Éditeur(s) : HAL CCSD Oldendorf/Luhe
Résumé : International audience
Large filamentous sulfur-oxidizing bacteria belonging to the Beggiatoacae family can cover large portions of shallow marine sediments surrounding mangroves in Guadeloupe (French West Indies). In order to assess the importance of Beggiatoa mats as an infaunal food source, observations were conducted of the area within mats and at increasing distances from mats. We used natural isotopic compositions and a C-13 enrichment study. Both revealed an ingestion of bacterial mats by associated meiofauna, dominated by rotifers and to a smaller extent by small polychaetes and nematodes. Compared to adjacent sites, sediment covered by bacterial mats presented a higher abundance of diatoms, whereas the total biomass of bacteria did not vary. This constant bacterial abundance suggests that the proportion of organic matter represented by sulfur bacteria is limited compared to the fraction of total bacteria. There was no significant difference in infaunal abundance in mats, suggesting that the availability of this chemosynthetic food resource had a limited local effect. Grazers presented a delta C-13 value increasing with distance from the mat. However, isotopic composition of phospholipid-derived fatty acids specific for diatoms and bacteria revealed that this change is related to modifications of delta C-13 dietary components rather than to changes in diet composition. These complementary methods revealed that the occurrence of sulfur-oxidizing bacterial mats does not necessarily affect grazer abundance and importance of bacteria in their diet. Despite its wide occurrence, Beggiatoa mats would consequently have a minor influence on the structure of the mangrove food web.
ISSN: 0171-8630

hal-01545912
https://hal.archives-ouvertes.fr/hal-01545912
DOI : 10.3354/meps11035

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
Haplognathia ruberrima is a cosmopolitan gnathostomulid species found in sulfur bacterial mats in mangroves in Guadeloupe (French West Indies). Haplognathia ruberrima presents a d13C value lower than all measured meiofaunal grazers and lower than the available measured food sources of this environment. This low d13C value can not be due to specific ingestion of 13C-depleted methanogenic bacteria because abundances of those bacteria are reduced in surficial and deep sediments as revealed by d13C of bacterial fatty acid. According to scanning electron microscope observations, no bacterial ectosymbionts were observed at the surface of the gnathostomulids, and transmission electronmicroscope views revealed the absence of bacterial endosymbionts. Energy-dispersive X-ray spectroscopy analysis detected low levels of sulfur (0.32%+-0.8) in biological tissues of H. ruberrima, confirming the absence of thioautotrophic bacterial symbionts in these animals. Consequently, the low d13C value of H. ruberrima can not be due to the presence of sulfur-oxidizing symbionts but more probably to the selective and exclusive consumption of free-living, sulfuroxidizing bacteria
ISSN: 0173-9565

hal-01253239
https://hal.archives-ouvertes.fr/hal-01253239
DOI : 10.1111/maec.12296

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
Background information. Marine nematodes belonging to the Stilbonematidae (Desmodoridae) family are described as living in obligatory association with sulfur-oxidizing chemoautotrophic ectosymbionts. The symbiotic bacteria carrying out this chemosynthesis should contain elemental sulfur in periplasmic granules as sulfur granules of chemoautotrophic endosymbionts described in various marine invertebrates. Results. Based on TEM analyses, extracellular bacteria surrounding Eubostrichus dianae possess these spherical periplasmic granules. Few investigative techniques can be used to identify elemental sulfur S8 such as EDXS (energy dispersive X-ray spectroscopy) and EELS (electron energy loss spectroscopy) associated with cryo-fixation of the sample to avoid sulfur loss. These techniques are time consuming, expensive and require technical skills. Raman microspectrometry applied to the analysis of E. dianae allowed us to detect elemental sulfur S8 and confirmed the location of these sulfur clusters in the bacterial coat. In the same way, Raman spectrometry was positively applied to the endosymbiotic bivalve Codakia orbicularis, suggesting that this technique can be used to characterize sulfur in ecto- as well as in endo-symbiotic sulfur-oxidizing bacteria. Conclusions. As Raman spectrometry can be used on living organisms (without preliminary fixation) without sample damage and preserving the molecular structure of the sulfur (denatured during chemical fixation) it represents a very well-adapted investigative tool for biologists. This technique therefore permits us to detect quickly and easily (in a few seconds and on entire living animals) the presence of sulfur compounds in the symbiotic nematode.
ISSN: 0248-4900

