Since the Viking missions (1970s), organic materials have been preserved from missions. Formal infrastructure and standard processes developed over time to form a biological and organic materials archive at JPL. Microbial cultures are preserved in the archive following sampling events in which spacecraft are verified for microbial cleanliness during assembly, test and launch operations.
Depending on the mission category (https://planetaryprotection.arc.nasa.gov/categories), the Planetary Protection Plan details the allowable bioburden (unsterilized number of microorganisms on a surface) for each mission. To verify the cleanliness of spacecraft, the NASA Standard Assay is used to determine the bioburden and whether or not it is within limit set forth by the Planetary Protection Plan. Although there has never been a formal requirement, until the Mars 2020 mission, to archive the microbial isolates recovered during such assays, having a microbial repository allows researchers to recognize future Earth-sourced microbial contaminants (for both extraterrestrial samples analyzed robotically on planets such as Mars and samples returned to Earth). A “false-positive” indication of life could lead to unnecessary increased Planetary Protection requirements for future missions.
One of the sources of such contaminants are microbes embedded in solid non-metallic materials. Microbes inside of these materials could survive the space journey and, in principle, be released into the environment of the destination planet or moon. An additional concern is that these embedded microbes seem to have great tolerances to sterilization efforts such as routine cleaning, heat microbial reduction, or UV exposure. Thus, another advantage in having an archive is that the information collected for each isolate could provide useful clues in how the isolate can withstand sterilization techniques. This data may ultimately lead to the development of technology and new approaches in keeping spacecraft clean.
The process of preserving isolates begins with bioassays from flight projects (NASA Standard Assay). If the assay results in colonies, those plates are set aside. From these plates, pure isolates are obtained and biochemically identified by various methods: The Matrix Assisted Laser Desorption Ionization Time-of-Flight (MALDI-TOF) is an analytical method of microbial identification and characterization based on the fast and precise assessment of the mass of molecules in a variable range of 100 Da to 100 KDa. Another method of identification is the 16S ribosomal RNA (or 16S rRNA), which is a component of the small subunit of prokaryotic ribosomes and is therefore used for phylogenetic interpretation. Information about the identified isolate is stored in a computer database, which provides information for the biochemical data on the isolate and physical location within the archive. Isolates are then stored into working and stock cultures.
Thus far, JPL has collected isolates from the following missions: Viking (1296), Mars Odyssey (90), Phoenix (209), Mars Pathfinder (47), Mars Exploration Rovers (395), Mars Science Laboratory (1123), Insight (in progress) and Mars 2020 (in progress). The majority of isolates come from spacecraft assembly cleanrooms at JPL and Kennedy Space Center (KSC). Studies performed by the Biotechnology and Planetary Protection Group at JPL show that the isolates are predominantly spore formers since they are collected from samples having been heat shocked at 80°C for 15 minutes. Among the spore-formers, the most prevalent species found on spacecraft are Bacillus sp. Among the non-spore formers, the most prevalent species found on spacecraft are Staphylococcus sp. Several other genera in smaller percentages include Paenibacillus, Pseudomonas, Brevibacillus, and Terribacillus species. Studies have also characterized isolates that can grow using various growth substrates (perchlorate and sulfate) found on other planets such as Mars. Many isolates show resistance to desiccation and UVC (ultraviolet radiation with wavelengths between 200 and 290 nm). Moreover, many of the isolates can grow in the presence of elevated salt conditions. Planetary Protection researchers occasionally identify novel species, whose characterization is valuable in determining how these species withstand sterilization efforts. These results and continued studies allow researchers to gauge if and what type of microorganisms can grow and survive in Mars-like conditions. Having a reference collection of microorganisms that can potentially contaminate celestial bodies is a rich resource for the invention of new spacecraft cleaning and sterilization technologies.
The Space Microbiology Lab located at JPL is home to the archive and provides an abundance of equipment and research opportunities for the Biotechnology and Planetary Protection staff, post-docs, and students. The facility includes autoclave, centrifuges, freezers, laminar flow hood, chemical fume hood, incubators, cryogenic grinder, cryo storage system, Omnilog, lyophilizing systems, MALDI-TOF, sonicators, water baths, ice machine, colony counters, microscopes, electrophoresis units, balance, and dishwasher.