High-Altitude Andean Lakes as a model extreme environment to study Early-Life development

FARIAS M.E.; ALBARRACÍN V.H.

COLONIA

Workshop; 11th European Workshop on Astrobiology, Planets and life: evolution and distribution; 2011

EUROPEAN ASTROBIOLOGY NETWORK ASSOCIATION (EANA)

Background. High-Altitude Andean Lakes (HAAL) are almost unexplored ecosystem of shallow lakes at altitudes from 3,000 to 6,000 m above sea level, located in the Puna-High Andes ecoregion, Northwest Argentina. Since 2002 our research group has been performing a thoughtfully characterization of their microbial communities surviving under the pressure of extreme conditions, which otherwise are very similar to the ones prevailing on the early Earth. In this work, we aim to point out the main characteristics that make the HAAL a model ecosystem for studying in vivo early-life development. Methods. From 2002 till present, twenty-four field trips to explore these pristine environments were performed. Environmental parameters were registered in each Lake that was visited. All eighteen lakes sampled were located above 3000 m at the Northwest of Argentina, covering five districts (Jujuy, Salta, La Rioja, Catamarca, Tucumán). Samples for microbial characterization and isolation were taken from different sources: shallow water, sediments, microbial mats, flamingo feces and even modern stromatolites. Microbial characterization of bacteria, archaea, fungi and cyanobacteria included phenotypic and genotypic data. The ability to grow under extreme conditions was investigated in vitro, by testing UV-B, antibiotic, arsenic and salt resistance. Results. HAAL present a number of remarkable properties for the study of extreme biological systems: (i) they are pristine and isolated with no access roads; (ii) they are distant from each other (more than 500–700 km); (iii) they are surrounded by desert; (iv) they are the habitat of enormous populations of three flamingos species that migrate among these wetlands and act as microbial dispersers; (v) due to their low latitude and high altitude, thin ozone layer and high UV irradiation are present; (vi) they are oligotrophic, resulting in deep UV penetration in the water column; (vii) they are subject to daily large temperature fluctuations (up to 35 ºC of difference between day and night); (vii) they display high salinity and high arsenic content (of geochemical origin). Even under these conditions, outstandingly diverse microbial communities have developed. Almost two-hundred extremophilic strains were isolated; being the proteobacteria and firmicutes the best represented taxonomic groups. As most isolates display resistance to multiple environmental stress conditions they can be considered as poly-extremophiles. But the distinctive feature that made the HAAL a treasure chest to study early life evolution was the recent discovery of modern stromatolites on them. The ones from HAAL´s are the only one on Earth surviving under extreme conditions and at high altitudes. Conclusion. HAAL are natural laboratories for exploring and monitoring in situ interactions between the geophysical environment and the dynamics of biodiversity. UV irradiation is without doubt the one factor given the greatest pressure on the ecology of the microbial communities thriving on these shallow lakes. Due to the fact that environmental conditions at the HAAL are similar to the ones prevailing on Early Earth, HAAL stromatolites can be considered the better modern models to study the evolution of their precambric counterparts. Keywords. Extremophiles, stromatolites, Early-Earth, biodiversity.