Search

The Atacama Desert (Chile), one of the most arid places on Earth, shows hostile conditions for the development of epilithic microbial communities. In this study, we report the association of cyanobacteria (Chroococcidiopsis sp.) and bacteria belonging to Actinobacteria and Beta-Gammaproteobacteria and Firmicutes phyla inhabiting the near surface of salt (halite) deposits of the Salar Grande Basin, Atacama Desert (Chile). The halite deposits were investigated by using optical, confocal and field emission scanning electron microscopes, whereas culture-independent molecular techniques, 16S rDNA clone library, alongside RFLP analysis and 16S rRNA gene sequencing were applied to investigate the bacterial diversity. These microbial communities are an example of life that has adapted to extreme environmental conditions caused by dryness, high irradiation, and metal concentrations. Their adaptation is, therefore, important in the investigation of the environmental conditions that might be expected for life outside of Earth.

At El Tatio hydrothermal field, located at more than 4,200 meters above mean sea level in the Andean Cordillera (Chile), massive and poorly coherent pyroclastic, rhyolitic ignimbrites make up most of the local substrate. In these rocks, light colored amorphous silica precipitated to form different types of deposits at geyser vents and, also, during the digression of braided streams departing from hot spring pools. The rapid sinter precipitation enabled the preservation of a variety of biotic and abiotic features along beds and margins of the streams in deeply weathered ignimbrites. Biofilms and filamentous communities provided a favorable substrate for silica precipitation and, together with the adhesive properties of diatom mucilage and other mineral precipitation, also played a primary role for holding together a porous and brittle ignimbrite rock. Optical and scanning electron microscopies associated with molecular methods based on the amplification and sequencing of small subunit (SSU) rRNA genes were carried out for a comparative evaluation of the microbial diversity associated with the silicified structures. The comparative study of the microbial diversity and the taphofacies preserved at El Tatio has allowed us to define some of the interactions between colloidal silica and microbes in a hydrothermally-influenced environment that, because of the high altitude, undergoes intense ultraviolet radiation and surface oxidation processes.

The Salar de Atacama, located in Northern Chile, is a wide salt flat that is characterized by several salt lakes, which are locally called lagunas. The Laguna de la Piedra is one of the salt lake systems that is located in the northernmost sector of the Salar de Atacama. The present paper examines some physicochemical properties of the Laguna de la Piedra as well as the microbial diversity of the evaporite deposits. Under extreme desiccation and ambient UV flux, the evaporite deposits can create favorable endolithic microniches for the development of microorganisms. In the Laguna de la Piedra these deposits host a variety of halophilic microorganisms, which were investigated by using an optical and environmental scanning electron microscope (ESEM) as well as molecular diversity studies based on the small subunit ribosomal (SSU) rRNA of Bacteria, Archaea and Eucarya.We detected a single phylotype of halophilic archaea and a oxytrichid ciliate.Within the bacteria, a variety of Cyanobacteria, Bacteroidetes, Alpha-, Beta- and Deltaproteobacteria, as well as members of the candidate division TM6, were identified.

Evaporite accumulations produced by artesian waters in the arid zones of southern Tunisia led to the formation of subrounded, gypsiferous mounds consisting of irregular alternations of mineral precipitates and aeolian sand. The joint occurrence of gypsum crusts and plant colonization determined the stabilization of their top surface. Careful examination of the pigmented (green-brown) crusts revealed endolithic microbial communities just below the surface. In previous optical and scanning electron microscope studies cyanobacteria were the dominant component of these communities. Molecular diversity studies based on small subunit ribosomal RNA (SSU rRNA) gene analysis revealed that Flavobacteria, Actinobacteria, Deinococcales, Alpha- and Gamma- Proteobacteria are also important components of the microbial assemblage. Their pigment analyses, determined by high performance liquid chromatography (HPLC), detected the presence of carotenoids and chlorophyll (chl) a and b. Microbial communities that produce pigme...