ALBARRACIN Virginia Helena
congresos y reuniones científicas
Eu-endolithic algae developing in modern stromatolites at High- Altitude Lakes in Argentinean Puna (4,000 m asl)
MORENO J.R.; ALBARRACÍN V.H.; TONEATTI D.; FARIAS M.E.
San Miguel de Tucuman
Congreso; VII Congreso Argentino De Microbiología General SAMIGE DEL BICENTENARIO; 2011
High-Altitude Andean Lakes (HAAL) at Argentinian-Puna-High Andes (between 3,000 to 6,000 m) are exposed to extreme conditions: volcanic settings, high UV-irradiation, hypersalinity, desiccation, high pH. An outstanding microbial biodiversity has developed, most of them ordered in multi-layered sedimentary mats formed by algae, bacteria and sediments called microbialites. Within them, stromatolites are of world-wide interest as they were common in ancient marine environments but today restricted to few lacustrine and perimarine settings; i) Shark Bay in Western Australia, ii) Exuma Sound in the Bahamas, and iii) Cuatro Ciénagas basin, México. All of these locations are situated at the sea level where microorganisms cope with little or no stress conditions. In turn, in the dessertic region of Salta, Northwestern Argentina, near the border of Chile we have found characteristic stromatolite-like ecosystems laying and developing in shallow hypersaline lakes located above 4,000 metters, under the pressure of harsh conditions, very similar to the ones present in the Early´s Earth atmosphere. The aim of this work is to make the first description of extreme algae developing within modern stromatolites at Laguna Socompa (4000 masl) in Salta, Argentina, Northwest-Argentina. Samples from the stromatolites were taken aseptically and fix in situ to perform further mineral characterization by X-ray diffraction and optical and scanning electron microscopic. Socompa microbialites can be classified as typical stromatolites as the main complexing-mineral was Aragonite. They are exposed to basic conditions (pH 9) hipersalinity (8.3%), and high arsenic content (35 mg L-1). Great quantities of Silicon (450 mg/kg) and chlorophyll (70 mg/L) were present, which agreed with the fact that diatoms and cyanobacteria were abundant in the samples. Among diatoms, we could recognize different genera using both, optic and electron microscopy, i.e.: Cymbella sp., Navicula sp., Hantzschia sp., Nitzschia sp., Synedra sp., Surirella sp., Rhopalodia sp., Asterionellia sp., Eucocconeis sp., and Pinnularia sp. Filamentous and nonfilamentous cyanobacteria were represented by: Scytonema sp., Microcoleus sp. and Phormidium sp. among others. Both, bacteria and algae were agglutinated by exopolysaccharides and associated to minerals, presenting typical microboring patterns produced by bacteria. The extreme stromatolites found at the highlands are of utmost interest as they provide a model to study ecology and biogeochemistry of their Precambrian counterparts in a very similar environment to the Early Eath´s one. Further research will help to clear up the metabolic process from these algae involved in the biogenesis of the stromatolites.