Xeropreservation of functionalized lipid biomarkers in hyperarid soils in the Atacama Desert

Abstract

Our understanding of long-term organic matter preservation comes mostly from studies in aquatic systems. In contrast, taphonomic processes in extremely dry environments are relatively understudied and are poorly understood. We investigated the accumulation and preservation of lipid biomarkers in hyperarid soils in the Yungay region of the Atacama Desert. Lipids from seven soil horizons in a 2.5 m vertical profile were extracted and analyzed using GC-MS and LC-MS. Diagnostic functionalized lipids and geolipids were detected and increased in abundance and diversity with depth. Deeper clay units contain fossil organic matter (radiocarbon dead) that has been protected from rainwater since the onset of hyperaridity. We show that these clay units contain lipids in an excellent state of structural preservation with functional groups and unsaturated bonds in carbon chains. This indicates that minimal degradation of lipids has occurred in these soils since the time of their deposition between >40,000 and 2 million years ago. The exceptional structural preservation of biomarkers is likely due to the long-term hyperaridity that has minimized microbial and enzymatic activity, a taphonomic process we term xeropreservation (i.e. preservation by drying). The degree of biomarker preservation allowed us to reconstruct major changes in ecology in the Yungay region that reflect a shift in hydrological regime from wet to dry since the early Quaternary. Our results suggest that hyperarid environments, which comprise 7.5% of the continental landmass, could represent a rich and relatively unexplored source of paleobiological information on Earth.

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

“…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 . However, other than cyanobacterial origin, pristane can also be sourced in plants or phytoplankton 82 , and phytane can be sourced www.nature.com/scientificreports/ in archaeol, the most commonly reported core lipid in archaea 31,83 . The contribution from archaea may also be inferred from the presence of squalene and crocetane (although squalene can also be synthetized by fungi), other isoprenoids characteristically attributed to halophilic 84,85 or methanogenic/methanotrophic 85 archaea, in line with the archaeal species found by NGS sequencing.…”

Phospholipid biomarkers in Mars-analogous soils of the Atacama Desert

“…According to PCA, (1) the dominance of fatty acid hydroxylation was associated with viability ( Fig. 3b): hydroxylation-driven alteration of membrane PLFAs might suggest the rapid degradation rate of dead cells after the unprecedented rainfall (Gutteridge, 1982;Green and Scow, 2000;Wilhelm et al, 2017), which decreased the percentage of non-viable cells and concomitantly increased viability. 2The link between C16:0, C18:0, C16:1ω9 and the two environmental factors conductivity and nitrate implied that the general bacteria and Proteobacteria rich in these even-numbered PLFAs were halophilic and had nitrate metabolisms.…”

Moisture activation and carbon use efficiency of soil microbial communities along an aridity gradient in the Atacama Desert

“…The role of (hyper)arid conditions on soil OC processing vs. stabilization continues to be debated (e.g. Skelley et al, 2007;Ewing et al, 2006;Ziolkowski et al, 2013;Wilhelm et al, 2017).…”