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Theses

Séquestration biologique du carbone par les cyanobactéries

Abstract : The use of marine or terrestrial microorganisms for long-term sequestration of CO2 is a possible solution to reduce the CO2 content in atmosphere. This thesis work focuses on calcifying organisms, in particular the cyanobacteria, which can fix CO2 as biomass and calcium carbonate. The latter is insoluble in water; precipitates may therefore constitute a long term sink. Understanding of the calcification mechanisms induced by cyanobacteria and the possibility of controlling these processes are necessary to develop a technology for CO2 sequestration. This biotechnology could be an alternative technology to CO2 capture and geological storage. Synechococcus strain PCC8806, marine cyanobacteria purified by the Institute Pasteur de Paris is used during the experimental work in this thesis. The first important result of this work is to develop an analytical strategy that allowed access to a mass balance of carbon and calcium in a cyanobacteria culture on hydrogencarbonate. The implementation of this strategy in various tests of this work has also allowed to accurately quantify the production of organic carbon (biomass) and inorganic carbon (CaCO3) according to the calcium and Ci introduced (hydrogencarbonate) in the medium. We then studied the calcite precipitation during growth of Synechococcus PCC8806 in the presence of calcium. For that, culture conditions were varied in order to understand the occurrence of precipitation events and the influence of nucleation sites. The development of crystals has also been carefully studied by scanning electron microscopy. Another part of this work has identified the inorganic carbon source used by Synechococcus PCC8806 for photosynthesis. This was an opportunity to rewrite the equations related to transfers between atmospheric CO2 and the carbonate medium, as well as the equations of photosynthesis depending on the conditions of availability of two sources of inorganic carbon (CO2 and hydrogencarbonate). In addition, we have revealed the effects of diurnal and nocturnal phases of the growth of cyanobacteria on the carbonate system balance and pH. This work also allowed estimating the cyanobacteria growth rates and thus calculating growth yields per unit area. This will ultimately optimize biomass and calcite production in an industrial process
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Lun Li. Séquestration biologique du carbone par les cyanobactéries. Sciences agricoles. Université Claude Bernard - Lyon I, 2010. Français. ⟨NNT : 2010LYO10208⟩. ⟨tel-00878524⟩

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