Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Large organic falls to the benthic environment, such as dead wood or whale bones, harbour organisms relying on sulfide-oxidizing symbionts. Nothing is known however, concerning sulfide enrichment at the wood surface and its relation to wood colonization by sulfide-oxidizing symbiotic organisms. In this study we combined in situ hydrogen sulfide and pH measurements on sunken wood, with associated fauna microscopy analyses in a tropical mangrove swamp. This shallow environment is known to harbour thiotrophic symbioses and is also abundantly supplied with sunken wood. A significant sulfide enrichment at the wood surface was revealed. A 72 h sequence of measurements emphasized the wide fluctuation of sulfide levels (0.1->100 lM) over time with both a tidal influence and rapid fluctuations. Protozoans observed on the wood surface were similar to Zoothamnium niveum and to vorticellids. Our SEM observations revealed their association with ectosymbiotic bacteria, which are likely to be sulfide- oxidizers. These results support the idea that sunken wood surfaces constitute an environment suitable for sulfide-oxidizing symbioses.
ISSN: 0141-1136

hal-00751649
https://hal.univ-antilles.fr/hal-00751649

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
The Caribbean bivalves Codakia orbicularis (Linnée, 1758) and C. orbiculata (Montagu, 1808) live in seagrass beds of Thalassia testudinum and harbor intracellular sulfuroxidizing gamma-proteobacteria. These bacterial symbionts fix CO2 via the Calvin Benson cycle and provide organic compounds to the bivalve. During experimentally induced starvation, no reduced sulfur compounds and no organic particle food are available; the symbionts could be considered as the sole nutrient source of the host bivalve. A previous study has shown that the intracellular bacterial population decreased considerably during starvation and that bacterial endosymbionts were not released by the bivalves. In this study, the activity of two lysosomal marker enzymes (acid phosphatase and arylsulfatase) was detected using cytochemical experiments coupled with energy-dispersive X-ray transmission electron microscopy during sulfide and organic particle starvation. The degradation of bacterial endosymbionts began after 2 weeks of starvation in C. orbiculata and after 3 weeks in C. orbicularis. Degradation processes seem to be continuous over several months and could be responsible for the disappearance of the bacterial endosymbionts within the gills during starvation. These data suggest that the host use symbionts as a nutrient source to survive a hunger crisis. The carbon transfer from the symbionts to the host could be flexible and could consist in transfer of organic matter, “milking,” under normal feeding conditions and digestion of the symbionts under starved conditions.
ISSN: 1059-910X

Droits : info:eu-repo/semantics/OpenAccess
hal-01206367
https://hal.univ-antilles.fr/hal-01206367
https://hal.univ-antilles.fr/hal-01206367/document
https://hal.univ-antilles.fr/hal-01206367/file/revised%20version%20to%20be%20submitted%20to%20the%20editor3oct.pdf
DOI : 10.1002/jemt.22458

Éditeur(s) : HAL CCSD Wiley-Blackwell
Résumé : International audience
Six morphotypes of small mussels (Bivalvia: Mytilidae) were found attached to naturally sunken wood collected in the Bohol Sea (Philippines). These specimens are related to the large Bathymodiolus mussels that are found worldwide at cold seeps and hydrothermal vents. In these habitats, the mytilids harbour sulphur- and methane-oxidizing endosymbionts in their gills and depend on the energy and carbon provided by the symbionts. In this study, bacteria associated with the gills of wood-associated mussels are characterized using molecular and microscopic techniques. The existence of bacteria in the lateral zone of gill filaments in all specimens is demonstrated. Comparative analyses of 16S rRNA gene and adenosine 5′-phosphosulphate (APS) reductase gene sequences indicate that the bacteria are closely related to sulphur-oxidizing endosymbionts of Bathymodiolus. FISHs using specific probes confirm that sulphur oxidizers are by far the most abundant, if not the only bacteria present. Electron micrographs displayed mostly extracellular bacteria located between microvilli at the apical surface of host gill epithelial cells all along the lateral zone of each gill filament. In some specimens, occasional occurrence of intracellular bacteria with similar morphology was noted. This study provides the first molecular evidence for the presence of possible thiotrophic symbiosis in sunken wood ecosystems. With their epibiotic bacteria, wood-associated mussels display a less integrated type of interaction than described in their seep, vent and whale fall relatives.
ISSN: 0168-6496

hal-00715244
https://hal.univ-antilles.fr/hal-00715244
DOI : 10.1111/j.1574-6941.2008.00438.x

