The International Space Station selects for microorganisms adapted to the extreme environment, but does not induce genomic and physiological changes relevant for human health

Abstract

The International Space Station (ISS) is a unique, completely confined habitat for the human crew and co-inhabiting microorganisms. Here, we report on the results of the ISS experiment “EXTREMOPHILES”. We aimed to exploit the microbial information obtained from three surface and air sampling events aboard the International Space Station during increments 51 and 52 (2017) with respect to: i) microbial sources, diversity and distribution within the ISS, ii) functional capacity of microbiome and microbial isolates, iii) extremotolerance and antibiotics-resistance (compared to ground controls), and iv) microbial behavior towards ISS-relevant materials such as biofilm formation, or potential for degradation. We used wipe samples and analyzed them by amplicon and metagenomics sequencing, cultivation, comparative physiological studies, antibiotic resistance tests, genome analysis of isolates and co-incubation experiments with ISS-relevant materials. The major findings were: i) the ISS microbiome profile is highly similar to ground-based confined indoor environments, ii) the ISS microbiome is subject to fluctuations and indicative for the (functional) location, although a core microbiome was present over time and independent from location, iii) the ISS selects for microorganisms adapted to the extreme environment, but does not necessarily induce genomic and physiological changes which might be relevant for human health, iv) cleanrooms and cargo seems to be a minor source of microbial contamination aboard, and v) microorganisms can attach to and grow on ISS-relevant materials. Biofilm formation might be a threat for spacecraft materials with the potential to induce instrument malfunctioning with consequences for mission success. We conclude that our data do not raise direct reason for concern with respect to crew health, but indicate a potential threat towards biofilm formation and material integrity in moist areas.

Microbiome dynamics during the HI-SEAS IV mission, and implications for future crewed missions beyond Earth

“…From a microbiological point of view, the risk of infection or transfer of antimicrobial resistant pathogens to crew members was found to be extraordinarily low and is thus in agreement with recent information from the ISS [24]. However, although the risk was deemed to be low, the need for monitoring microbial dynamics inside isolated and confined habitats became obvious, in order to understand the impact of special events like the contamination caused by the composting toilet.…”

“…Moreover, baselines of the microbiome inside the habitat, its crew and post sampling events would greatly improve evaluations of the impact of confinement on the crew and habitat surfaces. Most comparable studies, either ground-based like Mars500 [41,105] or in space aboard the ISS [24,89,106], showed a similar picture of longitudinal homogenization, composition and diversity of microbiomes.…”

“…However, the potential to form biofilms showed a constant maximum in samples retrieved from the kitchen floor (global median 0.18, maximum 0.27, cumulative average decrease/increase -0.25/0. 24) and anaerobes were increasing on the toilet bowl (minimum 0.06, maximum 0.21) while decreasing on human skin (0.02 to 0.01). Interestingly, potential pathogens showed an anticyclic pattern of samples from the built environment versus samples from the crew (Fig.…”

“…Technophiles were found onboard the Mir station [22,23] and onboard the ISS [13,19,24], leading to damage of various systems [25,26]. Second, microbial contaminants could interfere with biological life-support systems [27] which could greatly contribute to the feasibility of long-term missions on the Moon or Mars [28][29][30] by harming the system-relevant organisms through competition and/or toxicity or by making food products unsuitable for crew consumption.…”

“…In any case, microbial communities will be critical components of future space endeavors, with a potentially large influence on mission success [35]. Their importance is reflected in space agencies' efforts to characterize them onboard the ISS [13,19,24,[36][37][38][39][40].…”