hal-00753017
https://hal.univ-antilles.fr/hal-00753017

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The biogeochemistry of sulfur and carbon during early-diagenetic processes within organic-rich marine mangrove sediments was studied in the “Manche à Eau” lagoon, Guadeloupe, West Indies. These sediments are characterized by a total organic carbon content (TOC) mostly above 11 wt%, δ13CTOC below − 25‰ VPDB and C/Nmolar ratios exceeding 15. Rates of mangrove-derived organic carbon accumulation vary between ~ 200 and 400 gOC·m− 2·yr− 1, with highest rates at the shore of the lagoon. On the lagoon border, where colorless filamentous sulfur-oxidizing bacteria colonize the sediments, active sulfate reduction within the upper 20 cm, with a net removal rate of ~ 0.5 μmol·cm− 3·d− 1, is assumed to be essentially driven by organic carbon oxidation. This is expressed by relatively low apparent sulfur isotope fractionation (34εnet = − 33‰) and a gentle δ18O/δ34Ssulfate apparent slope of 0.36 ± 0.03 (2s). Further inside the lagoon, in the absence of sulfur-oxidizing bacteria, higher apparent sulfur isotope fractionation and a steeper δ18O/δ34Ssulfate slope (0.67 ± 0.20) suggest an overall lower sulfate removal rate that may be coupled to minor sulfur disproportionation. Spatial and vertical variation in sulfur cycling, reflected by oxygen and sulfur isotopic characteristics, seem to be mainly controlled by unsteady to relatively steady organic matter deposition and its reactivity. In all sediments, δ34S values of pyrite are positively correlated with the TOC/TS ratio and negatively correlated with δ13CTOC; suggesting a primary control of the quantity and quality of organic matter on the pyrite isotope records, despite potential iron-limiting conditions for the most active sites. Our results provide insights into the role of organic carbon input on sulfur cycling; stimulating sulfate reduction and in turn the presence of sulfur-oxidizing microbial mats, resulting in an intense cycling of both carbon and sulfur in these marine mangrove sediments.
ISSN: 0009-2541

hal-01507696
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01507696
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01507696/document
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01507696/file/Cr%C3%A9mi%C3%A8re%20et%20al.%20-%20Sulfur%20diagenesis%20under%20rapid%20accumulation%20of%20orga.pdf
DOI : 10.1016/j.chemgeo.2017.02.017

Éditeur(s) : HAL CCSD Wiley-Blackwell
Résumé : International audience
Here, the first description of an epsilon sulfur-oxidizing bacterium from sulfide-rich sediments of marine mangrove in Caribbean is reported. According to TEM, this new strain contains intracytoplasmic large internal sulfur granules as confirmed by EDXS analyses performed using ESEM. The sulfur distribution obtained for this sulfur-oxidizing bacterial strain allows to conclude that elemental sulfur is formed as an intermediate oxidation product and stored intracellularly. According to conventional SEM observations, bacterial cells are ovoid, extremely motile by lophotrichous flagella. Phylogenetic analyses based on the analysis of partial sequence of 16S rDNA confirm that such bacterial strain belongs to the Thiovulum cluster and could be a representative of a new species in this poorly studied genus of sulfur-oxidizing free-living bacteria. Thus, reduced sediment of marine mangrove represents sulfide-rich environment sustaining development of both gamma and epsilon sulfur-oxidizing Proteobacteria
ISSN: 0378-1097

hal-01682113
https://hal.univ-antilles.fr/hal-01682113
DOI : 10.1093/femsle/fnx172

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
In this study, the cellular organization of the gill that harbors symbiotic bacteria is described in the thyasirid Thyasira falklandica collected from South Shetlands in Antarctic. Sections of the gills revealed that T. falklandica belongs to the gill type 3, as described by Dufour (Biol Bull, 208:200-212, 2005), with an elongated lateral zone along the frontal-abfrontal axis of the gill Wlaments. The ciliated and intermediary zones looked similar to those described in symbionts-bearing bivalves. The lateral zone is more complex in T. falklandica than in other Thyasiridae already described. Such a zone is composed of four different cell types. Bacteriocytes are abundant in the frontal and abfrontal positions, while the middle part of the lateral zone is occupied mostly by numerous granule cells devoid of bacteria. All along the lateral zone, TEM and SEM observations show some ciliated cells, which are regularly interspersed between bacteriocytes and/or granule cells. Such cells, according to the long double ciliary roots of their cilia, should have a sensory function. Intercalary cells, which have never been observed between bacteriocytes, are restricted to the middle part of the lateral zone where their expansions overlap the adjacent granule cells. Bacterial symbionts occur only extracellularly among long microvilli diVerentiated by the bacteriocytes. They are abundant, usually spherical in shape (around 0.7 m length), and covered by the glycocalix from bacteriocyte microvilli. According to TEM views, the empty vesicles located in the periplasmic space should be sulfur storage, as known for other sulfur-oxidizing symbionts.
ISSN: 0720-213X

hal-00755289
https://hal.univ-antilles.fr/hal-00755289
DOI : 10.1007/s00435-007-0034-4

