Seminar Margot Bremaud

Estimation of bioavailable energy and potential biomass in the subsurface

Margot Bremaud (Geosciences Rennes)


The continental subsurface represents one of the largest reservoirs of microbial life on Earth. This deep biomass is notably made up of autotrophic microorganisms which obtain their energy from redox reactions, thus exerting an influence on geochemical cycles. Despite its importance, the quantification of this deep biomass still involves a lot of uncertainty. In this study, we developed a new thermodynamic modeling approach applied to in-situ geochemical data in order to estimate the biomass potentially supported in the subsurface. Field data were combined with thermodynamic calculations to determine and quantify the main energy sources that can support chemolithoautotrophic microorganisms. These calculations allowed us to determine the predominant microbial metabolism in the subsurface as well as the quantity of bioavailable energy that can be used for the maintenance or growth of the microbial community. From this bioavailable energy, coming from geochemical conditions, and the energy needs of microorganisms for maintenance and growth, it is possible to estimate the potential biomass supported by this microbial community. These calculations were applied along a flow path in the subsurface in order to study the structuring of this potential biomass at depth. Our results reveal the presence of an energetic front at depth where we observe a maximum of potential biomass.