Refining the ‘biosignature’ concept : An experimental investigation of the evolution of mineral surfaces upon bioalteration

Quantifying the contribution of microbes to rock dissolution rates is currently considered as one of the main challenges to improve numerical models of rock alteration. This process is particularly important since it contributes to the geochemical cycles of most chemical elements, and partly controls atmospheric CO2 uptake and Earth’s climate over geologic timescales. Defining the imprints left by microorganisms at the surface of altered minerals resulting from bioalteration appears as a prerequisite to shed new lights on this contribution, as well as for defining biogenicity criteria that are requested for the search of life in the geological record on Earth and beyond. Recently, we showed that calcite alteration mediated by cyanobacteria can be detected using statistical characterizations of nanoscale surface roughness. To get a more general picture of the systematic imprints left by microorganisms upon bioalteration, we are now interested in exploring the changes in surface properties (and especially, microtopography) associated with the bioalteration of minerals using microbial consortia. In the present project, we propose to investigate the impact of microbial consortia including siderophore-producing bacteria on the surface microtopography of calcite. Experiments will be conducted either under sterile conditions or with microbial consortia, and the reactivity and surface microtopography will be characterized through a combination of microscopy techniques (atomic force microscopy, vertical scanning interferometry, epifluorescence microscopy, transmission electron microscopy). Such characterizations will provide a baseline for the subsequent development of models of mineral surface evolution, which may be ultimately used to predict the patterns that are expected to be associated with bioalteration in the field. The work will mainly take place at ISTerre in Grenoble, with several visits to IMPMC (Paris) covered by the project expected over the course of the internship. To lead this project, the candidate must have skills in microbiology (e.g., bacterial cultivation) ; additional knowledge with setting-up fluid-mineral interaction experiments would be a plus. This internship is intended to be continued by a PhD thesis funded by the ERC project Mobidic (2021-2026).