Oceans health is intimately linked to animal and human health in a One Health framework. Marine zoonotic diseases threaten animal and human health and well-being, ecosystem integrity and economic development of marine coastal systems. Coastal waters, where oysters are produced, are low inerty systems highly sensitive to contaminants, which can also accelerate the emergence of epidemics/epizootics and zoonotic diseases in marine ecosystems. Among them, copper is a widespread pollutant that acts as a major selective pressure influencing microorganism survival and evolution as it can be deadly for many bacteria. Vibrio aestuarianus subsp. francensis is an emerging pathogen that threatens European aquaculture since 2011. Recent work revealed that this bacterium is an oyster-restricted specialized pathogen. The IHPE laboratory has evidenced that an intimate relationship between virulence and copper resistance conferred by a pathogenicity island could be key in the adaptation of the subspecies to the oyster host. This proposal aims to evaluate the role of copper resistance in V. aestuarianus francensis adaptation to oyster, and to unveil the copper resistance molecular pathways underlying this key phenotype and infection outcome. Specifically, we will address the following questions: -Is copper resistance required for V. aestuarianus adaptation and virulence to its host? -What is the diversity of V. aestuarianus copper resistance mechanisms? -Does accumulated copper in oyster have an impact in the host-pathogen outcome? By investigating resistance to copper and virulence as interlinked phenotypes of pathogens and its impact on oyster immunity, we will bring knowledge on the way copper influences the pathogens´dynamics, driving their evolution and specialization in marine ecosystems, but also modulating host-pathogen interactions. Ultimately, the project should help shellfish farmers and policy-makers mitigate the effects of anthropogenic pollution on aquaculture services.

Over geological times, the evolution of carbon isotope compositions of carbonates (δ13Ccarb) in sedimentary record highlights many positive isotopic excursions (CIEs), reflecting significant perturbations of the carbon cycle in Earth surface environments. Although generally interpreted as a consequence of an increase of organic carbon burial in sediments, the lack of high organic carbon content, as well as the strong spatial and temporal variability, observed in many sedimentary successions recording CIEs challenge this postulate. Among other alternative hypothesis involving regional or local control, the potential influence of methanogenesis, i.e. the biological process of anaerobic organic matter degradation producing methane (CH4), has been raised; its ability to generate similar isotopic signatures has been demonstrated in modern analogue. Although the processes behind CIEs are questioned, providing more information about methanogenesis impact is challenging based on traditional isotopic tool like δ13Ccarb, as its isotopic effect on is similar to that of organic carbon burial increase. Recently, stable isotope compositions of metals used as enzymatic cofactors of CH4-related processes were investigated to explore their potential as biomarkers of methanogenesis. During the last decade, significant advances have been made on using Ni isotopes as tracers of methanogenesis but important challenges remain to better constrains both their potential and limit. In order to improve our understanding of CH4 cycle and its impact on Earth’s surface environments through geological times, we will investigate further the potential of Ni isotopes and its potential couplings with traditional stable isotope in various modern settings and past environments to enhance our ability to track and discriminate the influence of CH4-related processes through Earth’s history.

