Adaptations respiratoires des invertébrés inféodés aux sources hydrothermales profondes

En 1993, j'obtenais un poste de Maître de Conférences à Roscoff et, début 1994, suite à la nomination d'André Toulmond au poste de Directeur de l'Observatoire Océanologique de Roscoff, celui-ci me confiait la responsabilité de l'équipe de recherche d'Ecophysiologie. Issue du rapprochement d’un groupe de phycologie benthique et d’un groupe de physiologie comparée, cette équipe est structurée autour d'une thématique commune, l’étude des mécanismes d’échange de métabolites et de leurs adaptations. Ainsi, nos études portent sur des organismes vivant dans des milieux marins particulièrement contraignants, la zone intertidale en régime mégatidal et les sources hydrothermales profondes, et nous nous intéressons à des fonctions diverses, respiration et excrétion chez les animaux, respiration et photosynthèse chez les végétaux. Mais, au-delà de cette diversité de modèles et de milieux d'étude, nous partageons surtout une approche comparative et intégrée. Comparative, car les problèmes biologiques que nous cherchons à comprendre sont étudiés en utilisant la variété des réponses offertes par les différentes espèces modèles que nous sélectionnons. Et intégrée car dans l'étude d'un problème donné nous nous efforçons d'aborder différentes échelles d’organisation biologique. Le pivot central, à la fois point de départ et objectif ultime, c'est la compréhension du fonctionnement de l'organisme dans son milieu, véritable définition de l'écophysiologie. Mais pour arriver à cette compréhension nous nous efforçons de décortiquer les mécanismes sous-jacents, jusqu'à l'échelle moléculaire si cela s'avère possible et nécessaire, en essayant de dégager des processus généraux à partir des relations structure-fontion particulières que nous sommes amenés à décrire. Enfin, plus récemment, nous nous sommes intéressés à la dimension évolutive de ces problèmes en travaillant à l'échelle de la population ou de l'espèce, analysant notamment nos résultats en termes de phylogénie. La double signification du terme adaptation prend alors tout son sens, à la fois processus physiologique permettant à un organisme de moduler les propriétés de tel ou tel système de façon à s'accommoder des variations du milieu dans lequel il vit, mais également le résultat d'un processus évolutif associant mutations et sélection naturelle et ayant abouti à l'espèce considérée. Dans l'un ou l'autre cas, je suis persuadé que l'approche comparative peut se révéler extrêmement fructueuse, surtout lorsque l’on s’intéresse à des milieux « extrêmes » dans lesquels les adaptations, qu’elles soit physiologiques ou évolutives, sont exacerbées. Cette démarche se rapproche de celle, courante dans le domaine de la recherche médicale, qui consiste à étudier des cas pathologiques (donc « anormaux ») pour en inférer des règles physiologiques « normales ».Naturellement, une telle approche, aussi transversale, réclame un éventail de techniques très large qui dépasse largement les capacités d'un seul individu. La constitution d'une équipe de recherche polyvalente prend alors tout son sens et, à la suite d'André Toulmond, je m'efforce de maintenir et de développer ce potentiel au sein de l'équipe d'Ecophysiologie. Celle-ci réunit ainsi des collaborateurs aux compétences diverses ce qui nous permet de maitriser un certain nombre des techniques nécessaires à la réalisation des projets abordés : anatomie et histologie (techniques de microscopie), biochimie fonctionnelle et structurale (enzymologie, spectroscopie), biologie moléculaire (séquençage, phylogénie), etc. Mais il n'en demeure pas moins essentiel de nous appuyer sur des collaborations scientifiques nationales et internationales. D'une part avec des équipes ayant une vision plus large, plus écologique, des milieux que nous étudions tout en nous offrant un accès privilégié aux campagnes océanographiques . D’autre part, avec des équipes ayant une approche plus pointue, plus biophysique, et maîtrisant parfaitement l'une ou l'autre des techniques qui nous sont nécessaires .Dans le texte qui suit, j'essaierai d'illustrer les deux approches évoquées ci-dessus, en me limitant à deux grands projets dans lesquels je suis plus particulièrement impliqué : •l'approche intégrée pour comprendre les mécanismes de transport du dioxyde de carbone et de l'hydrogène sulfuré chez le vestimentifère Riftia pachyptila;•l'approche comparative de l'équilibre acide-base et du transport de l'oxygène chez les crustacés hydrothermaux. A la suite de chacune des présentations rédigées en français, on trouvera une copie des articles originaux correspondants. Mes autres travaux concernent l'étude du transport de l'oxygène chez deux annélides polychètes inféodées au milieu hydrothermal: Alvinella pompejana, le ver de Pompéï qui colonise les cheminées, et Branchipolynoe, polynoidé commensal des modioles. Ces travaux ont fait l'objet de la thèse de Stéphane Hourdez et des articles qui en sont issus. Enfin, je concluerai en essayant de répondre à une question qui m’est souvent posée : pourquoi diable aller chercher des modèles biologiques aussi loin que sur les sources hydrothermales profondes

