uncontaminated surface sediments collected in a French River (Ain) were exposed for 21 days to Cu and/or As at nominal individual concentrations of 40 mg/kg in the artificial channels. The response of heterotrophic microbial communities to metals was evaluated both in terms of genetic structure (using ARISA analysis) and functional potential (using exo-enzymatic, metabolic and genetic analysis). A pollution induced community tolerance (PICT) approach was also performed to assess if the exposure led to an increase in the capacity of microbial communities to tolerate metals. Our results showed rapid (within 48 hours) and marked effects of Cu alone on the exposed communities. It led to a significant inhibition of microbial functions such as respiration and denitrification as well as beta-glucosidase, leucine aminopeptidase and phosphatase activities. Chronic Cu exposure also induced an increase in community tolerance to Cu, as observed by PICT measurement using beta-glucosidase activity. In contrast, the effects of As were mostly undetectable. Under mixture exposure, the effects were similar or higher than those provoked by Cu, depending on the measured parameter. All together those findings reveal that metals accumulation in sediments can impact exposed microbial communities thus affecting their functional role in aquatic ecosystems. It confirms the need for developing studies to better understand the ecotoxicological impact of contaminants on natural sediment communitie

Réponse des communautés microbiennes de sédiment à une exposition réaliste au cuivre : Remaniement structurel et acquisition de tolérance

Bien que de nombreux métaux s'accumulent dans les sédiments, les connaissances sur la réponse des communautés microbiennes benthiques à cette contamination sont rares. En prenant comme modèle le cuivre (Cu), cette étude en microcosmes visait à caractériser les processus d'adaptation de ces communautés à une exposition chronique réaliste au Cu (~50 mg Cu kg-1, 21 jours). Les liens entre changements de diversité et augmentation de la tolérance en réponse à cette exposition ont été appréhendés en couplant une méthode de séquençage haut débit sur une région du gène codant l'ARNr 16S avec une approche PICT (pollution induced community tolerance). Nos résultats montrent qu'une exposition chronique au Cu impacte fortement la diversité des communautés microbiennes en termes de richesse, d'équitabilité, de structure génétique et de composition taxonomique. Cette modification de diversité s'est accompagnée d'une augmentation de la tolérance de la communauté au Cu, illustrée par l'augmentation des CE50 obtenues lors des tests de toxicité sur les activités β-glucosidase et phosphatase. Pour compléter notre approche, nous avons également prévu de caractériser les mécanismes génétiques impliqués dans la résistance au Cu par l'analyse ultérieure de l'abondance des gènes cusA et copA à l'échelle de la communauté. En résumé, les résultats de cette étude confirment que l'exposition au Cu favorise le développement des microorganismes tolérants au détriment des taxons plus sensibles. Par conséquent et en raison de la forte implication des communautés microbiennes benthiques dans les cycles biogéochimiques, ces modifications de diversité pourraient avoir des répercussions importantes sur le fonctionnement global des écosystèmes aquatiques

Vers la mise en œuvre opérationnelle des approches PICT dans un contexte réglementaire du suivi de la qualité des milieux aquatiques et des sédiments

International audienceAssessing the ecological effects of pollutants is an important aspect of regulations dealing with the sustainable management of water resources. In this context, scientists and regulators face the challenge of going beyond the estimation of pollutant concentrations to take into account the ecotoxicological effects on exposed aquatic communities. Among microbial ecotoxicological approaches, the pollution induced community tolerance (PICT) concept has been proven to be a suitable biomonitoring tool for in situ assessmentof either the response of aquatic microbial communities to toxicant exposure or of their recovery following the improvement of water chemical quality. The PICT is a powerful microbial metric to better link the assessment of ecological and chemical status of ecosystems by providing causal analysis in effect-based monitoring of impacted field sites4. However, prior its implementation in regulatory frameworks, further work is required to standardize PICT measurement and define baseline tolerance levels at large geographical scales. In this context, we will present the first results of the application of PICT approaches in the sediment compartment (with copper as model compound). We will specifically focus on both the development of standardized protocols (from sampling to dose-response modeling) and on the evaluation and control of potential confounding factors to make measurements comparable in space and time by considering robust reference conditions

