Host interactions with Segmented Filamentous Bacteria: an unusual trade-off that drives the post-natal maturation of the gut immune system.

Segmented Filamentous Bacteria (SFB) are present in the gut microbiota of a large number of vertebrate species where they are found intimately attached to the intestinal epithelium. SFB has recently attracted considerable attention due to its outstanding capacity to stimulate innate and adaptive host immune responses without causing pathology. Recent genomic analysis placed SFB between obligate and facultative symbionts, unraveled its highly auxotrophic needs, and provided a rationale for the complex SFB life-style in close contact with the epithelium. Herein, we examine how the SFB life-style may underlie its potent immunostimulatory properties and discuss how the trade-off set up between SFB and its hosts can simultaneously help to establish and maintain the ecological niche of SFB in the intestine and drive the post-natal maturation of the host gut immune barrier.