Identification of proteins involved in the functioning of Riftia pachyptila symbiosis by Subtractive Suppression Hybridization

<p>Abstract</p> <p>Background</p> <p>Since its discovery around deep sea hydrothermal vents of the Galapagos Rift about 30 years ago, the chemoautotrophic symbiosis between the vestimentiferan tubeworm <it>Riftia pachyptila </it>and its symbiotic sulfide-oxidizing γ-proteobacteria has been extensively studied. However, studies on the tubeworm host were essentially targeted, biochemical approaches. We decided to use a global molecular approach to identify new proteins involved in metabolite exchanges and assimilation by the host. We used a Subtractive Suppression Hybridization approach (SSH) in an unusual way, by comparing pairs of tissues from a single individual. We chose to identify the sequences preferentially expressed in the branchial plume tissue (the only organ in contact with the sea water) and in the trophosome (the organ housing the symbiotic bacteria) using the body wall as a reference tissue because it is supposedly not involved in metabolite exchanges in this species.</p> <p>Results</p> <p>We produced four cDNA libraries: i) body wall-subtracted branchial plume library (BR-BW), ii) and its reverse library, branchial plume-subtracted body wall library (BW-BR), iii) body wall-subtracted trophosome library (TR-BW), iv) and its reverse library, trophosome-subtracted body wall library (BW-TR). For each library, we sequenced about 200 clones resulting in 45 different sequences on average in each library (58 and 59 cDNAs for BR-BW and TR-BW libraries respectively). Overall, half of the contigs matched records found in the databases with good E-values. After quantitative PCR analysis, it resulted that 16S, Major Vault Protein, carbonic anhydrase (RpCAbr), cathepsin and chitinase precursor transcripts were highly represented in the branchial plume tissue compared to the trophosome and the body wall tissues, whereas carbonic anhydrase (RpCAtr), myohemerythrin, a putative T-Cell receptor and one non identified transcript were highly specific of the trophosome tissue.</p> <p>Conclusion</p> <p>Quantitative PCR analyses were congruent with our libraries results thereby confirming the existence of tissue-specific transcripts identified by SSH. We focused our study on the transcripts we identified as the most interesting ones based on the BLAST results. Some of the keys to understanding metabolite exchanges may remain in the sequences we could not identify (hypothetical proteins and no similarity found). These sequences will have to be better studied by a longer -or complete- sequencing to check their identity, and then by verifying the expression level of the transcripts in different parts of the worm.</p

Determining gene flow and the influence of selection across the equatorial barrier of the East Pacific Rise in the tube-dwelling polychaete Alvinella pompejana