Vers un outil simple pour évaluer les effets fonctionnels des contaminants sur les communautés microbiennes et d'invertébrés des sédiments

International audienceSediments play a critical role in biogeochemical cycling and in the maintenance of the biodiversity. They are natural sinks for many contaminants which can accumulate over time and impact exposed communities, thereby disturbing the functioning of aquatic ecosystems. However, knowledge about the functional effects of contaminants on benthic communities is scarce and there is a need of ecosystem functioning indicators of ecotoxicological impacts. In the present microcosm study, we assessed the individual and combined effects of Cu and As (40 mg kg dw-1 each, 21 days of exposure) on the capacity of natural micro- and macro-organism communities from an uncontaminated river sediment to consume and decompose particulate organic matter using the bait lamina method (ISO 18311) as well as artificial tablets consisting of cellulose, bran flakes and active coal embedded in an agar matrix. The sediment toxicity was also evaluated using the standardized ostracod toxicity test (ISO 14371:2012). The two tested substrates (i.e. bait lamina and artificial tablets) showed similar results with low effects of As on feeding activity and organic matter breakdown whereas Cu demonstrated a strongest functional effect. When the two metals were combined, a total functional inhibition was observed, whatever the kind of substrate. The ostracod toxicity test also showed high toxicity of Cu-spiked and mixture-spiked sediments and low toxicity of As-spiked sediments. Our results highlight the relevance of artificial organic matter substrates to assess the functional effects of contaminants on sediment micro- and macro-organism communities, opening new perspectives to assess the functional integrity of contaminated sediments

The impact of ancient mining activity on the critical zone: the example of the Peisey-Nancroix Pb-Ag mine (19th-20th century)

International audienceA better understanding of long-term trace metals dispersal and their bioavailability in the critical zone is required toanticipate future impacts of present-day mining activity. The Pb-Ag district of Peisey-Nancroix (northern French Alps) isan excellent target to study the long-term environmental impacts (> 150 years) of former mines and trace metal dispersalin the critical zone, considering that every steps of the mining cycle, from ore extraction to ore processing, were locatedon a few hectares site that has been unmodified since mine closure in 1866 (no reclamation). A cross-disciplinary studyis conducted using several proxies (ore, waste dumps, soil, water, stream sediments and related microbial communities,vegetation) in order to characterize present-day contamination on the mining site, to determine trace metals transfer inthe various compartment of the critical zone, and to evaluate the effect of trace metals on microbial communitiesfunctioning.Topsoils are significantly enriched in Pb, and locally in As, Sb and Cu compared to the local geological background.Soils developed on top of waste deposits contains up to 3.4% Pb, 1695 ppm Zn, 381 ppm Sb and 168 ppm Cu. Tracemetal transfer from contaminated soils to the vegetation is evidenced by XRF profile across larch tree trunk sections.Contamination of streambed sediments is restricted to the vicinity of the mine and to the mine drainage outlets. Theconcentration of Pb2+ in pore waters, which ranges from 18 to 56 µg/L (EU potability limit = 10 µg/L), is well correlatedto the sediment total Pb content and represents the main source of bioavailable metal. Microbial investigations will beperformed to evaluate the ecotoxicological effects of Pb and Cu exposure on the genetic structure and the ecologicalfunctions (respiration, denitrification, organic matter decomposition...) of the bacterial communities naturally present inthe contaminated sediments and soil

Réponse structurelle et fonctionnelle de communautés microbiennes de sédiments exposées à des concentrations environnementales de Cuivre et d'Arsenic, seuls et en mélange

