Dynamique des communautés microbiennes des biofilms phototrophes à différents niveaux d'intégration biologique : des successions écologiques aux réponses à l'exposition à un herbicide

L'approche écotoxicologique ne se limite pas à l'évaluation des risques de toxicité de pesticides sur les organismes, elle s'élargit à la nécessité d'évaluer, à l'échelle de l'écosystème aquatique, les conséquences de la perturbation sur les communautés et les descripteurs de bio-indication associés. Dans ce contexte, les biofilms phototrophes d'écosystèmes aquatiques constituent un modèle d'étude pertinent de par la complexité des structures de communautés microbiennes, leur dynamique spatiale et temporelle, et la variété des fonctions hébergées. Par une première approche écologique, la manipulation de la structure de communautés microbiennes de biofilms phototrophes a été explorée en conditions " naturelles " dans des rivières, et en conditions " contrôlées " avec un prototype de bioréacteur photosynthétique à écoulement hydrodynamique du type Taylor - Couette. Ces expériences soulignent que la structure des communautés microbiennes résulte de processus de successions écologiques, gouvernés par des facteurs allogènes et/ou autogènes en fonction de leur stade de maturation. Enfin par une seconde approche écotoxicologique, les réponses structurelles et fonctionnelles de biofilms phototrophes exposés à l'alachlore ont été évaluées en intégrant le stade de maturation (facteurs autogènes) et l'histoire (facteurs allogènes) des biofilms phototrophes. Les résultats désignent les biofilms phototrophes comme des outils prometteurs en tant que bio-indicateurs de la qualité des eaux lorsqu'ils sont caractérisés par une approche multi-métrique composée de descripteurs fonctionnels et structurels.The intensive use of pesticides causes many disturbances in aquatic ecosystems, which are well known to offer a range of "ecological services" for society. In terms of ecotoxicology, environmental issue is not limited to the risk assessment of a pollutant toxicity on organisms but it expands to the ability to assess, at the ecosystem scale, the consequences of a disturbance and the use of bio-indicators. In this context, for aquatic ecosystems, phototrophic biofilms provide a particularly relevant model, based on their complex microbial community structures, spatial and temporal dynamics and variety of functions. In a first experiment our results suggested that microbial aggregates from different habitats (activated sludge and phototrophic biofilm) are characterized by comparable potential of an herbicide biodegradation: alachlor. Using an ecological approach, a manipulation of the structure of phototrophic biofilms microbial communities was explored in "natural" conditions in rivers exhibiting different physicochemical characteristics, and in "controlled" conditions with a photosynthetic bioreactor prototype (Taylor - Couette flow type). These experiments suggested that the microbial community structures are driven by autogenic and allogenic factors, depending upon maturation state. Finally using an ecotoxicological approach, structural and functional responses of phototrophic biofilms exposed to alachlor were evaluated, integrating the maturation stage (autogenic factors) and history (allogenic factors) of phototrophic biofilms. This work allowed us to undertake an ecotoxicological approach integrating the concepts of ecological succession in microbial communities. Our results demonstrate that phototrophic biofilms are promising tools as bio-indicators of water quality when they are characterized by a multi-metric approach including functional and structural descriptors

Changes in tolerance to herbicide toxicity throughout development stages of phototrophic biofilms

