MICROBIAL ECOLOGY OF THE MARS 500 HABITAT

Kurzfassung

Biocontamination in confined manned habitats poses a risk for the health of the crew and for the on-board equipment. The reduced immune response of humans that are exposed to extreme environmental conditions, like during long-term confinement, and the degradation capacities of some microorganisms call for continuous monitoring of biocontamination, and measures to mitigate it. Prevention includes taking the acquired knowledge into account for future habitat design. The MARS 500 project represented a unique opportunity to gain insight into the microbial distribution and its community structure during a long period of time. MARS 500 is the first full duration simulation of a manned flight to Mars, accomplished from June of 2010 to November of 2011. The six-man crew lived, worked, and performed scientific experiments in a closed spacecraft-like environment. The scientific experiment MICHAm (MIcrobial ecology of Confined Habitats and humAn health, modified) aimed to survey the microbial flora in the MARS 500 facility from the start to the end of the simulation study (520 days), and to investigate the impact of confinement. Therefore, the microbial load and biodiversity in the air and on surfaces as well as their changes over time were monitored. The determination of cultivable microorganisms showed that the overall microbial load in the air and on different surfaces was moderate compared to other non-confined rooms (air: 0 to 716 CFU per m³ with an average value of 86 CFU per m³; surface: 0 to 29,760 CFU per 10 m² with an average value of 675 CFU per 10 cm²). The highest number of microorganisms was found in the air of the habitable module, where the crew members spent most of their time. This corresponds roughly to the results obtained from surfaces at certain locations. During the project, fluctuations in microbial load were detected. Those were analyzed in more detail by taking into account the crew activities in the different modules, the cleaning regimes, the air conditioning processes, et cetera. However, none of the single parameters revealed a significant influence, thus it is assumed that the combination of all of them led to the site- and time-specific contamination levels. Phylogenetic investigations indicated a higher diversity in surface samples than in air samples. Dominance of microorganisms associated with humans, especially Staphylococcus species, was observed on surfaces and in the air. Environmental microorganisms, mainly spore-forming bacilli, were found to a lesser extent. Besides cultivation-based analyses, the microbial inventory was also studied on the molecular level via DNA isolation, 16S rRNA gene specific amplification, and subsequent PhyloChip analysis, to quantitatively measure the microbiome of two modules of the MARS 500 facility. The findings were surprising since the whole microbiome structure exhibited no significant influence for factor time, with the exception of a few taxa. However, significantly different microbiome structures were identified for both investigated modules, whereas the intragroup dissimilarity among samples was greater in the utility module than in the habitable module. Furthermore, by applying both cultivation and molecular methods, a deeper understanding of the microbiota and microbiome was obtained that also unveiled potentially pathogenic organisms (e.g. Staphylococcus sp., Propionibacterium sp., Enterococcus sp., and many more) and microbes with degradative capacities (e.g., Pseudomonas sp., Micrococcus sp., Bacillus sp., Acinetobacter sp., Flavobacterium sp., Escherichia sp., and Actinomyces sp.). However, the majority of microorganisms were not harmful, but belonged to the group of microbes that are even highly valuable to humans. During no point of the confinement study there was any alert and health concern due to potential danger caused by microorganisms. The scientific information obtained in this thesis is essential to evaluate biosafety risks, predict and mitigate the possible occurrence of biocorrosion, and improve the sanitary and hygienic quality of life for the crew inside closed habitats.