PhD student Jeanne Caumartin (Supervisors : Karim Benzerara (IMPMC) et Purificacion Lopez-Garcia (ESE))

Microbialites are organosedimentary structures consisting of microbial communities that can influence/induce mineral precipitation (Burne and Moore, 1987). Some currently grow in oxygenated aquatic environments while the oldest formed in the Precambrian under anoxic conditions. In 2019, living microbialites were discovered at anoxic depths in two lakes in Mexico; thus, they are interesting analogues to Precambrian microbialites. In this thesis, the mineralogy and microbial communities of natural samples of these anoxic microbialites are studied in the laboratory. For this purpose, microscopy techniques at different scales (SEM, Confocal), X-ray diffraction (DRX), spectrometry (FTIR), microbiology and water chemistry (ICP-AES) are used. Moreover, biofilms of these microbialites and cyanobacterial strains likely to switch from oxygenic to anoxygenic photosynthesis are maintained in anoxic mesocosms in order to identify the taxonomic variations of the microbial communities and to study the carbonatogenesis of these strains in an anoxic environment (metabarcoding and metatranscriptomics). In parallel, experiments of calcification of biofilms of these Mexican microbialites in open system will be conducted in the laboratory in order to better understand the first steps of formation of these structures.

Figure: Comparison of an oxic environment microbialite sample collected from Lake Alchichica at 5 m depth (left) and an anoxic environment microbialite sample from the same lake, collected at 40 m depth (right).

@ Purificacion Lopez-Garcia