Spatial structure and composition of polysaccharide-protein complexes from Small Angle Neutron Scattering

We use Small Angle Neutron Scattering (SANS), with an original analysis method, to obtain both the characteristic sizes and the inner composition of lysozyme-pectin complexes depending on the charge density. Lysozyme is a globular protein and pectin a natural anionic semiflexible polysaccharide with a degree of methylation (DM) 0, 43 and 74. For our experimental conditions (buffer ionic strength I = 2.5 10-2 mol/L and pH between 3 and 7), the electrostatic charge of lysozyme is always positive (from 8 to 17 depending on pH). The pectin charge per elementary chain segment is negative and can be varied from almost zero to one through the change of DM and pH. The weight molar ratio of lysozyme on pectin monomers is kept constant. The ratio of negative charge content per volume to positive charge content per volume, -/+, is varied between 10 and 0.007. On a local scale, for all charged pectins, a correlation peak appears at 0.2 {\AA}-1 due to proteins clustering inside the complexes. On a large scale, the complexes appear as formed of spherical globules with a well defined radius of 10 to 50 nm, containing a few thousands proteins. The volume fraction Phi of organic matter within the globules derived from SANS absolute cross-sections is around 0.1. The protein stacking, which occurs inside the globules, is enhanced when pectin is more charged, due to pH or DM. The linear charge density of the pectin determines the size of the globules for pectin chains of comparable molecular weights whether it is controlled by the pH or the DM. The radius of the globules varies between 10 nm and 50 nm. In conclusion the structure is driven by electrostatic interactions and not by hydrophobic interactions. The molecular weight also has a large influence on the structure of the complexes since long chains tend to form larger globules. This maybe one reason why DM and pH are not completely equivalent in our system since DM 0 has a short mass, but this may not be the only one. For very low pectin charge (-/+ = 0.07), globules do not appear and the scattering signals a gel-like structure. We did not observe any beads-on-a-string structure

Segmentation and along-strike asymmetry of the passive margin in Socotra, eastern Gulf of Aden: Are they controlled by detachment faults?

International audienceOn the island of Socotra, the southern passive margin of the Gulf of Aden displays along its strike two different types of asymmetric structures. Western Socotra is made up of a series of southward tilted blocks bounded by consistently northward dipping normal faults. Eastern Socotra consists of a broad asymmetric anticline with a steep northern limb and a gently dipping southern limb. A zone of NE-SW striking strike- slip and normal faults separates the two areas. The overall structure is interpreted as representing two rift segments separated by a transfer zone. The along-strike juxtaposition of crustal-scale asymmetric structures on the southern margin of the Gulf of Aden is complemented by the asymmetry of the conjugate margins on either side of the gulf. Whereas the western Socotra margin is narrow and characterized by oceanward dipping normal faults, the conjugate Oman margin is broader and dominated by horsts and graben. Considering that asymmetric structures in the upper crust are often associated with synthetic shear zones at deeper ductile levels, we propose that the western and eastern Socotra margin segments were controlled at depth by two detachment faults with opposite dips and senses of shear. The normal faults of western Socotra would sole out into a top-to-the-north ductile shear zone, whereas the asymmetric anticline of eastern Socotra would be associated with a top-to-the-south detachment fault

Putative cross-kingdom horizontal gene transfer in sponge (Porifera) mitochondria

BACKGROUND: The mitochondrial genome of Metazoa is usually a compact molecule without introns. Exceptions to this rule have been reported only in corals and sea anemones (Cnidaria), in which group I introns have been discovered in the cox1 and nad5 genes. Here we show several lines of evidence demonstrating that introns can also be found in the mitochondria of sponges (Porifera). RESULTS: A 2,349 bp fragment of the mitochondrial cox1 gene was sequenced from the sponge Tetilla sp. (Spirophorida). This fragment suggests the presence of a 1143 bp intron. Similar to all the cnidarian mitochondrial introns, the putative intron has group I intron characteristics. The intron is present in the cox1 gene and encodes a putative homing endonuclease. In order to establish the distribution of this intron in sponges, the cox1 gene was sequenced from several representatives of the demosponge diversity. The intron was found only in the sponge order Spirophorida. A phylogenetic analysis of the COI protein sequence and of the intron open reading frame suggests that the intron may have been transmitted horizontally from a fungus donor. CONCLUSION: Little is known about sponge-associated fungi, although in the last few years the latter have been frequently isolated from sponges. We suggest that the horizontal gene transfer of a mitochondrial intron was facilitated by a symbiotic relationship between fungus and sponge. Ecological relationships are known to have implications at the genomic level. Here, an ecological relationship between sponge and fungus is suggested based on the genomic analysis

INTEGRATION ET CONFLITS D'ESPACESLes dynamiques territoriales des Pokot(Nord-ouest du Kenya)

