Microbial Characterization of a gypsum endoevaporitic ecosystem in Salar de LLamara Chile

DANIEL KURTH; MARIA CECILIA RASUK; REGINA FLORES

Rosario, Santa Fe

Congreso; IX CONGRESO ARGENTINO DE MICROBIOLOGÍA GENERAL SAMIGE; 2013

SAMIGE

Evaporites typically consist of chloride, sulfate and potassium containing minerals. They originate from the evaporation of saline water in the shallow areas of saline lakes. One of Earth?s largest evaporites is located in the Chilean central Andes. This area in the northern part of Chile is comprised of a large number of closed basins in which salares form, which are a combination of evaporite crusts and saline lakes. One of these basins is Salar de Llamara, where large domed structures of seemingly evaporitic origin can be found. In this work we performed a detailed characterization of these domes. We measured the physicochemical characteristics of the site and performed a thorough study of the microbial community. Mineralogical studies of these structures revealed gypsum (CaSO4) as a major component. Electron microscopy at different layers showed diatoms and cyanobacteria in the upper layers, with decreasing numbers at increasing depths, while mineral structures (crystals) were more abundant in the lower layers. Diversity studies were performed using 16S amplicon sequencing with 454 technology. DNA isolated from upper and lower layers, and total sample was amplified and sequenced. Upper layers showed a predominance of Chromatiales (Gammaproteobacteria), Rhodospirillales (Alphaproteobacteria), and Sphingobacteriales (Bacteroidetes). Lower layers were dominated also by Chromatiales and Rhodospirillales, and in addition, Spartobacteriales (Verrucomicrobia). Even though not abundant, Cyanobacteria were visually identified by optical microscopy. Photosynthetic pigments were detected by HPLC, being more abundant on the upper photosynthetic layer. Finally, metagenomic studies allowed a comprehensive characterization of the metabolic capacities of the community. Sequence reads covered all enzymes required for complete nitrogen and sulfur cycles. Despite its low abundance, cyanobacteria were one of the preferred nitrogen fixers, along with different classes of proteobacteria. In microbialites, carbon fixation usually depends on cyanobacteria, but in this case most reads associated to carbon fixation through Calvin-Benson pathway were affiliated to Proteobacteria and Archea. Comparison of metabolic pathways with those of marine stromatolites at Highborne Cay showed distinct pathways exclusive of this environment and a increased number of reads associated to resistance to the extreme environment at Llamara. This environment might be a rich source of novel systems to cope with extreme conditions and lead to biotechnological applications.