Social stress changes gut microbiome composition in male, female, and aggressor mice.

Psychological stress causes gut dysbiosis, which is associated with adverse effects on physical and mental health in humans and mice. Identifying taxa of gut bacteria changed by stress, and whether stress differentially alters their relative abundance in males and females, has important implications for stress-related disorders. We modeled individual differences in resilience or susceptibility using the chronic social defeat stress (CSDS) paradigm. Here, C57BL/6 mice are exposed to a novel retired breeder CD-1 aggressor for 10 min per day for 10 days. In this paradigm, resilient and susceptible subpopulations can be identified using the social interaction paradigm following CSDS. Fecal samples were collected immediately following Day 1 and Day 10 of CSDS. 16S ribosomal RNA sequencing was used to identify the relative abundance of 200 bacteria species. We analyzed group differences in phyla, genera, and species in resilient, susceptible, and non-stressed control male and female C57/BL/6 intruders along with CD-1 aggressors. Stress reduced microbiome diversity and caused gut dysbiosis in all groups, including aggressors. These changes were not observed in non-stressed mice. CSDS altered the relative abundance of every gut bacteria phylum. CSDS reduced genera in the Firmicutes phylum whereas sex altered fewer genera. The relative abundance of an uncultured Ruminococcus species on Day 1 predicted social avoidance following CSDS, with a stronger correlation in stressed females compared to males. Together, our findings demonstrate that CSDS changes gut microbiome composition in male and female mice.