Assessing the Risk of Transfer of Microorganisms at the International Space Station Due to Cargo Delivery by Commercial Resupply Vehicles

Snehit Mhatre; Jason M Wood; Aleksandra Checinska Sielaff; Maximilian Mora; Stefanie Duller; Nitin Kumar Singh; Fathi Karouia; Christine Moissl-Eichinger; Kasthuri Venkateswaran

doi:10.3389/fmicb.2020.566412

Assessing the Risk of Transfer of Microorganisms at the International Space Station Due to Cargo Delivery by Commercial Resupply Vehicles

Front Microbiol. 2020 Nov 6:11:566412. doi: 10.3389/fmicb.2020.566412. eCollection 2020.

Affiliations

¹ Biotechnology and Planetary Protection Group, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, United States.
² Department of Internal Medicine, Medical University of Graz, Graz, Austria.
³ Space Bioscience Division, NASA Ames Research Center, Moffett Field, CA, United States.
⁴ Department of Pharmaceutical Chemistry, University of California, San Francisco, San Francisco, CA, United States.
⁵ BioTechMed-Graz, Graz, Austria.

Abstract

Background: With increasing numbers of interplanetary missions, there is a need to establish robust protocols to ensure the protection of extraterrestrial planets being visited from contamination by terrestrial life forms. The current study is the first report comparing the commercial resupply vehicle (CRV) microbiome with the International Space Station (ISS) microbiome to understand the risks of contamination, thus serving as a model system for future planetary missions.

Results: Samples obtained from the internal surfaces and ground support equipment of three CRV missions were subjected to various molecular techniques for microbial diversity analysis. In total, 25 samples were collected with eight defined locations from each CRV mission prior to launch. In general, the internal surfaces of vehicles were clean, with an order of magnitude fewer microbes compared to ground support equipment. The first CRV mission had a larger microbial population than subsequent CRV missions, which were clean as compared to the initial CRV locations sampled. Cultivation assays showed the presence of Actinobacteria, Proteobacteria, Firmicutes, and Bacteroidetes and members of Ascomycota and Basidiomycota. As expected, shotgun metagenome analyses revealed the presence of more microbial taxa compared to cultivation-based assays. The internal locations of the CRV microbiome reportedly showed the presence of microorganisms capable of tolerating ultraviolet radiation (e.g., Bacillus firmus) and clustered separately from the ISS microbiome.

Conclusions: The metagenome sequence comparison of the CRV microbiome with the ISS microbiome revealed significant differences showing that CRV microbiomes were a negligible part of the ISS environmental microbiome. These findings suggest that the maintenance protocols in cleaning CRV surfaces are highly effective in controlling the contaminating microbial population during cargo transfer to the ISS via the CRV route.

Keywords: International Space Station; commercial resupply vehicle; forward contamination; microbial diversity; viability.