On the theme
"Bioavailability of dissolved organic matter for heterotrophic prokaryotes in the Mediterranean coastal zone: characterisation and ranking of control factors".
before a jury composed of :
Fabien JOUX, University Professor, Sorbonne University UPMC (France), Rapporteur
Ms Julie LELOUP, Senior Lecturer (HDR), Sorbonne University UPMC (France), Rapporteur
Frédéric GARABETIAN, University Professor, University of Bordeaux (France), Examiner
Olivier PRINGAULT, Director of Research, IRD (France), Examiner
Véronique LENOBLE, Associate Professor, University of Toulon (France), Thesis co-director
Mr Benjamin MISSON, Senior Lecturer (HDR), University of Toulon (France), Thesis supervisor
Summary:
Dissolved organic matter (DOM) and heterotrophic prokaryotes (HPs) are recognised as important components of the carbon cycle in the oceans. The use of DOM by HP is dependent on its bioavailability. Bioavailability is subject to natural and anthropogenic variations, which are all the more significant in coastal areas. Several biotic and abiotic factors controlling bioavailability are known, but the hierarchy of their respective influences is widely debated. In this context, the objectives of this thesis were to study and understand the variations in DOM bioavailability in a coastal environment and the behaviour of the microbial community in the face of these fluctuations. To characterise, prioritise and identify the sources of the factors modifying DOM bioavailability. According to the results of this study, DOM bioavailability appears to be determined mainly by abiotic factors. Excessive organic nitrogen and inorganic phosphorus in highly anthropised coastal zones stimulated bacterial growth and altered community structure. A study of the molecular composition of DOM has also shown that the presence and consumption of nitrogenous molecules (proteins, amino sugars) and carbohydrates are associated with higher HP growth. These abiotic factors mainly influence the fate of carbon through the microbial loop. However, the reactivity of the microbial community to a labile DOM pool was found to be temperature dependent. Finally, sediment resuspension appeared to be a potential source of these factors controlling DOM bioavailability.
Key words: coastal ecosystems, Mediterranean Sea, dissolved organic matter, bioavailability, heterotrophic prokaryotes.