Ecotoxicological experiments have been performed in laboratory-scale microcosms to investigate thesensitivity of phototrophic biofilm communities to the alachlor herbicide, in relation to the stages ofphototrophic biofilm maturation (age of the phototrophic biofilms) and physical structure (intact biofilmversus recolonization). The phototrophic biofilms were initially cultivated on artificial supports in aprototype rotating annular bioreactor (RAB) with Taylor–Couette type flow under constant operatingconditions. Biofilms were collected after 1.6 and 4.4 weeks of culture providing biofilms with differentmaturation levels, and then exposed to nominal initial alachlor concentration of 10 ug L−1in either intactor recolonized biofilms for 15 days in microcosms (mean time-weighted average concentration – TWACof 5.52 ± 0.74 ug L−1).At the end of the exposure period, alachlor effects were monitored by a combination of biomass descrip-tors (ash-free dry mass – AFDM, chlorophyll a), structural molecular fingerprinting (T-RFLP), carbonutilization spectra (Biolog) and diatom species composition. We found significant effects that in terms ofAFDM, alachlor inhibited growth of the intact phototrophic biofilms. No effect of alachlor was observedon diatom composition or functional and structural properties of the bacterial community regardless ofwhether they were intact or recolonized. The intact three-dimensional structure of the biofilm did notappear to confer protection from the effects of alachlor. Bacterial community structure and biomass levelof 4.4 weeks – intact phototrophic biofilms were significantly influenced by the biofilm maturation pro-cesses rather than alachlor exposure. The diatom communities which were largely composed of mobileand colonizer life-form populations were not affected by alachlor.This study showed that the effect of alachlor (at initial concentration of 10 ug L−1or mean TWAC of5.52 ± 0.74 ug L−1) is mainly limited to biomass reduction without apparent changes in the ecologicalsuccession trajectories of bacterial and diatom communities and suggested that carbon utilization spec-tra of the biofilm are not damaged resulting. These results confirmed the importance of consideringthe influence of maturation processes or community age when investigating herbicide effects. This isparticularly important with regard to the use of phototrophic biofilms as bio-indicators

A photosynthetic rotating annular bioreactor (Taylor–Couette type flow) for phototrophic biofilm cultures

In their natural environment, the structure and functioning of microbial communities from river phototrophic biofilms are driven by biotic and abiotic factors. An understanding of the mechanisms that mediate the community structure, its dynamics and the biological succession processes during phototrophic biofilm development can be gained using laboratory-scale systems operating with controlled parameters. For this purpose, we present the design and description of a new prototype of a rotating annular bioreactor (RAB) (TayloreCouette type flow, liquid working volume of 5.04 L) specifically adapted for the cultivation and investigation of phototrophic biofilms. The innovation lies in the presence of a modular source of light inside of the system, with the biofilm colonization and development taking place on the stationary outer cylinder (onto 32 removable polyethylene plates). The biofilm cultures were investigated under controlled turbulent flowing conditions and nutrients were provided using a synthetic medium (tap water supplemented with nitrate, phosphate and silica) to favour the biofilm growth. The hydrodynamic features of the water flow were characterized using a tracer method, showing behaviour corresponding to a completely mixed reactor. Shear stress forces on the surface of plates were also quantified by computer simulations and correlated with the rotational speed of the inner cylinder. Two phototrophic biofilm development experiments were performed for periods of 6.7 and 7 weeks with different inoculation procedures and illumination intensities. For both experiments, biofilm biomasses exhibited linear growth kinetics and produced 4.2 and 2.4 mg cm-2 of ash-free dry matter. Algal and bacterial community structures were assessed by microscopy and T-RFLP, respectively, and the two experiments were different but revealed similar temporal dynamics. Our study confirmed the performance and multipurpose nature of such an innovative photosynthetic bioreactor for phototrophic biofilm investigations

Autogenic versus environmental control during development of river biofilm

In the natural environment, microbial community structure of river biofilm is controlled by biotic and abiotic factors. This study explored the capacity to manipulate the structure of microbial communities by modifying environmental conditions during the course of biofilm development. River epilithic biofilm was cultivated in situ on artificial substrates placed parallel to river water flow. Substrates were incubated for 3 and 5.5 weeks in river to allow natural biofilm development, at two sites with contrasting physico-chemical characteristics. The first site (Aurade´ , Gers, France) was located in an agricultural watershed basin and the second site (Larroque, Haute-Garonne, France) was located in a forested watershed basin. After 3 weeks of biofilm development, a subset of substrates was collected from one site and transplanted to the second site where they remained for 2.5 further weeks. Epilithic bacterial community structure (at 3 weeks from each site and at 5.5 weeks from biofilms with and without transplantation) was assessed using PCR-DGGE of 16S rDNA fragment. Biofilm biomass was estimated using ash free dry mass (AFDM). After 3 weeks of development, biofilms from the two sites exhibited comparable AFDM values (average of 1.4¡0.2 g.mx2). A difference between the two sites was observed after 5.5 weeks of development: AFDM decreased for biofilms from the agricultural watershed basin (from 1.4 to 0.18 g.mx2) as a consequence of grazing pressure (Bithynia), and increased for biofilms from the forested agricultural watershed (from 1.4 to 2.6 g.mx2). Microbial community analyses revealed a differentiated community structure between biofilms from the different sites and exhibited a change of microbial community structure after 5.5 weeks of biofilm development. These observations confirm a process of ecological succession in microbial communities. Changing the incubation site during biofilm development modified the trajectory of these ecological successions, suggesting that site characteristics mainly conditioned the structure of these microbial communities

