<i>Bacteroides thetaiotaomicron</i> uses a widespread extracellular DNase to promote bile-dependent biofilm formation.

Abstract

<i>Bacteroides thetaiotaomicron</i> is a gut symbiont that inhabits the mucus layer and adheres to and metabolizes food particles, contributing to gut physiology and maturation. Although adhesion and biofilm formation could be key features for <i>B. thetaiotaomicron</i> stress resistance and gut colonization, little is known about the determinants of <i>B. thetaiotaomicron</i> biofilm formation. We previously showed that the <i>B. thetaiotaomicron</i> reference strain VPI-5482 is a poor in vitro biofilm former. Here, we demonstrated that bile, a gut-relevant environmental cue, triggers the formation of biofilm in many <i>B. thetaiotaomicron</i> isolates and common gut Bacteroidales species. We determined that bile-dependent biofilm formation involves the production of the DNase BT3563 or its homologs, degrading extracellular DNA (eDNA) in several <i>B. thetaiotaomicron</i> strains. Our study therefore shows that, although biofilm matrix eDNA provides a biofilm-promoting scaffold in many studied Firmicutes and Proteobacteria, BT3563-mediated eDNA degradation is required to form <i>B. thetaiotaomicron</i> biofilm in the presence of bile.