Facilitation of endolithic microbial survival in the hyperarid core of the Atacama Desert by mineral deliquescence

Abstract

[1] The hyperarid core of the Atacama Desert is considered the dry limit for life on Earth. Soils in this region have very low abundance of heterotrophic bacteria and are practically barren of photosynthetic microorganisms because of the extreme dry conditions ( 2 mm a À1 rainfall). However, relatively abundant endolithic communities of cyanobacteria (Chroococcidiopsis) occur within halite crusts in paleolake evaporitic deposits. By means of continuous monitoring of the microclimate conditions (temperature, relative humidity, water vapor density, wetness, and photosynthetically active radiation) inside and around the halite crusts, we demonstrate here that water vapor condenses within the pore space of the halite at relative humidity (RH) levels that otherwise hinder the occurrence of liquid water in the surrounding environment. Water condensation occurs at RH >75%, which corresponds to the deliquescence point of halite. We have estimated a total of 57 deliquescence events (i.e., water condensation) within the halite crusts, as opposed to only 1 liquid water event outside. These wet events resulted in a total of 213.8 h of potential photosynthetic activity for the endolithic microorganisms versus only 6 h for organisms outside the halite crusts. Halite crusts may therefore represent the last available niche for photosynthetic activity in extreme arid environments on Earth.

Fluorescent Fingerprints of Endolithic Phototrophic Cyanobacteria Living within Halite Rocks in the Atacama Desert

“…However, when the RH increased to above 70%, fluorescence appeared within minutes and stabilized at relatively low, but significantly positive, values. It is significant that activation of PSII in the halite cyanobacteria did not occur until liquid water was produced through deliquescence (8) and/or water vapor condensed within the nanopores of halite (9). Hence, it seems that photosynthesis in cyanobacteria can only be activated in the presence of liquid water (50).…”

“…These cells seem to be biologically adapted to conditions of high salinity, and their presence indicates a water source other than the area's practically nonexistent rainfall. Davila et al (8) showed that water vapor condenses within the halite pinnacles at relative humidity (RH) levels that correspond to the deliquescence point of NaCl (RH ϭ 75%). More recently, it was shown that halite endoliths could obtain liquid water through spontaneous capillary condensation at a relative humidity much lower than the deliquescence RH of NaCl (9).…”

Are the Soft, Liquid-Like Structures Detected around Bacteria by Ambient Dynamic Atomic Force Microscopy Capsules?

“…As mentioned above, many divalent chlorides are deliquescent, and chlorine, which is usually incorporated in solutions in the form of chlorides, is a well-known disinfectant/antiseptic. In another field, it has indeed been recently discovered that certain microorganisms are taking advantage of the deliquescent nature of some minerals present in the Atacama Desert, the driest place on Earth, to survive in such a hostile environment (5). Finally, the use of deliquescent salts to stabilize and study ultrasmall liquid droplets on solid surfaces under normal ambient conditions, which is not possible with conventional liquids such as water or organic liquids due to almost instantaneous evaporation, could provide new avenues for the study of wetting properties at ultrasmall scales, a recently reviewed hot area in surface science (19), since liquid topography can be accurately tracked at high resolution using AFM.…”

Provision of water by halite deliquescence forNostoc communebiofilms under Mars relevant surface conditions

“…Halite, a palm sized piece, from the hyper-arid core of the Atacama Desert (Yungay region, Chile, donor Alfonso F. Davila, Davila et al 2008) have been employed in this study. For comparison, in particular for the hydration properties, very pure NaCl (Merck, 99.99%) and the smectite Ca-montmorillonite (STx, Gonzales County, Texas; source Clay Minerals Repository, 101 Geological Science Bldg., Columbia, MO 65211, USA) have been included in this study.…”

“…Because Wierzchos et al (2006) and Davila et al (2008Davila et al ( , 2013 showed that deliquescence of halite (sodium chloride) in the hyper-arid Atacama Desert provides a habitable environment, the Martian chloride deposits also might have an astrobiological potential . Möhlmann (2011) proposed temporary liquid cryobrines on Mars available as water source for biological processes.…”