Selon les prévisions de la FAO, l’aquaculture devrait jouer un rôle de plus en plus important au niveau de la satisfaction des besoins alimentaires des populations au cours des prochaines décennies. En 2030, l'aquaculture serait la principale source d'approvisionnement en poisson. Les maladies infectieuses représentent un facteur limitant majeur en aquaculture car elles sont à l’origine de pertes économiques considérables pour ce secteur d’activité. Les professionnels ont alors souvent recours à l’utilisation d’antibiotiques pour prévenir ou traiter les maladies. Cependant, il est maintenant largement reconnu que cette utilisation massive d’antibiotiques peut avoir des impacts négatifs en terme d’environnement et de santé publique. La FAO a d’ailleurs qualifié le développement de la résistance des bactéries aux antibiotiques comme « un des risques les plus graves pour la santé humaine à l’échelle mondiale ». Dans ce contexte, le projet de recherche proposé vise à faire émerger une approche susceptible de faciliter l’adaptation de l’aquaculture aux contraintes et objectifs du Développement Durable. En effet, l’objet du projet est d’évaluer le potentiel d’application de peptides antimicrobiens en aquaculture, en alternative à l’usage des antibiotiques. Ces molécules sont des effecteurs de l’immunité innée que l’on retrouve à l’état naturel chez les organismes et dont le large spectre d’activité permet d’envisager des applications pour le traitement des infections bactériennes et fongiques. De plus, leur mode d’action sur les membranes est susceptible de générer moins de résistance de la part des microorganismes. Du fait de leurs propriétés, les peptides antimicrobiens sont considérés comme « la famille la plus originale d’agents anti-infectieux découverte au cours de ces 25 dernières années ». Les objectifs de ce projet sont de montrer qu’en condition réelle d’élevage aquacole, ces molécules pourraient se substituer aux antibiotiques et conférer un effet protecteur aux animaux et à la conservation des aliments, sans induire de résistance bactérienne ni d’accumulation de résidus dans l’environnement ou l’animal. Trois partenaires travailleront ensemble pour réaliser les différentes phases expérimentales du projet : l’unité mixte de recherche (UMR 5171 ; Ifremer-CNRS-Université de Montpellier II), une équipe de la Station expérimentale Ifremer de Palavas ainsi qu’une équipe du CIRAD Montpellier. Le projet se décompose en 2 étapes : (1) une phase de production des peptides antimicrobiens, (2) une 2ème phase pendant laquelle des essais expérimentaux seront réalisés en bassin à la station expérimentale Ifremer de Palavas (France) et pendant laquelle seront analysés : l’effet protecteur des peptides antimicrobiens sur les poissons d’élevage, l’effet du traitement peptidique sur la microflore des animaux, la qualité microbiologique de l’eau du bassin d’élevage. Nous vérifierons aussi que les traitements n’entraînent pas de développement de résistance des bactéries de l’environnement aquacole (aux peptides eux-mêmes et aux antibiotiques). L’objectif final du projet est de convaincre un partenaire industriel de s’investir dans le développement et de transférer cette innovation au secteur aquacole.

Erosion is a group of processes, including chemical and mechanical weathering, by which material is worn away from the Earth's surface. Weathering of silicate rocks acts as an important sink for atmospheric CO2, and hence is thought to have played an important role in regulating the Earth’s climate over geological time. Despite the potential importance of this process, and its significance to the global carbon cycle, our ability to reconstruct past variations in silicate weathering remains limited. Another important issue is the degree to which human-induced environmental degradation has affected chemical weathering intensity on shorter time scales, from tens to thousands of years. There are clear evidence that human activities, such as land-use, agriculture, anthropogenic CO2 emission, are significantly changing the weathering rates of continental rocks, leading to increasing alkalinity export from large river systems to the ocean. A better understanding of how chemical weathering relates to climate change is necessary to further assess how sensitive our environment is to human activities. During the last decades, there has been a growing effort for unraveling the factors behind continental erosion, and for quantifying present and historical rates of weathering through experimental work, modelling, or direct investigation of river systems and soils. This was reflected in the increasing number of sessions dedicated to weathering issues at international conferences, and in the creation of large research programmes focused on Earth’s surface processes (e.g., the INSU programme ‘Reliefs de la Terre’ in France). Although this global effort led to major improvements in understanding the weathering mechanisms, and the links between erosion, tectonics, climate change, and ocean chemistry, there is still a lack of proxies for investigating silicate weathering signals from geological records. Here, we propose to explore the use of novel isotopic and molecular tracers in marine sediments as proxies for past continental weathering. Recent studies showed that the combined use of hafnium and neodymium isotopes in sediments preserved in the geological record could provide an unique tool for tracing the evolution of continental weathering through time. In addition, the emergence of molecular (biomarkers) tracers, in response to improving mass spectrometric techniques, has opened new fields of investigation in paleoclimatology in recent years, some of which (e.g., BIT-index) are particularly well-suited for the study of continental weathering through time. The complementary use of those novel isotopic and organic tracers can now provide a powerful tool to trace the evolution of continental weathering through time. In the first part of the project, we intend to further explore the use of Hf-Nd isotopes and biomarkers as paleoclimatic proxies by analysing an important set of sediments deposited worldwide on continental margins, near the mouth of rivers draining basins characterized by various geological, climatic, and land-use contexts. In the second part of the project, we intend to provide new insights into the global link between climate change and erosion, by applying our novel proxies to the study of two exceptional marine sediment records: 1) a 125 m-long drilled record from the Est-Corsican margin, providing a continuous record of river discharge for the last 500,000 years; and 2) a core recovered from the Gulf of Guinea, allowing the reconstruction of past silicate erosion in a continent-scale tropical watershed, the Congo Basin. The data acquired during the course of this project should significantly improve our understanding of the natural links between erosion of the continents and climate.