Andean Microbial Ecosystems: Traces in Hypersaline Lakes About Life Origin

Geomicrobiological characterization of the evaporitic ecosystem in the hypersaline lake Laguna Verde (Andean Puna, Northwestern Argentina)

Laguna Verde's dome-shaped structures are distinctive formations within the Central Andes, displaying unique geomicrobiological features. This study represents a pioneering investigation into these structures, assessing their formation, associated taxa, and ecological significance. Through a multifaceted approach that includes chemical analysis of the water body, multiscale characterization of the domes, and analysis of the associated microorganisms, we reveal the complex interplay between geology and biology in this extreme environment. The lake's alkaline waters that are rich in dissolved cations and anions such as chloride, sodium sulfate, and potassium, coupled with its location at the margin of the Antofalla salt flat, fed by alluvial fans and hydrothermal input, provide favorable conditions for mineral precipitation and support for the microorganism's activity. Laguna Verde's dome-shaped structures are mainly composed of gypsum and halite, displaying an internal heterogeneous mesostructure consisting of three zones: microcrystalline, organic (orange and green layers), and crystalline. The green layer of the organic zone is predominantly composed of Proteobacteria, Bacteroidetes, and Cyanobacteria, while the orange layer is mostly inhabited by Cyanobacteria. The results of the study suggest that oxygenic photosynthesis performed by Cyanobacteria is the main carbon fixation pathway in the microbial community, supported by carbon isotopic ratios of specific biomarkers. This finding highlights the important role played by Cyanobacteria in this ecosystem.

Microbialite Accretion and Growth: Lessons from Shark Bay and the Bahamas

Microbialites provide geological evidence of one of Earth's oldest ecosystems, potentially recording long-standing interactions between coevolving life and the environment. Here, we focus on microbialite accretion and growth and consider how environmental and microbial forces that characterize living ecosystems in Shark Bay and the Bahamas interact to form an initial microbialite architecture, which in turn establishes distinct evolutionary pathways. A conceptual three-dimensional model is developed for microbialite accretion that emphasizes the importance of a dynamic balance between extrinsic and intrinsic factors in determining the initial architecture. We then explore how early taphonomic and diagenetic processes modify the initial architecture, culminating in various styles of preservation in the rock record. The timing of lithification of microbial products is critical in determining growth patterns and preservation potential. Study results have shown that all microbialites are not created equal; the unique evolutionary history of an individual microbialite matters.

Disentangling microstructure and environmental conditions in high-altitude Andean microbialite systems (Catamarca, Argentine Puna)

The study of microbialites development is a key tool to understand environmental pathways during deposition. We provide a detailed analysis of modern Central Andean microbialites from high-altitude lakes. The stratigraphic record of Turquesa Lake shows a significant short-term recolonization by microbialite-producing microorganisms during environmental stress. Far from a crisis paradigm, the coasts and paleocoasts of Turquesa lake exhibit three microbialitic buildups formed along different stages, providing a good study case of biological resilience of these systems in harsh environments. The MI and MII microbialite buildups occupied two paleocoasts. Both are composed of oncoids with micritic to microsparitic textures. Morphological, textural and mineralogical similarities between the two buildups suggest that they were formed at different times, but under very similar environmental conditions. The microorganisms that produced the microbialitic buildup MIII are currently colonizing the coast of this lake. The previous oncoid morphology change to a parallel micritic-spartic lamination. This remarkable changes in the microstructure can be explained by an important environmental change caused by the isolation of the Peinado Lake, and a subsequently microorganism adaptation. This microbialite structures can be proposed as an interesting modern analogue for environmental changes along the geological record.

Short-term microbialite resurgence as indicator of ecological resilience against crises (Catamarca, Argentine Puna)

Microbialite-producing microorganisms that inhabit the Puna lakes are traditionally considered constituents of fragile microsystems, unable to resist important environmental variations. Nevertheless, this region has experienced significant climatic fluctuations during the Holocene, raising the unsolved issue on how microbialite-forming systems have been able to resist these changes. Turquesa lake, located within Quaternary Peinado lake-basin (Puna), faces a hydric crisis in the last decades, which modified their physicochemical conditions. However, there has been a rapid re-establishment of the microbialite systems once the main parameters were stabilized, which allowed the establishment of three new microbialite levels in the coast and paleo-coastline. The aim of this contribution is to report for the first time microbialite levels in Turquesa lake, providing a multiscale analysis, besides an accurate study of the physico-chemical context of the lake. This new record provided us the opportunity to demonstrate the short-term resilience capacity of these microbialite-producing microorganisms to climatic changes, offering a key approach to understand analogue processes throughout Earth history.