Novel water source for endolithic life in the hyperarid core of the Atacama Desert

Abstract

The hyperarid core of the Atacama Desert, Chile, is possibly the driest and most abiotic place on Earth, yet endolithic microorganisms thrive inside halite pinnacles that are part of ancient salt flats. The existence of this microbial community in an environment that excludes any other life forms suggests biological adaptation to high salinity and desiccation stress, and indicates an alternative source of water for life other than rainfall, fog or dew. Here we show that halite endoliths obtain liquid water through spontaneous capillary condensation at relative humidity (RH) much lower than the deliquescence RH of NaCl. We describe how this condensation occurs inside nano-pores smaller than 100 nm, in a newly identified halite phase that is intimately associated with the endolithic aggregates. This nano-porous phase helps retain liquid water for long periods of time by preventing its evaporation even in conditions of utmost dryness. Our results explain how life has colonized and adapted to one of the most extreme environments on our planet, expanding the water activity envelope for life on Earth, and broadening the spectrum of possible habitats for life beyond our planet

Microbial diversity and the presence of algae in halite endolithic communities are correlated to atmospheric moisture in the hyper‐arid zone of the Atacama Desert

“…The air RH values often above 75% that we measured in SG and SS likely produce almost continuous deliquescence of the halites, leading, together with water condensation, to constant moisture in these salt pinnacles. In contrast, in the YG area we never recorded air RH values above 75% (Wierzchos et al, 2012b). Davila and colleagues (2008) reported only 70 h year −1 of air RH above 75% for the same area, for the period of June 2007 to July 2008.…”

“…S2) showed that air RH values never exceeded 75% during an entire year in this area; 75% RH being the critical value considered as deliquescence RH for halite (Supporting Information Fig. S2) (Davila et al, 2008;Wierzchos et al, 2012b). In contrast, in SG and SS the air RH was significantly higher than in YG, with more than 1500 and 1100 h year −1 with RH > 75% for SG and SS, respectively, indicating frequent presence of liquid water within halite pinnacles due to deliquescence (Table 1; Supporting Information Fig.…”

“…2A-C). Visualization of cryo-fixed and cryo-fractured samples was essential in observing microbial communities in their 'natural' state Wierzchos et al, 2012b) and to expose the internal structure of the halite's features ( Fig. 2D-F).…”

“…Our sampling areas were characterized by annual precipitations of less than 3 mm year −1 , but major variations in air RH differentiated the salars of SG and SS from that of YG (McKay et al, 2003;Warren-Rhodes et al, 2006;Davila et al, 2008;Wierzchos et al, 2012b). The southwest area of the Tarapacá Region, where SG and SS are located, has been described as a 'foggy environment' (Cereceda et al, 2008a,b).…”

“…The halite pinnacles are colonized by endolithic (within rocks) communities of photosynthetic cyanobacteria and heterotrophic bacteria and archaea (Wierzchos et al, 2006;de los Ríos et al, 2010). Within the pinnacles, condensation of water vapour, at relative humidity (RH) corresponding to the deliquescence point of NaCl (RH = 75%), was reported as a potential source of water for microorganisms (Davila et al, 2008;Wierzchos et al, 2012b). Deliquescence of hygroscopic salts might also be a key factor in supporting microbial life in the hypersaline subsurface of the Atacama Desert (Parro et al, 2011).…”