International audienceBackground: Comparative phylogeography recently performed on the mitochondrial cytochrome oxidase I (mtCOI) gene from seven deep-sea vent species suggested that the East Pacific Rise fauna has undergone a vicariant event with the emergence of a north/south physical barrier at the Equator 1-2 Mya. Within this specialised fauna, the tube-dwelling polychaete Alvinella pompejana showed reciprocal monophyly at mtCOI on each side of the Equator (9 degrees 50'N/7 degrees 25'S), suggesting potential, ongoing allopatric speciation. However, the development of a barrier to gene flow is a long and complex process. Secondary contact between previously isolated populations can occur when physical isolation has not persisted long enough to result in reproductive isolation between genetically divergent lineages, potentially leading to hybridisation and subsequent allelic introgression. The present study evaluates the strength of the equatorial barrier to gene flow and tests for potential secondary contact zones between A. pompejana populations by comparing the mtCOI gene with nuclear genes. Results: Allozyme frequencies and the analysis of nucleotide polymorphisms at three nuclear loci confirmed the north/south genetic differentiation of Alvinella pompejana populations along the East Pacific Rise. Migration was oriented north-to-south with a moderate allelic introgression between the two geographic groups over a narrow geographic range just south of the barrier. Multilocus analysis also indicated that southern populations have undergone demographic expansion as previously suggested by a multispecies approach. A strong shift in allozyme frequencies together with a high level of divergence between alleles and a low number of `hybrid' individuals were observed between the northern and southern groups using the phosphoglucomutase gene. In contrast, the S-adenosylhomocysteine hydrolase gene exhibited reduced diversity and a lack of population differentiation possibly due to a selective sweep or hitch-hiking. Conclusions: The equatorial barrier leading to the separation of East Pacific Rise vent fauna into two distinct geographic groups is still permeable to migration, with a probable north-to-south migration route for A. pompejana. This separation also coincides with demographic expansion in the southern East Pacific Rise. Our results suggest that allopatry resulting from ridge offsetting is a common mechanism of speciation for deep-sea hydrothermal vent organisms

Conjugating effects of symbionts and environmental factors on gene expression in deep-sea hydrothermal vent mussels.

International audienceABSTRACT: BACKGROUND: The deep-sea hydrothermal vent mussel Bathymodiolus azoricus harbors thiotrophic and methanotrophic symbiotic bacteria in its gills. While the symbiotic relationship between this hydrothermal mussel and these chemoautotrophic bacteria has been described, the molecular processes involved in the cross-talking between symbionts and host, in the maintenance of the symbiois, in the influence of environmental parameters on gene expression, and in transcriptome variation across individuals remain poorly understood. In an attempt to understand how, and to what extent, this double symbiosis affects host gene expression, we used a transcriptomic approach to identify genes potentially regulated by symbiont characteristics, environmental conditions or both. This study was done on mussels from two contrasting populations. RESULTS: Subtractive libraries allowed the identification of about 1000 genes putatively regulated by symbiosis and/or environmental factors. Microarray analysis showed that 120 genes (3.5% of all genes) were differentially expressed between the Menez Gwen (MG) and Rainbow (Rb) vent fields. The total number of regulated genes in mussels harboring a high versus a low symbiont content did not differ significantly. With regard to the impact of symbiont content, only 1% of all genes were regulated by thiotrophic (SOX) and methanotrophic (MOX) bacteria content in MG mussels whereas 5.6% were regulated in mussels collected at Rb. MOX symbionts also impacted a higher proportion of genes than SOX in both vent fields. When host transcriptome expression was analyzed with respect to symbiont gene expression, it was related to symbiont quantity in each field. CONCLUSIONS: Our study has produced a preliminary description of a transcriptomic response in a hydrothermal vent mussel host of both thiotrophic and methanotrophic symbiotic bacteria. This model can help to identify genes involved in the maintenance of symbiosis or regulated by environmental parameters. Our results provide evidence of symbiont effect on transcriptome regulation, with differences related to type of symbiont, even though the relative percentage of genes involved remains limited. Differences observed between the vent site indicate that environment strongly influences transcriptome regulation and impacts both activity and relative abundance of each symbiont. Among all these genes, those participating in recognition, the immune system, oxidative stress, and energy metabolism constitute new promising targets for extended studies on symbiosis and the effect of environmental parameters on the symbiotic relationships in B. azoricus

Recent sedimentation of organic matter along the SE Atlantic Margin : A key for understanding deep offshore petroleum source rocks.

