A scientific team at Cal Poly Pomona, based in California (US), have published findings of the first biochemical evidence to suggest why spacecraft contamination occurs, despite assembly in a cleanroom.
In its cleanroom facilities, NASA implements a variety of planetary protection measures to minimise biological contamination of spacecraft.
These steps are important because contamination by Earth-based microorganisms could compromise life-detection missions by providing false positive results.
However, despite extensive cleaning procedures, molecular genetic analyses shows that cleanrooms harbour a diverse collection of microorganisms, or spacecraft microbiome, that includes bacteria, archaea and fungi.
"We designed the project to give students hands-on experience and to support the learn-by-doing philosophy of Cal Poly Pomona. The students did the research, mostly as thesis projects in the areas of enzymology, molecular microbiology and analytical chemistry," said Rakesh Mogul, lead author and Cal Poly Pomona professor of biological chemistry.
The Acinetobacter, a genus of bacteria, are among the dominant members of the spacecraft microbiome. To figure out how the spacecraft microbiome survives in the cleanroom facilities, the research team analysed several Acinetobacter strains that were originally isolated from the Mars Odyssey and Phoenix spacecraft facilities.
They found that under very nutrient-restricted conditions, most of the tested strains grew on and biodegraded the cleaning agents used during spacecraft assembly.
The work showed that cultures grew on ethyl alcohol as a sole carbon source while displaying reasonable tolerances towards oxidative stress. This is important, because oxidative stress is associated with desiccating and high radiation environments similar to Mars.
The tested strains were also able to biodegrade isopropyl alcohol and Kleenol 30, two other cleaning agents commonly used, with these products potentially serving as energy sources for the microbiome.
The research indicates that more stringent cleaning steps may be needed for missions focused on life detection and highlights the potential need to use differing and rotating cleaning reagents that are compatible with the spacecraft to control the biological burden.
"We're giving the planetary protection community a baseline understanding of why these microorganisms remain in the cleanrooms," said Mogul. "There's always stuff coming into the cleanrooms, but one of the questions has been why do the microbes remain in the cleanrooms and why is there a set of microorganisms that are common to the cleanrooms?"
Rakesh Mogul, a Cal Poly Pomona professor of biological chemistry, was the lead author of an article published in the Journal Astrobiology. Chemistry professor Gregory A. Barding, Jr., was a collaborator and second author on the paper. The remaining 22 coauthors are all Cal Poly Pomona students—14 undergraduates in chemistry, three chemistry graduate students and five undergraduates in biological sciences.
References
Rakesh Mogul et al. Metabolism and Biodegradation of Spacecraft Cleaning Reagents by Strains of Spacecraft-Associated Acinetobacter, Astrobiology (2018).