In front of a packed amphitheatre, Marc gave a brilliant presentation of his thesis on the following subject:
Hyperbaric methods, procedures and techniques for studying deep-sea microorganisms in in situ conditions
Thesis supervisor: Christian Tamburini, CNRS Research Director
Abstract
The ocean is largely deep, with the majority of its volume (> 80 %) at depths greater than 1000 m, and is poorly sampled (< 0.01 %). It is characterised by high hydrostatic pressure, low temperature, high inorganic nutrients and low concentrations of organic carbon. Substrate input is mainly provided in the form of organic matter (in particulate and/or dissolved form) by physical and biological processes. Bioavailable dissolved organic carbon (DOC) is mainly consumed in surface waters by prokaryotes, while most DOC in the deep ocean is recalcitrant, more difficult to degrade. Most measurements of metabolic activity and diversity of bathypelagic prokaryotes are generally underestimated due to technological limitations in recovering samples and maintaining them under in situ environmental conditions (high hydrostatic pressure, temperature, etc.). To study prokaryotes under in situ conditions, we have hyperbaric technology not only for use as a ready-to-use pressurised sampler, which can be adapted for use on a CTD sampling carousel and capable of collecting, transferring and incubating samples under in situ conditions (high hydrostatic pressure and temperature), but also increasing hydrostatic pressure along the water column. The results highlight that by maintaining pressure conditions, it is possible to sample piezophilic microorganisms representative of the deep environment. These results were confirmed by our experiment on the degradation of high molecular weight dissolved organic matter by a community adapted to the deep environment. Finally, we also demonstrated the importance of environmental conditions for studying the fate of organic matter in the water column.
Keywords: deep ocean, high pressure, prokaryotes, diversity, microbial activity, in situ sampling