A Putative Type V Pilus Contributes to Bacteroides thetaiotaomicron Biofilm Formation Capacity

Abstract

<i>Bacteroides thetaiotaomicron</i> is a prominent anaerobic member of the healthy human gut microbiota. While the majority of functional studies on <i>B. thetaiotaomicron</i> addressed its impact on the immune system and the utilization of diet polysaccharides, <i>B. thetaiotaomicron</i> biofilm capacity and its contribution to intestinal colonization are still poorly characterized. We tested the natural adhesion of 34 <i>B. thetaiotaomicron</i> isolates and showed that although biofilm capacity is widespread among <i>B. thetaiotaomicron</i> strains, this phenotype is masked or repressed in the widely used reference strain VPI 5482. Using transposon mutagenesis followed by a biofilm positive-selection procedure, we identified VPI 5482 mutants with increased biofilm capacity corresponding to an alteration in the C-terminal region of BT3147, encoded by the <i>BT3148-BT3147</i> locus, which displays homology with Mfa-like type V pili found in many <i>Bacteroidetes</i> We show that BT3147 is exposed on the <i>B. thetaiotaomicron</i> surface and that BT3147-dependent adhesion also requires BT3148, suggesting that BT3148 and BT3147 correspond to the anchor and stalk subunits of a new type V pilus involved in <i>B. thetaiotaomicron</i> adhesion. This study therefore introduces <i>B. thetaiotaomicron</i> as a model to study proteinaceous adhesins and biofilm-related phenotypes in this important intestinal symbiont.<b>IMPORTANCE</b> Although the gut anaerobe <i>Bacteroides thetaiotaomicron</i> is a prominent member of the healthy human gut microbiota, little is known about its capacity to adhere to surfaces and form biofilms. Here, we identify that alteration of a surface-exposed protein corresponding to a type of pili found in many <i>Bacteroidetes</i> increases <i>B. thetaiotaomicron</i> biofilm formation. This study lays the ground for establishing this bacterium as a model organism for <i>in vitro</i> and <i>in vivo</i> studies of biofilm-related phenotypes in gut anaerobes.