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Rivalland, C., Madhkour, S., Salvin, P., & Robert, F. (2015). Electrochemical and microbial monitoring of multi-generational electroactive biofilms formed from mangrove sediment. Bioelectrochemistry, 106, 125–132.
Abstract: Electroactive biofilms were formed from French Guiana mangrove sediments for the analysis of bacterial communities' composition. The electrochemical monitoring of three biofilm generations revealed that the bacterial selection occurring at the anode, supposedly leading microbial electrochemical systems (MESs) to be more efficient, was not the only parameter to be taken into account so as to get the best electrical performance (maximum current density). Indeed, first biofilm generations produced a stable current density reaching about 18A/m2 while second and third generations produced current densities of about 10A/m2. MES bacterial consortia were characterized thanks to molecular biology techniques: DGGE and MiSeq® sequencing (Illumina®). High-throughput sequencing data statistical analysis confirmed preliminary DGGE data analysis, showing strong similarities between electroactive biofilms of second and third generations, but also revealing both selection and stabilization of the biofilms. © 2015 Elsevier B.V.
Keywords: Dissimilarity; High-throughput sequencing; Mes; Microbial diversity; Syntrophism
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Touchard, A., Dejean, A., & Orivel, J. (2015). Intraspecific variations in the venom peptidome of the ant Odontomachus haematodus (Formicidae: Ponerinae) from French Guiana. Journal of Hymenoptera Research, 47, 87–101.
Abstract: Ant venoms are complex cocktails of toxins employed to subdue prey and to protect the colony from predators and microbial pathogens. Although the extent of ant venom peptide diversity remains largely unexplored, previous studies have revealed the presence of numerous bioactive peptides in most stinging ant venoms. We investigated the venom peptidome of the ponerine ant Odontomachus haematodus using LC-MS analysis and then verified whether the division of labor in the colonies and their geographical location are correlated with differences in venom composition. Our results reveal that O. haematodus venom is comprised of 105 small linear peptides. The venom composition does not vary between the different castes (i.e., nurses, foragers and queens), but an intraspecific variation in peptide content was observed, particularly when the colonies are separated by large distances. Geographical variation appears to increase the venom peptide repertoire of this ant species, demonstrating its intraspecific venom plasticity.
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Zinger, L., Chave, J., Coissac, E., Iribar, A., Louisanna, E., Manzi, S., et al. (2016). Extracellular DNA extraction is a fast, cheap and reliable alternative for multi-taxa surveys based on soil DNA. Soil Biology and Biochemistry, 96, 16–19.
Abstract: DNA metabarcoding on soil samples is increasingly used for large-scale and multi-taxa biodiversity studies. However, DNA extraction may be a major bottleneck for such wide uses. It should be cost/time effective and allow dealing with large sample volumes so as to maximise the representativeness of both micro- and macro-organisms diversity. Here, we compared the performances of a fast and cheap extracellular DNA extraction protocol with a total DNA extraction method in retrieving bacterial, eukaryotic and plant diversity from tropical soil samples of ca. 10 g. The total DNA extraction protocol yielded more high-quality DNA. Yet, the extracellular DNA protocol provided similar diversity assessments although it presented some differences in clades relative abundance and undersampling biases. We argue that extracellular DNA is a good compromise between cost, labor, and accuracy for high-throughput DNA metabarcoding studies of soil biodiversity. © 2016 Elsevier Ltd.
Keywords: DNA extraction protocol; DNA metabarcoding; Multi-taxa biodiversity; Tropical forest
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Dejean, A., Orivel, J., Azémar, F., Herault, B., & Corbara, B. (2016). A cuckoo-like parasitic moth leads African weaver ant colonies to their ruin. Sci. Rep., 6, 23778.
Abstract: In myrmecophilous Lepidoptera, mostly lycaenids and riodinids, caterpillars trick ants into transporting them to the ant nest where they feed on the brood or, in the more derived 'cuckoo strategy', trigger regurgitations (trophallaxis) from the ants and obtain trophic eggs. We show for the first time that the caterpillars of a moth (Eublemma albifascia; Noctuidae; Acontiinae) also use this strategy to obtain regurgitations and trophic eggs from ants (Oecophylla longinoda). Females short-circuit the adoption process by laying eggs directly on the ant nests, and workers carry just-hatched caterpillars inside. Parasitized colonies sheltered 44 to 359 caterpillars, each receiving more trophallaxis and trophic eggs than control queens. The thus-starved queens lose weight, stop laying eggs (which transport the pheromones that induce infertility in the workers) and die. Consequently, the workers lay male-destined eggs before and after the queen's death, allowing the colony to invest its remaining resources in male production before it vanishes.
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Houel, E., Nardella, F., Jullian, V., Valentin, A., Vonthron-Sénécheau, C., Villa, P., et al. (2016). Wayanin and guaijaverin, two active metabolites found in a Psidium acutangulum Mart. ex DC (syn. P. persoonii McVaugh) (Myrtaceae) antimalarial decoction from the Wayana Amerindians. Journal of Ethnopharmacology, 187, 241–248.
