The problematic of microplastics pollution in the marine environment is tightly linked to their colonization by a wide diversity of microorganisms, the so-called plastisphere. The composition of the plastisphere relies on a complex combination of multiple factors including the surrounding environment, the time of incubation along with the polymer type, making it difficult to understand how the biofilm evolves during the microplastic lifetime over the oceans. To better define bacterial community assembly processes on plastics, we performed a 5 months spatio-temporal survey of the plastisphere in an oyster farming area in the Bay of Brest (France). We deployed three types of plastic pellets in two positions in the foreshore and in the water column. Plastic-associated biofilm composition in all these conditions was monitored using 16 S rRNA metabarcoding and compared to free-living and attached bacterial members of seawater. We observed that bacterial families associated to plastic pellets were significantly distinct from the ones found in seawater, with a significant prevalence of filamentous Cyanobacteria on plastics. No convergence towards a unique plastisphere was detected between polymers exposed in the intertidal and subtidal area, emphasizing the central role of the surrounding environment on constantly shaping the plastisphere community diversity. However, we could define a bulk of early-colonizers of marine biofilms such as Alteromonas, Pseudoalteromonas or Vibrio. These early-colonizers could reach high abundances in floating microplastics collected in field-sampling studies, suggesting the plastic-associated biofilms could remain at early development stages across large oceanic scales. Our study raises the hypothesis that most members of the plastisphere, including putative pathogens, could result of opportunistic colonization processes and unlikely long-term transport.

We measured phytoplankton primary production and heterotrophic bacterial activities on microplastics and seawater in the Northwestern Mediterranean Sea during two 3-month spring periods over 2 consecutive years. Microorganisms growing on a 5 mm diameter low density polyethylene films (LDPE; 200 μm thick) faced two contrasting conditions depending on the year. Spring 2018 was characterized by consistent nutrient inputs and bloom development. In spring 2019, nutrient inputs and bloom were low. For the first time, we observed a clear coupling between primary production and heterotrophic prokaryote production on microplastics during both years, but with different intensity between years that reflected the crucial role of the trophic environmental conditions (nutrient supply) in shaping microbial activities on plastics. We found that high primary production on plastics could support the whole (net autotrophy) or the majority of the bacterial carbon demand needed for heterotrophic activities, supplemented by other carbon sources if surrounding waters are highly productive. We propose that microbial activity on plastics influences the microbial community in the surrounding seawater, especially when the environmental conditions are less favorable. An illustrative image of the role of plastics in the environment could be that of an inverter in an electrical circuit that mitigates both positive and negative variations. Our results highlight the potential role of the plastisphere in shaping biogeochemical cycles in the context of increasing amounts of plastic particles in the marine environment.

In fish, the gut microbiome plays a crucial role in homeostasis and health and is affected by several organic and inorganic environmental contaminants. Amphidromous fish are sentinel species, particularly exposed to these stressors. We used whole metagenome sequencing to characterize the gut microbiome of wild European eels (Anguilla anguilla) at a juvenile stage captured from three sites with contrasted pollution levels in term of heavy metals and persistent organic pollutants. The objectives were to identify what parameters could alter the gut microbiome of this catadromous fish and to explore the potential use of microbiota as bioindicators of environment quality. We identified a total of 1079 microbial genera. Overall, gut microbiome was dominated by Proteobacteria, Firmicutes and Actinobacteria. Alpha and beta diversity were different amongst sites and could be explained by a reduced number of environmental and biological factors, specifically the relative abundance of fish preys in eels’ diet, PCB101, γHCH (lindane), transnonachlor and arsenic. Furthermore, we identified a series of indicator taxa with differential abundance between the three sites. Changes in the microbial communities in the gut caused by environmental pollutants were previously undocumented in European eels. Our results indicate that microbiota might represent another route by which pollutants affect the health of these aquatic sentinel organisms.

International audience | Soil trace metal concentrations (e.g., cadmium, copper, lead, zinc) in vegetable gardens have often been observed as exceeding the geochemical background levels. These metals are a threat both to soil and plant functioning and to human health through consumption of contaminated vegetables. We used a mass balance-based model to predict the four metal (Cd, Cu, Pb, Zn) concentrations in soils after a century’s cultivation for 104 urban vegetable gardens, located in three French metropolises, Nancy, Nantes, and Marseille, based on a survey of gardening practices. If current gardening practices are maintained, an increase in soil Cd (35% on average), Cu (183%), and Zn (27%) contents should occur after a century. Soil Pb concentration should not vary consistently. Organic amendments are the major source of Cd, Pb, and Zn, followed by chemical fertilizer while fungicide application is the major source of Cu. Cessation of chemical fertilizer use would only slightly reduce the accumulation of the four metals. The solubility of the four metals would decrease significantly after a century, when pH increases by one unit. A liming practice of acidic soils should therefore be a feasible way to prevent any increase in the metal mobility and bioavailability.

International audience

International audience | The production and use of pharmaceutical products have increased over the past decades, and several are considered potential or proved hazardous wastes. When contaminating the environment, they can severely impact biodiversity. The catecholamine epinephrine (adrenaline) is no exception. Epinephrine can be administered as growth promoter in cattle, and is used for anaphylaxis treatment in human. While a range of studies has examined the effects of this catecholamine on vertebrate tissues, and evidenced that it can disrupt the oxidative stress status, the effects epinephrine could have on insects have remained poorly considered. Here, we examined the physiological effects of different concentrations (0, 25, 50, and 100 mu g/mL) of epinephrine on larvae of the flesh fly Sarcophaga dux. Following experimental treatments, levels of H2O2, GSH, CAT, GPx, and CEH were measured from the fat body, cuticle, gut, and hemolymph of 3rd instars. Significant differences are reported for these physiological endpoints among the considered body compartments, and epinephrine concentrations. Epinephrine treatments did not increase reactive oxygen species production (H2O2 amounts), except for gut tissues. Increased levels of GSH suggest that epinephrine may have enhanced glucose metabolism and flux towards the pentose phosphate pathway, while reducing glutamine oxidation. CAT activity was slightly increased when the concentration of epinephrine was higher. The decreased GPx activity in the fat body was consistent with GSH variations. In sum, the injection of epinephrine seemed to elicit the antioxidant response in S. dux larvae, in turn attenuating ROS production.

