A first result of this thesis is the building and validation of a circulation reactor named BCC (Biomineralization Control Cell). The reactor has the functionality of a biological reactor and allows a monitoring of physico-chemical characteristics such as Eh, pH, electrical conductivity, spectrophotochemical parameters. It also has a capability of percolation through rock cores. It is a first step toward an analogical modeling of interactions between injected CO2 and deep biospheric components. Moreover, a new spectrophotochemical method for monitoring reduced sulfur species has been developed wich allows efficient monitoring of sulfate-reducing metabolisms. In the thesis, we have tested four metabolisms relevant to biomineralisation or biological assimilation of CO2: a reference ureolytic aerobic strain, Bacillus pasteurii, a sulfate-reducing bacterium, Desulfovibrio longus, a sulfate-reducing consortium (DVcons) and an homoacetogenic bacterium, Acetobacterium carbinolicum.
In the case of B. pasteurii, which is considered as a model for non photosynthetic prokaryotic carbonate biomineralization, we have demonstrated that the biological basification and carbonate biomineralization processes can be modelled acurately both analogically and numerically under conditions relevant to deep CO2storage, using a synthetic saline groundwater. We have shown that salinity has a positive effect on CO2 mineral trapping by this bacterium; we have measured the limits of the system in terms of CO2 pressure and we have shown that the carbonates that nucleate on intracellular calcium phosphates have specific carbon isotope signatures.
The studied deep-subsurface strains (D. longus and A. carbinolicum) as well as the sulfate-reducing consortium also have capabilities of converting CO2 into solid carbonates, much less efficent though than in the case of B. pasteurii. However, once inoculated in synthetic saline groundwater and subjected to an H2/CO2 gas flow, A. carbinolicum and the sulfate-reducing consortium show important capabilities of CO2 biological assimilation either as cellular biomass or as extra-cellular polymeric substances. These experiments also demonstrated the strong capabilites of H2 absorption by these bacterial systems, allowing a good quantitative measurement of this phenomenon in future studies about the fate of H2 in the subsurface.