Lipid biomarkers reveal metabolic heterogeneity in Antarctic cryptoendolithic communities: implications for astrobiology - Research data

Description

We investigate lipid biomarkers (linear and branched hydrocarbons, n-alkanols, sterols, saturated and unsaturated fatty acids) in cryptoendolithic communities inhabiting Beacon Supergroup sandstones collected from four sites in Victoria Land, Antarctica. Total lipid extracts were obtained by accelerated solvent extraction, fractionated, and analyzed by GC-MS. Despite low total organic carbon contents, different lipid patterns were detected. Battleship Promontory and Linnaeus Terrace showed higher abundances of short-chain n-alkanes, n-alkenes, unsaturated fatty acids, ergosterol, and PUFAs, consistent with relatively active or recently active microbial communities and reflecting diverse environmental conditions. Overall, results demonstrate that lipid biomarkers can capture both recent biological activity and long-term molecular preservation in Antarctic cryptoendolithic systems and act as robust indicators of microbial habitability and biosignature preservation in extraterrestrial analog environments. Timber Peak exhibited lipid patterns indicative of transitional or mummified communities, whereas Mt. Fleming was characterized by lower organic carbon, scarce unsaturated compounds, and a predominance of stable saturated lipids, suggesting highly degraded or fossilized microbial remains.

Steps to reproduce

SAMPLE COLLECTION AND PREPARATION Rocks were collected using a sterile hammer and chisel, placed in sterile bags, stored and transported at -20 °C, then subsampled into ~ 5 cm3 fragments using a sterile hammer and covered in sterilized aluminum foil and kept frozen until analysis. Before analysis, samples were ground in a Retsch RM200 mortar grinder. SAMPLE PROCESSING Samples were extracted using a Dionex 350 Accelerated Solvent Extraction (ASE) system with stainless steel extraction cells (22 mL) from Thermo Scientific (Waltham, MA, USA). A cellulose filter was placed in a 22 mL cell prior to loading with 10 g of powdered sample dispersed with pre-conditioned diatomaceous earth (heated to 400 °C for 4 h). Samples were then spiked with internal standards. Extraction cells containing the blank were filled only with diatomaceous earth. Anhydrous sodium sulfate was added for residual water retention. DCM/MeOH (93:7, v/v) was used as an extraction solvent mixture, as reported in Carrizo et al. (2019, 2020), and three extraction cycles were performed at 100 °C and 1500 psi (Quenea et al., 2012). The extracts were concentrated to ~2 mL under a gentle stream of nitrogen at 23 °C. Extracts were separated in three fractions using a Pasteur pipette pre-packed with glass wool and ~0.5 g of Alumina (Al2O3) and preconditioned with two volumes of Hex:DCM (9:1) by eluting with 3.5 mL of Hex:DCM (9:1) (F1, hydrocarbons), followed by 3 mL of DCM (F2, alcohols and sterols) and 4 mL of MeOH (F3, fatty acids). F1 was concentrated to ~100 μL, while F2 and F3 were evaporated to dryness, then underwent trimethylsilylation (100 μL DCM+100 μL BSTFA, 1 hour at 70 °C) and methylation (2 mL of 0.5 M HCl in MeOH, 2 hours at 80 °C; +1 mL of milliQ water, extracted 3 times with 1 mL Hex, dried with Na2SO4), respectively. SAMPLE ANALYSIS All fractions were analyzed by GC-MS (Agilent Technologies 7890 GC + 5975C single quadrupole MSD, using a HP-5MS column (60 m × 0.25 mm i.d. × 0.25 μm film thickness) with He as a carrier gas at 1.1 mL min−1. For F1, the oven temperature was programmed at 50 °C for 5 min then 10 °C/min to 275 then 18 °C/min to 315 °C (held 20 min) and post run of 15 min. For the F2, the oven temperature was programmed from 70 °C to 130 °C at 10 °C/min, then 5 °C/min to 300 °C and held for 20 min and a post run of 10 min. For F3, the oven temperature was programmed at 100 °C for 3 min, then 10 °C/min to 180 °C and to 300 °C at 5 °C/min (held 5 min) and a post run of 15 min. The injector temperature was 290 °C, the transfer line 300 °C, the quadrupole 150 °C and the MS source 230 °C. The instrument was operated in selected ion monitoring (SIM) mode.

Institutions

• National Research Council

  Lazio, Rome
• Ca' Foscari University of Venice

  Veneto, Venice
• Agenzia Spaziale Italiana

  Lazio, Rome
• Università degli Studi della Tuscia

  Lazio, Viterbo
• Deutsches Zentrum für Luft- und Raumfahrt e. V. (DLR)

  North Rhine-Westphalia, Cologne
• University of Potsdam

  Brandenburg, Potsdam

Categories

Funders

• Agenzia Spaziale Italiana

  Lazio, Rome

  Grant ID: 2018-6- U.0

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