Rôle de la synergie microbiote intestinal-vers de terre sur la contamination des sols

Pesticides used to protect plants from pests, threat grievously non-target organisms such as earthworms. Due to their feeding and burrowing activities, earthworms are in direct contact with soil particles and microorganisms, as well as pollutants including pesticides. This work investigated (1) the effect of an organophosphate “ethyl-parathion” on the sensitivity of two endogeic earthworms’ species, Aporrectodea caliginosa and Allolobophora chlorotica; and (2) the role of the gut-microbiota, in synergy with the earthworm’s detoxification pathways, in pesticide tolerance or detoxification. In the first part, biochemical and behavioral responses showed that A. caliginosa is more sensitive to “ethyl-parathion” exposure than A. chlorotica. The endpoints measured ranged from physiological (weight), biochemical (AChE, CbEs, GST) to behavioral biomarkers (cast production and burrowing activity). Our findings showed that the sensitivity of A. caliginosa could be mainly due to the intrinsic sensitivity of its AChE to “ethyl-parathion”. The role of the carboxylesterases, acting as bioscavenger of OP, and the role of the detoxifying enzymes GST did not appear to be efficient mechanisms involved in A. chlorotica tolerance. In the second part, we aimed to characterize the microbiome within the ingested soil, the cast and the gut tissue of A. caliginosa and A. chlorotica in control or polluted soils. Our results showed differences in the microbial composition between these compartments. In this line, we suggested that these two earthworms’ species harbor a species-specific microbiome in their gut. In particular, our findings showed that the earthworm’s gut acts as a “biological filter” for ingested microbial communities during the gut passage. At the level of the gut, we identified four dominated genus within the gut of A. caliginosa versus two dominated genus in the gut of A. chlorotica. Notably, we identified a Rhodococcus strain, which is highly abundant in the gut of A. chlorotica. Previous studies reported Rhodococcus strains for their ability to degrade some group of pesticides. We suggest that the presence of this strain could contribute to the tolerance of A. chlorotica. Finally, we showed that the effect of ethyl-parathion on soil enzyme activities mainly depend on soil texture rather than the presence and/or the species of earthworms. According to our findings, it is of considerable importance to include more than one species to assess toxicity from organophosphorus insecticides, due to the interspecific differences that can occur within the same ecological category. Moreover, the identification and the functional analysis of the microorganisms found in the earthworm’s gut and able to intervene in pesticide detoxification could enhance our knowledge about the fate of the pesticide inside the organism, and could be an important tool for bioremediation program.Les pesticides utilisés pour protéger les plantes des insectes nuisibles constituent une menace pour les organismes non cibles tels que les vers de terre. En raison de leur activité de bioturbation de sol, les vers de terre sont en contact direct avec les particules et les micro-organismes du sol, ainsi qu'avec les polluants, notamment les pesticides. L‘objectif de ce travail est d‘étudier (1) l‘effet d‘un organophosphoré (OP) «éthyl-parathion» sur la sensibilité de deux espèces de vers de terre endogés, Aporrectodea caliginosa et Allolobophora chlorotica; et (2) le rôle du microbiote intestinal, en synergie avec les voies de détoxification du ver de terre, dans la tolérance ou la détoxification des pesticides. Dans la première partie, les réponses biochimiques et comportementales ont montré que A. caliginosa est plus sensible à l'exposition à «l‘éthyl-parathion» que A. Chlorotica. Les résultats portent sur l‘analyse de biomarqueurs physiologiques (poids), biochimiques (AChE, CbEs, GST) et comportementaux (production de turricules et activité de creusement). Nous avons montré que la sensibilité de A. caliginosa semble liée à la sensibilité intrinsèque de l‘AChE à «l‘éthyl-parathion». De plus, le rôle des carboxylestérases, capables de piéger les insecticides OP, ainsi que le rôle de détoxification des GST notamment, ne semblaient pas être des mécanismes efficaces impliqués dans la tolérance de A. chlorotica. Dans la deuxième partie, nous avons caractérisé, en présence ou non d‘insecticide, le microbiote dans le sol ingéré, les turricules et les intestins des 2 vers de terre. Nos résultats ont montré des différences dans la composition microbienne de ces compartiments. A cet égard, nous avons suggéré que chacune de ces espèces hébergent un microbiote spécifique de l‘espèce dans leur intestin. Nos résultats ont notamment montré que l‘intestin du ver de terre agit comme un «filtre biologique» pour les communautés microbiennes ingérées lors du passage dans l‘intestin. A ce niveau, nous avons identifié, au niveau bactérien, quatre genres dominants dans l'intestin de A. caliginosa et deux genres dominants dans l'intestin de A. chlorotica. Nous avons notamment identifié une souche de Rhodococcus, très abondante dans l'intestin de A. chlorotica. Des études ont montré que des souches de Rhodococcus peuvent dégrader certains groupes de pesticides. Nous suggérons que la présence de cette souche pourrait contribuer à la tolérance de A. chlorotica. Enfin, nous avons montré que l‘effet de l‘éthyl-parathion sur les activités enzymatiques du sol dépend principalement de la texture du sol et non pas de la présence et/ou de l‘espèce de ver de terre.Selon nos conclusions, il est extrêmement important d'inclure plus d'une espèce pour évaluer la toxicité des insecticides organophosphorés, en raison des différences interspécifiques pouvant se produire au sein d'une même catégorie écologique. De plus, l'identification et l'analyse fonctionnelle des micro-organismes présents au niveau de l‘intestin et susceptibles d'intervenir dans la détoxication des pesticides permettraient d‘améliorer nos connaissances sur le devenir du pesticide dans l'organisme et pourraient constituer un outil important dans les programmes de bioremédiation