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Ciliates represent a diversified group of protists known to establish symbioses with prokaryotic microorganisms. They are mainly phagotrophs and symbiotic relationships with bacteria can give them an important advantage in chemosynthetic environments. The aim of this study is to describe the thiotrophic association that occurs between the peritrich ciliate Pseudovorticella sp. and potential sulfur-oxidizing bacteria. Investigations at microscopic scale (LM, SEM, TEM) showed ectosymbiotic bacteria covering the surface of the body of Pseudovorticella sp. According to 16S rDNA phylogenetic analysis, these ectosymbiotic bacteria belong to-proteobacteria and are phylogenetically close to the symbiont of the recently described Zoothamnium ignavum, which inhabits shallow-water wood falls. FISH experiments, using symbiont specific probes, clearly indicate that these ectosymbiotic bacteria are also ingested into food vacuoles. Electron lucent granules observed in TEM in the cytoplasm of the ectosymbiotic bacteria have been identified as sulfur granules by Raman microspectrometry analyses. Raman microspec-trometry analyses confirmed the thiotrophic nature of this relationship already suggested by the results obtained by TEM and phylogeny. A complete sulfur map was then performed to investigate the sulfur distribution in the zooid. Results show that the relationship between this protist and its bacterial partner is a thiotrophic ectosymbiosis.
ISSN: 0932-4739

hal-01655933
http://hal.upmc.fr/hal-01655933
http://hal.upmc.fr/hal-01655933/document
http://hal.upmc.fr/hal-01655933/file/GRIMONPREZ_Adrien_sans%20marque.pdf
DOI : 10.1016/j.ejop.2017.11.002

Résumé : Les mattes de procaryotes constituent une niche écologique diversifiée. peu étudié!<..en mangrove et jamais décrjte dans les Antilles. L'objectif de cette thèse est de décrire les procaryotes filamenteux reposant sur le sédiment marin et de caractériser les interactions entre la matte, milieu et entre les différents micro-organismes. Nous avons d'abord caractérisé les micro-organismes majoritaires de la matte par le séquençage de l'ADNr 16S et des hybridations moléculaires (FISH). Il a ainsi été possible de décrire deux nouvelles espèces de Beggiatoaceae dont la structure a été étudiée par microscopie électronique. De plus, afin de caractériser l'environnement chimique de ces bactéries, des capteurs potentiométriques ont été utilisés. Ils ont permis de démontrer que les Beggiaotaceae oxydaient les sulfures en prélevant l'oxygène du milieu, tandis que des analyses de microscopie couplées à de l'EDX ont mis en évidence des réserves de soufre intracellulaires dans ces bactéries. Le séquençage de l'ADNr 16S des cyanobactéries filamenteuses a mis en évidence quatre nouvelles espèces de l'ord~e des Oscillatoriales. Deux d'entre elles, du genre Planktothricoides ont révélé une toxicité positive sur les Artemia sp:, les deux autres ont été identifiées comme proches d'Oscillatoria spongeliae, une espèce symbiotique d'éponge, bien que les coupes uItrafines d'une de ces souches aient montré une morphologie interne proche des Tychonema. L'analyse des données a permis d'étoffer les connaissances sur les communautés microbiennes de mangrove et constitue une base intéressante de travail sur la contribution des micro-organismes au fonctionnement de l'écosystème mangrove dans son ensemble
Procaryotic mats are ecological niches, occuring in many ecosystems. Those structures are little studied in marine mangrove sediment and have never been described in West Indies. The purpose ofthis thesis is to characterize the interactions between the mat and the environment, and between the different filamentous micro-organisms living into the mat. In a first place, we characterized the mainly micro-organisrns of the mat by sequencing 16S rDNA. We confirmed these sequences by molecular hybridization (FISH) with specific probes designed from sequences obtained. Thus, it was possible to describe two new Beggiatoaceae strains, whose structure has been studied by electronic microscopy. Furthemore, we used potentiometric captors in situ and in laboratory, by creating a mesocosm, in order to define the chemical environment where involved these bacteria. These experiences proved that the Beggiatoaceae of the mat oxidized the sulfur taking the oxygen from the medium, while the microscopic analysis coupled with EDX showed intracellular sulfur granules into the bacteria. The study of the filamentous cyanobacteria of the mat highlighted four new cyanobacteria strains, all studied by electronic rmcroscopy. Two of them belongs to Planktothrlcoides genus and showed positive toxicity on Artemia salina. The others species are close to Oscillatorla spongeliae, a sponge symbiont, nevertheless, one ofthem showed an intemal morphology close to Tychonema. The analysis of the different results adduces sorne knowledge about mangrove microbial communities. Furthermore, this study can be used as an interesting base to study the micro-organisms contribution in functioning mangrove ecosystem

