The Microbiome: The Forgotten Organ of the Astronaut's Body — Probiotics Beyond Terrestrial Limits

Amir Ata Saei; Abolfazl Barzegari


Future Microbiol. 2012;7(9):1037-1046. 

In This Article

Stress & Gut Microbiome

The Human Genome Project revealed that the human body is the habitat of microbial symbionts ten-times more in number than Homo sapiens cells.[4] The recognition of the complex interactional environment between the human and our symbiotic microflora led researchers to name this the 'human microbiome'.[11] In the human gut, the microbiome directly influences biochemical, physiological and immunological pathways and is the first line of resistance to various diseases.[12]

Traveling can act as an environmental stress causing changes in the microbiome composition or its gene expression.[13] This may lead to the transient (as in travelers' diarrhea) or permanent dominance of pathogenic gut bacteria. Recently, it was shown that exposure to a social stressor altered the composition of the intestinal microbiome, indicating stressor-induced immunomodulation.[14] It was demonstrated that stressor exposure changes the stability of the microflora and leads to bacterial translocation.[14] Circulating levels of IL-6 and MCP-1 increased with stressor exposure and these increases were significantly and positively correlated to changes in three bacterial genera (i.e., Coprococcus, Pseudobutyrivibrio and Dorea) in the cecum.[14] This suggested that the microbiome somehow contributed to stressor-induced immunoenhancement. To test the theory, in follow-up experiments, mice were treated with an antibiotic cocktail to determine whether reducing microflora would annul this stressor-induced increase in circulating cytokines. In the antibiotic-treated mice, exposure to the same stressor failed to increase IL-6 and MCP-1 confirming that intestinal microflora were necessary for the observed increase in circulating cytokines.[14]