Endoevaporites o gypsum stromatolites? Metagenome-based study on the carbon precipitation metabolic pathways in the hypersaline lake Laguna Verde

LUIS A. SAONA; FARÍAS, MARÍA EUGENIA; CARLOS CÓNSOLE GONELLA; VILLAFAÑE, PATRICIO G.

Congreso; M-fed Conference & Workshop 2021; 2021

Numerous bodies of water located in the salt flats of the Central Andes present important evaporite deposits associated with microbial ecosystems. In them, the presence of important evaporitic dome-shaped structures, capable of forming extensive reefs, stands out. Until now there is no consensus as to the degree of microbial influence in the generation of these structures. Hence, it is difficult to classify them as microbialites, if microorganisms have participated directly in the precipitation of their mineral facies; or endoevaporites, where microbial communities are protected against desiccation and UV-B radiation by chemically precipitated mineral facies. In order to know the relationship between microbial components and mineral facies, our work studies the evaporite domes present in Laguna Verde (Catamarca, Argentina). The mineral facies that compose these domes are analyzed, and by means of metagenomic DNA sequencing, the microbial diversity is determined together with the main metabolic pathways related to the formation of these structures.Laguna Verde is located on the western margin of the Salar de Antofalla. This water body, populated by numerous evaporite dome-shaped structures, has a hypersaline composition enriched in Cl?, Na+, K+, SO42?, Mg2+ and Ca2+ ions. The domes present a heterogeneous internal structure composed of: i) Organic zone (internal), organized in layers with orange and green coloration. ii) Microcrystalline zone characterized by the alternation of micritic (CaCO3) and crystalline layers. iii) Crystalline zone (external), composed of euhedral gypsum crystals.The green layer of the organic zone is mainly composed of Proteobacteria (ca. 50%), Bacteroidetes (ca. 25%) and Cyanobacteria (ca. 18%), while the orange layer is inhabited by approximately 80% Cyanobacteria. Thus, the primary production is carried out by oxygenic photosynthetic Cyanobacteria (mostly Dactylococcopsis). The analysis of the presence and abundance of metabolic pathways reveals that aerobic photosynthesis performed by Cyanobacteria is the main carbon fixation pathway. Based on this and the microstructure we can suggest a direct biological influence on carbonate precipitation in the microcrystalline zone. Finally, the lack of microbial metabolic pathways associated with gypsum precipitation, coupled with the chemical conditions of the water, allow us to suggest that the Crystalline Zone (external) precipitated chemically. Generating in its interior favorable environmental conditions for the development of the microbial communities mentioned above.