Abstract: Ethnopharmacological relevance Psidium acutangulum Mart. ex DC is a small tree used by the Wayana Amerindians from the Upper-Maroni in French Guiana for the treatment of malaria. Aim of the study In a previous study, we highlighted the in vitro antiplasmodial, antioxidant and anti-inflammatory potential of the traditional decoction of P. acutangulum aerial parts. Our goal was then to investigate on the origin of the biological activity of the traditional remedy, and eventually characterize active constituents. Materials and methods Liquid-liquid extractions were performed on the decoction, and the antiplasmodial activity evaluated against chloroquine-resistant FcB1 ([3H]-hypoxanthine bioassay) and 7G8 (pLDH bioassay) P. falciparum strains, and on a chloroquine sensitive NF54 ([3H]-hypoxanthine bioassay) P. falciparum strain. The ethyl acetate fraction (D) was active and underwent bioguided fractionation. All the isolated compounds were tested on P. falciparum FcB1 strain. In vitro anti-inflammatory activity (IL-1β, IL-6, IL-8, TNFα) of the ethyl acetate fraction and of an anti-Plasmodium active compound, was concurrently assessed on LPS-stimulated human PBMC and NO secretion inhibition was measured on LPS stimulated RAW murine macrophages. Cytotoxicity of the fractions and pure compounds was measured on VERO cells, L6 mammalian cells, PBMCs, and RAW cells. Results Fractionation of the ethyl acetate soluble fraction (IC50 ranging from 3.4 to <1 μg/mL depending on the parasite strain) led to the isolation of six pure compounds: catechin and five glycosylated quercetin derivatives. These compounds have never been isolated from this plant species. Two of these compounds (wayanin and guaijaverin) were found to be moderately active against P. falciparum FcB1 in vitro (IC50 5.5 and 6.9 μM respectively). We proposed the name wayanin during public meetings organized in June 2015 in the Upper-Maroni villages, in homage to the medicinal knowledge of the Wayana population. At 50 μg/mL, the ethyl acetate fraction (D) significantly inhibited IL-1β secretion (-46%) and NO production (-21%), as previously observed for the decoction. The effects of D and guiajaverin (4) on the secretion of other cytokines or NO production were not significant. Conclusions The confirmed antiplasmodial activity of the ethyl acetate soluble fraction of the decoction and of the isolated compounds support the previous results obtained on the P. acutangulum decoction. The antiplasmodial activity might be due to a mixture of moderately active non-toxic flavonoids. The anti-inflammatory activities were less marked for ethyl acetate fraction (D) than for the decoction. © 2016 Elsevier Ireland Ltd. All rights reserved.
Keywords: Antimalarial; Cytokines; French guiana; Glycosylated flavonols; Psidium acutangulum; Traditional remedy
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Vastra, M., Salvin, P., & Roos, C. (2016). MIC of carbon steel in Amazonian environment: Electrochemical, biological and surface analyses. International Biodeterioration and Biodegradation, 112, 98–107.
Abstract: In this study, the corrosion of S355 carbon steel was monitored for 50 days in equatorial environment. The experiments were conducted under three complementary approaches in a natural environment: (i) bacterial diversity was assessed with Miseq sequencing, (ii) observations of the surface and identifications of deposit compounds were realised with scanning electron microscopy (SEM), Raman spectrometry and EDX analyses, (iii) electrochemical measurements were used to calculate corrosion rate and to identify the phenomena which control corrosion. The results showed that the bacterial population had changed over immersion time from a dominance of β-proteobacteria to α-proteobacteria. This evolution decreased charge transfer resistance at the metal/deposit from 41.6 to 20.8 Ω/cm2 in 50 days, caused an increase in the corrosion rate by a factor of 2, from 0.13 to 0.27 mm/year. Surface analyses showed a progressive appearance of MIC markers in the deposit such as iron sulphide and manganese oxides that were detected after 30 days of immersion in the natural environment. In conclusion, this study describes in detail, the first stage of MIC activity on carbon steel surface in an equatorial brackish water, under aerobic conditions. © 2016 Elsevier Ltd.
Keywords: Biology; Electrochemistry; Mic; Short term; Surface analyses
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Fayad, I., Baghdadi, N., Guitet, S., Bailly, J. - S., Herault, B., Gond, V., et al. (2016). Aboveground biomass mapping in French Guiana by combining remote sensing, forest inventories and environmental data. International Journal of Applied Earth Observation and Geoinformation, 52, 502–514.
