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In comparison with northern countries, limited data are available on the occurrence and potential toxicity of cyanobacterial blooms in lakes and ponds in Sub-Saharan countries. With the aim of enhancing our knowledge on cyanobacteria and their toxins in Africa, we performed a 17-month monitoring of a freshwater ecosystem, Lagoon Aghien (Ivory Coast), which is used for multiple practices by riverine populations and for drinking water production in Abidjan city. The richness and diversity of the cyanobacterial community were high and displayed few variations during the entire survey. The monthly average abundances ranged from 4.1x104 cell mL− 1 to 1.8x105 cell mL− 1, with higher abundances recorded during the dry seasons. Among the five cyanotoxin families analyzed, only microcystins (MC) were detected with concentrations ranging from 0 to 0.364 µg L− 1 in phytoplankton cells, from 32 to 1,092 µg kg− 1 fresh weight of fish intestines and from 33 to 383 µg kg− 1 in fish livers. Even if the MC concentrations in water and fish are low, usually below the thresholds defined in WHO guidelines, these data raise the issue of the relevance of these WHO guidelines for Sub-Saharan Africa, where local populations are exposed throughout the year to these toxins in multiple ways.

International audience; Given the increasing eutrophication of water bodies in Africa due to increasinganthropogenic pressures, data are neededto better understand the responses ofphytoplankton communities to these changes in tropical lakes. These ecosystemsare used by local human populations for multiple purposes, including fish anddrinking water production, potentiallyexposing these populations to healththreats if, for example, an increase in toxic cyanobacterial blooms is associatedwith increasing eutrophication. To test the short‐term response of thephytoplankton community to the addition of nutrients (phosphorus and nitrogen,alone or in combination) and Nile tilapia, we developed an in situ mesocosmexperiment in a freshwater lagoon located near Abidjan (Ivory Coast). We foundthat phytoplankton growth (estimated by chlorophyll‐a quantification) was highlystimulated when both nitrogen and phosphorus were added, while there was noclear evidence for such colimitation by these two nutrients when consideringtheir concentrations in the lagoon. Phytoplankton growth was accompanied bysignificant changes in the diversity and composition of this community and didnot lead to an increase in the proportions of cyanobacteria. However, theaddition of fish to some mesocosms resulted in a drastic decrease inphytoplankton biomass and a dominance of chlorophytes in this community.Finally, these experiments showed that the addition of nitrogen, alone orcombined with phosphorus, stimulated microcystin production by cyanobacteria.; Compte tenu de l'eutrophisation croissante des masses d'eau en Afrique due à l'augmentation des pressions anthropiques, des données sont nécessaires pour mieux comprendre les réponses des communautés phytoplanctoniques à ces changements dans les lacs tropicaux. Ces écosystèmes sont utilisés par les populations humaines locales à des fins multiples, y compris la production de poisson et d'eau potable, exposant potentiellement ces populations à des menaces pour la santé si, par exemple, une augmentation des proliférations de cyanobactéries toxiques est associée à une eutrophisation croissante. Pour tester la réponse à court terme de la communauté phytoplanctonique à l'ajout de nutriments (phosphore et azote, seuls ou en combinaison) et de tilapia du Nil, nous avons développé une expérience de mésocosme in situ dans une lagune d'eau douce située près d'Abidjan (Côte d'Ivoire). Nous avons constaté que la croissance du phytoplancton (estimée par la quantification de la chlorophylle-a) était fortement stimulée lorsque l'azote et le phosphore étaient ajoutés, alors qu'il n'y avait aucune preuve claire d'une telle colimitation par ces deux nutriments lorsque l'on considère leurs concentrations dans le lagon. La croissance du phytoplancton s'est accompagnée de changements importants dans la diversité et la composition de cette communauté et n'a pas entraîné d'augmentation des proportions de cyanobactéries. Cependant, l'ajout de poissons à certains mésocosmes a entraîné une diminution drastique de la biomasse phytoplanctonique et une dominance des chlorophytes dans cette communauté. Enfin, ces expériences ont montré que l'ajout d'azote, seul ou associé au phosphore, stimulait la production de microcystines par les cyanobactéries. De plus, aucune preuve d'accumulation de microcystines dans les poissons n'a été trouvée. Pris ensemble

International audience; This article examines the role that the production of knowledge on the ecological state of aquatic ecosystems plays in the implementation of policies for protecting these environments, used for water supply. Based on interdisciplinary research carried out in two sub-Saharan countries (Côte d'Ivoire and Senegal) by a team of sociologists and ecologists, the article shows how expert knowledge of environmental quality assessment interacts with the local actors, existing management structures and with local representations of these environments. Through this interdisciplinary approach, we question the difficulties of integrating a diversity of points of view on water resources. We highlight the obstacles, uncertainties and controversies linked with the production of expertise and its integration into existing management systems. More specifically, we describe the main challenges for institutionalizing long-term monitoring of the water resources (Aquatic Ecosystems Observatories). We also discuss the possibilities and the interest for integrating expert and local knowledge for co-constructing a shared diagnosis.; Cet article questionne le rôle de la production des savoirs sur l’état écologique des milieux dans la gestion et la mise en oeuvre de politiques de surveillance et de protection des ressources en eau utilisées pour la production d’eau potable en Afrique subsaharienne. Sur la base d’une recherche interdisciplinaire réalisée en Côte d’Ivoire et au Sénégal par une équipe comprenant des sociologues et des écologues, l’article montre comment des savoirs experts d’évaluation de la qualité des milieux interagissent avec les jeux d’acteurs, les structures de gestion existantes et les représentations locales de ces mêmes milieux. Nous interrogeons à travers cette approche interdisciplinaire les difficultés d’articulation de la diversité de points de vue sur les ressources en eau, ainsi que les freins, les incertitudes et controverses autour de la production de savoirs et de leur intégration dans des dispositifs de gestion. Nous analysons plus particulièrement les principaux défis pour la mise en place des suivis de l’état écologique des milieux aquatiques, ainsi que les possibles contributions des savoirs experts et locaux à la co-construction d’un diagnostic partagé.