Discours féminin ou féministe ? : eune étude des oeuvres sélectionnées de Flora Nwapa et de Buchi Emecheta

This study examines the nature of the discourse to be found in the novels of Flora Nwapa and Buchi Emecheta, two Nigerian writers. On reading Nwapa's One Is Enough and Woman Are Different and Emecheta's The Joys of Motherhood and Second Class Citizen, we find that they do, indeed, convey an implicit message and that they show the black African woman subject to rather oppressive daily circumstances. By placing these novels within their African socio-cultural and literary contexts and by analysing the rhetorical and narratological tools used by these women writers, a specific identity can be given to the feminist claims of their novels. Finally, the possible existence of a specifically feminine writing in Nwapa and Emecheta's novels is discussed in the light of Hélène Cixous' theory of "écriture féminine".La problématique de ce travail de recherche repose sur la nature du discours qui émerge des oeuvres de Flora Nwapa et de Buchi Emecheta, deux écrivains d'origine nigériane. La lecture de One Is Enough et Women Are Different de Nwapa d'une part, et de The Joys of Motherhood et Second Class Citizen d'Emecheta d'autre part, véhicule en effet un message implicite et dévoile la femme noire africaine sous l'emprise d'un quotidien plutôt oppresseur. En resituant ces oeuvres dans les contextes socioculturel et littéraire africains, et en analysant les procédés rhétoriques et narratologiques utilisés par ces écrivaines, on parvient à donner une identité spécifique à la revendication féministe de leurs romans. Enfin, une analyse de la possible existence d'une écriture spécifique aux femmes chez Nwapa et Emecheta est effectuée à la lumière de la théorie de "l'écriture féminine" d'Hélène Cixous

Discours féminin ou féministe ? (une étude des oeuvres sélectionnées de Flora Nwapa et de Buchi Emecheta)

La problématique de ce travail de recherche repose sur la nature du discours qui émerge des oeuvres de Flora Nwapa et de Buchi Emecheta, deux écrivains d'origine nigériane. La lecture de One Is Enough et Women Are Different de Nwapa d'une part, et de The Joys of Motherhood et Second Class Citizen d'Emecheta d'autre part, véhicule en effet un message implicite et dévoile la femme noire africaine sous l'emprise d'un quotidien plutôt oppresseur. En resituant ces oeuvres dans les contextes socioculturel et littéraire africains, et en analysant les procédés rhétoriques et narratologiques utilisés par ces écrivaines, on parvient à donner une identité spécifique à la revendication féministe de leurs romans. Enfin, une analyse de la possible existence d'une écriture spécifique aux femmes chez Nwapa et Emecheta est effectuée à la lumière de la théorie de "l'écriture féminine" d'Hélène Cixous.NANCY2-BU Lettres (543952103) / SudocSudocFranceF

Microbiota and Phage Therapy: Future Challenges in Medicine

An imbalance of bacterial quantity and quality of gut microbiota has been linked to several pathologies. New strategies of microbiota manipulation have been developed such as fecal microbiota transplantation (FMT); the use of pre/probiotics; an appropriate diet; and phage therapy. The presence of bacteriophages has been largely underestimated and their presence is a relevant component for the microbiome equilibrium. As a promising treatment, phage therapy has been extensively used in Eastern Europe to reduce pathogenic bacteria and has arisen as a new method to modulate microbiota diversity. Phages have been selected and “trained” to infect a wide spectrum of bacteria or tailored to infect specific antibiotic resistant bacteria present in patients. The new development of genetically modified phages may be an efficient tool to treat the gut microbiota dysbiosis associated with different pathologies and increased production of bacterial metabolites and subsequently decrease systemic low-grade chronic inflammation associated with chronic diseases. Microbiota quality and mitochondria dynamics can be remodulated and manipulated by phages to restore the equilibrium and homeostasis of the system. Our aim is to highlight the great interest for phages not only to eliminate and control pathogenic bacterial infection but also in the near future to modulate the microbiota by adding new functions to selected bacteria species and rebalance the dynamic among phages and bacteria. The challenge for the medicine of tomorrow is to re-think and redesign strategies differently and far from our traditional thinking