Abstract: Mapping forest aboveground biomass (AGB) has become an important task, particularly for the reporting of carbon stocks and changes. AGB can be mapped using synthetic aperture radar data (SAR) or passive optical data. However, these data are insensitive to high AGB levels (>150 Mg/ha, and >300 Mg/ha for P-band), which are commonly found in tropical forests. Studies have mapped the rough variations in AGB by combining optical and environmental data at regional and global scales. Nevertheless, these maps cannot represent local variations in AGB in tropical forests. In this paper, we hypothesize that the problem of misrepresenting local variations in AGB and AGB estimation with good precision occurs because of both methodological limits (signal saturation or dilution bias) and a lack of adequate calibration data in this range of AGB values. We test this hypothesis by developing a calibrated regression model to predict variations in high AGB values (mean >300 Mg/ha) in French Guiana by a methodological approach for spatial extrapolation with data from the optical geoscience laser altimeter system (GLAS), forest inventories, radar, optics, and environmental variables for spatial inter- and extrapolation. Given their higher point count, GLAS data allow a wider coverage of AGB values. We find that the metrics from GLAS footprints are correlated with field AGB estimations (R2 = 0.54, RMSE = 48.3 Mg/ha) with no bias for high values. First, predictive models, including remote-sensing, environmental variables and spatial correlation functions, allow us to obtain “wall-to-wall” AGB maps over French Guiana with an RMSE for the in situ AGB estimates of ∼50 Mg/ha and R2 = 0.66 at a 1-km grid size. We conclude that a calibrated regression model based on GLAS with dependent environmental data can produce good AGB predictions even for high AGB values if the calibration data fit the AGB range. We also demonstrate that small temporal and spatial mismatches between field data and GLAS footprints are not a problem for regional and global calibrated regression models because field data aim to predict large and deep tendencies in AGB variations from environmental gradients and do not aim to represent high but stochastic and temporally limited variations from forest dynamics. Thus, we advocate including a greater variety of data, even if less precise and shifted, to better represent high AGB values in global models and to improve the fitting of these models for high values. © 2016 Elsevier B.V.
Keywords: Aboveground biomass mapping; Forests; French Guiana; ICESat GLAS; LiDAR
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Alméras, T., Gronvold, A., van der Lee, A., Clair, B., & Montero, C. (2017). Contribution of cellulose to the moisture-dependent elastic behaviour of wood. Composites Science and Technology, 138, 151–160.
Abstract: Wood has a hierarchical structure involving several levels of organisation. The stiffness of wood relies on its capacity to transfer mechanical stress to its stiffest element at the lowest scale, namely crystalline cellulose. This study aims at quantifying to what extend crystalline cellulose contributes to wood stiffness depending on its moisture content. The crystal strains of cellulose were measured using X-ray diffraction on wet and dry specimens of spruce, based on a previously published methodology. The comparison between crystal strain and macroscopic strain shows that, during elastic loading, cellulose strain is lower than macroscopic strain. The means ratio of crystal/macroscopic strain amounts 0.85 for dry specimens and 0.64 for wet specimens. This strain ratio cannot be explained just by the projection effect due to the difference in orientation between cellulose microfibrils and cell wall, but results from deformation mechanisms in series with cellulose. Analysis shows that this series contribution represents a non-negligible contribution to wood compliance and is strongly moisture-dependent. This contribution amounts 9% for dry specimens and 33% for wet specimens, corresponding to a 4-fold increase in compliance for the series contribution. The origin of these strains is ascribed to mechanisms involving bending or shear strain at different scales, due to the fact that reinforcing element are neither perfectly straight nor infinitely long. © 2016
Keywords: Cellulose; Crystal strain; Micromechanics; Wood; X-ray diffraction
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Piponiot, C., Sist, P., Mazzei, L., Peña-Claros, M., Putz, F. E., Rutishauser, E., et al. (2016). Carbon recovery dynamics following disturbance by selective logging in Amazonian forests. eLife, 5, e21394.
Abstract: When 2 Mha of Amazonian forests are disturbed by selective logging each year, more than 90 Tg of carbon (C) is emitted to the atmosphere. Emissions are then counterbalanced by forest regrowth. With an original modelling approach, calibrated on a network of 133 permanent forest plots (175 ha total) across Amazonia, we link regional differences in climate, soil and initial biomass with survivors' and recruits' C fluxes to provide Amazon-wide predictions of post-logging C recovery. We show that net aboveground C recovery over 10 years is higher in the Guiana Shield and in the west (21{plus minus}3 MgC ha-1) than in the south (12{plus minus}3 MgC ha-1) where environmental stress is high (low rainfall, high seasonality). We highlight the key role of survivors in the forest regrowth and elaborate a comprehensive map of post-disturbance C recovery potential in Amazonia.
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Marcon, E., & Puech, F. (2017). A typology of distance-based measures of spatial concentration. Regional Science and Urban Economics, 62, 56–67.
Abstract: Over the last decade, distance-based methods have been introduced and then improved in the field of spatial economics to gauge the geographic concentration of activities. There is a growing literature on this theme including new tools, discussions on their specific properties and various applications. However, there is currently no typology of distance-based methods. This paper fills that gap. The proposed classification helps understand all the properties of distance-based methods and proves that they are variations on the same framework. © 2016 Elsevier B.V.
Keywords: Agglomeration; Aggregation; Economic geography; Point patterns; Spatial concentration
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