PhD student: Dimitri Kalenitchenko, Thesis director: Galand Pierre
Thesis defended the 18th of september 2015

When wood sinks to the deep-sea floor it creates a new ecosystem that does not depend directly on energy from sunlight. This ecosystem is called chemosynthetic because of the presence of a fauna associated with symbiotic bacteria that can assimilate inorganic carbon from seawater. Furthermore this system is colonized by specialized fauna that use symbiotic bacteria to digest the wood matrix. Previous studies mostly focused on these symbiotic macroorganisms and the role played by non-symbiotic microorganisms in the sunken wood ecosystem remains unknown. We demonstrate in this thesis the important role played by non symbiotic microorganisms during the sunken wood ecosystem establishment. We reveal the ecological succession of microorganisms driven by time and wood structure. The first step of this succession is characterized by a microbial population able to produce hydrogen sulfide after one month of immersion. This hydrogen sulfide production is the basis for (1) a chemolithoautotroph biofilm development on the wood surface and (2) a recruitment of species associated with chemoautotrophic bacteria. Our results suggest a succession of different phases that transform a terrigeneous substrate into an environment that may have helped, million years ago, the colonization of the deep sea by chemosynthetic species.