Eco-tank Housing Maintains Wild-Type Microbiota and Rewilds the Laboratory Mouse Gut Microbiome to Restore Natural Immune Tone

Laboratory mice housed under individually ventilated cage (IVC) conditions harbor simplified gut microbiota and immune phenotypes that diverge substantially from those shaped by environmental exposure, limiting translational relevance. To reintroduce controlled ecological complexity while maintaining biosafety and reproducibility, we developed the Eco-tank, a pathogen-monitored semi-natural housing system incorporating environmental substrates and dietary diversity. Longitudinal 16S rRNA sequencing revealed that even wild-caught Mus musculus rapidly lose microbial richness and predicted metabolic breadth under IVC housing. Eco-tank conditions stabilized diversity and preserved elements of wild-associated community structure during extended captivity. In parallel, standardized C57BL/6 mice housed in Eco-tanks underwent rewilding-like restructuring, with increased richness and community shifts toward a wild-associated configuration. Functional inference analyses indicated expansion of predicted pathways linked to short-chain fatty acid production, amino acid metabolism, and environmental substrate utilization. Eco-tank housing enhanced baseline resistance to pulmonary Pseudomonas aeruginosa (Pa) infection without compromising vaccine-induced protection, indicating that restoration of environmental microbial signals does not impair adaptive immunity. Together, these findings identify housing ecology as a dominant determinant of microbiome structure and functional potential. The Eco-tank provides a scalable and tractable framework for integrating environmental microbial complexity into laboratory models to better align preclinical immunology with ecologically conditioned immune systems. ImportanceLaboratory mice are foundational models for immunology, yet their specific pathogen-free rearing and housing environments impose ecological constraints that reshape the gut microbiome and immune tone. This study introduces a scalable, pathogen-monitored Eco-tank system that restores environmental microbial complexity while preserving experimental control. By demonstrating that housing ecology reshapes microbiome functional potential and modulates baseline immune resistance without compromising vaccine responsiveness, this work highlights environmental context as a critical experimental variable in preclinical immunology and offers a tractable framework for improving translational relevance.