L'ensemble des activités en lien avec l'eau du lac de Guiers au Sénégal a potentiellement des conséquences importantes sur son état écologique. Cet article part du constat que la pollution par les pesticides concentre l'essentiel des débats et des actions entreprises tandis que l'enrichissement en nutriments des eaux du lac (représentant un risque d'eutrophisation) n'est un problème que rarement évoqué. Ce constat conduit les auteurs à s'interroger sur les facteurs sociopolitiques qui conduisent à " l'invisibilisation " de certaines causes de dégradation des milieux aquatiques. En nous appuyant sur une enquête de terrain auprès des gestionnaires et usagers du lac, nous montrons les concurrences entre les différents services administratifs qui conduisent à diverses formes de segmentation des causes de dégradation et à la sélection de l'une d'entre elles. Nous montrons ensuite comment cette formalisation du problème est diffusée et renforcée par la mise en oeuvre de bonnes pratiques agricoles, essentiellement centrées sur la question des produits phytosanitaires et relayées par des acteurs territoriaux. Cette analyse de la construction institutionnelle de l'ignorance est enfin complétée par une étude des représentations que les usagers se font de la dégradation de leur lac, permettant d'identifier les dynamiques sociales, les conflits et les jeux de pouvoir autour de l'appropriation de l'espace et de l'accès à l'eau, qui conduisent à l'invisibilisation du problème de l'eutrophisation.

In this work, we develop a rules-based µ-estimation algorithm which is independent of any tyre model and may be employed independently by brake control systems of the vehicle. The algorithm propose...

International audience; Although they are widespread, diverse and involved in biogeochemical cycles, microbial eukaryotes attract less attention than their prokaryotic counterparts in environmental microbiology. In this study, we used publicly available 18S barcoding data to define biases that may limit such analyses and to gain an overview of the planktonic microbial eukaryotic diversity in freshwater ecosystems. The richness of the microbial eukaryotes was estimated to 100 798 operational taxonomic units (OTUs) delineating 1267 clusters or phylogenetic units (PUs, i.e. monophyletic groups of OTUs that are phylogenetically close). By summing the richness found in aquatic environments, we can predict the microbial eukaryotic richness to be around 200 000- 250 000 species. The molecular diversity of protists in freshwater environments is generally higher than that of the morphospecies and cultivated species catalogued in public databases. Amoebozoa, Viridiplantae, Ichthyosporea, and Cryptophyta are the most phylogenetically diverse taxa, and characterisation of these groups is still needed. A network analysis showed that Fungi, Stramenopiles and Viridiplantae play central role in lake ecosystems. Finally, this work provides guidance for compiling metabarcoding data and identifies missing data that should be obtained to increase our knowledge on microbial eukaryote diversity.

Marine benthic cyanobacteria in tropical areas have recently been associated with several human poisoning events. To enhance the characterization of these microorganisms and their potential toxicity, benthic cyanobacterial communities were sampled in the lagoons of two islands (Raivavae and Rurutu) located in French Polynesia where human poisoning events by seafood had been reported. The morphological appearance of the mats was used to identify four types of cyanobacterial mat. By a 16S rRNA sequencing approach, it appeared that these mats were usually dominated by a restricted number of operational taxonomic units (OTUs), which were closely related to Leptolyngbya, Oscillatoria, Hydrocoleum, and Anabaena sequences, as previously reported in other tropical lagoons. Interestingly, we determined that these dominant filamentous OTUs were associated in the mats with other cyanobacteria, including unicellular species. By using a population genetic approach based on the sequencing of the internally transcribed spacer (ITS) of the rRNA operon, we found a very restricted genetic diversity in the most common OTU, which displayed a high sequence similarity with Leptolyngbya sp. In addition, there was no geographic differentiation at various spatial scales in the distribution of the different genotypes, suggesting that this species is able to spread over large distances. Finally, PCR screening of genes involved in the biosynthesis of known cyanotoxins revealed the presence of the saxitoxin gene (stxG) in two mats containing a mix of filamentous and unicellular cyanobacterial species.

Glycogen is mainly found as the principal storage form of glucose in cells. Many bacteria are able to synthesize large amounts of glycogen under unfavorable life conditions. By combining infrared spectroscopy, single molecule force spectroscopy (SMFS) and immuno-staining technique, we evidenced that planktonic P. fluorescens (Pf) cells are also able to produce glycogen as an extracellular polymeric substance. For this purpose, Pf suspensions were examined at 3 and 21 h of growth in nutritive medium (LB, 0.5 g/L). The conformation of the extracellular glycogen, revealed through its infrared spectral signature, has been investigated by SMFS measurements using Freely Jointed Chain model. The analysis of force versus distance curves showed over growth time that the increase of glycogen production was accompanied by an increase in glycogen contour lengths and ramifications. These results demonstrated that the production of extracellular bacterial glycogen can occur even if the cells are not subjected to unfavorable life conditions.

Marine benthic cyanobacteria in tropical areas have recently been associated with several human poisoning events. To enhance the characterization of these microorganisms and their potential toxicity, benthic cyanobacterial communities were sampled in the lagoons of two islands (Raivavae and Rurutu) located in French Polynesia where human poisoning events by seafood had been reported. The morphological appearance of the mats was used to identify four types of cyanobacterial mat. By a 16S rRNA sequencing approach, it appeared that these mats were usually dominated by a restricted number of operational taxonomic units (OTUs), which were closely related to Leptolyngbya, Oscillatoria, Hydrocoleum, and Anabaena sequences, as previously reported in other tropical lagoons. Interestingly, we determined that these dominant filamentous OTUs were associated in the mats with other cyanobacteria, including unicellular species. By using a population genetic approach based on the sequencing of the internally transcribed spacer (ITS) of the rRNA operon, we found a very restricted genetic diversity in the most common OTU, which displayed a high sequence similarity with Leptolyngbya sp. In addition, there was no geographic differentiation at various spatial scales in the distribution of the different genotypes, suggesting that this species is able to spread over large distances. Finally, PCR screening of genes involved in the biosynthesis of known cyanotoxins revealed the presence of the saxitoxin gene (stxG) in two mats containing a mix of filamentous and unicellular cyanobacterial species.

