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Boost for Efforts to Prevent Microbial Stowaways on Interplanetary Spacecraft

Efforts to expunge micro-organisms from spacecraft assembly cleanrooms, and the spacecraft themselves, inadvertently select for the organisms that are often the most fit to survive long journeys in space. This has the risk of thwarting the goal of avoiding contaminating other celestial bodies, as well as samples brought back to earth, according to Myron La Duc of the Jet Propulsion Laboratory (JPL), California Institute of Technology, and his collaborators. Their research is published in the August issue of the journal Applied and Environmental Microbiology (click source to download the .pdf of the journal article).

Mars, the Jovian moon, Europa, and a few other denizens of our solar system may harbor life, and might be capable of supporting some terrestrial microbes. Contaminating planets or moons that already support extraterrestrial life—a possibility on Mars, the big Jovian moon, Europa, and the tiny Saturnian moon, Enceladus—could interfere with efforts to understand that life, and its origins. For example, life on all of these orbs may have a common origin—likely on Earth or Mars—and contamination of samples could confound efforts to determine which planet was the source of life, and how life arose. For these reasons, sterilization processing of spacecraft bound for such planetary bodies is a very high priority for the National Aeronautics and Space Administration.
Species of bacteria have long been considered capable of surviving space travel, but examples of a fungal species that is capable of such survival have only recently been demonstrated, according to the report. Additionally, due to their extraordinary ability to withstand various extreme environments, some archaea "have been proposed as being capable of tolerating the Martian environment," the investigators write. "In light of this, the breadth of current spacecraft-associated microbial diversity assessments must expand to include eukaryotes and archaea."

Because of this, better methods are needed for determining microbial populations on surfaces that have a very low density of individual microbes. In this study, the researchers became the first to take the microbial census using so-called pyrosequencing studies. Pyrosequencing is a recent method of sequencing DNA from entire microbial communities that is much faster and simpler than other methods, and extremely thorough.

Further findings in the study pointed up the value of pyrosequencing in demonstrating where vigilance in sterilizing equipment is needed. Of most import, certain archaeal sequences, notably from the ammonia-oxidizing genus, Nitrososphaeraceae of the recently proposed phylum, Thaumarchaeota, appeared in ground support equipment samples, both before and after cleaning. Archaea of this phylum can survive on ammonia or urea, or other inorganic chemicals, enhancing their ability to survive extreme conditions, according to the report, so prevention of their transfer to the spacecraft is key.

"Methanobacteriaceae sequences were also observed in the spacecraft hardware samples," the researchers write. "This is particularly relevant for astrobiological issues, since members of this family have been reported to be obligate anaerobic, hydrogenotrophic, and methanogenic organisms and capable of utilizing carbon dioxide as their sole carbon source." The challenge for the JPL's spacecraft team is to ensure that the DNA sequences only arise from dead Methanobacteriaceae, and not from live ones.

(M.T. La Duc, P. Vaishampayan, H.R. Nilsson, T. Torok, and K. Venkateswaran, 2012. Pyrosequencing-derived bacterial, archaeal, and fungal diversity of spacecraft hardware destined for Mars. Appl. Environ. Microbiol. 78:5912-5922.)

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