Lipid Profiles From Fresh Biofilms Along a Temperature Gradient on a Hydrothermal Stream at El Tatio (Chilean Andes), as a Proxy for the Interpretation of Past and Present Biomarkers Beyond Earth

Abstract

Hydrothermal systems and their deposits are primary targets in the search for fossil evidence of life beyond Earth. However, to learn how to decode fossil biomarker records in ancient hydrothermal deposits, we must first be able to interpret unambiguously modern biosignatures, their distribution patterns, and their association with physicochemical factors. Here, we investigated the molecular and isotopic profile of microbial biomarkers along a thermal gradient (from 29 to 72°C) in a hot spring (labeled Cacao) from El Tatio, a geyser field in the Chilean Andes with abundant opaline silica deposits resembling the nodular and digitate structures discovered on Mars. As a molecular forensic approach, we focused on the analysis of lipid compounds bearing recognized resistance to degradation and the potential to reconstruct the paleobiology of an environment on a broader temporal scale than other, more labile, biomolecules. By exploiting the lipid biomarkers’ potential to diagnose biological sources and carbon fixation pathways, we reconstructed the microbial community structure and its ecology along the Cacao hydrothermal transect. The taxonomic adscription of the lipid biomarkers was qualitatively corroborated with DNA sequencing analysis. The forensic capacity of the lipid biomarkers to identify biosources in fresh biofilms was validated down to the genus level for Roseiflexus, Chloroflexus, and Fischerella. We identified lipid biomarkers and DNA of several new cyanobacterial species in El Tatio and reported the first detection of Fischerella biomarkers at a temperature as high as 72°C. This, together with ecological peculiarities and the proportion of clades being characterized as unclassified, illustrates the ecological singularity of El Tatio and strengthens its astrobiological relevance. The Cacao hydrothermal ecosystem was defined by a succession of microbial communities and metabolic traits associated with a high- (72°C) to low-(29°C) temperature gradient that resembled the inferred metabolic sequence events from the 16S rRNA gene universal phylogenetic tree from thermophilic to anoxygenic photosynthetic species and oxygenic phototrophs. The locally calibrated DNA-validated lipidic profile in the Cacao biofilms provided a modern (molecular and isotopic) end member to facilitate the recognition of past biosources and metabolisms from altered biomarkers records in ancient silica deposits at El Tatio analogous to Martian opaline silica structures.

Immunoanalytical Approach for Detecting and Identifying Ancestral Peptide Biomarkers in Early Earth Analogue Environments

“…We validated the approach depicted above (Figure ) by screening several natural samples with a set of antibodies raised against ancestral resurrected proteins: one biofilm and three samples from different silica sinters from the El Tatio geyser field in Chile, one biofilm and one fumarole regolith sample from two hydrothermal areas in Iceland, one biofilm and two sediment samples from a hydrothermal field in New Zealand, one salt crust sample from a hypersaline perennial spring in the Canadian High Arctic, and one soil sample from a Mediterranean forest near Madrid (Spain; Table S1 and Figure S7). ,− Out of them, sample ET1 , from El Tatio geothermal field, showed positive immunodetection with anti-β-lactamase_PNCA and anti-Trx_LBCA antibodies (Figure ), the antibodies against the theoretically oldest proteins as inferred by ASR (Table ). Later, we demonstrated that analogues to peptides A and B were indeed present in the sample (Figure ).…”

“…Eleven natural samples were tested in this work, corresponding to different environments (hydrothermal, arctic, and mediterranean) and different types (silica precipitates, biofilm, salt crust, sediment, and soil). Most samples have been described elsewhere, ,− and their main features are gathered in Table S1. Crude liquid sample extracts to be analyzed by FSMI were prepared by ultrasonication and filtered (see SI, Experimental Section).…”

An Overview of Lipid Biomarkers in Terrestrial Extreme Environments with Relevance for Mars Exploration

“…The lipid biomarkers for Chloroflexi are not rare within hot spring environments. They have been identified at the Orakei Korako geothermal area in the TVZ (New Zealand) (Pancost et al ., 2005 ; Kaur et al , 2015 ), in Hveravellir (Iceland) (van der Meer et al , 2008 ) and at El Tatio Middle Basin springs (Megevand et al , 2022 ).…”

“…Still, broad distinctions such as prokaryote versus eukaryote, bacteria versus archaea, or bacteria versus algae, for example, are easily attainable (Brocks et al , 2003 ; Meyers, 2003 ; Derrien et al , 2017 ; Sánchez-García et al , 2020b ; Summons et al , 2022 ). Thus, specific lipids and their ratios in membranes may be used as biomarkers to identify organisms (Brocks and Summons, 2003 ; Willers et al , 2015 ), to study their adaptability and responses to environmental challenges (Cook and McMaster, 2002 ; Nichols et al , 2004 ; Sturt et al ., 2004 ; de Carvalho and Caramujo, 2018 ) and to disclose metabolic traits (van der Meer et al ., 2003 ; Carrizo et al ., 2022 ; Megevand et al , 2022 ).…”

“…Lipids and hydrocarbons can be extracted from environmental samples as diverse as soil (Amelung et al , 2008 ; Tinoco et al , 2018 ; Vega-García et al , 2021 ), sediment (Sánchez-García et al ., 2008 ; Carrizo et al , 2019a ), ice, snow (Nemirovskaya, 2006 ), particulate organic matter (Vonk et al , 2010 ; Okuno and Yokomizo, 2015 ), biofilms and microbial mats (Sánchez-García et al , 2020a ; Megevand et al , 2022 ), or even meteorites (Nagy, 1966 ; Sephton et al , 2001 ; Huang et al ., 2005 ).…”