Parabolic flight induces site specific microbiome changes in women

The vaginal microbiome plays a central role in women's health by supporting immune function, maintaining mucosal homeostasis, and preventing infections. Spaceflight and its analogs can induce acute physiological stress, which can alter host microbiome interactions. While other studies have analyzed the microbiome changes at certain body sites, the female-specific microbiome changes have not been explored in depth in space medicine research.

Pre- and post-parabolic flight vaginal and oral microbiome were analyzed via metagenomic shotgun sequencing to assess taxonomic composition and metabolic pathways. Host DNA and bad quality sequences were removed using the KneadData tool. Taxonomic and functional profiles were analyzed with MetaPhlAn and HUMAnN. Microbiome data were integrated with stress response parameters including cortisol, proinflammatory cytokines, and urinary short-chain fatty acids.

Both alpha- and beta diversity analysis showed minimal impact of parabolic flight on oral microbiome while vaginal microbiome showed significant differences. Taxonomic profiling showed marked restructuring of the vaginal microbiome, characterized by increased Firmicutes dominance and enrichment of Lactobacillus species, particularly Lactobacillus crispatus and Lactobacillus jensenii, whereas oral microbiome stayed relatively stable. Overall, only 2.54% of oral species showed significant postflight changes compared to 57.9% of vaginal species (p < 0.0001). Random Forest model identified L. crispatus as a key discriminator of postflight vaginal microbiome composition. Metabolic pathway analysis revealed minimal postflight pathway redistribution in saliva samples but greater number of changes in the vaginal microbiome, with significant postflight enrichment of fatty acid biosynthesis and nucleotide metabolism. Vaginal samples demonstrated a threefold greater proportion of altered metabolic pathways compared to oral samples. In addition, urinary acetate, butyrate, and valeric acid levels were significantly reduced postflight. Salivary cortisol increased postflight and positively correlated with L. jensenii.

Parabolic flight induces body site-specific microbiome changes in reproductive age women, with greater taxonomic and functional metabolic remodeling in the vaginal microbiome than in the oral microbiome. These findings highlight the sensitivity of the vaginal microbial ecosystem to spaceflight stressors and underscore the need for longitudinal and mechanistic studies to determine the persistence, clinical significance, and potential health implications of these changes during longer duration space missions.