http://www.theses.fr/2013AGUY0614/document

Éditeur(s) : HAL CCSD Wiley-Blackwell
Résumé : International audience
Archaea may be involved in global energy cycles, and are known for their ability to interact with eukaryotic species (sponges, corals and ascidians) or as archaeal-bacterial consortia. The recently proposed phylum Thaumarchaeota may represent the deepest branching lineage in the archaeal phylogeny emerging before the divergence between Euryarchaeota and Crenarchaeota. Here we report the first characterization of two marine thaumarchaeal species from shallow waters that consist of multiple giant cells. One species is coated with sulfur-oxidizing g-Proteobacteria. These new uncultured thaumarchaeal species are able to live in the sulfide-rich environments of a tropical mangrove swamp, either on living tissues such as roots or on various kinds of materials such as stones, sunken woods, etc. These archaea and archaea/bacteria associations have been studied using light microscopy, transmission electron microscopy and scanning electron microscopy. Species identification of archaeons and the putative bacterial symbiont have been assessed by 16S small subunit ribosomal RNA analysis. The sulfur-oxidizing ability of the bacteria has been assessed by genetic investigation on alpha-subunit of the adenosine-5_- phosphosulfate reductase/oxidase's (AprA). Species identifications have been confirmed by fluorescence in situ hybridization using specific probes designed in this study. In this article, we describe two new giant archaeal species that form the biggest archaeal filaments ever observed. One of these species is covered by a specific biofilm of sulfur-oxidizing g-Proteobacteria. This study highlights an unexpected morphological and genetic diversity of the phylum Thaumarchaeota.
ISSN: 1462-2912

hal-00715219
https://hal.univ-antilles.fr/hal-00715219
DOI : 10.1111/j.1462-2920.2010.02309.x

Éditeur(s) : HAL CCSD Nature Publishing Group
Résumé : International audience
The shallow water bivalve Codakia orbicularis lives in symbiotic association with a sulfur-oxidizing bacterium in its gills. The endosymbiont fixes CO2 and thus generates organic carbon compounds, which support the host's growth. To investigate the uncultured symbiont's metabolism and symbiont-host interactions in detail we conducted a proteogenomic analysis of purified bacteria. Unexpectedly, our results reveal a hitherto completely unrecognized feature of the C. orbicularis symbiont's physiology: the symbiont's genome encodes all proteins necessary for biological nitrogen fixation (diazotrophy). Expression of the respective genes under standard ambient conditions was confirmed by proteomics. Nitrogenase activity in the symbiont was also verified by enzyme activity assays. Phylogenetic analysis of the bacterial nitrogenase reductase NifH revealed the symbiont's close relationship to free-living nitrogen-fixing Proteobacteria from the seagrass sediment. The C. orbicularis symbiont, here tentatively named `Candidatus Thiodiazotropha endolucinida', may thus not only sustain the bivalve's carbon demands. C. orbicularis may also benefit from a steady supply of fixed nitrogen from its symbiont-a scenario that is unprecedented in comparable chemoautotrophic symbioses.
ISSN: 2058-5276

hal-01545904
https://hal.archives-ouvertes.fr/hal-01545904
DOI : 10.1038/nmicrobiol.2016.193

