Dominant effects of the immediate environment on the gut microbiome of mice used in biomedical research

Studies using genetically engineered mouse (GEM) models are often performed over extended periods. The microbiomes of GEM colonies are expected to retain some of the microbial features present in the founder mice used to generate each GEM model and to acquire new features through dietary and environmental sources. The rate at which these processes occur over time likely varies between institutions. To assess the relative effect size of environment on the microbiome of GEMs used in biomedical research, we performed 16S rRNA metabarcoding of fecal samples from 275 distinct GEM lines (<i>n</i> = 351) maintained by 139 different laboratories at 84 different research institutions in 34 U.S. states or districts and seven other countries, and compared intra-strain, inter-strain, inter-lab, and inter-institution similarities. Reference data from mice harboring supplier-origin (SO) microbiomes (<i>n</i> = 1,171) were used to determine the relative contribution and nature of microbes from known and unknown sources. Paradoxically, the data indicate that the immediate laboratory-level environment is the dominant factor shaping the microbiome of GEM models, but that the microbiome of GEMs develops similarities in beta-diversity, regardless of other factors. Related to this, we detected an unexpectedly high prevalence and abundance of <i>Helicobacter</i> spp. in GEM microbiomes, the abundance of which correlated significantly with the abundance of multiple resident taxa colonizing the mucosa. These findings suggest a higher prevalence of <i>Helicobacter</i> spp. in laboratory mice than previously appreciated, and the possibility of positive and negative interactions with other taxa is found to affect GEM model phenotypes.IMPORTANCEThere are concerns regarding the reproducibility and predictive value of mouse models of human disease. Notwithstanding those legitimate concerns, genetically engineered mouse (GEM) models provide an invaluable platform to investigate gene function or effects of environmental factors in a biological system. The microbiome of GEM models significantly influences model phenotypes and thus represents a possible source of poor reproducibility. While the microbiome is often incorporated in research investigating disease mechanisms using GEMs, limited information is available regarding the similarity of the microbiome of GEM models within and between research labs at the same institution, or across institutions. Moreover, while the microbiome of founder mice from different suppliers is known to differ, the degree to which features present in supplier-origin microbiomes are retained in GEM colonies throughout experimentation is unclear. These data demonstrate the robust effect of lab-level environment and the need for sample collection concurrent with phenotyping.