International Journal of Agricultural Research, Innovation and Technology (IJARIT)
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Copper mobilization in the lower continental crust beneath cratonic margins, a Cu isotope perspective
No full textInternational audienceLower crustal sulfide-bearing cumulates beneath the convergent plate margins represent a major copper reservoir. However, how Cu is mobilized and migrated in the lower crust is still a matter of debate. Here, we analyzed the Cu elemental and isotopic compositions of well-characterized lower crustal xenoliths from the north margin of the North China Craton to decode Cu mobilization in the lower continental crust beneath cratonic margins. The mafic lower crustal rocks have experienced varying degrees of sulfide accumulation, with Cu contents ranging from 15 to 112 ppm. The majority of lower crustal xenoliths have variable and generally low (compared to the Bulk Silicate Earth) δ65Cu (the permil deviation of the 65Cu/63Cu ratio from the NIST 976 standard) values ranging from −3.17‰ to 0.13‰ (n = 24). Many intragranular and interstitial sulfide grains in these lower crustal xenoliths were partially dissolved and oxidized along the mineral fractures and boundaries. Oxidative dissolution of sulfide will preferentially release 65Cu into the liquids, leaving the residual sulfides enriched in the light isotope, implying that oxidized melt-rock interactions could account for the light Cu isotopic compositions of the lower crustal xenoliths. Sulfide accumulation and oxidative dissolution are responsible for the enrichment, mobilization, and transfer of Cu in the lower continental crust beneath cratonic margins
Emergence des entérobactéries Escherichia coli productrices des carbapénèmases NDM-5 et OXA-181 à la Réunion
No full textIn Reunion island, the number of carbapenemase-producing Enterobacteriaceae rises each year with a predominance since 2015-2016 of the NDM-5 and OXA-181 beta-lactamases from the Escherichia coli species. After having established the final epidemiologic assessment of the EPC in La Reunion from January 2010 to December 2020, we have selected all clinical isolates of NDM-5 and OXA-181-producing E. coli from La Reunion and Mayotte for the analysis of their phenotypical resistance and genetic proximity. In La Reunion, 33 (i.e. 87%) and 17 (i.e. 100%) of patients carrying NDM-5 and OXA-181-carbapenemase-producing bacteria went abroad mainly in Mayotte, Comoros and Madagascar. The analysis of the NDM-5 strains showed an almost complete resistance against the beta-lactams, including the aztreonam. Furthermore, the susceptibility of aztreonam was restored for 72% (n = 41/57) of the strains when combined with clavulanic acid and for 75% (n = 43/57) of the strains when combined with avibactam. For the OXA-181, the susceptibility to beta-lactams was found to be more varying with a good efficacy to the ceftazidime-avibactam. The genotypical analysis confirmed the existence of many epidemic clones among clonal group such as ST-58, ST-167, ST-405 and ST-410. In La Reunion, the impact of the NDM-5 and OXA-181 E. coli strains coming mainly via importations from outside La Reunion has been rising. More particularly, some STs have been found to be preferentially associated to certain areas in the Southwest Indian Ocean and notably in the Comoros Archipelago and Madagascar. This emergence raises concern about the implantation of this kind of EPC in the hospitals and communities in La Reunion.Il existe chaque année à La Réunion une augmentation des entérobactéries productrices de carbapénèmases (EPC) avec une prédominance depuis 2015-2016 des bêta-lactamases NDM-5 et OXA-181 chez l'espèce Escherichia coli. Après avoir établi le bilan épidémiologique des EPC à La Réunion de janvier 2010 à décembre 2020, nous avons sélectionné l'ensemble des souches E. coli NDM-5 et OXA 181 de La Réunion et de Mayotte pour analyser les résistances phénotypiques mais aussi leur proximité génétique. À La Réunion, 33 (soit 87%) et 17 (soit 100%) patients porteurs respectivement de E. coli NDM-5 et OXA-181 avaient un lien avec l'étranger, principalement de Mayotte, des Comores et de Madagascar. L'analyse phénotypique des souches NDM-5 a montré une résistance quasi-totale à toutes les bêta-lactamines, y compris l'aztréonam. La sensibilité à l'aztréonam a été restaurée pour 72% (n = 41/57) et 75% (n = 43/57) des souches lorsque ce dernier était combiné respectivement à l'acide clavulanique et à