Éditeur(s) : HAL CCSD
Résumé : This work focus on the characterization of the source and dynamic of compactional fluids during sedimentary burial, through two complementary examples of late orogenic oil‐field half‐grabens: The exhumed Lodève Permian Basin and a deep buried Jurassic basin in the North Viking Graben (North Sea).Constituting the main part of the thesis, a multi‐disciplinary approach was conducted in the Lodève Basin where Ba‐F‐Cu‐Pb polymetallic mineralized systems are trapped into synrift faults and paleokarsts in the carbonate basement at the hinge point of the rollover. The source, timing and P/T conditions of fluid migration were deduced from the analysis of the microfabric, the fluid inclusions microthermometry, and the isotopic (Sr, S, O, H) and Rare Earth Element (REE) signature. Results are then crossed with a structural and thermal modeling that consolidates the sequence and dynamics of fluid during burial.A similar approach was conducted in the North Viking Graben where fluid markers are restricted to 3D seismic and well core data. Comparable Ba‐Pb‐Zn veins are reported in basin margin, plugging one of the most important siliciclastic hydrocarbon reservoir in the substratum. This analysis provides additional constraints on basinal fluid behavior and allows us to propose a global dynamic model for various compositions of fluids and reservoirs.We conclude to a polyphase fluid sequence history including:(a) In the carbonate basement of the Lodève Basin, karstic paleocanyon incisions and associated cavities coupled to synrift fault, act as major drain for fluids. These structures are early affected by hypogen‐sulfuric karstification in response to the interaction between bacterial oxidation of sulfides entrapped within Lower Permian blackshales and the basement oxidizing aquifer.(b) Disequilibrium compaction initiates overpressure‐driven basinal fluid migration towards basin margins, characterized by temperatures around 150‐180°C and salinities between 9 et 18wt%eq.NaCl. Isotopic (Sr, S, O) and REE analyses reveal that Ba‐M+‐rich mineralizing fluids derived mainly from buried blackshales diagenesis. External fluids coming from the lower crust are also identified that play a key role in fluorite precipitation by the leaching of late hercynian granites (mean temperature of 250°C and salinity > 20wt%eq.NaCl).(c) During the synrift period, fluid overpressure is responsible for the periodic reactivation of fault plane according to seismic‐valve process, bedded‐control shearing and hydraulic brecciation at the basement‐seal interface. These mechanisms induce cyclic polymetallic mineralization by the mixing between in‐situ formation water and deep ascending basinal fluids.(d) Thermogenic fluids expulsion starts with last basinal fluids during late burial stage. Hydrocarbons thus migrate along the same regional pathways up to the rollover crest, where they are partly rerouted by the previous mineralized baffle.(e) In the Lodève basin, post‐rift exhumation of the margins led to the remobilization of synrift deposits by subaerial biochemical processes at the sulfate‐methane transition. The latter results from the interaction between the still active hydrocarbon dysmigration with a playa lake sulfate‐rich aquifer. Secondary low‐temperature barite fronts precipitate then within basement meteoric karsts.In addition to the « source to sink » model of basinal fluids, this work provides new insights on the early plugging of hydrocarbon reservoirs and for the metallogenesis of Mississippi Valley‐Type deposits.
Ce travail porte sur la caractérisation de la source et de la dynamique des fluides de bassin au cours de leur chargement à travers deux exemples complémentaires de demi‐grabens tardi‐orogéniques pétroliers : Le Bassin Permien de Lodève, aujourd’hui à l’affleurement et un bassin jurassique enfouis dans le North Viking Graben (Mer du Nord).Le coeur de la thèse concerne le Bassin de Lodève où, à partir d’une approche pluridisciplinaire intégrée, nous avons caractérisé l’architecture des minéralisations (Ba, F, Cu, Pb) piégées dans un réseau paléokarstique alimenté par les failles syn‐rift, dans le substratum carbonaté à l’apex du roll‐over. La source, le calendrier et les conditions de migration des fluides ont été approchés à partir de l’analyse de la micro‐fabrique, la microthermométrie sur inclusions fluides, les analyses isotopiques (Sr, S, O, H) et de Terres Rares. Les résultats analytiques ont été enfin croisés avec un modèle thermique et structural du bassin qui conforte la séquence et la dynamique du système fluide en cours d’enfouissement.Une démarche similaire, mais plus limitée, a été conduite dans le bassin du North Viking Graben où l’accès aux marqueurs fluides est restreint aux données de sismique 3D et de carottes. Comme à Lodève, les minéralisations Ba‐Pb‐Zn colmatent un réservoir dans le substratum à l’apex du roll‐over. Elles se présentent sous forme de ciments dans des grès ou des fractures. Cette analyse apporte des contraintes complémentaires et permet de proposer un modèle dynamique général avec des variantes en fonction de la nature des fluides et des réservoirs.On retiendra donc la séquence fluide suivante :(a) Dans le cas du bassin de Lodève sur substratum carbonaté, les chemins préférentiels de drainage se développent dans des paléocanyons N‐S couplés à un réseau de fractures et d’endokarsts météoriques. Ces derniers sont élargis en début de rifting par la dissolution hypogène sulfurique produite par l’oxydation bactérienne des sulfates et des pyrites des blackshales, au contact de l’aquifère oxydant du Cambrien.(b) Le déséquilibre de compaction initie la migration des fluides interstitiels en surpression vers les marges avec des températures autour de 150‐180°C et des salinités entre 9 et 18wt%eq.NaCl. Les analyses isotopiques (Sr, S, O) révèlent que la majorité des fluides provient de l’altération diagénétique des blackshales riches en métaux. Des interactions sont également mises en évidence avec des fluides profonds (entre 240°C et 260°C ; salinités > à 20wt%eq.NaCl), qui lessivent les granites tardi‐hercyniens.(c) Pendant le syn‐rift, les conditions de surpression de fluide permettent la réactivation cyclique des failles, les décollements stratigraphiques et la formation de brèches hydrauliques, favorisant la mise en connexion avec les réservoirs superficiels à l’apex du rollover. Le modèle de Sibson ajusté aux fluides de bassins est alors le moteur de la migration verticale.(d) Les fluides thermogéniques commencent à être expulsés avec les derniers fluides de compaction au cours d’un stade plus évolué de l’enfouissement en empruntant les mêmes chemins jusqu’à l’apex du roll over. Ils sont alors partiellement freinés et déviés par les colmatages minéralisés antérieurs.(e) A Lodève, la continentalisation des minéralisations antérieures au cours de l’exhumation post‐rift conduit à leur remaniement partiel au niveau de la transition sulfate‐méthane induite par l’interaction entre une playa évaporitique et la dysmigration des hydrocarbures. Des barytines secondaires de basse température, déprimées en Sr sont alors précipitées de manière synsédimentaire dans des karsts météoriques du socle.Outre l’illustration d’un modèle complet (source to sink) de dynamique des fluides dans un bassin, ce travail apporte de nouvelles contraintes dans l’approche du colmatage des réservoirs à hydrocarbures sur les têtes de blocs basculés et sur la genèse des gîtes miniers de type Mississippi Valley‐Type.
https://hal.archives-ouvertes.fr/tel-01457583

