Extremophiles in spacecraft assembly cleanrooms

Abstract

Spacecraft are usually assembled, tested, and launched in cleanrooms. Besides particles, microbial contamination can also be a serious concern. Depending on the target of a mission, terrestrial biomolecules or even surviving microorganisms could contaminate the extraterrestrial environment but also cause false-positive life-detection results. Spacecraft assembly cleanrooms and the instruments themselves are subjected to strict monitoring of the bioburden and cleanliness regimes. Due to their confinement, the humidity and temperature control, and the barely available nutrients, cleanrooms are considered extreme environments for microorganisms. In addition, numerous sterilization and cleanliness procedures pose extraordinary stresses to microorganisms in these habitats, reducing the overall load of microbes tremendously but supporting specifically adapted microorganisms. In many cases, these microbes are (multi)resistant toward harshest conditions. In this chapter, characteristics of numerous extremophilic and extremotolerant microorganisms that have been detected in spacecraft assembly cleanrooms and on spacecraft itself are summarized, including spore-forming, oligotrophic, alkaliphilic, autotrophic, anaerobic, thermophilic, and psychrophilic microorganisms. It becomes clear that the cleanroom microbial community develops a smart strategy to withstand the severe stresses applied, making some cleanroom microbes even more resistant than their counterparts in natural biotopes.