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Laguna Tebenquiche is one of the largest waterbodies in the Salar de Atacama. The prokaryotic microorganisms inhabiting this lake are subjected to extreme conditions such as high solar radiation due to a lower barometric pressure at high altitude, extreme daily temperature fluctuations, severe changes in salinity caused by net evaporation, and high arsenic concentrations in the water owing to volcanic events. The microbial community of Laguna Tebenquiche was studied using culture-dependent and culture-independent molecular methods and more recently, metagenomic analyses. These multifarious approaches allowed determination of the prokaryotic diversity in the various microbial ecosystems comprising Laguna Tebenquiche. Here, we describe the main results from the different approaches/analyses, the most relevant results for understanding the ecology of this extreme environment, and discuss future perspectives for diversity/microbial ecological studies.

Peatlands are plant formations established in an edaphic environment, mainly organic, characterized by a water condition of permanent saturation, which works as an oasis that promotes abundant biological diversity in the arid high-altitude environment. Peatlands present cultural, environmental, and economic social relevance because they are sources of life and development for people who live in and depend on these ecosystems. These wetlands have begun to dry up, consequently leading to the loss of natural resources (flora and fauna) and damage to the ancestral rights to natural resources (including water) of indigenous communities, due to the acquisition and exploitation of water rights for non-agricultural uses (mainly mining) that are endangering the sustainability and survival of these groups. The relationship between microbial diversity and function in soil is largely unknown, but biodiversity is assumed to influence ecosystem stability, productivity, and resilience toward stress and disturbance. In this chapter, we will present the first performed approach of microbial diversity in peatland soils.

High-altitude Andean lakes (HAALs) represent unique environments on the Earth where one can study the biological chemistry of life in one of its most extreme versions. The Atacama Desert, Argentine Puna, and Bolivian Altiplano harbor hypersaline lakes where polyextremophilic Andean Microbial Ecosystems (AMEs) inhabit microbial mats, evaporitic mats, biofilms (BF), evaporites (EV), and microbialites (Mi). These AMEs have two remarkable characteristics: (i) they are the only ones in the world that inhabit areas ranging from 3100 to 4200 masl; and (ii) they are excellent modern analogues of those which populated the primitive Earth ~3 billion years ago. In this chapter, we will delve into the different kinds of AMEs present in the HAAL, their formation, structure, and their adaptation to conditions largely influenced by volcanic activity, UV radiation, arsenic content, high salinity, low dissolved oxygen content, extreme daily temperature fluctuation, and oligotrophic conditions. All of these physicochemical parameters recreate the early Earth and even extraterrestrial conditions. The relevance of studying these ecosystems does not lie only in scientific-descriptive and/or economic interest. The scientific research community has a great responsibility to address climate change. In this scenario, the AMEs could have played a key role, influencing changes that allowed the origin of aerobic life and those who have faced the great climatic events of the Earth.

Diamante Lake is located at 4589 m above sea level (m a.s.l.) inside the Galan Volcano caldera and presents extreme environmental conditions, such as high arsenic concentration (210 mg l−1), salinity, pH and UV radiation. Until 2010, most studies in the area had largely overlooked the microbial biodiversity in Diamante Lake. With the advent of high throughput sequencing, it became possible to study the microbial communities of environmental samples using metagenomic approaches. In a recent work, we discovered red biofilms forming on the surface of sedimentary rocks on the bottom of the lake containing the rare mineral gaylussite. A metagenomic analysis of these biofilms revealed a predominance of haloarchaea (>96%) over other prokaryotic or eukaryotic organisms. To thrive under the extreme conditions in the lake, these biofilms use different metabolic and physiologic strategies: (1) to avoid the arsenic uptake into the cell, this is done through highly specific phosphate transporters (Pst) and consequently, (2) to take advantage bioenergetically of the high extracellular arsenic concentration and obtain energy from arsenite oxidation and to perform anaerobic respiration of arsenate. Contrary to what could be expected, the required enzymes for these arsenic metabolisms were likely not acquired recently by the selective pressure within Diamante Lake, but rather correspond to reminiscences of primitive metabolisms that could date back to even the origins of the haloarchaea lineage billions of years ago. Diamante Lake is a unique environment in the world and represents an open window to study the evolution of life on Earth and the adaptations required to survive under the extreme conditions that prevailed on the ancient Earth and that are currently found on other planets.

While it is true that the chemistry of current life is well defined, 3.5 billion years ago, everything could have been different. Other elements may have been part of the chemical reactions that finally triggered an endless iteration with well-defined laws that gave way—and continue to give way—to the evolution of life. In this sense, arsenic could have been a key element for life back then. Its high reactivity and its abundance in the context of a reduced atmosphere could have given this element a key role, whereas nowadays it is so alien to the development of life. In this chapter, we address this question with a special emphasis on the description of one of the best natural laboratories to study early life that our planet presents: the Andean Puna.

Salar de Llamara is situated in the north of the Atacama Desert, which is the driest desert and one of the most irradiated places on Earth. Besides, its subterranean hypersaline waters contain a high content of arsenic, among other compounds such as heavy metals that are poisonous to life in the concentrations present. Despite these extreme conditions, diverse microbial communities flourish in gypsum stratified ecosystems (microbial mats and evaporitic domes).

The Salar de Atacama depression is a unique geomorphologic structure in northern Chile and is the oldest and largest evaporitic basin in that country. In the lowest region of the Atacama basin, groundwater surfaces forms a series of lakes that are exposed to the extreme conditions of the salar, including high ultraviolet radiation, low humidity, high water-column conductivity, and arsenic concentrations. Among these lakes, Laguna La Brava harbors a variety of living microbialites and microbial mats. Several studies have determined the microbial diversity and the genomic basis of the main metabolic pathways that allow these microbial ecosystems to thrive in such extreme conditions, which resemble Precambrian/Paleoproterozoic conditions. This chapter reviews the results published since these unusual ecosystems were first described 4 years ago.

Puna wetlands and salars are a unique extreme environment all over the world, since their locations are in high-altitude saline deserts, largely influenced by volcanic activity. Ultraviolet radiation, arsenic content, high salinity, and low dissolved oxygen content, together with extreme daily temperature fluctuations and oligotrophic conditions, shape an environment that recreates the early Earth and, even more so, extraterrestrial conditions. Microbes inhabiting extreme environments face these conditions with different strategies, including formation of intricate microbial communities with an increasing degree of complexity. In that way, biofilms, mats, endoevaporitic mats, domes, and microbialites have been found to exist in association with salars, lagoons, and even volcanic fumaroles in Central Andean extreme environments. They form microbial ecosystems, where light and O2 availability decrease with depth stratification, promoting functional group diversity. This microbial diversity, together with the geochemistry, may favor the precipitation of minerals. This chapter summarizes general concepts in the environmental microbiology of extreme Andean ecosystems, which are explored throughout this book.