Elucidating pesticide sensitivity of two endogeic earthworm species through the interplay between esterases and glutathione S-transferases

International audienceEarthworms are common organisms in soil toxicity-testing framework, and endogeic species are currently recommended due to their ecological role in agroecosystem. However, little is known on their pesticide metabolic capacities. We firstly compared the baseline activity of B-esterases and glutathione-5-transferase in Allolobophora chlorotica and Aporrectodea caliginosa. Secondly, vulnerability of these species to pesticide exposure was assessed by in vitro trials using the organophosphate (OP) chlorpyrifosethyl-oxon (CPOx) and ethyl-paraoxon (POx), and by short-term (7 days) in vivo metabolic responses in soil contaminated with pesticides. Among B-esterases, acetylcholinesterase (AChE) activity was abundant in the microsomal fraction (80% and 70% of total activity for A. caliginosa and A. chlorotica, respectively). Carboxylesterase (CbE) activities were measured using three substrates to examine species differences in isoenzyme and sensitivity to both in vitro and in vivo exposure. CbEs were mainly found in the cytosolic fraction (80% and 60% for A. caliginosa and A. chlorotica respectively). GST was exclusively found in the soluble fraction for both species. Both OPs inhibited B-esterases in a concentration-dependent manner. In vitro trials revealed a pesticide-specific response, being A. chlorotica AChE more sensitive to CPOx compared to POx. CbE activity was inhibited at the same extent in both species. The 7d exposure showed A. chlorotica less sensitive to both OPs, which contrasted with outcomes from in vitro experiments. This non-related functional between both approaches for assessing pesticide toxicity suggests that other mechanisms linked with in vivo OP bioactivation and excretion could have a significant role in the OP toxicity in endogeic earthworms

Role of soil texture and earthworm casts on the restoration of soil enzyme activities after exposure to an organophosphorus insecticide

International audiencePesticides exert important effects on the soil fauna and health. However, little is known about the interactions of soil, microorganisms and earthworms in the presence of pesticides and about their respective roles in the soil biological activity. The aim of this study was to evaluate the effect of the soil type on enzyme activities, measured in bulk soil and in casts of two earthworm species, after exposure to the organophosphorus pesticide parathion. To this aim, two endogeic earthworm species (Apporectodea caliginosa and Allolobophora chlorotica) were cross-acclimated in two different soil textures (each representing the most favorable soil environment for that spe-cies). Enzyme activities were measured as a soil quality indicator in samples of bulk soil (collected at day 4 and day 7 of exposure to parathion) and in earthworm casts (collected at day 7). A short exposure (4 days) to parathion significantly (ANOVA, p < 0.001) inhibited carboxylesterases (25-43 % of inhibition) and alkaline phosphatase (-23 % of inhibition). At day 7 of exposure, parathion impact on the overall soil enzyme activities mainly depended on the soil texture. Indeed, activity inhibition was higher (ANOVA, p < 0.001) in silt-clay soil (decrease by 37 %) than in silt-loamy soil (decrease by-18 %). Conversely, parathion effect was not influenced by earthworm presence/absence and earthworm species. However, after soil exposure to parathion, earthworms (both species) improved enzyme activity restoration in their casts

Interspecific differences in biochemical and behavioral biomarkers in endogeic earthworms exposed to ethyl-parathion

