Geobiology of Andean Microbial Ecosystems Discovered in Salar de Atacama, Chile

Abstract

The Salar de Atacama in the Chilean Central Andes harbors unique microbial ecosystems due to extreme environmental conditions, such as high altitude, low oxygen pressure, high solar radiation, and high salinity. Combining X-ray diffraction analyses, scanning electron microscopy and molecular diversity studies, we have characterized twenty previously unexplored Andean microbial ecosystems in eight different lakes and wetlands from the middle-east and south-east regions of this salt flat. The mats and microbialites studied are mainly formed by calcium carbonate (aragonite and calcite) and halite, whereas the endoevaporites are composed predominantly of gypsum and halite. The carbonate-rich mats and microbialites are dominated by <i>Bacteroidetes</i> and <i>Proteobacteria</i> phyla. Within the phylum <i>Proteobacteria</i>, the most abundant classes are <i>Alphaproteobacteria</i>, <i>Gammaproteobacteria</i> and <i>Deltaproteobacteria</i>. While in the phylum <i>Bacteroidetes</i>, the most abundant classes are <i>Bacteroidia</i> and <i>Rhodothermia</i>. <i>Cyanobacteria</i>, <i>Chloroflexi</i>, <i>Planctomycetes</i>, and <i>Verrucomicrobia</i> phyla are also well-represented in the majority of these systems. Gypsum endoevaporites, on the contrary, are dominated by <i>Proteobacteria</i>, <i>Bacteroidetes</i>, and <i>Euryarchaeota</i> phyla. The <i>Cyanobacteria</i> phylum is also abundant in these systems, but it is less represented in comparison to mats and microbialites. Regarding the eukaryotic taxa, diatoms are key structural components in most of the microbial ecosystems studied. The genera of diatoms identified were <i>Achnanthes</i>, <i>Fallacia</i>, <i>Halamphora</i>, <i>Mastogloia</i>, <i>Navicula</i>, <i>Nitzschia</i>, and <i>Surirella</i>. Normally, in the mats and microbialites, diatoms form nano-globular carbonate aggregates with filamentous cyanobacteria and other prokaryotic cells, suggesting their participation in the mineral precipitation process. This work expands our knowledge of the microbial ecosystems inhabiting the extreme environments from the Central Andes region, which is important to ensure their protection and conservation.