Periodic Reporting for period 1 - NanoBioS (Nanoscale mineral-microbial interactions, associations, and biosignatures in gypsum stromatolites)
Période du rapport: 2021-10-01 au 2023-09-30
Gypsum microbialites and microbial-rich gypsum formations occur in drylands worldwide as a result of the interplay of diverse microorganisms with the geochemical parameters of the evaporitic setting in which they grow. Owing to ongoing climate change and desertification currently affecting over 45% of exposed land, such evaporitic ecosystems will dramatically expand. Yet, at present, they remain largely unexplored. In particular there is very little information about: i) which microorganisms are hosted in gypsum microbialites and if they include novel divergent microbial lineages, ii) what is the exact role of microorganisms in sulfur cycling in evaporitic systems, iii) which microbial traces and mineral-microbial associations can be preserved in fossil gypsum stromatolites, and how to differentiate them from inorganic biomorphs. NanoBioS aimed to address these questions by employing a multidisciplinary approach making use of advanced microbiology and mineralogy tools, to study the gypsum microbialites from the newly explored salt-lakes of the drylands of Ethiopia. The overarching goal of this project was to shed light on biogeochemical sulfur cycling in extreme evaporitic ecosystems as well as, to develop insights for distinguishing traces of microbial-mineral interactions and other biosignatures on Earth and Martian chemical sediments.
To achieve our research objectives we studied various lakes and their associated gypsum microbialites, examining their hydrochemical, isotopic, and mineralogical features to comprehend the diverse conditions influencing their formation. Distinct patterns emerged: moderate salinity lakes featured mineralizing microbial mats transitioning into stromatolites, while hypersaline lakes hosted endolithic communities within gypsum formations.
Sulfur isotope measurements unveiled insights into the origin of sulfur in these formations, pointing to abiotic processes involving seawater mixing with hydrothermal brines. Geochemical analysis indicated an enrichment of gypsum formations in specific elements and revealed a diverse array of mineral phases associated with these stromatolites, encompassing gypsum, anhydrite, smectites, brushite, pyrite, iron-monosulfides, halite, sylvite, and amorphous silica.
Microbial diversity and structure analysis showed different dominant phyla in the microbialites of moderate salinity and hypersaline lakes. Taxon-based metabolic predictions indicated the presence of sulfur metabolizing microorganisms, such as anoxygenic photosynthetic bacteria in the moderate salinity formations and sulfate reducing bacteria in the hypersaline endolithic communities. Metagenomic analysis confirmed these results identifying the principal clades that harbour genes for the oxidation of sulfur compounds and for sulfate reduction. These results are indicative of the active sulfur cycling within these microbialites, affecting gypsum mineral precipitation and dissolution.
Microscopic investigations indicated detailed associations between microbial communities and minerals within the stromatolites, showing abundant microbial presence among gypsum crystals and their association with specific mineral phases. Synchrotron-based techniques provided insight into nanoscale mineral phases linked to microbial relics, confirming the diverse sulfur species present in the stromatolites and corroborating the active biologic sulfur cycling in these environments. Finally, statistical analyses revealed correlations between microbial community composition, metabolic functions related to sulfur, and environmental factors like salinity and sulfur isotopic composition. These results have already been presented in three international conferences, two workshops and three invited talks while they are included in at least two manuscripts in preparation. In addition, the overarching goal of this MSCA project and its broader implications have been presented in science communication talks in secondary schools and in science festivals.
Sulfur isotope measurements unveiled insights into the origin of sulfur in these formations, pointing to abiotic processes involving seawater mixing with hydrothermal brines. Geochemical analysis indicated an enrichment of gypsum formations in specific elements and revealed a diverse array of mineral phases associated with these stromatolites, encompassing gypsum, anhydrite, smectites, brushite, pyrite, iron-monosulfides, halite, sylvite, and amorphous silica.
Microbial diversity and structure analysis showed different dominant phyla in the microbialites of moderate salinity and hypersaline lakes. Taxon-based metabolic predictions indicated the presence of sulfur metabolizing microorganisms, such as anoxygenic photosynthetic bacteria in the moderate salinity formations and sulfate reducing bacteria in the hypersaline endolithic communities. Metagenomic analysis confirmed these results identifying the principal clades that harbour genes for the oxidation of sulfur compounds and for sulfate reduction. These results are indicative of the active sulfur cycling within these microbialites, affecting gypsum mineral precipitation and dissolution.
Microscopic investigations indicated detailed associations between microbial communities and minerals within the stromatolites, showing abundant microbial presence among gypsum crystals and their association with specific mineral phases. Synchrotron-based techniques provided insight into nanoscale mineral phases linked to microbial relics, confirming the diverse sulfur species present in the stromatolites and corroborating the active biologic sulfur cycling in these environments. Finally, statistical analyses revealed correlations between microbial community composition, metabolic functions related to sulfur, and environmental factors like salinity and sulfur isotopic composition. These results have already been presented in three international conferences, two workshops and three invited talks while they are included in at least two manuscripts in preparation. In addition, the overarching goal of this MSCA project and its broader implications have been presented in science communication talks in secondary schools and in science festivals.
Here we report on the geomicrobiology and biogeochemistry of gypsum microbialites from the drylands of the Danakil depression in Ethiopia. These fragile, evaporitic ecosystems were explored and studied for the first time in the framework of NanoBioS. Among the different gypsum microbialites we encountered, we discovered true gypsum stromatolites in Bakili lake, analogous to the carbonate ones, being one of the very few occurrences of modern gypsum stromatolites globally. Nonetheless, the originality of the NanoBioS is not only related to the topic itself, but also to the methodology/techniques that were employed here. To address our research questions we applied a novel, interdisciplinary approach, combining expertise and techniques from molecular biology and phylogeny, geochemistry, nanomineralogy, and material science. This was achieved using state-of-the-art DNA metabarcoding and metagenomics, aside to SR-based tools/ TEM and multiple sulfur isotopes for the combined microbiological and mineralogical characterization of the gypsum microbialites. Given no such investigation has been previously performed for the study of gypsiferous microbialites and sediments in general, we aspire that these results will provide new insights on i) biologic sulfur cycling in extreme evaporitic ecosystems, ii) the role of the microbial communities in gypsum precipitation/dissolution, iii) biosignatures detection in gypsiferous deposits of Earth & Mars.