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

Microbiote intestinal de la truite arc-en-ciel : déterminisme génétique et alimentaire

National audienc

Optimization of alkaline protease production by Streptomyces sp. strain isolated from saltpan environment

Proteolytic activity of a Streptomyces sp. strain isolated from Ezzemoul saltpans (Algeria) was studied on agar milk at three concentrations. The phenotypic and phylogenetic studies of this strain show that it represents probably new specie. The fermentation is carried out on two different media, prepared at three pH values. The results showed the presence of an alkaline protease with optimal pH and temperature of 8 and 40°C, respectively. The enzyme is stable up to 90°C, having a residual activity of 79% after 90 min. The enzyme production media are optimized according to statistical methods while using two plans of experiences. The first corresponds to the matrixes of Plackett and Burman in N=16 experiences and N-1 factors, twelve are real and three errors. The second is the central composite design of Box and Wilson. The analysis of the results allowed the selection of two factors having a significant effect on the production of the enzyme (fructose and malt extract), then defining theirs optima (7 g/l of fructose and 12 g/l of malt extract).Keywords: Protease, streptomyces, identification, fermentation, optimizatio

The REPLIM Project: a lake and wetland network to monitor global changes in the Pyrenees

IPA-IAL 2018 Joint Meeting (2018. Estocolmo)Instituto Pirenaico de Ecología, EspañaCentre National de la Recherche Scientifique, FranciaLaboratoire Geode, FranciaUniversité Toulouse, FranciaCentre d'Estudis Avançats de Blanes, EspañaUniversidad del País Vasco, EspañaCentro de Investigación Ecológica y Aplicaciones Forestales, EspañaUniversité de Pau et des Pays de l'Adour, FranciaUniversidad de Navarra, EspañaInstituto Geológico y Minero de España, EspañaPeer reviewe

Les communautés bactériennes de biofilms épilithiques dans le continuum du Gave de Pau (dynamique et réponse aux herbicides.)

Dans le cadre de ce travail de thèse nous nous sommes intéressés à la réponse des communautés bactériennes des biofilms épilithiques du Gave de Pau à la contamination en herbicides. Des expériences en microcosmes ont été réalisées parallèlement à plusieurs campagnes de prélèvements et de transplantation de biofilms épilithiques naturels le long du Gave de Pau sur des sites présentant des niveaux de contamination en différents pesticides. La structure des communautés bactériennes a été étudiée grâce à des techniques de biologie moléculaire (T-RFLP et clonage-séquençage). Le contrôle de la présence et l'estimation de la contamination en pesticides ont été réalisés avec des techniques de prélèvements ponctuels et l'utilisation d'échantillonneurs passifs (PO-CIS). Nos résultats montrent que le Gave de Pau présente en été une contamination en pesticides mais qui ne semble pas excéder les niveaux de pollution moyens des cours d'eau français et qui augmente lors de traitements agricoles printaniers. L'impact des molécules détectées dans le Gave de Pau sur les communautés bactériennes des biofilms épilithiques ne paraît pas plus important que l'impact d'autres facteurs environnementaux. Les expériences en microcosmes indiquent que le diuron pourrait générer chez des biofilms épilithiques préalablement moins exposés le développement de communautés bactériennes plus hétérogènes. Finalement, les capacités de dégradation du diuron par des biofilms épilithiques printaniers du Gave de Pau ont été mises en évidence. Cela n'est pas le cas pour l'isoproturon en hiver.The responses of bacterial communities of epilithic biofilms to herbicides were studied in a French river : the Gave de Pau. In parallel with microcosm experiments, several campaigns of sampling and transplantion of natural epilithic biofilms along the Gave de Pau were conducted on sites with various contamination levels. Bacterial community structures were studied through molecular biology techniques (T-RFLP and cloning-sequencing). The presence of pesticides and their contamination levels were monitored through spot analyses and passive samplers (POCIS). Our results showed that the herbicide contamination of the Gave de Pau did not appear to exceed the average pollution levels of French rivers and that the contamination increased during agricultural treatment season (spring). The impact of molecules detected in the Gave de Pau on biofilm bacterial communities did not appear to exceed the impact of other environmental factors. In microcosms experiments, the bacterial communities of epilithic biofilms previously less exposed to diuron were found to be more heterogeneous. Finally, the capacity of degradation of diuron by epilithic biofilms of Gave de Pau was demonstrated during the spring season. In the case of isoproturon this herbicides was not degraded during winter experiment.PAU-BU Sciences (644452103) / SudocSudocFranceF

Isolation of a type 2 metallothionein-like gene preferentially expressed in the tapetum in Zea mays

International audienceA Zea mays cDNA, MZm3-4, was isolated by differential screening of a cDNA library obtained from meiotic stage anthers against a cDNA of 3-week-old seedlings. Northern blot analysis of RNA from different maize tissues and from male reproductive organs at various developmental stages demonstrated expression of a single transcript in anthers, from the pollen mother cell stage through the uninucleated microspore stage. In situ hybridization to anther sections resulted in a distinct signal only in the tapetum. The MZm3-4 cDNA is 743 nucleotides in length and has an open reading frame encoding a protein of 75 amino acids. Sequence comparisons with various databases revealed that MZm3-4 exhibits high similarities with type 2 plant metallothioneins at both the nucleotide and the amino-acid level. Primer extension analysis indicated that MZm3-4 cDNA is deleted of 13 bp at the 5∞ end. Southern blot analysis showed that the MZm3-4 gene may be present in one or two copies in a Z. mays inbred line genome. This is the first report of the isolation of a type 2 metallothionein-like protein in maize. Moreover, the expression of this type 2 metallothionein-like gene is high in the male reproductive organs engaged in microsporogenesis