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
The embryonic development in Chione cancellata, from fertilization to straighthinge D-stage veliger larva, occurs in 24 h at 251C. Transmission (TEM) and scanning (SEM) electron microscopy show that morphogenetic processes result in a gastrula with two depressions, 4 h after fertilization (T014 h). Two hours later, one depression, located at the animal pole, develops into an open cave, the floor of which becomes the shell field, characterized by scarce microvilli, located below the lower face of the prototrochal pad. The invagination located at the vegetal pole is characterized by regular microvilli and constitutes the digestive tract. At T018 h, the late gastrula differentiates into a typical motile trochophore, possessing a well-developed prototroch delimiting anterior and posterior embryonic regions. At T019h, the shell field, located between the prototroch and the telotroch, appears as a saddle-shaped region with a wrinkled surface extending on both sides of the embryo, establishing bilateral symmetry. From TEM observations, the apical surface of the underlying cells possesses a modified glycocalyx featuring a dense pellicle overlapping the cells of the shell field. At T0112 h, the prototroch is displaced toward the anterior region by outgrowth of the shell material. TEM views show that the wrinkled surface observed with SEM corresponds to the periostracum, attached dorsally to the hinge and ventrally to the cells of the future mantle edge. At T0115 h, an alveolar matrix of proteinaceous material, which could contain calcite crystals, appears between the periostracum and the mantle. At T0124 h, prodissoconch I formation is completed and the D-stage larvae possess a calcified shell. At this stage of development, only one mantle fold is present, representing the outer fold. The periostracumsecreting cells are in contact with the marginal cells of the velum. This functional velum is composed of four bands of cilia. Our TEMobservations confirm previous descriptions of the velum ciliary bands obtained only from SEM analyses, such as described in other bivalves. The apical sense organ and the digestive tract are poorly developed. From observations at the ultrastructural level of shell differentiation in C. cancellata, we propose a new interpretation of shell differentiation, including hinge and ligament for bivalves as opposed to that described for gastropods.
ISSN: 1077-8306

hal-00755283
https://hal.univ-antilles.fr/hal-00755283
DOI : 10.1111/j.1744-7410.2006.00036.x

Éditeur(s) : HAL CCSD Public Library of Science
Résumé : International audience
BACKGROUND: Dengue and malaria are two major public health concerns in tropical settings. Although the pathogeneses of these two arthropod-borne diseases differ, their clinical and biological presentations are unspecific. During dengue epidemics, several hundred patients with fever and diffuse pain are weekly admitted at the emergency room. It is difficult to discriminate them from patients presenting malaria attacks. Furthermore, it may be impossible to provide a parasitological microscopic examination for all patients. This study aimed to establish a diagnostic algorithm for communities where dengue fever and malaria occur at some frequency in adults. METHODOLOGY/PRINCIPAL FINDINGS: A sub-study using the control groups of a case-control study in French Guiana - originally designed to compare dengue and malaria co-infected cases to single infected cases - was performed between 2004 and 2010. In brief, 208 patients with malaria matched to 208 patients with dengue fever were compared in the present study. A predictive score of malaria versus dengue was established using .632 bootstrap procedures. Multivariate analysis showed that male gender, age, tachycardia, anemia, thrombocytopenia, and CRP>5 mg/l were independently associated with malaria. The predictive score using those variables had an AUC of 0.86 (95%CI: 0.82-0.89), and the CRP was the preponderant predictive factor. The sensitivity and specificity of CRP>5 mg/L to discriminate malaria from dengue were of 0.995 (95%CI: 0.991-1) and 0.35 (95%CI 0.32-0.39), respectively. CONCLUSIONS/SIGNIFICANCE: The clinical and biological score performed relatively well for discriminating cases of dengue versus malaria. Moreover, using only the CRP level turned to be a useful biomarker to discriminate feverish patients at low risk of malaria in an area where both infections exist. It would avoid more than 33% of unnecessary parasitological examinations with a very low risk of missing a malaria attack.
ISSN: 1935-2727

inserm-00872353
http://www.hal.inserm.fr/inserm-00872353
http://www.hal.inserm.fr/inserm-00872353/document
http://www.hal.inserm.fr/inserm-00872353/file/journal.pntd.0002420.pdf
DOI : 10.1371/journal.pntd.0002420

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
In order to estimate the seismic anisotropy of subducted crust, polycrystalline samples of KA1Si(3)O(8) K-lingunite (25% of the total subducted transformed sediments), have been synthesized and deformed under the temperature and pressure conditions of the subducted slabs. Transmission electron microscopy (TEM) characterizations of the recovered samples reveal that the microstructures are clearly dominated by [001] glide involving screw dislocations. For this reason, only {100} could be identified as glide planes, the question of [001] slip on {110} remains open. Few 1/2 < 111 > dislocations were observed gliding on {110} planes, which implies that 1/2 < 111 > {110} is a harder slip system than those involving [001] slip. The occurrence of sub-grain boundaries suggests that diffusion and climb might be active under these conditions.;To assess the texture of polycrystalline K-lingunite, the crystal preferred orientations (CP05) were calculated using visco-plastic self-consistent (VPSC) polycrystalline plasticity model in simple shear using the slip systems identified by TEM. Finally, the seismic properties of K-lingunite aggregates were calculated from the CPO and single crystal elasticity tensor. K-lingunite is predicted to have a high seismic anisotropy, which could combine constructively with one of the stishovite (same proportion as K-lingunite at the transition zone depth ranges).
ISSN: 0031-9201

hal-00534050
https://hal.archives-ouvertes.fr/hal-00534050
DOI : 10.1016/j.pepi.2010.06.013