Effects of Oxygen-Containing Salts on the Detection of Organic Biomarkers on Mars and in Terrestrial Analog Soils

Abstract

The detection of chlorinated hydrocarbons by Curiosity on Mars has been attributed to the presence of unidentified indigenous organic matter. Similarly, oxychlorines on Earth have been proposed to be responsible for the apparent lack of organics in the Atacama Desert. The presence of perchlorate (ClO 4 -) poses a unique challenge to the measurement of organic matter due to the oxidizing power of oxychlorines during commonly used pyrolysis-gas chromatography-mass spectrometry (py-GC-MS) methods. Here, we show that perchlorates and other oxyanion salts inhibit the detection of organic compounds, but that removing these problematic species prior to pyrolysis by using an optimal sample extraction duration and suitable ratios of water to sample mass enables analysis. We have characterized leached and unleached samples containing perchlorates from the Atacama Desert and have found that after leaching, the py-GC-MS chromatograms of the dried mineral residues show identifiable biomarkers associated with indigenous cyanobacteria. Samples which were pyrolyzed without leaching showed no detectable organic matter other than background siloxane and very weak or no trace of detectable polychlorinated benzenes Dried sample residues remaining after leaching, the mineral matrix and water-insoluble organic matter, showed a strong organic response in all cases when analyzed by py-GC-MS. These residues are most likely the product of the pyrolysis of water insoluble organics originally present in the samples. In addition, our results imply that previous soil analyses which contained high levels of oxyanions and concluded that organics were either not present, or at extremely low levels, should be re-examined.

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

“…Similar results were reported for several members of the family Halobacteriaceae which were resistant to perchlorate when growing in a NaCl-based medium (Oren et al, 2014). Evidence of perchlorate at saline soils in Yungay, at the hyperarid core of Atacama, and its oxidative effects on organic matter, has been recently reported by Montgomery et al (2019); then, tolerance to perchlorate was investigated in strain SGH1, considering that it is the first extremely halophilic archaeon isolated from halite communities. Haloterrigena sp.…”

“…Chloride and perchlorate salts form brines and hydrates at a lower relative humidity level (Gu et al, 2017;Jia et al, 2018). Perchlorate salts are present in Mars soils as well as at the Atacama Desert, and microbial growth in the presence of these salts has important metabolic and astrobiological implications (Jackson et al, 2015;Gu et al, 2017;Jia et al, 2018;Laye and DasSarma, 2018;Vega et al, 2018;Montgomery et al, 2019;Nazarious et al, 2019). Perchlorate reduction has been well-studied in Bacteria representatives, but perchlorate metabolism has expanded to the Archaea domain after studies on Archaeoglobus fulgidus strains and other haloarchaea (Liebensteiner et al, 2013;Oren et al, 2014).…”

ORIGIN: a novel and compact Laser Desorption – Mass Spectrometry system for sensitive in situ detection of amino acids on extraterrestrial surfaces

“…Past space exploration missions have focused on detecting biomolecules on Mars and Saturn's moon Titan [3][4][5] , albeit without success. Under the premise that life exists or has existed on extraterrestrial bodies, current instruments, such as pyrolysis gas chromatography-mass spectrometry (pyr GC-MS), struggle with the detection of the biosignatures, partly due to the presence of (chloride) salts and minerals [6][7][8][9][10][11] . To continue the search for molecular biosignatures 1,2 , novel and robust life detection instruments and measurement techniques are important.…”

The Complex Molecules Detector (CMOLD): A Fluidic-Based Instrument Suite to Search for (Bio)chemical Complexity on Mars and Icy Moons

“…Goals and challenges of biomarker detectors in space exploration. The instrumentation deployed on planetary exploration missions for the detection of organic molecules (only on Mars, so far) has been primarily based on the analysis of heat-extracted volatile compounds (GC/ MS) (Klein et al, 1976;Cannon et al, 2012;Ming et al, 2014), a methodology that, due to its limited sensitivity, may be blind to the presence of low levels of organics (Navarro-González et al, 2006;Montgomery et al, 2019). We note, however, that SAM and MOMA have a nonpyrolysis mode, that is, derivatization with MTBSTFA.…”