A meta-analysis of peatland microbial diversity and function responses to climate change

International audienceClimate change threatens the capacity of peatlands to continue storing carbon (C) belowground. Microorganisms are crucial in regulating the peatland C sink function, but how climate change affects the richness, biomass and functions of peatland microbiomes still remains uncertain. Here, we conducted a global meta-analysis of the response of peatland bacterial, fungal and micro-eukaryote communities to climate change by synthesizing data from 120 climate change experiments. We show that climate drivers such as warming, drought and warming-induced vegetation shift strongly affect microbial diversity, community composition, trophic structure and functions. Using meta-analytic structural equation modelling, we developed a causal understanding among the different strands of microbial properties. We found that climate drivers influenced microbial metabolic rates, such as CO2 fixation and respiration, methane production and oxidation, directly through physiological effects, and indirectly, through microbial species turnover and shifts in the trophic structure of microbial communities. In particular, we found that the response of microbial CO2 fixation increased for each degree in air temperature gained, while the response of microbial CO2 respiration tended to decline. When extrapolated at the global peatland scale using the CMIP6 model under the SSP5-8.5 scenario, our findings suggest that the increasingly positive response of microbial CO2 fixation to temperature anomalies in northern latitudes might compensate to some extent for the possible loss of C from microbial CO2 respiration, possibly allowing peatlands to remain C sinks on long-term. Our findings have crucial implications for advancing our understanding of carbon-climate feedback from peatlands in a warming world

L'influence de l'hétérogénéité environnementale dans les variations de la diversité et de la composition des communautés microbiennes dans une tourbière de l'étage montagnard pyrénéen

National audienceLes tourbières sont des écosystèmes emblématiques des Pyrénées où se concentre une biodiversité originale et bien souvent menacée du fait de la régression de ces milieux par l’action du changement climatique et de l’utilisation de ces espaces naturels. Bien que l’étude de la diversité des micro-organismes dans les tourbières soit l’objet d’un intérêt croissant, les processus maintenant cette diversité et son rôle dans le fonctionnement et la stabilité des tourbières reste à ce jour très peu explorés. Il apparait donc primordial de mieux connaître ces microorganismes à la fois au niveau taxonomique et fonctionnel, d’identifier les variables environnementales responsables de la variabilité spatio-temporelle de ces communautés pour mieux quantifier leur réponse face aux bouleversements climatiques futurs. Nous avons donc cherché à mieux comprendre l’écologie des communautés microbiennes des tourbières pyrénéennes en étudiant la distribution spatiale et temporelle de ces communautés au sein de la tourbière de Bernadouze (haute vallée du Vicdessos en Ariège). Grâce à un échantillonnage intensif, nous avons pu mettre en évidence que la saison et les microhabitats (e.g. buttes, gouille) avaient peu d’influence sur la structure des communautés. A l’inverse, le pH, la distance à la nappe phréatique et dans une moindre mesure le rapport carbone/azote ont été identifiés comme étant les déterminants majeurs des variations de diversité et composition des communautés microbiennes, traduisant une distribution spatiale non aléatoire des bactéries et des archées. L’importante masse de données acquises dans le cadre de ce projet a également permis d’établir une base solide pour comprendre et suivre le fonctionnement des tourbières pyrénéennes

Bacteria-mediated reduction of As(V)-doped lepidocrocite in a flooded soil sample

International audienceUnderstanding the processes involved in the control of arsenic (As) dynamics within soils has become a challenging issue for soil and water quality preservation. Interactions between mineralogical phases, organic ligands and bacterial communities - closely linked to the chemical conditions of the medium - were thus investigated through a geochemical and microbiological experimental study involving the reduction of As(V)-doped lepidocrocite within the soil. Reducing conditions were established as soon as the experiment started, followed by a release of dissolved organic carbon corresponding to a release of acetate. Scanning Electron Microscopy observations pointed out a large bacterial colonization occurring on the lepidocrocite leading to a 3-dimensionally shaped biodissolution of lepidocrocite. The taxonomic diversity evolved throughout the experiment, and thus it demonstrated the evolution of the metabolic activities of the bacteria. At the beginning, lepidocrocite was mainly colonized by bacteria belonging to the Geobacter genus (Deltaproteobacteria) (26%) and Bacillus and Oxalophagus fermentative related genera (Firmicutes) (72%). After two weeks, Geobacter spp. and Firmicutes represented 54% and 30% of the bacterial community, respectively. Although still dominated by Geobacter spp. (34%) at the end of the experiment, the bacterial diversity had increased. After 3 and 8 weeks of incubation, the presence of the arsB and ACR3(1) genes, encoding transporters involved in As detoxification processes, indicated that this community harbored As-resistant or As-transforming genera able to contribute to the transformation of As(V) into As(III)