The detection of microbes in Martian mudstone analogues using laser ablation ionization mass spectrometry at high spatial resolution

2019 
The detection and identification of biosignatures on planetary bodies such as Mars is extremely challenging. Current knowledge from space exploration missions suggests that a suite of complementary instruments is required for a successful identification of past or present life. For future exploration missions, new and innovative instrumentation capable for 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 micrometre scale. The aim of this study is to extend the current measurement capabilities of a miniature laser ablation ionisation mass spectrometer designed for space exploration missions to detect signatures of microbial life. In total, fourteen Martian mudstone analogue samples were investigated regarding their elemental composition. Half of 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 γ-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, sulphur, iron, etc. When an enrichment in carbon was measured in the samples but no simultaneous increase in other biologically relevant elements was detected, it suggests carbon-grain inclusions; 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.
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