The Detection of Elemental Signatures of Microbes in Martian Mudstone Analogs Using High Spatial Resolution Laser Ablation Ionization Mass Spectrometry

Abstract

The detection and identification of biosignatures on planetary bodies such as Mars in situ is extremely challenging. Current knowledge from space exploration missions suggests that a suite of complementary instruments is required in situ for a successful identification of past or present life. For future exploration missions, new and innovative instrumentation capable of high spatial resolution chemical (elemental and isotope) analysis of solids with improved measurement capabilities is of considerable interest because a multitude of potential signatures of extinct or extant life have dimensions on the micrometer scale. The aim of this study is to extend the current measurement capabilities of a miniature laser ablation ionization mass spectrometer (LIMS) designed for space exploration missions to detect signatures of microbial life. In total, 14 martian mudstone analogue samples were investigated regarding their elemental composition. Half the samples were artificially inoculated with a low number density of microbes, and half were used as abiotic controls. The samples were treated in a number of ways. Some were cultured anaerobically and some aerobically; some abiotic samples were incubated with water, and some remained dry. Some of the samples were exposed to a large dose of g radiation, and some were left un-irradiated. While no significant elemental differences were observed between the applied sample treatments, the instrument showed the capability to detect biogenic element signatures of the inoculated microbes by monitoring biologically relevant elements, such as hydrogen, carbon, sulfur, iron, and so on. When an enrichment in carbon was measured in the samples but no simultaneous increase in other biologically relevant elements was detected, it suggests, for example, a carbon-containing inclusion; when the enrichment was in carbon and in bio-relevant elements, it suggests the presences of microbes. This study presents first results on the detection of biogenic element patterns of microbial life using a miniature LIMS system designed for space exploration missions.

Current Progress in Femtosecond Laser Ablation/Ionisation Time-of-Flight Mass Spectrometry

“…In recent studies, the capabilities of fs-LMS to identify bio-organic material within geological samples were investigated in the context of instrument selection for the next planetary missions [33]. In total, 14 Martian mudstone analogue samples were investigated regarding their elemental composition.…”

“…The mass spectrometric analysis of these data allows for complex correlation analyses between isotopes and elements leading to improved quantification and identification of molecular parent compounds, and their location within the sample volume. These interesting new features can be of importance in analysing highly heterogeneous materials, including micrometre-sized mineralogical grains or identifying extant or fossilised microorganisms within rocks and soils [28,[32][33][34][35].…”

Planetary Mass Spectrometry for Agnostic Life Detection in the Solar System

“…Elemental distribution of biogenic elements or molecules at micron scales can be detected using techniques such as LDI-MS or SIMS. For example, Riedo et al (2020) was able to distinguish biologically relevant elements, such as H, C, S, N, P, and Fe, between microbial life and its mineral matrix in a biologically-spiked Mars analog sample via a high spatial resolution LDI-MS. Similarly, Tulej et al (2015) was able to study the elemental composition of Terran-based natural samples using LDI-MS, and used the information to distinguish the differences between microfossils and mineral matrix background.…”

“…Larger molecules have also been investigated using MS imaging, such as the characterization of lipid biomarkers in modern microbial mats and fluid inclusions using a TOF-SIMS (Siljeström et al, 2010;Leefmann et al, 2013). The spatial resolution of MS imaging approaches such as MALDI have typically been on the order of 10 s of microns (Cornett et al, 2007;Riedo et al, 2020), implying the requirement of multicellular structures to ensure biological detection, but advances in matrix application has allowed for 1.4 µm resolution in a study of metabolite, lipid, and peptide arrangements (Kompauer et al, 2017). As MS imaging resolution continues to improve toward that of a single microbial cell, the approach will gain relevance in an astrobiological context, where single-cell detection is a priority.…”

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.…”