Bacteroides thetaiotaomicron uses a widespread extracellular DNase to promote bile-dependent biofilm formation

ABSTRACT Bacteroides thetaiotaomicron is a gut symbiont that inhabits the mucus layer and adheres to and metabolizes food particles, contributing to gut physiology and maturation. Whereas adhesion and biofilm formation could be key features for B. thetaiotaomicron stress resistance and gut colonization, little is known about the determinants of B. thetaiotaomicron biofilm formation. We previously showed that the B. thetaiotaomicron 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 B. thetaiotaomicron isolates and common gut Bacteroidales species. We identified the genetic determinants of this bile-dependent biofilm formation and showed that it involves the production of the DNase BT3563, degrading extracellular DNA, in biofilms formed in the presence of bile. Our study therefore identifies a physiologically relevant condition inducing B. thetaiotaomicron biofilm and shows that, in contrast to the biofilm-promoting role played by bacterial eDNA scaffold in Firmicutes and Proteobacteria models, degradation of eDNA by BT3563 DNAse and its widespread homologs is required to achieve B. thetaiotaomicron bile-dependent biofilm formation.