Thesis defense of Mélissa GARRY

Dynamics of microbial communities in redox interfaces of the continental subsurface:
diversity, biomass, metabolisms and biogeochemical kinetics


The heterogeneity of the continental subsurface favors the mixing of groundwater fluxes with distinct biogeochemical signatures, creating microbiological hotspots. In oxic-anoxic interfaces, hotspots of microaerophilic bacteria result with the orange microbial mat formations, rich in iron-oxidizing bacteria (FeOB). In underground environments, several diversity studies on these FeOB have shown the abundance of the Gallionellaceae family, chemolithoautotrophic bacteria producing a large quantity of biomass. This thesis focuses on the diversity and activity of these bacteria, their influence on the kinetics of reactions and their production of biomass within the redox gradient environments which constitute their habitats. To reproduce the optimal growth conditions of this microbial community, reactive oxygen tracer-test was carried out and the microbial and geochemical responses were monitored. In the laboratory, experiments with low O2 concentrations made it possible to specify the growth range of these bacteria and to quantify their contribution to primary production. To learn more about the ecological niche of these bacteria, the first FeOB from the continental subsurface was isolated and characterized. This work highlights the effect of oxygen on the growth dynamics of these bacteria and suggests a significant capacity for adaptation to environmental variations and an ability to exploit energy resources as soon as they become available. Our results demonstrate also interactions of FeOB with other microorganisms and their role in the cycles of C, Fe, S, and N.

Keywords: Deep biosphere; Biomass; Microbial diversity; Groundwaters; Redox interfaces; Biogeochemical cycles

The defense will also be accessible by videoconference:

Meeting ID: 932 0054 8960