Astronaut intestinal health may be impacted by microgravity, radiation, and diet. The aim of this study was to characterize how high and low linear energy transfer (LET) radiation, microgravity, and elevated dietary iron affect colon microbiota (determined by 16S rDNA pyrosequencing) and colon function. Three independent experiments were conducted to achieve these goals: 1) fractionated low LET γ radiation (137Cs, 3 Gy, RAD), high Fe diet (IRON) (650 mg/kg diet), and a combination of low LET γ radiation and high Fe diet (IRON+RAD) in male Sprague-Dawley rats; 2) high LET 38Si particle exposure (0.050 Gy), 1/6 G partial weight bearing (PWB), and a combination of high LET38Si particle exposure and PWB in female BalbC/ByJ mice; and 3) 13 d spaceflight in female C57BL/6 mice. Low LET radiation, IRON and spaceflight increased Bacteroidetes and decreased Firmicutes. RAD and IRON+RAD increased Lactobacillales and lowered Clostridiales compared to the control (CON) and IRON treatments. Low LET radiation, IRON, and spaceflight did not significantly affect diversity or richness, or elevate pathogenic genera. Spaceflight increased Clostridiales and decreased Lactobacillales, and similar trends were observed in the experiment using a ground-based model of microgravity, suggesting altered gravity may affect colonic microbiota. Although we noted no differences in colon epithelial injury or inflammation, spaceflight elevated TGFβ gene expression. Microbiota and mucosal characterization in these models is a first step in understanding the impact of the space environment on intestinal health.

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Published in PLOS One, v. 10, no. 6, article e0125792, p. 1-16.

This is an open access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication

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This study was funded by the NASA Human Research Program's Human Health Countermeasures Element by a grant to SRZ, SMS, and NDT; a National Institutes of Health/National Institute of Diabetes and Digestive and Kidney Diseases grant (P30 DK34987) to MAAP, and a National Space Biomedical Research Institute grant (NCC 9-58) to NDT. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

journal.pone.0125792.s001.DOCX (21 kB)
S1 Appendix. Methodologies and results for Experiment 2.

journal.pone.0125792.s002.DOCX (199 kB)
S1 Table. Assay ID for selected gene targets and relative expression in scraped colonic mucosa from mice exposed to radiation and reduced gravity (Experiment 2 and 3).

journal.pone.0125792.s003.DOCX (199 kB)
S2 Table. Relative abundance (%) of bacterial taxa in feces of rats resulting from low LET radiation exposure and elevated dietary iron content (Experiment 1).

journal.pone.0125792.s004.DOCX (197 kB)
S3 Table. Relative abundance (%) of bacterial taxa in feces of mice resulting from high LET radiation exposure and simulated lunar gravity (Experiment 2).

journal.pone.0125792.s005.DOCX (196 kB)
S4 Table. Relative abundance (%) of bacterial taxa in feces of mice resulting from 13 days spaceflight (Experiment 3).