Friend or foe? Contextualizing Bacteroides through the lens of niche remodeling.

The genus Bacteroides comprises canonical commensals of the gastrointestinal microbiota that maintain intestinal homeostasis and contribute to host health. Yet, emergent evidence has revealed that these same bacteria can also increase host susceptibility to infectious and noninfectious diseases, as well as directly drive intestinal inflammatory pathology. In this review we reconcile this duality with the paradigm that Bacteroides' pathogenic potential scales with the degree to which it remodels its intestinal niches. Understanding the molecular and ecological mechanisms underlying this niche remodeling is essential to defining when Bacteroides acts as friend or foe. This review highlights recent advances that illuminate these context-dependent behaviors and their implications for gut health and disease.