In search of a primer set that could be used to study Planctomycetes dynamics in lakes and especially via fingerprinting methods, e.g. denaturing gradient gel electrophoresis (DGGE), three existing specific primer sets, developed for marine and soil systems, have been tested on water samples from four freshwater ecosystems. The first primer set (PLA46F/ PLA886R) allowed PCR amplification of Planctomycetes sequences in only one of the four ecosystems, whereas the second primer set (PLA40F/ P518R) amplified Planctomycetes sequences in all the studied ecosystems but with a low specificity, since sequences belonging to Verrucomicrobiales and Chlamydiales clades were also amplified. Finally, the third primer set (PLA352F/PLA920R) allowed amplification of Planctomycetes sequences in the four ecosystems with a very high specificity. It amplified all known Planctomycetes genera and yielded the highest Operational Taxonomic Unit (OTU) richness and diversity estimates. In silico analyses supported these results. Further experiments comparing PLA352F/PLA920R to PLA46F/P1390R (a primer set generating a longer PCR fragment, also used to study Planctomycetes) yielded very similar results. Our findings suggest that the primer set PLA352F/ PLA920R provides good estimates of Planctomycetes richness and diversity compared with other, and can thus be used to study Planctomycetes dynamics in lentic freshwater ecosystems.

The effects of temperature, light intensity, and quality on the growth of the cyanobacteria Planktothrix agardhii (Gomont) Anag. et Komarek and P. rubescens (Gomont) Anag. et Komarek were assessed in batch cultures. The relative competitiveness of the green-pigmented P. agardhii and the red-pigmented P. rubescens was evaluated in separate and mixed cultures, under different light intensities and qualities (green, red, and white), and at two different temperatures, chosen as representative of the natural conditions favoring the respective blooms of each species. In monocultures, the P. rubescens strain appeared to be particularly well adapted to low intensities of green light and displayed a strong photoinhibition under high irradiance levels. The P. agardhii strain appeared less specialized with regard to light quality and also less sensitive to photoinhibition at higher irradiances. In competition experiments, temperature (15°C vs. 25°C) was the most important parameter in determining relative fitness of the species and competitive success. At 15°C, P. rubescens appeared to be much more competitive than P. agardhii, while P. agardhii was more competitive at 25°C. Under low irradiance, however, the pigmentation of these strains was of primary importance in determining the outcomes of the competition experiments. On the basis of our experimental results and on field observations, we propose that the successful growth leading to the proliferation of these two differently pigmented strains may largely depend on the combined conditions of light and temperature. The two strains, being genetically close relatives, could therefore be considered as two ecotypes that are adapted to different light and temperature environments. Competition experiments showed that the combination of these parameters largely controls the success of one strain in comparison to the other.

International audience; Over the last decade reports of animal poisoning following accidental consumption of neurotoxin-producing benthic cyanobacteria (mainly Phormidium spp.) have increased. There is a need for rapid and cost-effective tools to survey benthic cyanobacteria. In this study we assessed the performance of the BenthoTorch, a fluorometric probe that provides in situ estimations of cyanobacteria, diatoms and green algae biomass in biofilms. Biofilms = 288) were analysed from two rivers in France and eight in New Zealand. Correlations between chlorophyll-a measured using the BenthoTorch and spectrophotometry were higher for thin (2 mm) biofilms (r(2) = 0.58 and 0.27 respectively; p < 0.001). When cyanobacteria represented less than 50% of the total biomass (based on biovolumes), microscopic and BenthoTorch compositional estimations were significantly correlated (r(2) = 0.53, p < 0.001). Conversely, there was no correlation when cyanobacteria exceeded 50% of the total biomass. Under this scenario diatoms were overestimated. Our results suggest that the observed biases occur because the BenthoTorch only measures the upper biofilm layer and it underestimates the biomass of phycoerythrin-containing cyanobacteria. To improve the performance of this sensor and render it a useful tool for a rapid evaluation of benthic cyanobacterial biomass in rivers, we propose that: (i) the algorithms based on the LEDs responses currently available on this tool need revision, (ii) new excitation wavelengths should be included that allow the fingerprints of phycoerythrin-containing cyanobacteria to be discriminated, and (iii) a sensor that penetrates the biofilms is needed to obtain more accurate estimates of cyanobacterial biomass. (C) 2016 Elsevier Ltd. All rights reserved.

Ecosystem functioning depends on multiple interactions among physical, chemical and biological factors. Indeed, ecosystem processes (e.g., productivity and nutrient recycling) result directly from the diversity of functional traits in biotic communities, which in turn are determined by species composition and diversity. Species diversity results both from biotic introductions and from environmental pressures. As a result, changes in biodiversity in response to environmental selection pressures tend to have a direct impact on ecosystem processes. The relationships between biodiversity and ecosystem functioning have been the focus of numerous research studies for several years. Based on these studies, it appears that a low level of biodiversity allows an ecosystem to function effectively under constant conditions, but that greater biodiversity is called for in fluctuating environments. In this paper, we outline the concepts underlying the relationships between biodiversity and ecosystem functioning, and illustrate these concepts with examples from aquatic ecosystems. The importance of spatial scale will also be considered.