l'avibactam. Pour les OXA-181, la sensibilité aux bêta-lactamines était plus variable avec une bonne efficacité de la ceftazidime-avibactam. L'analyse génotypique a confirmé l'existence de nombreux clones épidémiques au sein de groupes clonaux tels que ST-58, ST-167, ST-405 et ST-410. Il existe à La Réunion une augmentation de l'incidence des souches E. coli NDM-5 et OXA-181 issues pour la majorité d'importations et dont certains STs sont associés préférentiellement à certaines régions du Sud-Ouest de l'océan Indien notamment de l'archipel des Comores et de Madagascar. Cette émergence fait craindre l'implantation de ce type d'EPC dans le secteur hospitalier et communautaire de La Réunion
A newly emerging alphasatellite affects banana bunchy top virus replication, transcription, siRNA production and transmission by aphids
No full textInternational audienceBanana bunchy top virus (BBTV) is a six-component ssDNA virus (genus Babuvirus , family Nanoviridae ) transmitted by aphids, infecting monocots (mainly species in the family Musaceae) and likely originating from South-East Asia where it is frequently associated with self-replicating alphasatellites. Illumina sequencing analysis of banana aphids and leaf samples from Africa revealed an alphasatellite that should be classified in a new genus, phylogenetically related to alphasatellites of nanoviruses infecting dicots. Alphasatellite DNA was encapsidated by BBTV coat protein and accumulated at high levels in plants and aphids, thereby reducing helper virus loads, altering relative abundance (formula) of viral genome components and interfering with virus transmission by aphids. BBTV and alphasatellite clones infected dicot Nicotiana benthamiana , followed by recovery and symptomless persistence of alphasatellite, and BBTV replication protein (Rep), but not alphasatellite Rep, induced leaf chlorosis. Transcriptome sequencing revealed 21, 22 and 24 nucleotide small interfering (si)RNAs covering both strands of the entire viral genome, monodirectional Pol II transcription units of viral mRNAs and pervasive transcription of each component and alphasatellite in both directions, likely generating double-stranded precursors of viral siRNAs. Consistent with the latter hypothesis, viral DNA formulas with and without alphasatellite resembled viral siRNA formulas but not mRNA formulas. Alphasatellite decreased transcription efficiency of DNA-N encoding a putative aphid transmission factor and increased relative siRNA production rates from Rep- and movement protein-encoding components. Alphasatellite itself spawned the most abundant siRNAs and had the lowest mRNA transcription rate. Collectively, following African invasion, BBTV got associated with an alphasatellite likely originating from a dicot plant and interfering with BBTV replication and transmission. Molecular analysis of virus-infected banana plants revealed new features of viral DNA transcription and siRNA biogenesis, both affected by alphasatellite. Costs and benefits of alphasatellite association with helper viruses are discussed
A genome-wide assessment of the genetic diversity, evolution and relationships with allied species of the clonally propagated crop Vanilla planifolia Jacks. ex Andrews
No full textEarly accessInternational audienceThe Vanilla genus is a complex taxonomic group characterized by a vegetative reproduction mode combined with intra- and inter-specific hybridizations, and polyploidy events. These factors strongly impact the diversification of the genus and complicate the delimitation of taxa. Among the hundred Vanilla species, Vanilla planifolia Jacks. ex Andrews and Vanilla × tahitensis J. W. Moore are the main cultivated aromatic species. We applied Genotyping-by-Sequencing to explore the genetic diversity of these two cultivated vanilla species, seven closely related species and nineteen interspecific hybrids. The inter- and intra-specific relationships of 133 vanilla accessions were examined based on 2004 filtered SNPs. Our results showed a strong genetic structuring between the nine species studied, with wild species showing much lower heterozygosity levels than cultivated ones. Moreover, using Bayesian clustering analyses, the kinship of several hybrids could be verified. We evidenced in particular that Vanilla sotoarenasii and Vanilla odorata C.Presl may be the parental species of V. x tahitensis . The analysis of 1129 SNPs for 84 V . planifolia accessions showed a clear genetic demarcation between the vegetatively propagated traditional vanilla cultivars compared to the accessions derived from sexual reproduction, and a higher genetic diversity and lower heterozygosity of the latter (Ho = 0.206) compared to the former (Ho = 0.362). Our data are consistent with a single-step domestication for V. planifolia in accordance with the recent history of its cultivation. It also opens avenues to breed new V. planifolia varieties adapted to biotic and abiotic constraints and to reduce mutational load induced by clonal propagation
