Abstract
As human exploration missions to Mars are on the horizon, microbial cross-contamination remains a key issue to address. These issues can be approached today using advances in molecular metagenomics methods, which include rapid and sensitive sequencing platforms for characterizing microbial populations. Combined with analog missions, these methods provide powerful tools for assessing the challenges associated with planetary exploration. Here, we designed a protocol to monitor forward and backward contamination events and progression in an 11-days Mars analog mission in the Ramon crater in Israel. Forward contamination soil samples were collected daily from three sites–two sites in close proximity to the habitat and one isolated site. Backward contamination was determined in samples from nitrile gloves of six analog astronauts before and after extravehicular activities Temperature, relative humidity and soil composition data were also collected for all sites. Environmental DNA samples were extracted in the main habitat and 16S (bacterial) and 18S (eukaryotic, fungal) rRNA gene amplicons were sequenced and analyzed to study microbial population diversity and composition. Shannon Diversity index analysis and Principal Coordinates analysis (PCoA) of rRNA genes indicated that differences in the diversity and population composition were significant in sites closer to the habitat when compared to a reference site. These samples also demonstrated the introduction of human-associated taxa to the environment. Backward contamination consisted of bacterial taxa found on gloves upon return from EVA and also detected in soil, altogether 44 genera, indicating backward contamination events. To our knowledge, this is the first protocol to utilize advanced molecular technologies to investigate forward and backward contamination in a Mars analog mission.
Highlights
Even before the Viking landers successfully landed on Mars in 1976, NASA’s principles of planetary-protection policies were conceived and embedded in mission design
While the maximal temperature was equal across all sites, both minimal and mean temperatures were higher in site A (Table 3)
As discussed in the 2015 COSPAR workshop, there is a need for research on sampling methodology in low biomass environments, with special attention to determining spatial and temporal detection limits (Race et al, 2015)
Summary
Even before the Viking landers successfully landed on Mars in 1976, NASA’s principles of planetary-protection policies were conceived and embedded in mission design. Prevention of forward and backward contamination is the main goal of planetary-protection policies, to eliminate and reduce the potential of cross-transferring life forms from one planet to another. Such contamination is possible either by carrying terrestrial microorganisms via a spacecraft (forward contamination) or by bringing extraterrestrial microorganisms from other planets or celestial bodies back to Earth (backward contamination), via various mechanisms such as sample return missions (Cockell 2005; Pratt and Smith, 2020). The study of backward contamination was designed to detect microorganisms carried on the AA’s gloves, upon return from EVAs. Baseline for the nitrile gloves was conducted so each “after EVA” sample was compared and paired to its “before EVA” sample (new glove). The dominant and shared family in both “after” and “before” samples was Moraxellaceae, the genus Acinetobacter, with average RA 9.6 ± 16% in the “before” samples, and average
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