The tropical bloom-forming cyanobacterium Cylindrospermopsis raciborskii (Woloszynska) Seenaya et Subba Raju is causing increasing concern because of its potential toxicity and invasive behavior at midlatitudes. This species has recently been identified in several temperate areas and was first reported in France in 1994, but the mechanisms underlying this acclimation process remain to be elucidated. We performed a range of laboratory experiments in an attempt to identify the physiological characteristics that could account for this behavior. We investigated the three following hypotheses: 1) clones of C. raciborskii adapted to temperate climate have been selected as it advanced north, 2) C. raciborskii has high physiological tolerance that allows it to prosper in a wide range of conditions, and 3) changes in climate (global warming) have favored the development of C. raciborskii in mid-latitudes. Ten strains of C. raciborskii from Australia n 51), Brazil (2), France (2), Germany (1), Hungary (1), Mexico (1), and Senegal (2) were cultured at different temperatures and light intensities. The in vitro growth parameters (l and Topt) were the same for the tropical and temperate strains. All 10 strains displayed positive net growth in a wide range of temperatures (from 20 to 351 C) and light intensities (from 30 to 400lmol photons.m � 2.s � 1 ), with maximum growth rates at around 301 Ca nd 80lmol photons.m � 2.s � 1 . This suggests that the colonization of mid-latitudes by C. raciborskii may result from a combination of its ability to tolerate a rather wide range of climatic conditions and the global warming phenomenon, which provides this species with better environmental conditions for its growth.

Pour caracteriser l'etat d'un ecosysteme aquatique contamine par des toxiques il est necessaire de developper des methodes d'evaluation des impacts ecotoxicologiques, basees a la fois sur l'etude de reponses physiologiques et sur la structure des communautes vivant dans cet ecosysteme. La methode PICT (Pollution-Induced Community Tolerance) proposee par Blanck et al. (1988), repond a ces deux criteres. Elle est fondee sur l'hypothese qu'une communaute biologique naturelle est constituee de differents «composants» ayant des sensibilites variables vis-a-vis d'un toxique donne. Ainsi, suite a une exposition a un toxique, les organismes les plus sensibles ne sont plus concurrentiels et sont remplaces par des organismes plus tolerants. La communaute resultante presente alors une tolerance vis-a-vis du toxique, superieure a celle observee pour une communaute semblable mais n'ayant pas connu de pression de selection par ce toxique. Cette difference de reponse peut donner une indication sur l'etat de pollution des milieux dans lesquels ont ete echantillonnees differentes communautes. Le choix du test physiologique pour evaluer la tolerance de la communaute est fondamental car la reponse depend d'une part, du mode d'action du toxique et d'autre part, des mecanismes a l'origine de la tolerance de la communaute. Il existe peu d'outils de bioevaluation des milieux naturels soumis a des contaminations toxiques, et cette methode merite donc d'etre developpee. Des travaux appliquant la methode PICT a des communautes variees et dans divers milieux, permettraient de valider la methode et de resoudre certains problemes, quant a la detection de la tolerance. Le developpement de methodologies nouvelles pour caracteriser la structure et la tolerance des communautes etudiees est fondamental pour progresser dans nos connaissances sur le risque ecotoxicologique.

The resistance of gastro-intestinal nematodes of small ruminants (sheep and goat) to benzimidazole anthelmintic drugs seems to be linked primarily to a single mutation in the isotype 1 β-tubulin gene. This study was carried out to investigate the origin and diversity of benzimidazole-resistance alleles in trichostrongylid nematodes. We sequenced a 550 bp fragment of the isotype 1 β-tubulin gene from several benzimidazole-resistant Teladorsagia circumcincta populations isolated from dairy goat farms in the central and south-western France. We also sequenced the same β-tubulin fragment from Trichostrongylus colubriformis and Haemonchus contortus populations in south-western France. We found eight benzimidazole-resistance alleles in all T . circumcincta populations studied, six in H . contortus populations, and only one in T . colubriformis populations. In most cases, only one benzimidazole-resistance allele was present in T . circumcincta and H . contortus populations, but two alleles were found in a fewer number of them. Some T . circumcincta populations shared the same benzimidazole-resistance allele whereas some others had a specific benzimidazole-resistance allele. Similar findings were obtained for H . contortus . As no parasites are introduced once the flock of dairy goat farms has been constituted, these data indicate for the three studied species that rare pre-existing benzimidazole-resistance alleles already present before the isolation of populations had been selected. On the other hand, the fact that some benzimidazole-resistance alleles were specific to one population of T . circumcincta or H . contortus , seems to be in agreement with the hypothesis of the selection of spontaneous mutations. Thus, the origin of benzimidazole-resistance alleles in trichostrongylid nematodes seems to involve primarily the selection of rare alleles and possibly of spontaneous mutations.

A recently available submersible fluorescent probe was configured and used to survey the vertical distribution of the deep-living toxic and filamentous cyanobacterium Planktothrix (Oscil- latoria) rubescens among the autochthonous algal communities in Lake Bourget, France. This in situ measuring spectrofluorometer, which can be used to perform chlorophyll analysis and integrated algal class determination, provides a realistic estimation of the abundance and dynamics of the cyanobacterial population that is known to produce the hepatotoxic heptapeptides microcystin RR and LR. Data provided from in-line measurements using the probe and from P. rubescens cell counts obtained by discrete sampling were closely correlated (r = 0.899, p < 0.01), as were in-line data and spectrophotometric total chlorophyll a measurements (r = 0.775, p < 0.01). A survey conducted from December 1999 to May 2001 revealed that P. rubescens exhibits a deep maximum level (typically between 10 and 15 m) in spring and summer (reaching concentrations of up to 20 µg equivalent chl a l -1 , i.e. 27000 cells ml -1 ), whereas it spreads from the surface either to the top of the thermocline or to the bottom of the lake, in autumn and winter respectively. We propose that the probe could be used as a powerful tool for assaying the occurrence and dynamics of microalgal blooms, typically toxic cyanobacteria, that call for accurate and rapid monitoring to assess the health of the ecosystem and to alert the authorities about potential risks regarding pumping and use of the lake water for drinking-water production purposes.

