Survival of Bacillus pumilus Spores for a Prolonged Period of Time in Real Space Conditions

Abstract

To prevent forward contamination and maintain the scientific integrity of future life-detection missions, it is important to characterize and attempt to eliminate terrestrial microorganisms associated with exploratory spacecraft and landing vehicles. Among the organisms isolated from spacecraft-associated surfaces, spores of Bacillus pumilus SAFR-032 exhibited unusually high resistance to decontamination techniques such as UV radiation and peroxide treatment. Subsequently, B. pumilus SAFR-032 was flown to the International Space Station (ISS) and exposed to a variety of space conditions via the European Technology Exposure Facility (EuTEF). After 18 months of exposure in the EXPOSE facility of the European Space Agency (ESA) on EuTEF under dark space conditions, SAFR-032 spores showed 10–40% survivability, whereas a survival rate of 85–100% was observed when these spores were kept aboard the ISS under dark simulated martian atmospheric conditions. In contrast, when UV ( > 110 nm) was applied on SAFR-032 spores for the same time period and under the same conditions used in EXPOSE, a ~7-log reduction in viability was observed. A parallel experiment was conducted on Earth with identical samples under simulated space conditions. Spores exposed to ground simulations showed less of a reduction in viability when compared with the ‘‘real space’’ exposed spores (~3-log reduction in viability for ‘‘UV-Mars,’’ and ~4-log reduction in viability for ‘‘UV-Space’’). A comparative proteomics analysis indicated that proteins conferring resistant traits (superoxide dismutase) were present in higher concentration in spaceexposed spores when compared to controls. Also, the first-generation cells and spores derived from spaceexposed samples exhibited elevated UVC resistance when compared with their ground control counterparts. The data generated are important for calculating the probability and mechanisms of microbial survival in space conditions and assessing microbial contaminants as risks for forward contamination and in situ life detection.