International audienceWhile many metals are known to accumulate in sediments, knowledge about the resulting ecotoxicological effects on sediment microbial communities is scarce. The present study aimed at evaluating the structural and functional impact of chronic exposure to environmental concentrations of copper (Cu) and arsenic (As), alone or mixed together, on river sediment microbial communities. Natural uncontaminated surface sediments collected in a French River (Ain) were spiked with As and Cu at a nominal concentration of 40 mg/kg and then were exposed for 21 days in laboratory channels with overlying waters. The response of heterotrophic microbial communities to metals was evaluated both in terms of genetic structure (using ARISA analysis) and functional potential (using exo-enzymatic, metabolic and qPCR analyses). A pollution induced community tolerance (PICT) approach was also performed to assess if the exposure led to an increase in the capacity of microbial communities to tolerate metals. Our results showed rapid and marked effects of Cu alone on the structure and the functions of the exposed communities. Chronic Cu exposure also induced an increase in community tolerance to Cu, as observed by PICT measurement using beta-glucosidase activity. In contrast, the effects of As were mostly undetectable. Under mixture exposure (Cu+As), the effects were similar or higher than those provoked by Cu alone, depending on the measured parameter. Altogether those findings reveal that metals accumulation in sediments can impact exposed microbial communities thus affecting their functional role in aquatic ecosystems

Effets combinés du cuivre et de l'arsenic sur des communautés microbiennes naturelles de sédiments de rivière

International audienceSediments are an essential component of aquatic ecosystems in terms of biodiversity and of ecological functioning. They receive direct or indirect inputs from the water column or from the watershed including some toxic and persistent contaminants (e.g. trace metals and PCBs) which can accumulate over time and impact exposed organisms. Among benthic organisms, microbial communities are major players in various key ecological processes such as organic matter recycling, greenhouse gas production and biomass production contributing to benthic food webs. The study of ecotoxicological effects on microbial communities paves the way to assess the impacts of contaminants on both taxonomic and functional microbial biodiversity which support many ecosystem functions and ensure their stability and resilience. Accordingly, microbial ecotoxicology offers prospects to develop new ecosystem quality indicators. However, knowledge about the effects of accumulated contaminants on sediment microbial communities is scarce. In this context, the main aim of this work was to evaluate the structural and functional impact of chronic exposure to environmental concentrations of copper (Cu) and arsenic (As), alone or mixed together, on river sediment microbial communities. Natural uncontaminated surface sediments collected in a French River (Ain) were spiked with As and Cu at a nominal concentration of 40 mg/kg and then were exposed for 21 days in laboratory channels with overlying waters. The response of heterotrophic microbial communities to metals was evaluated both in terms of genetic structure (using ARISA analysis) and functional potential (using exo-enzymatic, metabolic and metagenomic analyses). A pollution induced community tolerance (PICT) approach was also performed to assess if the exposure led to an increase in the capacity of microbial communities to tolerate metals. Our results showed rapid (within 48 hours) and marked effects of Cu alone on the exposed communities. It led to a significant inhibition of microbial functions such as respiration and denitrification as well as beta-glucosidase, leucine aminopeptidase and phosphatase activities, and affected the proportion of functional genes involved in denitrification pathways. Chronic Cu exposure also induced an increase in community tolerance to Cu, as observed by PICT measurement using beta-glucosidase activity. In contrast, the effects of As were mostly undetectable. Under mixture exposure (Cu+As), the effects were similar or higher than those provoked by Cu alone, depending on the measured parameter. Altogether those findings reveal that metals accumulation in sediments can impact exposed microbial communities thus affecting their functional role in aquatic ecosystems. They also show that PICT approaches have the potential to be a powerful microbial indicator to assess in situ the ecological quality of metal-contaminated sediments. These results open new perspectives to assess the ecological quality of sediments and confirm the need for developing studies to better understand the ecotoxicological impact of contaminants on natural sediment communities

Utilisation de substrats organiques artificiels pour évaluer les effets fonctionnels de métaux sur des communautés naturelles de sédiments (microorganismes et invertébrés)

International audienceBenthic ecosystems are important areas both in terms of biodiversity and functioning. They are receiving direct or indirect inputs from the water column or from the watershed and may therefore be accumulating zones for contaminants. Many benthic and epibenthic organisms may be exposed to these substances, with as consequences, disruption of ecological traits and functions at the ecosystem level such as changes in benthic community structure and ecosystem functioning. However, knowledge about the ecotoxicological effects of accumulated contaminants at the benthic community level is scarce. Accordingly, the present study aimed at assessing the functional impact of chronic exposure to environmental concentrations of metals on natural sediment communities. We evaluate the usefulness of assessing/studying feeding activity and organic matter breakdown as endpoints, using two kinds of artificial organic matter substrates