PhD thesis offer on multiscale analysis of microbial rocks

Microbialites are organosedimentary structures formed by microbial communities. These mineralizing microbial mats, often laminated (stromatolites), are preserved in the fossil record and indicate the presence of phototrophic microbial communities on Earth since ~3.5 Ga. Modern microbialites form in lacustrine environments with specific hydrochemistry, often linked to evaporitic processes, and their formation may be influenced by climate change and human activities such as mining. Microbialites contribute to CO₂ fixation in organic and mineral forms through photosynthesis and carbonate precipitation, playing a role in the carbon cycle amid global climate change and increasing desertification.

About the role

The Chilean Andean Altiplano (~4,000 m altitude) hosts salt-flats (salares) with varying salinities due to strong evaporitic processes in the Atacama Desert. Several of these salares contain modern microbialites, most of which remain unstudied. During recent field trips, 24 salares were sampled along a 1,100 km transect, some under geothermal influence from regional volcanic activity. Approximately one-fourth of these systems contain unstudied microbialites with diverse morphologies and textures.

This project aims to combine metabarcoding and/or metagenomic analyses of microbial diversity with mineralogy analyses and multi-scale imaging to address:

• What microbial communities compose these stromatolites, and what metabolic functions drive mineral precipitation and biosedimentary structure formation?
• What mineral-microbe interactions exist in the local hydrochemical context, and what biomineralization conditions lead to microbialite formation along evaporitic gradients?
• What traces of microbial activity and environmental conditions are recorded at micro- and mesoscales?

The goal is to model stromatolite formation based on the hydrochemical and evaporitic context of the Altiplano salares, informing understanding of lacustrine paleoenvironments and predicting future system evolution amid climate change and lithium extraction impacts.

Requirements

• Familiarity with microbial diversity, ecology, and evolution, as well as geosciences.
• Experience with molecular approaches (metabarcoding, metagenomics) and/or analytical and high-resolution microscopy for mineralogy and geochemistry is highly valued.

Work Context

This PhD is funded by the Interdisciplinary Mission of the CNRS (MITI 80Prime) and involves collaboration between two teams from laboratories affiliated with the Biology and Ecology-Environment and Physics and Earth Sciences CNRS institutes. The co-supervisors lead the DEEM – Diversity, Ecology and Evolution of Microbes (http://www.deemteam.fr/en/) and BIOMIN – Biomineralogy: history, mechanisms and applications (https://impmc.sorbonne-universite.fr/en/research_teams/biomin-biomineralogy.html) teams, which have a long-standing collaboration.

Constraints and Risks

• The PhD work follows normative security rules and does not involve major risks.
• Field trips at high altitude may be required.
• The student must adapt to working across two laboratories in the same geographic area, requiring flexibility.

Keywords: Stromatolite, metabarcoding, metagenomics, biosignatures, geomicrobiology, paleoenvironment, C sequestration, astrobiology