Reservoir depressurization driven by passive gas emissions at Ambrym volcano
No full textInternational audienceDespite being a widespread and common process, the impact of passive volcanic degassing on the pressurization state of a magma reservoir is not well understood. If mass loss due to gas emissions results in reservoir depressurization and surface subsidence, the pressure difference between a shallow reservoir and deep magma source may result in magma recharge and eventually trigger an eruption. It is therefore important to determine how a simplified reservoir-conduit system responds to such degassing processes. Here we use an extreme example of persistent volcanic degassing—Ambrym—as a case study to relate sulphur dioxide mass flux with reservoir depressurization and edifice-scale subsidence, both measured from satellite-based remote sensing observations. A geodetic inversion of surface displacements measured with Interferometric Synthetic Aperture Radar modeled using the Boundary Element Method provides bounds on the reservoir pressure change during an episode of subsidence at Ambrym from 2015 to 2017. These results are input into a lumped parameter theoretical model developed by Girona et al. (2014), and the free parameters (e.g., reservoir size and conduit radius) are systematically explored. We find that the 2015–2017 subsidence episode is consistent with pressure decreasing at a rate of −5.2 to −2.0 MPa year−1 in a reservoir at ∼2 km b.s.l., as a result of passive degassing. The subsidence episode is observed to end abruptly in October 2017, and no significant deformation is detected in the 14 months leading up to a rift zone intrusion and submarine eruption in December 2018, despite substantial degassing. We explain this lack of pre-eruptive deformation by an influx of ∼0.16 km3 of magma into a shallow (<2 km b.s.l.) reservoir that counterbalances the depressurization caused by degassing. This recharge volume is comparable with the volume of magma subsequently extracted from Ambrym's reservoir in December 2018. We conclude that at some open-vent passively degassing volcanoes, deflation caused by degassing may reduce or even cancel any inflation signal caused by magma influx. Nonetheless, detection of pre-eruptive recharge can be achieved by monitoring changes in the long-term deformation rate
Origin, Persistence, and Vulnerability to Climate Changes of Podocarpus Populations in Central African Mountains
No full textInternational audienceBackground and objectives—Podocarpus latifolius (synonym of P. milanjianus) is a key tree representative of Afromontane forests where it is highly threatened by climate and land-use changes. While large populations occur in East Africa, only a few isolated and usually small populations remain in western Central Africa (Cameroon to Angola). Studying the evolutionary history of such relictual populations can thus be relevant to understand their resilience under changing environments. Materials and Methods—we developed nine polymorphic nuclear microsatellites (nSSRs) to estimate genetic variability, (historical) gene flow, and demographic changes among natural populations from Central to East Africa. Results—despite the extended distribution range of P. latifolius, a strong isolation-by-distance pattern emerges at the intra-population scale, indicating low seed and pollen dispersal capacities. Central African populations display a lower genetic diversity (He = 0.34 to 0.61) and are more differentiated from each other (FST = 0.28) than are East African populations (He = 0.65 to 0.71; FST = 0.10), suggesting high genetic drift in the Central African populations. Spatial genetic structure reveals past connections between East and West Africa but also a gene flow barrier across the equator in western Central Africa. Demographic modelling anchors the history of current lineages in the Pleistocene and supports a strong demographic decline in most western populations during the last