Modern stromatolite ecosystems at alkaline and hipersalyne high-altitude lakes at the Argentinean Puna

FARÍAS, MARIA EUGENIA; POIRÉ DANIEL GUSTAVO; ARROUY, MARIA JULIA; ALBARRACÍN VIRGINIA HELENA

Stromatolites: interaction of microbes with sediments

Springer

Año: 2011; p. 1 - 745

High-Altitude Lakes at the northwest of Argentina in the Puna and Andean regions (HAAL), are considered extreme environments of biotechnological interest (Fig. 1; Seufferheld et al., 2008). The HAAL ecosystems are almost unexplored systems of shallow lakes formed during the Tertiary geological period, distributed in the geographical area called the Puna at altitudes from 3,000 to 6,000 m above sea level. Most of these wetlands are completely isolated, experience a wide daily range in temperatures (40 ºC), are slight saline to hypersaline, and are subject to low phosphate availability and to high intensity of solar UV-B radiation. The HAAL ecosystems are unique not only for their geographical characteristics and broad range of extreme environments but also for their abundant biodiversity. The microbial communities that have evolved within these high-altitude aquatic ecosystems tolerate chemical and physical stresses such as wide fluctuations in daily temperatures, hypersalinity, and variable pH and have proved to be adapted to high levels of UV radiation, a low level of nutrient availability, and high concentrations of heavy metals, especially arsenic (Demergaso et al., 2004; Ferrero et al., 2004; Escudero et al., 2007; Fernandez Zenoff et al., 2006; Zenoff et al., 2006; Dib et al., 2008; 2009a, 2009b; Ordoñez et al., 2009; Flores et al., 2009; Farías et al., 2009). The high altitude and low latitude geographical position of the HAAL expose the indigenous extremophilic communities to high solar irradiance (i.e. 165% higher than at sea level) with instantaneous UV-B flux reaching 17 Wm-2; UV-flux is twice the amount of present-day equatorial Mars, while UV-B is half the amount on Mars. Hence, these environments have been proposed for prospection studies on astrobiology (Farias et al., 2009). So far these outstanding microbial diversity and resistance mechanisms to extreme factors have been described in most Lakes at these locations, i.e. Laguna Azul, Laguna Verde, Laguna Negra, Laguna Vilama, Laguna Aparejos, Laguna Chaxas (Fernandez Zenoff et al., 2006; Zenoff et al., 2006; Dib et al., 2008; 2009a, 2009b; Ordoñez et al., 2009; Flores et al., 2009; Farías et al., 2009). Nevertheless, there has been no studies nor description on two interesting hypersaline lakes located near the border with Chile: i.e. Laguna Socompa and “Sea Eyes” at Tolar Grande (Fig. 2). Yet, these environments due to their high salinity content (Table 1) present a great potential to harbour modern stromatolite-like ecosystems and deserve further studies. Stromatolites—internally-laminated, macroscopic sedimentary structures, commonly of biological origin—form the dominant part of Earth’s early fossil record and so provide a potentially important source of information about early life. The oldest examples of these preserved formations are more than 3 billion years old and are found mainly in Western Australia and South Africa (Lowe, 1980; Walter et al., 1980; Byerly et al., 1986). Recent studies have reflected a widespread and growing acceptance of the oldest stromatolites from the Pilbara region of Western Australia as biogenic (Allwood et al., 2006). However, stromatolites are shaped by a complex interaction of physical, chemical, and biological processes, and identifying unambiguous signatures of life from the preserved morphology of the structures can be extremely difficult (Poire et al 2004). Modern stromatolites provide a way to study all these process in a “in vivo” approach and, in this sense, are of ulmost importance to give insights on the ecology and biogeochemistry of their Precambrian counterparts and to understand how Earth and its early biosphere may have co-evolved (Goh et al., 2009, Baumgartner et al, 2009). Modern stromatolites have been so far recorded i) an hypersaline region of Hamelin Pool, Shark Bay in Western Australia (Goh et al., 2009), ii) shallow subtidal regions at the margin of Exuma Sound in the Bahamas (Foster et al., 2009), iii) fresh-water areas at the Cuatro Ciénagas basin in Mexico (Desnues et al., 2008); and iv) Yellowstone Hot Spring (Lau et al., 2005). All of these locations are situated at the sea level where microorganisms cope with little or no stress conditions. In turn, in the dessertic region of Salta, Northwestern Argentina, near the border of Chile we have found characteristic stromatolite-like ecosystems laying and developing in shallow hypersaline lakes located above 4,000 metters, under the pressure of harsh conditions, very similar to the ones present in the Early´s Earth atmosphere (Belluscio, 2009). The aim of this work is to make the first description of extreme living stromatolites surviving above 4,000 metters at Laguna Socompa. The environment, morphological description, preliminary biological and mineralogical composition of these new modern stromatolites are presented in this study.