Biogeochemical determinants of microbialite formation – Microbialites

To meet our objectives, we combine a variety of methods including genomic, metagenomic and metatranscriptomic analysis of microbial communities, chemical, isotopic and mineralogical analyses as well as high-resolution observation of microbialites and multivariate statistical analyses.

Our first results comprise:

- The identification, genome reconstruction and analysis and metabolic potential inference for Lithoflexus mexicanus, a new potentially biomineralising quasi-clonal species of Chloroflexi identified at different depths in Alchichica microbialites that carries out anoxygenic photosynthesis (Saghaï et al, Genome Biol Evol, 2020)

- The identification of a “core microbiome” shared by microbialite-associated microbial communities from 10 different Mexican lakes (Iniesto et al, Environ Microbiol, in press)

- The alkalinity of Mexican lakes harbouring microbialites correlates with their abundance and massiveness, which allows putting forward a scenario of chemical evolution for these lakes in parallel to that of the abundance, mineral and chemical composition of microbialites (Zeyen et al, submitted).

Near future perspectives:
- Finish the detailed characterization of samples collected during our field trip to Mexico in 2019 (chemistry, mineralogy, isotopes)
- Progress in ongoing comparative metagenomic and metatranscriptomic work
- Initiate comparative analyses with microbialites collected in Sardinia coastal lagoons
- Comparative analysis and building up a synthetic model about microbialite formation

Peer-reviewed articles:

1. Saghaï A, Zivanovic Y, Moreira D, Tavera R, López-García P (2020) A novel microbialite-associated phototrophic Chloroflexi lineage exhibiting a clonal pattern along depth. Genome Biol Evol, 12: 1207–1216

2. Iniesto M, Moreira D, Reboul G, Deschamps P, Benzerara K, Bertolino P, Saghaï A, Tavera R, López-García P. Core microbial communities of lacustrine microbialites sampled along an alkalinity gradient. Environ Microbiol, in press.

3. Integrative analysis of the mineralogical and chemical composition of modern microbialites from ten Mexican lakes: what do we learn about their formation? Nina Zeyen, Karim Benzerara, Olivier Beyssac, Damien Daval, Jérôme Gaillardet, Christophe Thomazo, Rosaluz Tavera, Purificación López-García, David Moreira and Elodie Duprat. Submitted

Séminaires/conférences/communications: 2 international, 7 national

Outreach:
- 5 lectures/courses
- Participation to the documentary ‘Et si la Terre était unique ?’ by L. Lichtenstein partly filmed during our Mexican expedition in 2019 - www.francetvpro.fr/france-5/communiques-de-presse/et-si-la-terre-etait-unique-41196103

Stromatolites and, more generally, microbialites are organosedimentary structures formed under the influence of phylogenetically and functionally diverse microbial communities in interaction with abiotic factors. They are C reservoirs (as biomass and carbonates). Fossil stromatolites represent the oldest undisputed evidence of life on Earth (~3.7 Ga). Yet, the specific identity and functions of associated microorganisms and the local environmental conditions resulting in their formation are poorly understood. We propose an interdisciplinary project at the geology-chemistry-biology interface to decipher the formation process of modern microbialites from the nanoscale to the macroscale. We will combine different types of analyses (‘omics’ methods, (cryo)microscopy, morphology, mineralogy, isotopes) to culture-based carbonatogenesis experiments and natural microbialites from freshwater systems (Mexican crater lakes) to identify common determinants of microbialite formation.