Detectability of biosignatures in a low-biomass simulation of martian sediments

Abstract

Discovery of a remnant habitable environment by the Mars Science Laboratory in the sedimentary record of Gale Crater has reinvigorated the search for evidence of martian life. In this study, we used a simulated martian mudstone material, based on data from Gale Crater, that was inoculated and cultured over several months and then dried and pressed. The simulated mudstone was analysed with a range of techniques to investigate the detectability of biosignatures. Cell counting and DNA extraction showed a diverse but low biomass microbial community that was highly dispersed. Pellets were analysed with bulk Elemental Analysis – Isotope Ratio Mass Spectrometry (EA-IRMS), high-resolution Laser-ablation Ionisation Mass Spectrometry (LIMS), Raman spectroscopy and Fourier Transform InfraRed (FTIR) spectroscopy, which are all techniques of relevance to current and future space missions. Bulk analytical techniques were unable to differentiate between inoculated samples and abiotic controls, despite total levels of organic carbon comparable with that of the martian surface. Raman spectroscopy, FTIR spectroscopy and LIMS, which are high sensitivity techniques that provide chemical information at high spatial resolution, retrieved presumptive biosignatures but these remained ambiguous and the sedimentary matrix presented challenges for all techniques. This suggests challenges for detecting definitive evidence for life, both in the simulated lacustrine environment via standard microbiological techniques and in the simulated mudstone via analytical techniques with relevance to robotic missions. Our study suggests that multiple co-incident high-sensitivity techniques that can scan the same micrometre-scale spots are required to unambiguously detect biosignatures, but the spatial coverage of these techniques needs to be high enough not to miss individual cellular-scale structures in the matrix.

Evaluating Biogenicity on the Geological Record With Synchrotron-Based Techniques

“…It possible to retrieve infrared spectra in absorption or emission of samples in gas, liquid or solid state, with high spectral resolutions and in a wide spectral range. Although there are several studies using conventional infrared techniques for the study of biosignatures (Guido et al, 2012; Preston et al, 2014; Gordon and Septhon, 2016; Gaboyer et al, 2017; Igisu et al, 2018; Stevens et al, 2019), there is still a lack of reference in the use of synchrotron-based FTIR (SR-FTIR) techniques for this purpose. The synchrotron-based approach has the advantage of the high flux and broad range of energy, which allows the acquisition of fast spectra with high signal-noise ratio.…”

Detecting the elemental and molecular signatures of life: Laser-based mass spectrometry technologies

“…Recent measurement campaigns demonstrate that LIMS systems not only have the measurement capabilities to analyze the elemental composition of minerals 11 , lunar regolith 12 , and meteorites 13 but can also identify putative fossil structures of micrometer dimensions embedded in a host material by monitoring elements relevant to life, such as carbon 14,15 . Measurements conducted on Martian mudstone analog material allowed the identification of the elemental signatures of single microbes that were inoculated artificially at low number density 16 . Moreover, LIMS systems, such as LAb-CosmOrbitrap 4 , have been able to successfully characterize the chemical composition of organics and tholins mixed with minerals 17,18 , making use of metal-organic clusters for identification and the high mass resolving power of Orbitrap to disentangle isobaric interferences of possible biogenic and non-biogenic molecular fragments.…”

On Topological Analysis of fs-LIMS Data. Implications for in Situ Planetary Mass Spectrometry

“…LIMS modification of this instrument has been reported to measure ppbw level trace elements and routinely measure fine chemistry from a variety of samples ( Riedo et al, 2013a ; Neuland et al, 2016 ; Wiesendanger et al, 2017 ). Moreover, a number of reports have indicated that LIMS, particularly fs-LIMS, might be applicable to the detection of faint signatures of life from microscopic inclusions ( Tulej et al, 2015 ; Wiesendanger et al, 2018 ) and low-biomass Martian analogs ( Stevens et al, 2019 ; Riedo et al, 2020 ). However, the field of study of early and primitive life remains profoundly complex ( Brasier and Wacey 2012 ; Westall et al, 2015 ; Wacey et al, 2016 ) with no single chemical criterion that can be assigned as definitive proof of biogenicity.…”

“…Reduction in performance occurs due to the strict constraints on size, power consumption, and weight of the scientific payload. Therefore, the development of new miniature instruments and analytical methods with improved capabilities is a continuously pressing issue (Li et al, 2017;Arevalo et al, 2018;Stevens et al, 2019;Wurz et al, 2020).…”