In order to comply with the national low carbon strategy (SNBC) and the energy decarbonization objectives by 2050, it is necessary to develop decarbonized energy transformations and productions, i.e. not based on fossil carbon but on renewable carbon stocks, so either biomass or gaseous carbon dioxide. The transformation of CO2, whether it is of industrial origin (smoke) or biogenic (from biogas, for example), is proving to be an important asset for the future. In this project, we propose to work on the valorization of CO2 into calcium/magnesium carbonate in the form of rocks. This transformation will be carried out by microorganisms and in particular microbial consortia. The objective is therefore to select, from environmental microbial consortia, populations of APSB (Anaerobic Phototrophic Sulfur Bacteria) and to characterize their activity in terms of yields and microbial kinetics, production of exopolymers, and this according to of different growth conditions. In a second step, the addition of calcium and magnesium will make it possible to study the potential for inducing the precipitation of carbonates, for a subsequent coupling with a sulphate-reducing activity. Finally, the study proposes to focus on the microbial pathways involved in the sulfur cycle. Indeed, in the environment (ocean, lake sediments), the sulfur cycle participates via different biological and physico-chemical reactions in the bioprecipitation of carbonate salt. In particular, sulphate-reduction leads to the alkalinization of media, and the production of bicarbonate ions from MO, a phenomenon favorable to this type of reaction. The production of reduced sulfur in the form of H2S during this reaction is a potential substrate for phototrophic sulfur bacteria (APSB). This type of coupling, between chemotrophic and phototrophic pathways, takes place in the environment within microbial mats (ocean and lake sediments). By associating two complementary teams in this collaboration, the project will make it possible to understand and qualify the mechanisms involved and the role of APSBs, and to investigate the potential of such a coupling for the capture of CO2 by the culture in a bioreactor of APSB for optimization of carbonate precipitation.