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The impact of microgravity and gravitational countermeasures on the gut microbiome of humans enrolled in the AGBRESA study
The Artificial Gravity Bed Rest Study – AGBRESA – was the first joint study conducted by DLR, ESA and NASA
to simulate the effects of microgravity on healthy subjects. Moreover, the study included the use of artificial
gravity protocols in a short-arm human centrifuge as a measure to counteract the negative effects of
weightlessness. The health of the gut translates into the overall wellbeing since the disruption of the gut
symbiotic networks – dysbiosis – could be due to either diet, antibiotic ingestion, sleep disturbance, physical
activity or psychological stresses. In recent times, the gut microbiome has changed from being a complementary
addition to our digestive tract to a potentially life-changing role by directly being the source of stimuli which
revealed to impact neurochemistry, behavior and overall physiological status. Combined, microbial fluctuations
could alter the intestinal microbiota composition and bacterial metabolite production, or more severely, in the
disruption of host intestinal barrier integrity and the immune system activity, triggering intestinal inflammation
syndromes and making the gut a very relevant organ to be studied in the context of spaceflight.
Thus, 12 subjects, 8 males, were subjected to bed rest at negative 6-degree inclination for a period of 60
days with a preceding baseline of 15 days and posterior recovery period of 14 days. In other to characterize the
gut microenvironment of healthy humans in simulated microgravity, fecal samples were collected during the
baseline stage (once), during the head-down tilt treatment (at days 10, 30, and 50) and during the recovery
period (once), and the samples were then processed for 16S rRNA sequencing and taxonomic analysis of the
gut microenvironment.
The characterization of the prokaryote flora was conducted 1) throughout time in contrast to the baseline
reference and 2) in the context of the gravitational countermeasure vs the bed-rest-only control. The analysis
revealed the detection of commensal microorganisms described to positively impact the gut such as
Bifidobacterium spp., Lactobacillus spp., Akkermansia spp. and Enterococus spp.. Interestingly, we were able
to detect pathogens like Campylobacter hominis which has been linked to severe bowel diseases ulcerative
colitis and Crohn's disease. Also, opportunistic microorganisms such as Fusobacterium spp., Prevotella spp.,
Pseudomonas spp., Staphylococcus and Streptococcus spp., could potentially indicate an imbalance of the
microbial networks and be a good an indicator of dysbiosis. Additionally, we set aside samples to undergo
proteomic and metabolite analysis to improve the characterization of the gut microenvironment under
microgravity simulation and the extent of the gravitational countermeasure recovery on bowel condition.
Overall, the microgravity simulation performed on the AGBRESA study did not impact dramatically the fitness
of the participants. Nonetheless, the analysis of the gut provides important insights on the triggers that occur
during the adaptation of human physiology to long term exposure to spaceflight conditions and whether these
relate to the described complications associated with gut disease