glacial period. By contrast, no signature of demographic change was detected in East African populations. Conclusions—in Cameroon, our results exclude a recent (re)colonization from one source population of all mountain ranges, but rather indicate long-term persistence of populations in each mountain with fluctuating sizes. A higher impact of genetic drift and further loss of diversity can be expected by survival through climatically unfavorable periods in such small refugial populations. Tracking the Quaternary legacy of podocarp populations is thus essential for their conservation since there is a temporal gap between environment crises and an ecological/genetic answer at the population level
An analysis of core-mantle boundary Stoneley mode sensitivity and sources of uncertainty
No full textInternational audienceStoneley modes are a special subset of normal modes whose energy is confined along the core-mantle boundary (CMB). As such, they offer a unique glimpse into Earth structure at the base of the mantle. They are often observed through coupling with mantle modes due to rotation, ellipticity and lateral heterogeneity, though they can be detected without such coupling. In this study, we explore the relative sensitivities of seismic spectra of two low-frequency Stoneley modes to several factors, taking as reference the fully coupled computation up to 3 mHz in model S20RTS. The factors considered are (i) theoretical, by exploring the extent to which various coupling approximations can accurately reproduce reference spectra and (ii) model-based, by exploring how various Earth parameters such as CMB topography, attenuation and S- and P-wave structures, and the seismic source solution may influence the spectra. We find that mode-pair coupling is insufficiently accurate, but coupling modes within a range of ±0.1 mHz produces acceptable spectra, compared to full coupling. This has important implications for splitting function measurements, which are computed under the assumption of isolated modes or at best, mode-pair or group coupling. We find that uncertainties in the P-wave velocity mantle model dominate compared to other model parameters. In addition, we also test several hypothetical models of mantle density structure against real data. These tests indicate that, with the low-frequency Stoneley mode spectral data considered here, it is difficult to make any firm statement on whether the large-low-shear-velocity-provinces are denser or lighter than their surroundings. We conclude that better constraints on long wavelength elastic mantle structure, particularly P-wave velocity, need to be obtained, before making further statements on deep mantle density heterogeneity. In particular, a dense anomaly confined to a thin layer at the base of the mantle (less than ~100-200 km) may not be resolvable using the two Stoneley modes tested here, while the ability of higher frequency Stoneley modes to resolve it requires further investigations
Spi-OPS: Spitzer and CHEOPS confirm the near-polar orbit of MASCARA-1 b and reveal a hint of dayside reflection
No full textInternational audienceContext. The light curves of tidally locked hot Jupiters transiting fast-rotating, early-type stars are a rich source of information about both the planet and star, with full-phase coverage enabling a detailed atmospheric characterisation of the planet. Although it is possible to determine the true spin-orbit angle Ψ - a notoriously difficult parameter to measure - from any transit asymmetry resulting from gravity darkening induced by the stellar rotation, the correlations that exist between the transit parameters have led to large disagreements in published values of Ψ for some systems. Aims: We aimed to study these phenomena in the light curves of the ultra-hot Jupiter MASCARA-1 b, which is characteristically similar to well-studied contemporaries such as KELT-9 b and WASP-33 b. Methods: We obtained optical CHaracterising ExOPlanet Satellite (CHEOPS) transit and occultation light curves of MASCARA-1 b, and analysed them jointly with a Spitzer/IRAC 4.5 μm full-phase curve to model the asymmetric transits, occultations, and phase-dependent flux modulation. For the latter, we employed a novel physics-driven approach to jointly fit the phase modulation by generating a single 2D temperature map and integrating it over the two bandpasses as a function of phase to account for the differing planet-star flux contrasts. The reflected light component was modelled using