Intracellular offspring released from SFB filaments are flagellated

The gut commensal segmented filamentous bacterium (SFB) attaches to the ileal epithelium and potently stimulates the host immune system. Using transmission electron microscopy (TEM), we show that mouse and rat SFB are flagellated above the concave tip at the unicellular intracellular offspring (IO) stage and that flagellation occurs prior to full IO differentiation and release of IOs from SFB filaments. This finding adds a missing link to the SFB life cycle. Electron micrographs show that mouse and rat segmented filamentous bacterium (SFB) unicellular intracellular offspring (IO) are flagellated and that flagellation occurs before IO release from SFB filaments.