From Donor to Patient: Collection, Preparation and Cryopreservation of Fecal Samples for Fecal Microbiota Transplantation

International audienceFecal Microbiota Transplantation (FMT) is suggested as an efficacious therapeutic strategy for restoring intestinal microbial balance, and thus for treating disease associated with alteration of gut microbiota. FMT consists of the administration of fresh or frozen fecal microorganisms from a healthy donor into the intestinal tract of diseased patients. At this time, in according to healthcare authorities, FMT is mainly used to treat recurrent Clostridium difficile. Despite the existence of a few existing stool banks worldwide and many studies of the FMT, there is no standard method for producing material for FMT, and there are a multitude of factors that can vary between the institutions. The main constraints for the therapeutic uses of FMT are safety concerns and acceptability. Technical and logistical issues arise when establishing such a non-standardized treatment into clinical practice with safety and proper governance. In this context, our manuscript describes a process of donor safety screening for FMT compiling clinical and biological examinations, questionnaires and interviews of donors. The potential risk of transmission of SARS-CoV-2 virus by the use of fecal microbiota for transplantation must be taken urgently into consideration. We discuss a standardized procedure of collection, preparation and cryopreservation of fecal samples through to the administration of material to patients, and explore the risks and limits of this method of FMT. The future success of medicine employing microbiota transplantation will be tightly related to its modulation and manipulation to combat dysbiosis. To achieve this goal, standard and strict methods need to be established before performing any type of FMT

Influence du milieu naturel d'origine sur la sensibilité du biofilm phototrophe à un herbicide

International audienceEcotoxicological experiments were performed in laboratory-scale microcosms to investigate community-level responses of river phototrophic biofilms from different environments to herbicide exposure. Biofilms were initially cultivated on artificial substrates placed in situ for 4 weeks at two sites, site M, located in an agricultural watershed basin and site S, located in a forested watershed basin. The biofilms were subsequently transferred to microcosms and, after an acclimatization phase of 7 days, were exposed to alachlor at 10 and 30 µg L-1 for 23 days. Alachlor effects were assessed by a combination of structural parameters, including biomass (ash free dry mass and chlorophyll a), molecular fingerprinting of the bacterial community (polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE) and diatom species composition. Alachlor impacted the chlorophyll a and ash-free dry mass levels of phototrophic biofilms previously cultivated at site S. The structural responses of bacterial and diatom communities and diatom were difficult to distinguish from changes linked to the microcosm incubation period. Phototrophic biofilms from site S exposed at 30 µg L-1 alachlor were characterised by an increase of Achnanthidium minutissimum (K-z.) Czarnecki abundance, as well as a higher proportion of abnormal frustules. Thus, phototrophic biofilms with different histories, exhibited different responses to alachlor exposure demonstrating the importance of growth environment. These observations also confirm the problem of distinguishing changes induced by the stress of pesticide toxicity from temporal evolution of the community in the microcosm

The architecture of monospecific microalgae biofilms 2

International audienceMicroalgae biofilms have been proposed as an alternative to suspended cultures in 10 commercial and biotechnological fields. However, little is known about their architecture which 11 may strongly impact biofilm behavior, bioprocess stability and productivity. In order to unravel the 12 architecture of microalgae biofilms, four species of commercial interest were cultivated in 13 microplates and characterized using a combination of confocal laser scanning microscopy and FTIR-14 spectroscopy. In all the species, the biofilm biovolume and thickness increased over time and 15 reached a plateau after 7 days, the final biomass reached was very different though. The roughness 16 decreased during maturation, reflecting cell division and voids filling. The extracellular polymeric 17 substances content of the matrix remained constant in some species and increased over time in some 18 others. Vertical profiles showed that young biofilms presented a maximum cell density at 20 µm 19 above the substratum co-localized with matrix components. In mature biofilms, the maximum 20 density of cells moved at a greater distance from the substratum (30-40 µm) whereas the maximum 21 coverage of matrix components remained in deeper layer. Carbohydrates and lipids were the main 22 macromolecules changing during biofilm maturation. Our results revealed that the architecture of 23 microalgae biofilms is species-specific. However, time is similarly affecting the structural and 24 biochemical parameters. 2