Impact of a Model Used to Simulate Chronic Socio-Environmental Stressors Encountered during Spaceflight on Murine Intestinal Microbiota

Abstract

During deep-space travels, crewmembers face various physical and psychosocial stressors that could alter gut microbiota composition. Since it is well known that intestinal dysbiosis is involved in the onset or exacerbation of several disorders, the aim of this study was to evaluate changes in intestinal microbiota in a murine model used to mimic chronic psychosocial stressors encountered during a long-term space mission. We demonstrate that 3 weeks of exposure to this model (called CUMS for Chronic Unpredictable Mild Stress) induce significant change in intracaecal β-diversity characterized by an important increase of the Firmicutes/Bacteroidetes ratio. These alterations are associated with a decrease of Porphyromonadaceae, particularly of the genus Barnesiella, a major member of gut microbiota in mice and humans where it is described as having protective properties. These results raise the question of the impact of stress-induced decrease of beneficial taxa, support recent data deduced from in-flight experimentations and other ground-based models, and emphasize the critical need for further studies exploring the impact of spaceflight on intestinal microbiota in order to propose strategies to countermeasure spaceflight-associated dysbiosis and its consequences on health.

Keywords: Barnesiella; chronic unpredictable mild stress; gut microbiota; spaceflight.

Figure 1

Stress status of mice. (a) Chronic Unpredictable Mild Stress (CUMS) protocol, (b) body weights, (c) serum corticosterone concentrations, (d) thymus weights normalized to body weight in control and CUMS mice. No statistically significant differences were found using the Mann–Whitney U test.

Figure 2

Comparison of microbiota diversity between CUMS and control mice. (a) Total bacterial load quantification by qPCR corresponding to the total number of 16S rRNA gene copies per mg of intracaecal content in mice subjected to CUMS (n = 10) and in control mice (n = 7) (p = 0.19). (b) α-diversity indexes: Observed OTUs (richness, p = 0.73), Evenness (p = 0.52), Shannon index (p = 0.84), Simpson index of diversity (p = 0.69), and Simpson’s reciprocal index (p = 0.81). Statistical analyses were done using the Mann-Whitney U test. The upper and lower ranges of the box represent the 75% and 25% quartiles, respectively. Error bars reflect standard error of the mean. (c) PCA of microbiomes from CUMS vs. control mice (Pr(>F) = 0.029). The variance explained by each of the main two dimensions of the PCA is indicated in parentheses on the axes.

Figure 3

Differential abundance of bacterial taxa. (a) Mean relative abundance (%) of bacterial phyla and (b) Firmicutes/Bacteroidetes ratio in the caecal content of mice subjected to 21 days of CUMS compared to controls. Statistical analyses were done using the Mann-Whitney U test. * p < 0.01; ** p < 0.001. (c) Differentially abundant main genera in control mice (green) and CUMS mice (red) identified using Linear Discriminant Analysis (LDA) Effect Size (LEfSe) analysis. (d) Schematic representation of core microbiome at the species level. Green circle: number of species shared in all control mice. Red circle: number of species shared in all CUMS mice. Intersection and numbers inscribed within refer to shared species and in parentheses shared with all mice.