the general ab initio solution for a semi-infinite atmosphere. Results: When fitting the CHEOPS and Spitzer transits together, the degeneracies are greatly diminished and return results consistent with previously published Doppler tomography. Placing priors informed by the tomography achieves even better precision, allowing a determination of Ψ = 72.1−2.4+2.5 deg. From the occultations and phase variations, we derived dayside and nightside temperatures of 3062−68+66 K and 1720 ± 330 K, respectively.Our retrieval suggests that the dayside emission spectrum closely follows that of a blackbody. As the CHEOPS occultation is too deep to be attributed to blackbody flux alone, we could separately derive geometric albedo Ag = 0.171−0.068+0.066 and spherical albedo As = 0.266−0.100+0.097 from the CHEOPS data, and Bond albedoAB = 0.057−0.101+0.083 from the Spitzer phase curve.Although small, the Ag and As indicate that MASCARA-1 b is more reflective than most other ultra-hot Jupiters, where H− absorption is expected to dominate. Conclusions: Where possible, priors informed by Doppler tomography should be used when fitting transits of fast-rotating stars, though multi-colour photometry may also unlock an accurate measurement of Ψ. Our approach to modelling the phase variations at different wavelengths provides a template for how to separate thermal emission from reflected light in spectrally resolved James Webb Space Telescope phase curve data. The photometric time series data are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/658/A75</a
Geochemistry of serpentinized and multiphase altered Atlantis Massif peridotites (IODP Expedition 357): Petrogenesis and discrimination of melt-rock vs. fluid-rock processes
No full textInternational audienceInternational Ocean Discovery Program (IODP) Expedition 357 drilled 17 shallow sites distributed ~10 km in the spreading direction (from west to east) across the Atlantis Massif oceanic core complex (Mid-Atlantic Ridge, 30°N). Mantle exposed in the footwall of the Atlantis Massif oceanic core complex is predominantly nearly wholly serpentinized harzburgite with subordinate dunite. Altered peridotites are subdivided into three types: (I) serpentinites, (II) melt-impregnated serpentinites, and (III) metasomatic serpentinites. Type I serpentinites show no evidence of melt-impregnation or metasomatism apart from serpentinization and local oxidation. Type II serpentinites have been intruded by gabbroic melts and are distinguishable in some cases on the basis of macroscopic and microscopic observations, e.g., mm-cm scale mafic-melt veinlets, rare plagioclase (˂0.5 modal % in one sample) or by the local presence of secondary (replacive) olivine after orthopyroxene; in other cases, ‘cryptic’ melt-impregnation is inferred on the basis of incompatible element enrichments. Type III serpentinites are characterized by silica metasomatism manifest by alteration of orthopyroxene to talc and amphibole, and by anomalously high anhydrous SiO2 concentrations (59–61 wt%) and low MgO/SiO2 values (0.48–0.52). Although many chondrite-normalized rare earth element (REE) and primitive mantle-normalized incompatible trace element anomalies, e.g., negative Ce-anomalies, are attributable to serpentinization, other compositional heterogeneities are due to melt-impregnation. On the basis of whole rock incompatible trace elements, a dominant mechanism of melt-impregnation is distinguished in the central and eastern serpentinites from fluid-rock alteration (mostly serpentinization) in the western serpentinites, with increasing melt-impregnation manifest as a west to east increase in enrichment in high-field strength elements and light REE. High degrees of melt extraction are evident in low whole-rock Al2O3/SiO2 values and low concentrations of Al2O3, CaO and incompatible elements. Estimates of the degree of melt extraction based on whole rock REE patterns suggest a maximum of ~20% non-modal fractional melting, with little variation between sites. As some serpentinite samples are ex situ rubble, the magmatic histories observed at each site are consistent with a local source (from the fault zone) rather than rafted rubble that would be expected to show more heterogeneity and no spatial pattern. In this case, the studied sites may provide a record of enhanced melt-rock interactions with time, consistent with proposed geological models. Alternatively, sites may signify heterogeneities in these processes at spatial scales of a few km