Publication online; International audience; Metatranscriptome analysis relates to the transcriptome of microbial communities directly sampled in the environment. Accessing the mRNA pool in natural bacterial communities presents some technical challenges such as the RNA extraction, rRNA depletion, and the choice of the high-throughput sequencing technique. The lack of technical details in scientific articles is a major problem to correctly obtained mRNA from a microbial community and thus the corresponding sequencing data. In our study, we present the methodological procedure that was developed in order to access to the metatranscriptome of the microbial communities during two cyanobacterial blooms successively occurring in a freshwater eutrophic lake. Each procedure step was detailed and discussed with regard to the choices and difficulties encountered and to the recent literature. Finally, the two major limits for metatranscriptomic approaches targeting bacterial communities from natural environments were (i) the removal of rRNA in order to increase the putative mRNA reads number after sequencing, and (ii) for most of the bacterial communities living in natural environments, the lack of reference genomes in databases that leads to the non-assignation of numerous reads. Once these challenges overcome, we managed to access putative mRNA of dominant species, i.e. cyanobacteria (from 6 to 72 % of mRNA assigned), and of the surrounding bacteria (from 1 to 5 % of mRNA assigned).

This paper investigates the uptake, transport, state and self-diAusion of water in twigs and buds of Picea abies L. (Karst.) trees in winter until reactivation in spring. The presence or absence of xylem in embryonic shoots, as well as the intensity and type of bud dormancy were also studied. Three clones of P. abies were grown in a forest in northeastern France. The clones diAered in their timing of bud-burst, with the two clones from the Vosges showing diAerent degrees of early bud-burst and the clone from Poland showing late bud-burst. One-bud cuttings grown in standard forcing conditions showed a great diAerence in dormancy between the two provenances, but only a small diAerence between the two Vosges clones. Earliness of bud-burst was not strongly linked to the intensity of dormancy. A dye experiment combined with light microscopy indicated increased velocity of water transport in stems up to a maximum in April, initial entry of water into embryonic shoots, protoxylem diAerentiation in embryonic shoots from April, and then, shortly before bud-burst, water transport through the newly-formed protoxylem almost up to the meristem. Nuclear magnetic resonance measurements of the transverse relaxation time (T2) and the self-diAusion coeAcient of water confirmed these observations and showed water availability in embryonic shoots. The sequence of water-related phenomena occurring in early spring was the same in the three clones, but was earliest in the Vosges clone with the earliest bud-burst and latest in the Polish clone with late bud-burst. The results imply that this sequence of water-related phenomena leads to bud-burst. # 2000 Annals of Botany Company

Random amplified polymorphic DNA (RAPD) fragments were prepared from samples of Calonectris diomedea (Cory's shearwater, Aves) and Haemonchus contortus (Nematoda) DNA by polymerase chain reaction (PCR) using decamers containing two restriction enzyme sites as primers. Six of 19 studied RAPD fragments probably originated from traces of commensal microorganisms. Many rearranged fragments, absent in the original genomic DNA, were synthesized and amplified during the processing of all the DNA samples, indicating that interactions occur within and between strands during the annealing step of PCR. The model of interactions between molecular species during DNA amplification with a single arbitrary oligonucleotide primer was modified to include nested primer annealing and interactions within and between strands. The presence of these artefacts in the final RAPD have a major effect on the interpretation of polymorphism studies.

Radiofrequency field gradients ( B 1 gradients) are known to be insensitive to the background static field gradients ( B 0 gradients) which arise from zones of different magnetic susceptibility within the object under investigation. This feature is exploited here in order to detect restricted diffusion at the edge of a standard cylindrical glass tube containing water. A simple method based on B 1 gradients has been devised for producing a spatially resolved map in which translational diffusion coefficients are displayed along the third dimension. A decrease of the apparent self-diffusion coefficient at the liquid–glass boundary is indeed observed and explained by a simple theory used previously in the case of very rapidly diffusing systems [Y.Q. Song, B.M. Goodson, B. Sheridan, T.M. de Swiet, A. Pines, J. Chem. Phys. 108 (1998) 6233].

The use of microsatellites as highly polymorphic DNA markers for the typing of isolates of Aspergillus fumigatus was investigated. Four CA repeats were selected by screening an A. fumigatus DNA library with a (CA) 10 oligonucleotide. Primers flanking these CA repeats were designed to amplify each locus. One primer of each pair was labeled with a fluorophore, and the PCR products were analyzed with an automatic sequencer and the GeneScan software. For each primer set and for a given isolate, one band was detected and was assigned to an allele because A. fumigatus is haploid. With 50 clinical isolates, 50 environmental isolates, and 2 reference strains we obtained 12, 11, 10, and 23 different alleles for the four CA microsatellites, respectively (discriminatory power, 0.994). The results were identical by whatever DNA extraction technique was used. Interestingly, no clustering between environmental and clinical isolates was observed, suggesting that every isolate is potentially pathogenic. Microsatellite markers appear suitable for use in large epidemiological studies of invasive aspergillosis.

Experiments were conducted with water samples from two perialpine lakes with differing eutrophication status in order to examine the effects of inorganic-nutrient amendments (nitrogen as NO 3 − or NH 4 + and phosphorus as PO 4 3− ) on the dynamics, structure, and composition of Planctomycetes and to test the hypothesis that the community structure of Planctomycetes members and that of the other bacteria (without Planctomycetes , here referred to as bacteria-wP, the most represented groups within the community) would be similarly impacted by nutrient additions. Initial samples were characterized by high total nitrogen-to-total phosphorus ratios (range, 39 to 55), suggesting P rather than N was the limiting nutrient for microbial communities. Consistent with this, P additions stimulated phytoplankton growth and affected the community structure of bacteria-wP but, surprisingly, not that of Planctomycetes . N additions did not significantly affect the community structures of bacteria-wP and Planctomycetes or the Planctomycetes phylotype composition. The estimated generation time of Planctomycetes was 123 h. These findings could suggest that the generally well-accepted statement that bacteria (as a whole) are superior to phytoplankton in the ability to obtain phosphorus under P limitation might actually not hold for Planctomycetes . Planctomycetes might be poor competitors for P that do not respond quickly to the nutrient supply, which may help explain why their abundance is low in aquatic systems. The alternative view that Planctomycetes could be strong competitors for P (storing it) is also discussed. Our findings highlight the need for further studies examining Planctomycetes -phosphorus relationships in aquatic ecosystems.

