Promoteur de thèse: Monsieur Ruddy WATTIEZ

Résumé de la dissertation doctorale:

Being the primary producers, cyanobacteria play an important role in balancing the carbon and nitrogen cycles on Earth. The long established ability of photosynthetic cyanobacteria Arthrospira sp. PCC 8005 (now reclassified as Limnospira indica) to produce O2, recycle CO2 and produce nutritious biomass is being investigated by European Space Agency for their bioregenerative life support system (BLSS; MELiSSA Project). The main aim of MELiSSA project is to make future space missions self-sufficient in terms of water-recycling, air-revitalization and food production. Interestingly, while nitrate salts are commonly used for Arthrospira sp. cultivation, most of the wastewater generated on spaceflights and Earth, is rich in urea and ammonium. This thesis was realized in the context of the BIORAT-2 project with the aim to investigate the possibility of (a) completely or partially by-passing the nitrification step in MELiSSA-BLSS and (b) use alternative nitrogen (N) sources (ammonium, urea and nitrite) for Arthrospira sp. cultivation, with a focus on CO2 recycling and O2 production.
High concentrations of urea and ammonium are known to inhibit Arthrospira sp. growth. Hence during this thesis, we evaluated the effects of different concentrations of alternative N-sources (individual and as a mixture) on the metabolic, biochemical and photosynthetic characteristics of Arthrospira sp. The cultivation strategy adopted for this study helped us to increase the tolerance of Arthrospira sp. to high concentrations of urea. The proteomic characterization of cyanobacterial biomass helped us to characterize the effects of alternative N-sources on the functional proteins involved in photosynthetic and metabolic pathways of Arthrospira sp. PCC 8005. The biochemical and stoichiometric data obtained under this study helped us to update the light-transfer based ‘Photosym-Model’ in context of BIORAT-2 working conditions. Through the ground demonstration study, we demonstrated that it is possible to cultivate Arthrospira sp. using fluctuating streams of alternative N-sources and revitalize air under the BLSS-setup. Interestingly, urea was found to be better N-source for Arthrospira sp.
Though all these results were obtained in the context of MELiSSA-BLSS, they can also be adapted for commercial applications on Earth. Increasing bioprocess yields with low cost urea could significantly decrease Arthrospira sp. production