Based on an analysis of the Pokot situation, this study aims to define the models used to integrate the populations in the North-West of Kenya in the nation state and examine how these models are appropriated by the local society. Designed as a buffer zone between the semi-arid no mans's land in the North and the high, fertile plateau in the South, the West Pokot District is today an Incontestable territorial referent that is the object of political claims and the border conflicts. Yet, the organisation of the cattle and grain commodity chains generates differentiated evolution processes in the plains and mountain areas. Farmers elaborate territorial re-composition and strengthening strategies, with no consideration of complementarity exchanges and relations of proximity between the high and low areas of the Rift. Thus, a vision of two distinct production territories between which new conflicts emerge is therefore imposing itself over the vision of a asingle homogenous ethic territoryS'appuyant sur une analyse de ls situation des Pokot, cette etude vise a definir les modeles employes pour integrer les populations du nord-ouest kenyan a l'Etate-nation et a examiner sous quelle forme ces modeles sont appropries par la societe locale. Concu comme une zone tampon entre les no man's land semi-arides du nord et les hauts plateaux fertiles du sud, le district de West-Pokot est aujourd'hui un referent teritorial indiscutable, objet de revendications politiques et de conflicts sur ses bordures. Poutant, l;organisation des filieres betail et cereales genere unprocessus d'evolution differenciee entre les espaces de la plaine et de la montagne. Les producteurs elaborent des strategies de recomposition et de reforcement teritorial, en dehors de toutes considerations des echanges de complemtarite et des relations de proximite entre l haut et le bas de l'escarpement du Rift. A la vision d'un seul territoire ethnique homogen s'impos donc plutot celle de deux territoires de productions distinct entre lesqueles naissent de nouveax conflicts

Diversity of sponge mitochondrial introns revealed by cox 1 sequences of Tetillidae

<p>Abstract</p> <p>Background</p> <p>Animal mitochondrial introns are rare. In sponges and cnidarians they have been found in the <it>cox 1 </it>gene of some spirophorid and homosclerophorid sponges, as well as in the <it>cox 1 </it>and <it>nad 5 </it>genes of some Hexacorallia. Their sporadic distribution has raised a debate as to whether these mobile elements have been vertically or horizontally transmitted among their hosts. The first sponge found to possess a mitochondrial intron was a spirophorid sponge from the Tetillidae family. To better understand the mode of transmission of mitochondrial introns in sponges, we studied <it>cox 1 </it>intron distribution among representatives of this family.</p> <p>Results</p> <p>Seventeen tetillid <it>cox 1 </it>sequences were examined. Among these sequences only six were found to possess group I introns. Remarkably, three different forms of introns were found, named introns 714, 723 and 870 based on their different positions in the <it>cox 1 </it>alignment. These introns had distinct secondary structures and encoded LAGLIDADG ORFs belonging to three different lineages. Interestingly, sponges harboring the same intron form did not always form monophyletic groups, suggesting that their introns might have been transferred horizontally. To evaluate whether the introns were vertically or horizontally transmitted in sponges and cnidarians we used a host parasite approach. We tested for co-speciation between introns 723 (the introns with the highest number of sponge representatives) and their nesting <it>cox 1 </it>sequences. Reciprocal AU tests indicated that the intron and <it>cox 1 </it>tree are significantly different, while a likelihood ratio test was not significant. A global test of co-phylogeny had significant results; however, when cnidarian sequences were analyzed separately the results were not significant.</p> <p>Conclusions</p> <p>The co-speciation analyses thus suggest that a vertical transmission of introns in the ancestor of sponges and cnidarians, followed by numerous independent losses, cannot solely explain the current distribution of metazoan group I introns. An alternative scenario that includes horizontal gene transfer events appears to be more suitable to explain the incongruence between the intron 723 and the <it>cox 1 </it>topologies. In addition, our results suggest that three different intron forms independently colonized the <it>cox 1 </it>gene of tetillids. Among sponges, the Tetillidae family seems to be experiencing an unusual number of intron insertions.</p

Dans le nord-ouest du Kenya, des lieux qui disparaissent et qui émergent au gré des politiques d’intégration

La carte du nord-ouest du Kenya donne une image trompeuse de cette périphérie, faisant état d’une plaine vide de points de fixation et d’autres bourgs ruraux, à l’exception de centres de contrôle établis durant la conquête coloniale et qui ont aujourd’hui disparus sous la végétation ou dont la fonction reste encore strictement militaire. Pourtant, cette vaste plaine encadrée par les escarpements du Rift est loin d’être vide de lieux de référence. Cet article propose des pistes pour une nouvelle cartographie des centres du nord-ouest du Kenya. En phase avec l’élargissement de la notion de sécurité (tel que rappelé dans le rapport du PNUD de 1994, qui présente comme interdépendantes les notions de sécurité individuelle, sanitaire, environnementale, économique, alimentaire, politique, culturelle, sociale), il souligne l’importance de l’évolution des concepts du développement et des politiques associées. Il replace ainsi le dynamisme du développement local en milieu pastoral dans une perspective historique, et montre comment un espace de non-lieux peut se densifier sous l’impulsion de nouveaux acteurs.In the North Western Kenya, local development dynamics of the pastoral areas in its historical perspectives and change with the arrival of new local actors. The map of the north western Kenya presents a misleading picture of a large plain without any place or centre, except control and security centres established under the colonization time, which are nowadays shroud under the vegetation or which the function is still strictly military. Yet, this large plain surrounding the rift escarpments is a living environment for a local population with its own reference places. This article sketches out a new mapping of the north western Kenya. Following the enlarged definition of security (including individual, sanitary, economic, environmental, nutritional, political, cultural and social security as interdependent and inseparable), it illustrates the importance of the evolution of development concepts and public policies associated. It replaces the local development dynamics of the pastoral areas in its historical perspectives and shows how a map can change with the arrival of new local actors

