One of the main challenges of CCS technology is to estimate and control the stability of the storage zone. Among all the parameters that can be listed on that subject, the knowledge about the local biosphere effect is poor. However, its activity has been already proven to be important, especially for BECCS systems where the CO2 incoming flux contains organic compounds. Indeed, these latter might significantly enhance the interaction between the biosphere and the CO2 plume. In this context, the goal of this study is to give first insights for the quantification of the impact of CO2 front on microbial biomass that occurs in saline aquifers during carbon geological storage. A sulfate reducing bacterium (Desulfotomaculum geothermicum) was tested with sediments (carbonaceous sandstone) in a pressurized column (10 bar of CO2 and 40 bar of nitrogen) at 54°C during a percolation test in saline artificial groundwater. Different measurements were realized in order to quantify the respective metabolic activities and the spatial speciation of organic and inorganic carbon in those systems. Despite a protective effect of the mineral matrix, the results showed a high sensitivity of autotrophic microorganisms to the stress induced by few bars of CO2 and revealed that a part of this stress was mainly due to direct toxic effects. Still an equilibration is reached and appeared to moderate these effects. Biomineralization processes of carbonates were not observed for D. geothermicum during these experiments and demonstrated variations in accordance with the availability of sediments. All these results were analyzed in correlation with previous results with that strain and demonstrated the feasibility to integrate geobiological data in speciation models as regards geological exploitation processes.