Classical views for the deposition of organic-rich sediments in deep-sea environments invoke two principal types of oceanographic and sedimentologic settings. The first is confined basins in which stratified oxygen depleted waters lead to anoxic preservation of organic matter in the water column and in underlying sediments (Demaison and Moore, 1980). The second is an open ocean setting where the episodic mass transfers due to slope sediment instability lead to the rapid burial of outer-shelf and upper slope-derived organic matter and its consequent preservation due to limited oxic or anoxic degradation (Stow, 1987). Other studies have shown, however, that organic matter in modern deep-sea sediments may occur in high amounts where oxygen is not significantly depleted (Pedersen and Calvert, 1990). Recent studies have demonstrated that highly biological productive areas, such as the upwelling zones associated to the Benguela Current in S-E Atlantic, may deliver sufficient quantity of organic material to (1) outbalance the degradative capacity of the water column and (2) sustain the formation of organic-rich sediments even in deep and oxygenated conditions (Bertrand et al., 2003). It appears that the S-E Atlantic margins provide a good example for revisiting the sedimentology of organic matter in deep water environments in the frame of the GDR Marges Continentales. This may have important implications for a better understanding of the distribution of ancient source rocks in deep offshore petroleum systems (Huc et al., 2001; Bertrand et al., 2003)

Analyse qualitative thématique de la phénoménologie des expériences de mort imminente

peer reviewedNear-death experiences (NDEs) refer to profound psychological events that can have an important impact on the experiencers’ (NDErs) lives. Previous studies have shown that NDEs memories are phenomenologically rich. In the present study, we therefore aimed to extract the common themes (referred to as “features” in the NDE literature) reported by NDErs by analyzing all the concepts stored in the narratives of their experiences. A qualitative thematic analysis has been carried out on 34 cardiac arrest survivors’ NDE narratives. Our results shed the light on the structure of the narratives by identifying 10 “time-bounded” themes which refer to isolated events encountered during the NDE and 1 “transversal” theme which characterizes the whole narrative and generally appears as a retrospective comment of self-reflection on the experience. The division of narratives into themes provides us with detailed information about the vocabulary used by NDErs to describe their experience. This established thematic method enables a rigorous description of the phenomenon, ensuring the inclusion of all self-reported manifestations of themes in narratives

Insights into metazoan evolution from Alvinella pompejana cDNAs.

International audienceBACKGROUND: Alvinella pompejana is a representative of Annelids, a key phylum for evo-devo studies that is still poorly studied at the sequence level. A. pompejana inhabits deep-sea hydrothermal vents and is currently known as one of the most thermotolerant Eukaryotes in marine environments, withstanding the largest known chemical and thermal ranges (from 5 to 105°C). This tube-dwelling worm forms dense colonies on the surface of hydrothermal chimneys and can withstand long periods of hypo/anoxia and long phases of exposure to hydrogen sulphides. A. pompejana specifically inhabits chimney walls of hydrothermal vents on the East Pacific Rise. To survive, Alvinella has developed numerous adaptations at the physiological and molecular levels, such as an increase in the thermostability of proteins and protein complexes. It represents an outstanding model organism for studying adaptation to harsh physicochemical conditions and for isolating stable macromolecules resistant to high temperatures. RESULTS: We have constructed four full length enriched cDNA libraries to investigate the biology and evolution of this intriguing animal. Analysis of more than 75,000 high quality reads led to the identification of 15,858 transcripts and 9,221 putative protein sequences. Our annotation reveals a good coverage of most animal pathways and networks with a prevalence of transcripts involved in oxidative stress resistance, detoxification, anti-bacterial defence, and heat shock protection. Alvinella proteins seem to show a slow evolutionary rate and a higher similarity with proteins from Vertebrates compared to proteins from Arthropods or Nematodes. Their composition shows enrichment in positively charged amino acids that might contribute to their thermostability. The gene content of Alvinella reveals that an important pool of genes previously considered to be specific to Deuterostomes were in fact already present in the last common ancestor of the Bilaterian animals, but have been secondarily lost in model invertebrates. This pool is enriched in glycoproteins that play a key role in intercellular communication, hormonal regulation and immunity. CONCLUSIONS: Our study starts to unravel the gene content and sequence evolution of a deep-sea annelid, revealing key features in eukaryote adaptation to extreme environmental conditions and highlighting the proximity of Annelids and Vertebrates

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