A High-Altitude Extremophile Haven
Salar de Uyuni is the world's largest salt flat, covering over 10,000 square kilometers at an altitude of 3,656 meters. The environment is a challenge for life. It faces intense ultraviolet (UV) radiation due to the high altitude and thin atmosphere, dramatic daily temperature shifts, and extreme dryness. The ground itself is a crust of salt, primarily halite and gypsum, overlaying a lithium-rich brine. Yet, in this poly-extreme setting, complex microbial communities thrive.
These communities are dominated by extremophiles—organisms adapted to harsh conditions. They include a variety of bacteria and archaea, particularly halophiles (salt-lovers). Researchers have identified members of the classes Halobacteria and Nanohaloarchaea, along with bacteria from the Proteobacteria and Bacteroidetes phyla. Cyanobacteria, such as those from the genus Nostoc, are also important, forming microbial mats that structure the ecosystem. These organisms cope with high salinity and UV exposure but also with high concentrations of chaotropic salts like magnesium chloride and lithium chloride, which can destabilize biological molecules.
Living Rocks and UV Shields
The visible evidence of this life is the formation of microbial mats that create stromatolite-like structures. Stromatolites are layered sedimentary formations created by the growth of microorganisms, which trap and bind sediment. The ones in Salar de Uyuni are modern versions of the ancient stromatolites responsible for oxygenating Earth's early atmosphere. The microbes, particularly cyanobacteria, precipitate minerals like gypsum and carbonates, building up layered, dome-like structures over time.
To survive the intense solar radiation, these microbes have developed several defense mechanisms. One of the most direct is using the environment itself. The salt crystals of the flat, particularly halite, physically block damaging UV rays, as a natural sunscreen for the microbial communities living within and just beneath the crust. Besides this physical shield, the microbes have biological adaptations. Many produce protective pigments. Some cyanobacteria create compounds like scytonemin, a UV-screening pigment stored in their extracellular sheath. They also produce copious amounts of extracellular polymeric substances (EPS), a slimy coating that helps retain water, protects from desiccation, and provides an additional layer of UV defense.