International audienceEarthworms are common organisms in the soil toxicity-testing framework, and the epigeic Eisenia andrei and E. fetida are the recommended species. However, Eisenia species are rarely found in agricultural soils and recent studies have pointed out endogeic species are more sensitive to pesticides than Eisenia. Allolobophora chlorotica and Aporrectodea caliginosa are two endogeic soil-dwelling species that are abundant in the agroecosystem. However, knowledge on pesticide impact on this ecological group of earthworms is still incipient. Herein, we compared the biochemical (acetylcholinesterase [AChE] and carboxylesterase [CbE] activities) and behavioral (burrowing, casting and feeding) biomarker responses of these two endogeic earthworm species exposed for 7 days to soils contaminated with 0.1, 1 and 10 mg kg−1 ethyl-parathion. The results showed marked species-specific differences in both groups of biomarkers, suggesting A. caliginosa the most sensitive species to this organophosphorus pesticide under the exposure conditions in this study. Moreover, an in vitro inhibition trial with ethyl-paraoxon evidenced a higher sensitivity of A. caliginosa AChE activity compared with that of A. chlorotica. This finding suggested that this molecular target endpoint could contribute to the interspecific differences of behavioral responses rather than CbE activity; this latter considered a potent mechanism of OP removal. Our results suggest the inclusion of more than one endogeic earthworm species to assess toxicity from organophosphorus insecticides. However, the use of A. caliginosa in the environmental risk assessment framework of organophosphorus contamination is highly recommended because of its higher sensibility to this class of pesticides, in addition to its abundance in the agroecosystem

Effect of an organophosphorus insecticide, soil texture and earthworm species on the turnover of soil, gut and cast microbiota during the earthworm's gut transit

International audienceThe growing usage of plant protection products in agroecosystems questions their unintentional deleterious effects on non-target organisms such as earthworms and their related ecological function. The aim of this study was to investigate the turnover of soil microbiota during the gut transit of two endogeic earthworms (Aporrectodea caliginosa and Allolobophora chlorotica) and how it is possibly affected by the organophosphorus insecticide ethyl-parathion (Pt). We measured prokaryotic and micro-eukaryotic community composition and abundances using two different soil types in the continuum of bulk soil, gut and casts samples collected during and after one week exposure to Pt. The presence of earthworm and Pt had limited effects on the soil microbiota, although Pt altered temporarily soil microbial abundances in the presence of earthworms, not in their absence. The earthworms’ gut harbored a remarkably low prokaryotic diversity, dominated by two molecular Operational Taxonomic Units (mOTUs) affiliated to Rhodococcus and Pseudarthrobacter. Contrastingly, gut micro-eukaryotic communities were maintained at diversity levels similar to that of the soil, yet Pt augmented their diversity and changed their composition. Fresh casts collected out of the soil revealed evident variation of abundance, diversity and community composition according to the soil origin and the earthworm species. In particular, following gut transit casts were enriched with Bacteroidia and -Proteobacteria while depleted of Acidobacteria. Exposure to Pt increased the diversity and relative abundance of depleted mOTUs, which paves the way for future investigations on the role of Pt in rising microbial consumption due to an over-excitation of gastrointestinal motility

Photodegradation of disposable polypropylene face masks: Physicochemical properties of debris and implications for the toxicity of mask-carried river biofilms

International audienceCOVID-19 outbreak led to a massive dissemination of protective polypropylene (PP) face masks in the environment, posing a new environmental risk amplified by mask photodegradation and fragmentation. Masks are made up of a several kilometres long-network of fibres with diameter from a few microns to around 20 µm. After photodegradation, these fibres disintegrate, producing water dispersible debris. Electrokinetics and particle stability observations support that photodegradation increases/decreases the charge/hydrophobicity of released colloidal fragments. This change in hydrophobicity is related to the production of UV-induced carbonyl and hydroxyl reactive groups detectable after a few days of exposure. Helical content, surface roughness and specific surface area of mask fibres are not significantly impacted by photodegradation. Fragmentation of fibres makes apparent, at the newly formed surfaces, otherwise-buried additives like TiO2 nanoparticles and various organic components. Mortality of gammarids is found to increase significantly over time when fed with 3 days-UV aged masks that carry biofilms grown in river, which is due to a decreased abundance of microphytes therein. In contrast, bacteria abundance and microbial community composition remain unchanged regardless of mask degradation. Overall, this work reports physicochemical properties of pristine and photodegraded masks, and ecosystemic functions and ecotoxicity of freshwater biofilms they can carr