Abstract
BackgroundThe International Space Station (ISS) is a unique built environment due to the effects of microgravity, space radiation, elevated carbon dioxide levels, and especially continuous human habitation. Understanding the composition of the ISS microbial community will facilitate further development of safety and maintenance practices. The primary goal of this study was to characterize the viable microbiome of the ISS-built environment. A second objective was to determine if the built environments of Earth-based cleanrooms associated with space exploration are an appropriate model of the ISS environment.ResultsSamples collected from the ISS and two cleanrooms at the Jet Propulsion Laboratory (JPL, Pasadena, CA) were analyzed by traditional cultivation, adenosine triphosphate (ATP), and propidium monoazide–quantitative polymerase chain reaction (PMA-qPCR) assays to estimate viable microbial populations. The 16S rRNA gene Illumina iTag sequencing was used to elucidate microbial diversity and explore differences between ISS and cleanroom microbiomes. Statistical analyses showed that members of the phyla Actinobacteria, Firmicutes, and Proteobacteria were dominant in the samples examined but varied in abundance. Actinobacteria were predominant in the ISS samples whereas Proteobacteria, least abundant in the ISS, dominated in the cleanroom samples. The viable bacterial populations seen by PMA treatment were greatly decreased. However, the treatment did not appear to have an effect on the bacterial composition (diversity) associated with each sampling site.ConclusionsThe results of this study provide strong evidence that specific human skin-associated microorganisms make a substantial contribution to the ISS microbiome, which is not the case in Earth-based cleanrooms. For example, Corynebacterium and Propionibacterium (Actinobacteria) but not Staphylococcus (Firmicutes) species are dominant on the ISS in terms of viable and total bacterial community composition. The results obtained will facilitate future studies to determine how stable the ISS environment is over time. The present results also demonstrate the value of measuring viable cell diversity and population size at any sampling site. This information can be used to identify sites that can be targeted for more stringent cleaning. Finally, the results will allow comparisons with other built sites and facilitate future improvements on the ISS that will ensure astronaut health.Electronic supplementary materialThe online version of this article (doi:10.1186/s40168-015-0116-3) contains supplementary material, which is available to authorized users.
Highlights
The International Space Station (ISS) is a unique built environment due to the effects of microgravity, space radiation, elevated carbon dioxide levels, and especially continuous human habitation
In contrast with the Jet Propulsion Laboratory (JPL) cleanrooms, the most common organisms in the ISS environment were members of the Actinobacteria that are frequently associated with humans
As on the ISS, human traffic is common in the cleanrooms, but clearly the more stringent procedures possible on Earth are more effective in eradicating these organisms
Summary
The International Space Station (ISS) is a unique built environment due to the effects of microgravity, space radiation, elevated carbon dioxide levels, and especially continuous human habitation. The primary goal of this study was to characterize the viable microbiome of the ISS-built environment. Since built environments are known to have specific microbiomes [6], it is of the highest interest to the National Aeronautics and Space Administration (NASA) scientific community to explore the environmental microbiome of the ISS as a closed environment. The National Research Council (NRC) recommended that NASA study changes in microbial populations in response to selective pressure associated with microgravity, which characterizes life aboard the ISS [7]. Due to the technically rigorous methods required for culturing many microorganisms, characterization of human-associated microbial populations in the ISS environment remains a significant challenge. Understanding of the ISS microbiome could facilitate the necessary maintenance of this closed habitat and thereby assist in preventing degradation of its components by some microorganisms [4]
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