tel-01457583
https://hal.archives-ouvertes.fr/tel-01457583
https://hal.archives-ouvertes.fr/tel-01457583/document
https://hal.archives-ouvertes.fr/tel-01457583/file/th%C3%A8seLaurent2015V2.pdf

Résumé : La zone latérale des filaments branchiaux des bivalves Codakia orbiculata et Lucina pensylvanica est le lieu d'une symbiose chimioautotrophe avec des bactéries sulfo-oxydantes hébergées dans des cellules spécialisées, appelées bactériocytes. Dans cette étude, nous nous sommes proposés de déterminer les mécanismes qui sous-tendent la plasticité cellulaire et tissulaire observée au cours des processus de décolonisation et de recolonisation bactérienne. Pour ce faire, des individus collectés dans leur milieu naturel, ont été maintenus au laboratoire dans des bacs d'eau de mer filtrée en absence de nourriture et de soufre réduit, afin de provoquer la décolonisation bactérienne des filaments branchiaux. Lorsque la branchie apparaissait purgée de ses symbiotes, les individus ont été remis dans leur habitat naturel afin de provoquer sa recolonisation. L'analyse des branchies au cours de ces processus a fait appel à des techniques variées (histologie, immunohistochimie, hybridation in situ, cytométrie en flux, dosage des protéines et spectrométrie de fluorescence X). Les résultats obtenus ont permis de montrer que l'acquisition environnementale mise en évidence chez les juvéniles des Codakia se poursuivait tout au long de la vie des adultes. Cette étude a également permis une meilleure compréhension des mécanismes tissulaires sous-jacents à la plasticité du filament branchial en mettant en évidence les processus d'apoptose et de prolifération cellulaire qui ont lieu au cours des processus de décolonisation et de recolonisation. Ces processus s'accompagnent d'une variation de la teneur en soufre élémentaire, ainsi que de la taille relative et du contenu génomique des symbiotes
The lateral zone of gills filaments of coastal bivalves Codakia orbiculata and Lucina pensylvanica is the site of chemoautotrophic symbiosis with sulfur-oxidizing bacteria, housed in specialized cells called bacteriocytes. The objective of this thesis is to determine the mechanisms underlying cel1 plasticity and tissue plasticity observed in the lateral zone of gills filaments during the processes of bacterial decolonization and recolonization. In order to do this, the individuals collected in their natural habitat were maintained at the laboratory in seawater filtered tanks, without food and reduced sulfur, to cause bacterial decolonization. When the gills seemed to be purged, the individuals were returned to their natural habitat in order to cause the bacterial recolonization of gills filaments. The analysis of the gills during these processes involves several techniques (histology, immunohistochemistry, molecular hybridization, flow cytometry, total protein assays, protein sulfur assays, X-ray fluorescence spectrometry).This study shows that symbiont acquisition can occur during the entire life of Codakia bivalves. It also allows a better understanding of gills filaments plasticity by highlighting apoptosis and cell proliferation during decolonization and recolonization processes.Theses processes are accompanied with of elemental sufur, relative size and genomic content of symbiontes.

http://www.theses.fr/2011AGUY0461/document

Éditeur(s) : HAL CCSD
Résumé : International audience
Seven individuals of a single morphotype of mussels (Bivalvia: Mytilidae) were found attached to a naturally sunken whale intervertebral disk collected in Guadeloupe (Caribbean) at 800 m depth. These specimens resemble small Idas mussels which are found worldwide at cold seeps and hydrothermal vents, and typically harbor ectosymbiotic bacteria on their gills upon which they depend for nutrition. Based on multi-locus gene sequencing, these specimens appear to belong to a new species closely related to two species now included within the genus Terua. Unexpectedly, its closest relatives are found in the Pacific, questioning how this species has reached the Antilles arc. Based on marker gene sequence analysis, electron and fluorescence microscopy, Terua n. sp. harbors two distinct and abundant extracellular bacterial symbionts located between microvilli at the apical surface of host gill epithelial cells. One is a sulfur-oxidizing bacterium similar to the symbionts previously identified in several deep-sea mussels, while the other is related to Colwellia species, a group of cold-adapted heterotrophic bacteria able to degrade organic compounds. This study provides the first evidence for the existence of a dual symbiosis in mussels from whale fall ecosystems in the Caribbean. The evolutionary history of Terua n. sp. and potential role of its Colwellia symbionts are discussed.
Deep Sea Research Part I: Oceanographic Research Papers

