Abstract
Significant progress is being made in the development of the next generation of low cost life detection instrumentation with much smaller size, mass and energy requirements. Here, we describe in situ life detection and sequencing in the field in soils over laying ice wedges in polygonal permafrost terrain on Axel Heiberg Island, located in the Canadian high Arctic (79°26′N), an analog to the polygonal permafrost terrain observed on Mars. The life detection methods used here include (1) the cryo-iPlate for culturing microorganisms using diffusion of in situ nutrients into semi-solid media (2) a Microbial Activity Microassay (MAM) plate (BIOLOG Ecoplate) for detecting viable extant microorganisms through a colourimetric assay, and (3) the Oxford Nanopore MinION for nucleic acid detection and sequencing of environmental samples and the products of MAM plate and cryo-iPlate. We obtained 39 microbial isolates using the cryo-iPlate, which included several putatively novel strains based on the 16S rRNA gene, including a Pedobacter sp. (96% closest similarity in GenBank) which we partially genome sequenced using the MinION. The MAM plate successfully identified an active community capable of L-serine metabolism, which was used for metagenomic sequencing with the MinION to identify the active and enriched community. A metagenome on environmental ice wedge soil samples was completed, with base calling and uplink/downlink carried out via satellite internet. Validation of MinION sequencing using the Illumina MiSeq platform was consistent with the results obtained with the MinION. The instrumentation and technology utilized here is pre-existing, low cost, low mass, low volume, and offers the prospect of equipping micro-rovers and micro-penetrators with aggressive astrobiological capabilities. Since potentially habitable astrobiology targets have been identified (RSLs on Mars, near subsurface water ice on Mars, the plumes and oceans of Europa and Enceladus), future astrobiology missions will certainly target these areas and there is a need for direct life detection instrumentation.
Highlights
The search for life on other solar system bodies is and will be a major focus of planetary exploration in the coming decades
Due to the stochastic nature of internet access and poor weather during the latter half of the expedition at McGill Arctic Research Station (MARS) we were only able to carry out one data transfer of a MinION sequencing run in which raw data was uplinked to the cloud-based base calling service, Metrichor (Oxford Nanopore), and the base called nucleic acid sequences downlinked back to MARS
To evaluate the accuracy of the MinION sequencing data obtained in the field, we extracted only Bacterial reads from the MinION metagenomic data sets and compared the assigned taxa with Bacterial 16S rRNA gene amplicon sequences (Illumina MiSEQ) generated from the same DNA extract used in the field with the MinION
Summary
The search for life on other solar system bodies is and will be a major focus of planetary exploration in the coming decades. The primary targets for astrobiology investigations of other solar system bodies are Mars, in the short term, as well as Europa and Enceladus, in the mid to longer term (Hays et al, 2015). The Mars Science Laboratory (MSL) mission has reported ample evidence of past fluvial, deltaic, and lacustrine environments within Gale Crater (Grotzinger et al, 2014); the recent report of surface brine water at several reoccurring slope linaea (RSL) locations on Mars (Ojha et al, 2015) opens up the possibility that extant microbial life (which would be most likely cold-adapted and halophilic) could be present at these sites and will almost certainly be the targets of future missions in the mid-2020s and beyond, including potential sample return missions. Exciting discoveries over the last 5–10 years point to the existence of cold, salty oceans under the ice covers of Europa and Enceladus (Kargel et al, 2000; Melosh et al, 2004; Waite et al, 2006; McKay et al, 2008; Roth et al, 2014) which could support extant microbial ecosystems based on our knowledge of similar salty cryoenvironments on Earth (Goordial et al, 2013)
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