The search for a better understanding of why cyanobacteria often dominate phytoplankton communities in eutrophic freshwater ecosystems has led to a growing interest in the interactions between cyanobacteria and bacteria. Against this background, we studied the location of bacteria within Microcystis colonies, and compared the structural and phylogenetic diversity of Microcystis-attached and free-living bacterial communities living in the same French lake, the Villerest reservoir. Using transmission electron microscopy, we show that most of the bacteria inside the colonies were located close to detrital materials that probably resulted from lysis of Microcystis cells. The 16S rRNA sequencing approach revealed a clear distinction between the attached and free-living communities at the levels of both their general structure and their operational taxonomic unit (OTU) composition. In particular, Microcystis colonies appeared to be depleted of Actinobacteria, but conversely enriched in Gammaproteobacteria, in particular when the bloom was declining. At the OTU level, a clear distinction was also found between attached and free-living bacteria, and new clades were identified among our sequences. All these findings suggest that Microcystis colonies constitute a distinct habitat for bacteria living in freshwater ecosystems, and that direct and indirect interactions (cell lysis, nutrient recycling, etc.) may occur between them inside these colonies.

In this work, we described a new approach for the isolation of a species-specific probe for the Eimeria media parasite of the rabbit based on the use of the random amplified polymorphic DNA (RAPD) technique. A specific fragment of 800 bp of the studied species was isolated after RAPD and then cloned and DIG-radiolabeled. After dot-blotting, we observed that this probe was specific for E. media. Sequencing of the 3′ and 5′ ends of this probe enabled the determination of two primers that could be used in a PCR reaction. The amplified product of 750 bp was specific for E. media. The use of these primers and of our probe allowed the detection of a very small number of oocysts. With a new protocol of DNA purification, 10 purified oocysts were detected by PCR. The efficiency of the amplification was not changed when two species were mixed. The threshold of detection of oocysts in fecal matter was equal to 30.

The search for a better understanding of why cyanobacteria often dominate phytoplankton communities in eutrophic freshwater ecosystems has led to a growing interest in the interactions between cyanobacteria and bacteria. Against this background, we studied the location of bacteria within Microcystis colonies, and compared the structural and phylogenetic diversity of Microcystis-attached and free-living bacterial communities living in the same French lake, the Villerest reservoir. Using transmission electron microscopy, we show that most of the bacteria inside the colonies were located close to detrital materials that probably resulted from lysis of Microcystis cells. The 16S rRNA sequencing approach revealed a clear distinction between the attached and free-living communities at the levels of both their general structure and their operational taxonomic unit (OTU) composition. In particular, Microcystis colonies appeared to be depleted of Actinobacteria, but conversely enriched in Gammaproteobacteria, in particular when the bloom was declining. At the OTU level, a clear distinction was also found between attached and free-living bacteria, and new clades were identified among our sequences. All these findings suggest that Microcystis colonies constitute a distinct habitat for bacteria living in freshwater ecosystems, and that direct and indirect interactions (cell lysis, nutrient recycling, etc.) may occur between them inside these colonies.

International audience; Sampling cyanobacteria in freshwater ecosystems is a crucial aspect of monitoring programs in both basic and applied research. Despite this, few papers have dealt with this aspect, and a high proportion of cyanobacteria monitoring programs are still based on monthly or twice-monthly water sampling, usually performed at a single location. In this study, we conducted high frequency spatial and temporal water sampling in a small eutrophic shallow lake that experiences cyanobacterial blooms every year. We demonstrate that the spatial and temporal aspects of the sampling strategy had a considerable impact on the findings of cyanobacteria monitoring in this lake. In particular, two peaks of Aphanizomenon flos-aquae cell abundances were usually not picked up by the various temporal sampling strategies tested. In contrast, sampling once a month was sufficient to provide a good overall estimation of the population dynamics of Microcystis aeruginosa. The spatial frequency of sampling was also important, and the choice in the location of the sampling points around the lake was very important if only two or three sampling points were used. When four or five sampling points were used, this reduced the impact of the choice of the location of the sampling points, and allowed to obtain fairly similar results than when six sampling points were used. These findings demonstrate the importance of the sampling strategy in cyanobacteria monitoring, and the fact that it is impossible to propose a single universal sampling strategy that is appropriate for all freshwater ecosystems and also for all cyanobacteria.

Blooms of freshwater cyanobacteria are typically accompanied by an important decrease in phytoplankton biodiversity in the water bodies where they occur. This study examines the potential production of growth-inhibiting substances by the toxic, bloom-forming cyanobacterium Planktothrix rubescens, following the observation of physical segregation between this and another cyanobacterium during previously performed mixed-culture competition experiments. Inhibition assays examining the growth of target strains exposed to donor culture filtrates showed that the growth of Planktothrix agardhii TCC 83-2, P. agardhii PMC 75.02 and Mougeotia gracillima TCC 50-2 was significantly inhibited in the presence of culture filtrate from P. rubescens TCC 29-1, isolated from Lake Bourget, France. Filtrates from P. rubescens TCC 69-6 and P. rubescens TCC 69-7, isolated from Lakes Nantua and Paladru (France), respectively, did not, however, inhibit the growth of P. agardhii TCC 83-2. This brief exploration of the allelopathic activity of P. rubescens suggests that it may potentially inhibit coexisting competitors as well as phytoplankton isolated from other freshwater ecosystems, and that this capacity may vary among different strains of Planktothrix. The potential importance of this phenomenon in pelagic competition dynamics is discussed.

