Optimization of the growth and marennine production by the diatom Haslea ostrearia in photobioreactor
Résumé
The benthic diatom Haslea ostrearia which has the capacity to excrete a blue pigment called marennine remains a challenging organism to culture in a photobioreactor (PBR). This study investigates the interest of culture in conventional mixed PBR over immobilized-cell protocols which proved successful but have rather low extracellular marennine (EMn) due to a limitation in mass or light transfer in the biofilm. In contrary, culture in mixed PBR has been proven to overcome culture mass transfer limitation, and to provide a high level of control over light access to cells, enabling the application of systematic optimization of photosynthesis-related kinetics. Increasing the dissolved inorganic carbon concentration up to values of around 5-10 mM was found to increase both growth kinetics and EMn production. Growth medium enrichment with silica (Si) was however found to be challenging due to chemical precipitation. A fed-batch strategy on SiP supply was implemented, leading to an increase in biomass productivity (51.8 ± 2.3 mg X L − 1 d − 1). Although EMn was produced continuously, the nutrient-limited conditions led to higher productivity with 9.2 ± 1.7 mg EMn m − 2 d − 1 , 37.9 ± 0.7 mg EMn m − 2 d − 1 and 54.5 ± 1.8 mg EMn m − 2 d − 1 for phosphorus, silicon and nitrogen deprivation respectively. The effect of light availability was also investigated, as represented by the Mean Rate of Photon Absorption (MRPA). A direct relation was shown for both biomass and EMn production kinetics. However, maximal biomass and EMn productivities were found at different MRPA values, respectively 1.7 ± 0.1 g x m − 2 d − 1 at 12.3 μmol hν g x − 1 s − 1 and 11.0 ± 0.5 mg EMn m − 2 d − 1 at 8.4 μmol hν g x − 1 s − 1. Finally, a continuous EMn production was obtained in optimal conditions, leading to a productivity of 4.5 ± 0.16 mg EMn L − 1 d − 1 , enabling validation of the conventional mixed PBR for H. ostrearia culture and continuous EMn production.
Domaines
Génie des procédés
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