The microbiome holds great promise as a source of novel therapeutic targets for many diseases. Mining for causative microorganisms that impact processes underlying disease states should utilize Koch’s postulates. Here we show a functional screen for the bacterial microbiota of intestinal immunoglobulin A (IgA)-deficient mice; we identified a novel Gram-negative bacterium, proposed to be named as Tomasiella immunophila that induces and degrades IgA in mouse intestine. T. immunophila is auxotrophic for the bacterial cell wall amino sugar N-acetylmuramic acid (MurNAc). T. immunophila secretes IgA-degrading enzymes into outer membrane vesicles that preferentially degrade rodent antibodies with kappa but not lambda light chains. We propose this study uncovers a new paradigm for the role of symbionts in immunodeficiency that can ultimately be applied to human disease.

This dataset consists of a phylogenomic tree, generated using Phylophlan3.