| Summary: | The EDEN-ISS container is a mobile test facility in Antarctica used to investigate new plant cultivation techniques for future space programs. Manned missions to Mars are already planned but still in need of a reliable food production system. The EDEN-ISS container was used from January to December 2018 for fresh food production for the overwintering Neumayer III crew. During the nine month operation time, samples from the different plants, from the nutrition solution of the planting system and from diverse surfaces within different areas of the container (future exploration greenhouse, service section, cold porch) were taken. This work presents the microbial investigation of these samples at the German Aerospace Center in Cologne, Germany. Quantity as well as diversity of microorganisms were examined. The microbial burden on different surfaces in the container and on the plant samples was generally lower than expected. In case of the plant samples, microbial quantities were in a range between 102 and 104 colony forming units (CFU) per gram plant material. Compared to purchased plants from German groceries, the produce hosted much more microorganisms. The EDEN-ISS plant samples showed mainly fungi and a few, most probably harmless bacteria. The CFU per milliliter in the nutrition solutions increased constantly over time but never reached critical values. The surface samples revealed high differences in the microbial burden between the greenhouse part of the container and the service section. However, the numbers of CFU per square centimeter found on the surfaces in the planted greenhouse were still not critical. For identification, the isolated bacteria were sent for 16S rRNA gene sequencing. The most abundant phyla were Firmicutes, Actinobacteria and Proteobacteria. These phyla all include plant- and human-associated bacterial species. All sequenced bacteria were identified as members of German risk group 1 and 2 (TRBA, 2015). In general, there is a low risk of hazard due to microbial contamination according to the results of this study.
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