The Owen Ridge uplift in the Arabian Sea: Implications for the sedimentary record of Indian monsoon in Late Miocene

International audienceThe pelagic cover of the Owen Ridge in the Arabian Sea recorded the evolution of the Indian monsoon since the Middle Miocene. The uplift of the Owen Ridge resulted from tectonic processes along the previously unidentified Miocene India-Arabia plate boundary. Based on seismic reflection data tied with deep-sea drilling to track the Miocene India-Arabia plate boundary, we propose a new timing for the uplift of the Owen Ridge and highlight its impact on the record of climate changes in pelagic sediments. The new dataset reveals a fracture zone east of the Owen Ridge corresponding to the fossil plate boundary, and documents that the main uplift of the Owen Ridge occurred close to ∼8.5 Ma, and is coeval with a major uplift of the east Oman margin. Late Miocene deformation at the India-Arabia plate boundary is also coeval with the onset of intra-plate deformation in the Central Indian Ocean, suggesting a kinematic change of India and surrounding plates in the Late Miocene. The uplift of the Owen Ridge above the lysocline at ∼8.5 Ma accounts for a better preservation of Globigerina bulloides in the pelagic cover, previously misinterpreted as the result of a monsoon intensification event

Owen Ridge deep-water submarine landslides: implications for tsunami hazard along the Oman coast

International audienceThe recent discovery of voluminous submarine landslides along the Owen Ridge may represent a source of tsunami hazard for the nearby Oman coast. We as- sess the severity of this potential hazard by performing numerical simulations of tsunami generation and propaga- tion from the biggest landslide (40km3 in volume) ob- served along the Owen Ridge. A finite-difference model, assimilating the landslide to a visco-plastic flow, simulates tsunami generation. Computation results show that Salalah city(190000inhabitants)isimpactedby2.5m-hightsunami waves one hour after sediment failure. Higher wave eleva- tion values (4 m) are reached in the low populated Sawqara Bay over 80 min after slide initiation. Although large subma- rine failures along remote oceanic ridges are infrequent, this study reveals an underestimated source of tsunami hazard in theArabianSea

Diversity and evolution of myxozoan minicollagens and nematogalectins

Background: Myxozoa are a diverse group of metazoan parasites with a very simple organization, which has for decades eluded their evolutionary origin. Their most prominent and characteristic feature is the polar capsule: a complex intracellular structure of the myxozoan spore, which plays a role in host infection. Striking morphological similarities have been found between myxozoan polar capsules and nematocysts, the stinging structures of cnidarians (corals, sea anemones and jellyfish) leading to the suggestion that Myxozoa and Cnidaria share a more recent common ancestry. This hypothesis has recently been supported by phylogenomic evidence and by the identification of a nematocyst specific minicollagen gene in the myxozoan Tetracapsuloides bryosalmonae. Here we searched genomes and transcriptomes of several myxozoan taxa for the presence of additional cnidarian specific genes and characterized these genes within a phylogenetic context. Results: Illumina assemblies of transcriptome or genome data of three myxozoan species (Enteromyxum leei, Kudoa iwatai, and Sphaeromyxa zaharoni) and of the enigmatic cnidarian parasite Polypodium hydriforme (Polypodiozoa) were mined using tBlastn searches with nematocyst-specific proteins as queries. Several orthologs of nematogalectins and minicollagens were identified. Our phylogenetic analyses indicate that myxozoans possess three distinct minicollagens. We found that the cnidarian repertoire of nematogalectins is more complex than previously thought and we identified additional members of the nematogalectin family. Cnidarians were found to possess four nematogalectin/ nematogalectin-related genes, while in myxozoans only three genes could be identified. Conclusions: Our results demonstrate that myxozoans possess a diverse array of genes that are taxonomically restricted to Cnidaria. Characterization of these genes provide compelling evidence that polar capsules and nematocysts are homologous structures and that myxozoans are highly degenerate cnidarians. The diversity of minicollagens was higher than previously thought, with the presence of three minicollagen genes in myxozoans. Our phylogenetic results suggest that the different myxozoan sequences are the results of ancient divergences within Cnidaria and not of recent specializations of the polar capsule. For both minicollagen and nematogalectin, our results show that myxozoans possess less gene copies than their cnidarian counter parts, suggesting that the polar capsule gene repertoire was simplified with their reduced body plan. Electronic supplementary material The online version of this article (doi:10.1186/s12862-014-0205-0) contains supplementary material, which is available to authorized users