Microbial adaptation to the environment and biogeochemistry of extreme environments

• We are interested in the geobiology and biogeochemical functioning of contemporary aquatic ecosystems (such as crater lakes; Figure) sometimes considered as modern analogues of ancient oceans and sharing common features with some petroleum source rocks. The predominance of prokaryotic communities in such stratified ecosystems characterized by the presence of marked chemoclines (inducing strong redox gradients, prolonged anoxia of deep waters, strong dissolved element concentrations, etc.) makes such ecosystems adequate for studying microbial life under 'extreme conditions'. Based on the molecular (lipid biomarkers) and isotopic composition of the organic matter in the water column and the underlying sediments (http://lgltpe.ens-lyon.fr/news/carotte-a-mayotte), on the diversity of microbial communities (Archaea, Bacteria, Eukarya), and on the speciation and isotopic signature of chemical species (e.g., carbon, sulfur), we are characterizing the functioning and the evolution of such exceptional ecosystems since their (post-eruptive) formation. A main goal is to constrain the origins and modes of formation of organic and inorganic geochemical signatures specifically preserved in such depositional environments, in order to use them for a better understanding of ancient systems and of the formation of source rocks (collaboration with TOTAL E&P).

• In collaboration with (bio)chemists and (micro)biologists, we are also studying microbial models grown under controlled conditions (laboratory cultures) and chosen according to their natural origin and/or physiological and evolutive characteristics. These works allow i) a better understanding of how micro-organisms adapt to environmental conditions prevailing in extreme environments (e.g., anoxia, euxinia, high temperature, pressure and salt concentration; Figure) often comparable to the 'primitive' biosphere and, ii) to characterize new microbial metabolic pathways (e.g. biosynthesis of specific lipids) with a potential interest for biotechnology and/or environmental studies.

Participants : Vincent Grossi (Research Director), Ingrid Antheaume (Engineer), Ivan Jovovic (PhD 2016-2020).