This project concerns the role of marine micro-organisms in the mineralization of particulate (POM) and dissolved (DOM) organic matter and on the regeneration of biogenic compounds (silicates, carbonates) in the meso- and bathypelagic zones of the oceans. Actually, most of the information concerning these processes comes from the epi-pelagic zone and/or does not take into account the effect of increasing pressure with depth. Yet, it is essential to integrate this process (as well as the associated decrease in temperature) when studying oceanic organic matter (OM) mineralization.

The LMGEM has not only a thorough knowledge but also the required equipment (hyperbaric bottles and samplers, sinking particles simulator) developed in collaboration with a private society (Métro-Mesures SA) that make it one of the international leader laboratories on high-pressure studies in microbial ecology.

A double and innovative approach based on laboratory experiments and in situ studies (ANTARES and DYFAMED sites, Mediterranean sea) will allow to determine the effect of pressure on prokaryotes (e.g. community structure), and on their activity (transformation and mineralization of OM). Due to the high inputs of anthropic OM to the oceans (wind inputs, rain falls, maritime transport), we will focus on the fate of both biogenic and anthropic OM. In this context, petroleum hydrocarbons will be considered as a model, as their fate in the meso- and bathypelagic zones remain actually unknown.

The proposed experiments will specifically allow to characterize and quantify the effects of an increase in hydrostatic pressure and a decrease in temperature on :

(i) processes of OM mineralization (transformation of POC into DOC, respiration, hydrocarbon biodegradation) and on the regeneration of biogenic compounds (silicates, carbonates) in intermediary and deep oceanic waters ;

(ii) the structural ((phylo)genetic) and functional (activities) dynamics of prokaryotic communities ;