“…A parallel experiment, MICHA (MIcrobial ecology of Confined Habitats and humAn health), has instead drawn attention to the microbiology of the environments where space travelers dwell, identifying areas with human activity as hotspots for dispersal and accumulation of crew's microorganisms, especially of potential pathogenic, stress-tolerant or mobile element-bearing microbes (Schwendner et al, 2017). More recently, ground-based space simulations have provided intriguing (although not entirely unequivocal) insights into the possibility of maintaining a eubiotic gut microbiome layout (poor in potential pathobionts while rich in health-promoting SCFA producers) through a bioregenerative life-support system (BLSS), i.e., a confined, selfsustained artificial ecosystem to biologically regenerate O 2 , food, water and other basic living necessities (Hao et al, 2018;Chen et al, 2020). In short, the crewmembers followed a fixed schedule that included contact with plants for several hours a day and a high-plant high-fiber diet.…”