1/ Interactions between thioautotrophic bacteria and marine invertebrates: a case of chemosynthetic models.

Various marine organisms, living in sulphidic environments, are associated with symbiotic bacteria. In our lab we completely control the shallow water lucinid (Codakia orbicularis), associated with intracellular bacteria that colonized its gills. Usually, tropical bivalves belonging to the lucinidae family offer interesting perspectives of research like those actually in progress in the lab concerning the cellular and tissular plasticity of the gill during a stress and the evolution of the intracellular bacterial population kept in starvation. This bivalve family, easily maintained in the lab, becomes a unique generic model to understand symbiosis relationships between bacteria and deep-sea organisms like those colonizing hydrothermal vents or cold seeps. We also studied the interaction between sulfur-oxidizing bacteria with other invertebrates (nematodes, protozoan, bryozoans, etc) colonizing sunken organic substrates such as wood falls or whale falls.

2/ Organisation and functioning of the mangrove in association with sedentary species.

This topic concerns vertebrates (Fishes), invertebrates (Molluscs), protists (vorticellids, diatoms, etc.) and microorganisms (eubacteria and archae). We try to better understand the mangrove ecosystem focusing on the geochemical cycles (nitrogen-, sulfur- and carbon-cycle) involving the complex prokaryotic flora found in the mangrove sediment. We also study the flux between various sedentary species living in this marine ecosystem. Thus, it is a multidisciplinary topic (involving chemistry, geochemistry, physics, and biology) which will represent the main axis of our research for the next years. We will focus on microorganisms (especially on giant mesophilic archae (Thaumarchae) recently described by our lab in this ecosystem. Mangrove is an incredible ecosystem to study biodiversity for this kind of archae with huge biomass whose organization and role in the mangrove remains unknown at this time.