Molecular biomarkers in the subsurface of the Salar Grande (Atacama, Chile) evaporitic deposits

Abstract

The Late Miocene-Pliocene aged hyperarid evaporitic system of Salar Grande is a unique, halite-rich sedimentary basin in the Cordillera de la Costa of the Central Andes (Chile) whose biosedimentary record is poorly understood. The persistence of hyperacidity over millions of years, the hypersalinity, and the intense UV radiation make it a terrestrial analogue to assess the potential presence of organic matter in the halite deposits found on Mars. We investigated the occurrence and distribution of biomolecules along a 100-m depth drill down to the * 9 Ma old detrital deposits topped by La Soledad Formation (ESF). We have identified two well-defined mineralogical and geochemical units by X-ray diffractometry (XRD) and ion chromatography: a nearly pure halite down to 40 m, and a detrital one down to 100 m depth. One-dimensional GC-MS and two-dimensional GC 9 GC-TOF-MS gas chromatography-mass spectrometry techniques allowed us to detect a variety of lipidic compounds (n-alkanes, n-alkanols, isoprenoids, steroids, and hopanoids), and a relative abundance of functionalized hydrocarbons (n-fatty acids or n-aldehydes), mostly in the upper halite. We also detected biopolymers and microbial markers by fluorescence sandwich-microarray immunoassays. A dominant prokaryotic origin was associated with halophile bacteria and archaea, with minor contributions of lichens, macrophytes, or higher plants. The lipidic record was also imprinted by oxic (high pristane over phytane ratios) and saline (squalane, and mono-methyl n-alkanes) signatures. The vertical abundance and distribution of biomarkers in the Salar Grande was explained by a generalized effect of xeropreservation, combined with salt encapsulation in the upper halite deposits, or with protective organics-mineral interactions in the deeper detrital unit. The results contribute to the interpretation of

Inhabited subsurface wet smectites in the hyperarid core of the Atacama Desert as an analog for the search for life on Mars

“…The dominance of the C17 chain within the low molecular-weight n-alkanes ( Fig. 6c) and the presence of branched (mostly mono-methylated) n-alkanes supported the presence of cyanobacterial sources too [77][78][79][80] , as previously described in other surface sites of the Atacama 46,80 . The detection of pristane and phytane also supports the input from surface cyanobacteria, as both isoprenoids are widely viewed as transformation products of phytol 81 .…”

“…Because these are highly recalcitrant biomolecules, able to resist decay even for billions of years 83 , and considering that the samples were collected at 40 cm depth, their presence may be potentially explained by the aerial input of allochthonous material coming from elsewhere in the distant past 30,69,80 . The aerial transport of such recalcitrant biomolecules have been described in the Atacama in places such as the neighboring Salar Grande 80 and in other www.nature.com/scientificreports/ those inhabiting surface halites 40,56,71 . The use of source-specific lipid biosignatures in these samples allowed us to elucidate the structure of the microbial community and the different carbon assimilation pathways operating in the clay-rich microenvironment.…”

Microbial Biomarker Transition in High-Altitude Sinter Mounds From El Tatio (Chile) Through Different Stages of Hydrothermal Activity

“…Inorganic anions and organic acids of low molecular weight were determined by ion chromatography in the water-extractable phase of the three sinter samples (liquid, steam, and dry), or in the water sample from New Betsy, according to previous descriptions (Parro et al, 2011a; Sánchez-García et al, 2018). Briefly, 2 g of the sinter samples and 1 ml of the water sample were sonicated (3 min × 1 min cycles) and diluted in 10 mL of deionized water; then filtered (0.22 μm GFF), and analyzed in a Metrohm 861 Advanced compact ion chromatographer (Metrohm AG, Herisau, Switzerland), using 3.6 mM sodium carbonate (NaCO 3 ) as eluent.…”

Haloterrigena sp. Strain SGH1, a Bacterioruberin-Rich, Perchlorate-Tolerant Halophilic Archaeon Isolated From Halite Microbial Communities, Atacama Desert, Chile

“…Salar Grande is a coastal endorheic basin located at the eastern slopes of the Coastal Range in northern Chile and subjected to high solar insolation and desiccation for millions of years (Sánchez-García et al, 2018). This fossil saltflat is a rich sodium chloride deposit where lithobiontic communities live inside and at the surface of halite nodules, with a surprising and still non-culturable microbial diversity (Robinson et al, 2015;Crits-Christoph et al, 2016a,b;Gómez-Silva, 2018).…”