Background The colonial cyanobacterium Microcystis proliferates in a wide range of freshwater ecosystems and is exposed to changing environmental factors during its life cycle. Microcystis blooms are often toxic, potentially fatal to animals and humans, and may cause environmental problems. There has been little investigation of the genomics of these cyanobacteria. Results Deciphering the 5,172,804 bp sequence of Microcystis aeruginosa PCC 7806 has revealed the high plasticity of its genome: 11.7% DNA repeats containing more than 1,000 bases, 6.8% putative transposases and 21 putative restriction enzymes. Compared to the genomes of other cyanobacterial lineages, strain PCC 7806 contains a large number of atypical genes that may have been acquired by lateral transfers. Metabolic pathways, such as fermentation and a methionine salvage pathway, have been identified, as have genes for programmed cell death that may be related to the rapid disappearance of Microcystis blooms in nature. Analysis of the PCC 7806 genome also reveals striking novel biosynthetic features that might help to elucidate the ecological impact of secondary metabolites and lead to the discovery of novel metabolites for new biotechnological applications. M. aeruginosa and other large cyanobacterial genomes exhibit a rapid loss of synteny in contrast to other microbial genomes. Conclusion Microcystis aeruginosa PCC 7806 appears to have adopted an evolutionary strategy relying on unusual genome plasticity to adapt to eutrophic freshwater ecosystems, a property shared by another strain of M. aeruginosa (NIES-843). Comparisons of the genomes of PCC 7806 and other cyanobacterial strains indicate that a similar strategy may have also been used by the marine strain Crocosphaera watsonii WH8501 to adapt to other ecological niches, such as oligotrophic open oceans.

Spatial variations in the abundance and diversity of the free-living bacterioplankton community of a large Alpine lake, Lake Bourget (France), were investigated in the pelagic zone by means of two two-dimensional samplings taken in 2003. Lake-water samples were collected in winter during water mixing, and in early summer during stratification. The population abundance in each sample was determined by flow cytometry. Denaturing gradient gel electrophoresis of PCR-amplified 16S rRNA gene fragments from organisms measuring less than 2 mum was used to assess eubacterioplankton community composition. In winter, no obvious differences were observed in either the abundance or the diversity of the bacterial community, on either the horizontal or the vertical scales. The only influence detected was that of river water input, but this was at a very minor scale relative to the surface area of the lake. In early summer, changes were found in the community composition on the vertical scale related to the thermal stratification of the water column. There were also marked differences on the horizontal scale at 15 m depth due to internal waves. The implications of these findings for sampling strategies are very important from the perspective of comparative studies of free-living bacterial community diversity and functioning in large and deep lakes.

Although the molecular bases of resistance to anthelmintic families have been intensively studied, the contributing factors for the development of anthelmintic resistance are less well known. Clear recommendations must be given to farmers in order to delay the onset of anthelmintic resistance. Until now, the main advice has concerned the reduction of treatment frequency in order to slow down the spread of resistance. Anthelmintic resistance development depends mostly on an efficient selection pressure. This means that a high treatment frequency is neither necessary nor sufficient to select for resistance. The contribution of resistant worms, which have survived an anthelmintic treatment, to the subsequent generation is the key factor that controls resistance spread. This point is illustrated by five surveys conducted on sheep and goat farms from France and Morocco. In the 52 farms studied, less than three anthelmintic treatments were given each year. Three characteristics of breeding management can be identified in the build up of anthelmintic resistance: (1) the introduction of resistant worms through the purchase of sheep/goats or the use of common pastures, grazed by several herds/flocks, (2) under-dosing of hosts and the repeated use of one class of drugs, (3) the size of the population in refugia (infective larvae on pastures) at the time of the treatment. The role played by these breeding management factors in selecting for resistance is discussed. The most efficient way to limit the increase of anthelmintic resistance remains the reduction of the selection pressure by drugs, and optimal timing to maximise their efficacy.

The cellular fatty acid content of 22 cyanobacterial strains belonging to the genera Anabaena, Aphanizomenon, Calothrix, Cylindrospermum, Nostoc, Microcystis and Planktothrix were analysed. The identities of the major peaks were confirmed by MS. Correspondence analysis of the data revealed three distinct groups formed by the Microcystis strains, the Nostoc/Planktothrix strains and the Anabaena/Aphanizomenon/Cylindrospermum strains. The Calothrix strain did not cluster with the other heterocystous cyanobacteria, supporting its morphological classification separate from the Nostocaceae family. The presence of large amounts of the fatty acids 18:30omega6,9,12c and 18:0 iso distinguished the Microcystis strains from the other cyanobacteria studied. The high content of 16:1omega7c grouped the Nostoc strains with the Planktothrix strains. A free-living strain of Nostoc contained 16:1omegao5c and 16: 1omega7c (about 1: 1), separating it from the symbiotic Nostoc strain and the Planktothrix strains. the strains of Anabaena, Aphanizomenon and Cylindrospermum grouped tightly and were characterized by the presence of 16:1omega9c and 16:0 anteiso fatty acids. Correspondence analysis of Anabaena, Aphanizomenon and Cylindrospermum showed that all hepatotoxic Anabaena strains grouped together, whereas the non-toxic and neurotoxic Anabaena strains grouped with the non-toxic Aphanizomenon strains.

The genetic diversity of the mtDNA ND4 gene in 11 Teladorsagia circumcincta populations from France and Morocco was assessed by sequencing. Some of these nematode populations were resistant to benzimidazole (BZ) anthelmintics, while others were susceptible. The nucleotide diversity in all populations studied was very high, probably due to a high mutation rate in nematodes, but there was no significant difference between them. This suggests that no strong, recurrent bottlenecks occur during the acquisition of BZ resistance by a worm population. The conservation of genetic variations during the acquisition of BZ resistance is probably due to the fact that anthelmintic treatments do not kill all the susceptible adult worms and to the presence of numerous free-living larvae that are not submitted to this anthelmintic pressure. There was no genetic subdivision between worm populations on a small geographical scale (less than 200 km), but significant F S T s were found on a larger geographical scale. This kind of subdivision cannot be explained by different genetic flows between populations because all these populations were isolated from each other. This subdivision is probably due to the breeding management practices and the large size of these worm populations, which limit genetic drift.