hal-01336943
http://hal.upmc.fr/hal-01336943
http://hal.upmc.fr/hal-01336943/document
http://hal.upmc.fr/hal-01336943/file/Duperron_Colwellia_and.pdf
DOI : 10.1016/j.dsr.2016.05.012

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
PurposeMarine mangrove sediments in the Manche-à-Eau lagoon (Guadeloupe, Caribbean Sea) harbor locally extensive, white microbial mats. These mats cover the surface of reduced sediments near the roots of red mangrove trees, Rhizophora mangle, and are mainly composed of sulfur-oxidizing bacteria belonging to the Beggiatoaceae family, with some filamentous cyanobacteria. The goal of this study was to investigate the possible influence of sediment characteristics on the presence of these microbial mats.Materials and methodsFour push cores were collected in April 2013, two from zones with microbial mats and two from zones without mats. Sediment characteristics (grain-size distribution, mineralogy, total organic carbon (TOC) and total nitrogen (TN) contents, atomic TOC/TN ratios, and organic matter (OM) δ13C values) were compared for all four cores.Results and discussionSignificant differences were observed between sediments below microbial mats and those without mats. Sediments with microbial mats contained greater amounts of clay, and higher TOC, TN, and TOC/TN ratios, with lower total carbonate content and δ13C values. The higher clay content most likely results from lower fluid flow velocity near to mangrove roots, while higher TOC/TN ratios and lower δ13C values indicate higher inputs of OM from mangrove trees. These results are consistent with the fact that microbial mats were observed near the roots of mangrove trees, which trap OM from terrestrial vegetation and fine sediments.ConclusionsThe grain-size distribution of sediment particles, the total carbonate content, and the δ13C values are the main parameters discriminating between zones with microbial mats and those without mats. Variations in total carbonate content, which is mainly of biogenic origin, result from conditions that are more favorable for benthic organisms in zones without microbial mats. Variations of the TOC/TN ratios are controlled by the presence of a non-negligible amount of inorganic nitrogen bound to surface clay mineral particles and/or by microbial processes.
ISSN: 1439-0108

hal-01545903
https://hal.archives-ouvertes.fr/hal-01545903
DOI : 10.1007/s11368-016-1555-6

Éditeur(s) : HAL CCSD Wiley-Blackwell
Résumé : International audience
Associations between marine invertebrates and chemoautotrophic bacteria constitute a wide field for the study of symbiotic associations. In these interactions, symbiont transmission must represent the cornerstone allowing the persistence of the association throughout generations. Within Bivalvia, in families such as Solemyidae or Vesicomyidae, symbiont transmission is undoubtedly vertical. However, in Lucinidae, symbiont transmission is described in the literature as 'environmental', symbionts being acquired from the environment by the new host generations. Hence, if there is transmission, symbionts should be transmitted from adults to juveniles via the environment. Consequently, we should observe a release of the symbiont by adults. We attempted to detect such a release within two Lucinidae species of the genus Codakia. We sampled 10 Codakia orbicularis and 20 Codakia orbiculata distributed in 10 crystallizing dishes containing filtered seawater. During 1 month of investigation, we analyzed water of the dishes in order to detect any release of a symbiont using catalyzed report deposition-FISH techniques. For 140 observations realized during this period, we did not observe any release of symbionts. This suggests that the idea of host-to-host passage in Lucinidae is inaccurate. We could therefore consider that the transmission mode from generation to generation does not occur within Lucinidae, symbiosis appearing to be advantageous in this case only for the host, and constitutes an evolutionary dead-end for the bacteria.
ISSN: 0168-6496

hal-00751560
https://hal.univ-antilles.fr/hal-00751560
DOI : 10.1111/j.1574-6941.2008.00626.x