International audience | Abstract France is the first pesticide-consuming country in Europe. Glyphosate is the most used pesticide worldwide and glyphosate is detected in the general population of industrialized countries, with higher levels found in farmers and children. Little data was available concerning exposure in France. Our objective was to determine glyphosate levels in the French general population and to search for an association with seasons, biological features, lifestyle status, dietary habits, and occupational exposure. This study includes 6848 participants recruited between 2018 and 2020. Associated data include age, gender, location, employment status, and dietary information. Glyphosate was quantified by a single laboratory in first-void urine samples using ELISA. Our results support a general contamination of the French population, with glyphosate quantifiable in 99.8% of urine samples with a mean of 1.19 ng/ml + / − 0.84 after adjustment to body mass index (BMI). We confirm higher glyphosate levels in men and children. Our results support glyphosate contamination through food and water intake, as lower glyphosate levels are associated with dominant organic food intake and filtered water. Higher occupational exposure is confirmed in farmers and farmers working in wine-growing environment. Thus, our present results show a general contamination of the French population with glyphosate, and further contribute to the description of a widespread contamination in industrialized countries.

International audience | Soil trace metal concentrations (e.g., cadmium, copper, lead, zinc) in vegetable gardens have often been observed as exceeding the geochemical background levels. These metals are a threat both to soil and plant functioning and to human health through consumption of contaminated vegetables. We used a mass balance-based model to predict the four metal (Cd, Cu, Pb, Zn) concentrations in soils after a century’s cultivation for 104 urban vegetable gardens, located in three French metropolises, Nancy, Nantes, and Marseille, based on a survey of gardening practices. If current gardening practices are maintained, an increase in soil Cd (35% on average), Cu (183%), and Zn (27%) contents should occur after a century. Soil Pb concentration should not vary consistently. Organic amendments are the major source of Cd, Pb, and Zn, followed by chemical fertilizer while fungicide application is the major source of Cu. Cessation of chemical fertilizer use would only slightly reduce the accumulation of the four metals. The solubility of the four metals would decrease significantly after a century, when pH increases by one unit. A liming practice of acidic soils should therefore be a feasible way to prevent any increase in the metal mobility and bioavailability.

International audience | Intercropping or assistant endophytes promote phytoremediation capacities of hyperaccumulators and enhance their tolerance to heavy metal (HM) stress. Findings from a previous study showed that intercropping the hyperaccumulator Sonchus asper (L.) Hill grown in HM-contaminated soils with maize improved the remediating properties and indicated an excluder-to-hyperaccumulator switched mode of action towards lead. In the current study, RNA-Seq analysis was conducted on Sonchus roots grown under intercropping or monoculture systems to explore the molecular events underlying this shift in lead sequestering strategy. The findings showed that intercropping only slightly affects S. asper transcriptome but significantly affects expression of root-associated microbial genomes. Further, intercropping triggers significant reshaping of endophytic communities associated with a ‘root-to-shoot’ transition of lead sequestration and improved phytoremediation capacities of S. asper . These findings indicate that accumulator activities of a weed are partially attributed to the root-associated microbiota, and a complex network of plant–microbe-plant interactions shapes the phytoremediation potential of S. asper . Analysis showed that intercropping may significantly change the structure of root-associated communities resulting in novel remediation properties, thus providing a basis for improving phytoremediation practices to restore contaminated soils.

International audience | Organic waste (OW) reuse in agriculture is a common practice fostered by benefits in terms of waste recycling and crop production. However, OW amendments potentially affect the fate of pesticide spread on fields to protect the crops from pests and weeds. The influence of OW on the sorption, degradation, and leaching of pesticides is generally studied for each mechanism separately under artificial laboratory conditions. Our study aims at evaluating the balance of these mechanisms under more realistic conditions to clarify the influence of three common OW amendments on the fate, in soil, of the widely used herbicide S-Metolachlor. We performed leaching experiments in large undisturbed soil cores amended with raw sewage sludge, composted sludge, and digested pig slurry (digestate), respectively. We monitored S-Metolachlor and its two main metabolites MET-OA and MET-ESA in the leachates during a succession of 10 rainfall events over 126 days. We also quantified the remaining S-Metolachlor and metabolites in the soil at the end of the experiments. S-Metolachlor leaching didn't exceed 0.1% of the applied dose with or without OW amendment. Despite a soil organic carbon increase of 3 to 32%, OW amendments did not significantly affect the amount of S-Metolachlor that leached through the soil (0.01 to 0.1%) nor its transformation rate (6.0 to 8.6%). However, it affected the degradation pathways with an increase of MET-OA relative to MET-ESA formed after OW amendment (28 to 54%) compared to the controls (8%). Concentration of S- Metolachlor and metabolites in the leachates of all treatments greatly exceeded the regulatory limit for groundwater intended for human consumption in Europe. These high concentrations were probably the consequence of preferential macropore flow. Colloids had comparable levels in the leachates after S-Metolachlor application. Dissolved organic carbon was also comparable in the controls, digestate, and sludge treatments but was 65% higher in the compost-amended cores. These results, along with a great variability among replicates inherent to experiments performed under realistic conditions, partly explain the limited impact of OW on the transport of S-Metolachlor.