The project investigates the effect of geogenic CO₂ on deep microbial communities and their surrounding sedimentary life habitat and can be considered as natural analog for a probable leakage of a CO₂ storage reservoir. The project is part of a set of pre-studies for the ICDP project “Probing of Intra-continental magmatic activity: drilling the Eger Rift (PIER)” and is funded by the Deutsche Forschungsgemeinschaft (DFG). Within the scope of these pre-studies GFZ drilled a nearly 110 m deep borehole into a mofette system near the small village of Hartoušov (Cheb Basin, NW Bohemia). A mofette is a natural cold either wet or dry CO₂ degassing structure. The Hartoušov mofette is located in an area characterized by active seismicity in form of periodically occurring swarm earthquakes and permanent lithospheric mantle-derived CO₂ gas emanations. The exhaling gas shows a relative heavy carbon isotope signal and is probably integrated into microbial metabolism. Furthermore, the ascending CO₂, dissolved in the ground- or formation water, forms an acid interacting with the surrounding mineral matrix due to dissolution and precipitation processes. The objective of the project is to investigate the interaction of the ascending CO₂ with present and past microbial life (bacteria and archaea) as well as with the surrounding mineral life habitat. In this context the interaction with microbial communities are examined by microbial cell membrane lipids and their carbon isotope composition. Furthermore, the influence of CO₂ on the mineral matrix during early diagenesis is determined by microscopy (SEM, FIB-TEM).