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-Blackwell
Résumé : International audience
In marine invertebrates that acquire their symbionts from the environment, these are generally only taken up during early developmental stages. In the symbiosis between lucinid clams and their intracellular sulfur-oxidizing bacteria, it has been shown that the juveniles acquire their symbionts from an environmental stock of free-living symbiont forms, but it is not known if adult clams are still competent to take up symbiotic bacteria from the environment. In this study, we investigated symbiont acquisition in adult specimens of the lucinid clam Codakia orbiculata, using transmission electron microscopy, fluorescence in situ hybridization, immunohistochemistry and PCR. We show here that adults that had no detectable symbionts after starvation in aquaria for 6 months, rapidly reacquired symbionts within days after being returned to their natural environments in the field. Control specimens that were starved and then exposed to seawater aquaria with sulfide did not reacquire symbionts. This indicates that the reacquisition of symbionts in the starved clams returned to the field was not caused by high division rates of a small pool of remaining symbionts that we were not able to detect with the methods used here. Immunohistochemistry with an antibody against actin, a protein involved in the phagocytosis of intracellular bacteria, showed that actin was expressed at the apical ends of the gill cells that took up symbionts, providing further evidence that the symbionts were acquired from the environment. Interestingly, actin expression was also observed in symbiontcontaining cells of untreated lucinids freshly collected from the environment, indicating that symbiont acquisition from the environment occurs continuously in these clams throughout their lifetime.
ISSN: 1462-2912

hal-00743019
https://hal.univ-antilles.fr/hal-00743019
DOI : 10.1111/j.1462-2920.2012.02748.x

Éditeur(s) : HAL CCSD American Society for Microbiology
Résumé : International audience
The bivalve Codakia orbicularis, hosting sulfur-oxidizing gill endosymbionts, was starved (in artificial seawater filtered through a 0.22- m-pore-size membrane) for a long-term experiment (4 months). The effects of starvation were observed using transmission electron microscopy, fluorescence in situ hybridization and catalyzed reporter deposition (CARD-FISH), and flow cytometry to monitor the anatomical and physiological modifications in the gill organization of the host and in the symbiotic population housed in bacteriocytes. The abundance of the symbiotic population decreased through starvation, with a loss of one-third of the bacterial population each month, as shown by CARD-FISH. At the same time, flow cytometry revealed significant changes in the physiology of symbiotic cells, with a decrease in cell size and modifications to the nucleic acid content, while most of the symbionts maintained a high respiratory activity (measured using the 5-cyano-2,3-ditolyl tetrazolium chloride method). Progressively, the number of symbiont subpopulations was reduced, and the subsequent multigenomic state, characteristic of this symbiont in freshly collected clams, turned into one and five equivalent genome copies for the two remaining subpopulations after 3 months. Concomitant structural modifications appeared in the gill organization. Lysosymes became visible in the bacteriocytes, while large symbionts disappeared, and bacteriocytes were gradually replaced by granule cells throughout the entire lateral zone. Those data suggested that host survival under these starvation conditions was linked to symbiont digestion as the main nutritional source.
ISSN: 0099-2240

hal-00750419
https://hal.univ-antilles.fr/hal-00750419
DOI : 10.1128/AEM.02659-08

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
Purpose: Marine mangrove sediments in the Manche-à-Eau lagoon (Guadeloupe, Caribbean Sea) harbor locally extensive, white microbial mats. These mats cover the surface of reduced sediments near the roots of red mangrove trees, Rhizophora mangle, and are mainly composed of sulfur-oxidizing bacteria belonging to the Beggiatoaceae family, with some filamentous cyanobacteria. The goal of this study was to investigatethe possible influence of sediment characteristics on the presence of these microbial mats. Materials and methods: Four push cores were collected in April 2013, two from zones with microbial mats and two from zones without mats. Sediment characteristics (grain-size distribution, mineralogy, total organic carbon (TOC) and total nitrogen (TN) contents, atomic TOC/TN ratios, and organic matter (OM) δ13C values) were compared for all four cores.Results and discussion: Significant differences were observed between sediments below microbial mats and those without mats. Sediments with microbial mats contained greater amounts of clay, and higher TOC, TN, and TOC/TN ratios, with lower total carbonate content andδ13C values. The higher clay content most likely results from lower fluid flow velocity near to mangrove roots, while higher TOC/TN ratiosand lower δ13C values indicate higher inputs of OM from mangrove trees. These results are consistent with the fact that microbial mats were observed near the roots of mangrove trees, which trap OM from terrestrial vegetation and fine sediments.Conclusions: The grain-size distribution of sediment particles, the total carbonate content, and the δ13C values are the main parameters discriminating between zones with microbial mats and those without mats. Variations in total carbonate content, which is mainly of biogenic origin, result from conditions that are more favorable for benthic organisms in zones without microbial mats. Variations of the TOC/TN ratios are controlled by the presence of a non-negligible amount of inorganic nitrogen bound to surface clay mineral particles and/or by microbial processes.
ISSN: 1439-0108

hal-01682110
https://hal.univ-antilles.fr/hal-01682110
DOI : 10.1007/s11368-016-1555-6