We compared the species composition in phytobenthic communities at different sampling sites in a small French river presenting polluted and unpolluted areas. For each sampling point, the total DNA was extracted and used to construct an 18S rRNA gene clone library after PCR amplification of a ca 400 bp fragment. Phytobenthic community composition was estimated by random sequencing of several clones per library. Most of the sequences corresponded to the Bacillariophyceae and Chlorophyceae groups. By combining phylogenetic and correspondence analyses, we showed that our molecular approach is able to estimate and compare the species composition at different sampling sites in order to assess the environmental impact of xenobiotics on phytobenthic communities. Changes in species composition of these communities were found, but no evident decrease in the diversity. We discuss the significance of these changes with regard to the existing level of pollution and their impact on the functionality of the ecosystem. Our findings suggest that it is now possible to use faster molecular methods (DGGE, ARISA.) to test large numbers of samples in the context of ecotoxicological studies, and thus to assess the impact of pollution in an aquatic ecosystem.

Combination of the Super Fast Inversion Recovery (SUFIR) method (D. Canet, J. Brondeau, and K. Elbayed, J. Magn. Reson. 77, 483 (1988)) and imaging procedures by radiofrequency field gradients (P. Maffei, P. Mutzenhardt, A. Retournard, B. Diter, R. Raulet, J. Brondeau, and D. Canet, J. Magn. Reson. A 107, 40 (1994)) provides spatially resolved maps of longitudinal relaxation times (T1). In addition to accurate T1 values, enhanced spatial resolution is obtained.

We have developed a new molecular tool for the diagnosis of the benzimidazole (BZ)-susceptibility or resistance in Teladorsagia circumcincta a nematode parasite of small ruminants. This tool is based on the use of the PCR and allows the genotyping of resistant (rr) or susceptible (rS and SS) adult worms or larvae. By using four primers in the same reaction mixture, worms can be genotyped in regard to the mutation on the residue 200 (phenylalanine to tyrosine) of the β-tubulin which is implicated in BZ resistance. A very high proportion of homozygous SS (Phe/Phe) individuals characterized the BZ susceptible populations, whereas a variable proportion of homozygous rr (Tyr/Tyr) individuals characterized the BZ resistant populations. A positive correlation was observed between the LD 50 estimated by egg hatch assay, and the proportion of mutant homozygous individuals rr (Tyr/Tyr). Our PCR method allows the rapid genotyping of numerous worms and permits the detection of the first resistant individuals in a worm population.

We compared, some fitness-related traits of benzimidazole resistant (rr) and susceptible (rS, SS) worms of Teladorsagia circumcincta, a gastrointestinal parasite of the small ruminants, under laboratory conditions. PCR was used to determine the genotypes (rr, SS, rS) and the fitness of each was compared within the same strain. There was no significant difference in egg production, development rate from egg to infective larvae stage, establishment of these larvae in the host or the survival of adult worms and infective larvae for the 3 genotypes. The same results were obtained for the establishment rate of larvae in the host and the production of infective larvae under conditions of strong competition between resistant and susceptible worms. The fact that there were no differences in fitness suggests that the installation of benzimidazole resistance in a worm population is irreversible. This agrees with field observations.

Revue électronique adresse : http://tto.trends.com/cgi-bin/tto/pr/pg...0076l/cgi-bin/tto/pr/pg_cat.cgi?cc=CAT 1; International audience

A method for age determination of adults from single rooted teeth is presented. It is based on the measurement of two dental features: periodontosis height times 100/root height (P) and transparency of the root height times 100/root height (T). These measurements are made on the labial surface of the entire tooth without section and do not require special equipment or training. The application of multiple regression analysis to a working sample of 306 teeth of known age, sex and race provided the following equation: Age (years) = 0.18 x P + 0.42 x T + 25.53. The mean error between the actual and estimated age was +/- 10 years on the working sample and +/- 8.4 years on a control sample made of 45 forensic science cases. Upper incisors showed a better precision than the other single rooted teeth and accuracy was not sex related. A comparison of the Gustafson and Lamendin methods on a control sample of 39 teeth resulted in an advantage of the latter considering the mean error on the estimation (14.2 +/- 3.4 years for Gustafson versus 8.9 +/- 2.2 for Lamendin). The Lamendin method can be practical interest for any forensic pathologist or dentist as it is fast, easy to use, and reasonably accurate except for cases of individuals under age 40 where other methods must be preferred.

Le comportement de l'intensite integree infrarouge a ete observe pour divers vibrateurs correspondant soit a des molecules polaires (nitriles) soit a des molecules non polaires (CS2 , C2 CI4 , C6 H12 ) etudiees en solution dans de nombreux solvants polaires et non polaires sur tout le domaine de concentration.La theorie developpee utilisant le modele a cavite d'Onsager conduit a une formulation reliant l'intensite integree d'une vibration de coordonnee normale Q au moment µ, a la polarisabilite a de la molecule, aux derivees |dµ/dQ| et |dα/dQ| ainsi qu'a la constante dielectrique du milieu et aux indices de refraction du solant et du solute.Cette theorie appliquee a de nombreuses vibrations fondamentales rend tres correctement compte de la variation d'intensite integree observee et relie cette grandeur aux caracteristiques de la molecule consideree. « L'effet de solvant » trouve ainsi son explication dans la modification du champ de reaction sous l'effet de la permittivite et de l'indice du milieu qui vient modifier la reponse des termes vibrationnels dµ/dQ et dα/dQ de la molecule libre.

The genetic diversity of two freshwater cyanobacteria, Planktothrix rubescens and P. agardhii, was studied by sequencing a 519 bp fragment of the 16S rRNA gene, a 550bp fragment of the psaAB locus, a 517bp fragment of the rbcLX locus and a 550bp fragment of the 16S-23S ITS. Most of the 19 isolates were obtained from five alpine lakes, except for four purchased from culture collections. There was no polymorphism between the P. rubescens/agardhii strains for the 16S rRNA gene (partial sequencing) and only a few polymorphic sites were found in the other sequences. These informative sites had a mosaic structure in the Planktothrix strains, suggesting the occurrence of recombination between them. In contrast, the population structure during a bloom appears to be clonal. The existence of recombinations between the strains of P. rubescens and P. agardhii and the 16S sequencing data suggest that they are conspecific.