TonB‐dependent transporters in the Bacteroidetes: Unique domain structures and potential functions

The human gut microbiota endows the host with a wealth of metabolic functions central to health, one of which is the degradation and fermentation of complex carbohydrates. The Bacteroidetes are one of the dominant bacterial phyla of this community and possess an expanded capacity for glycan utilization. This is mediated via the coordinated expression of discrete polysaccharide utilization loci (PUL) that invariantly encode a TonB‐dependent transporter (SusC) that works with a glycan‐capturing lipoprotein (SusD). More broadly within Gram‐negative bacteria, TonB‐dependent transporters (TBDTs) are deployed for the uptake of not only sugars, but also more often for essential nutrients such as iron and vitamins. Here, we provide a comprehensive look at the repertoire of TBDTs found in the model gut symbiont Bacteroides thetaiotaomicron and the range of predicted functional domains associated with these transporters and SusD proteins for the uptake of both glycans and other nutrients. This atlas of the B. thetaiotaomicron TBDTs reveals that there are at least three distinct subtypes of these transporters encoded within its genome that are presumably regulated in different ways to tune nutrient uptake. The human gut microbiota endows the host with a wealth of metabolic functions including the degradation and fermentation of complex carbohydrates. The Bacteroidetes are a dominant component of the human gut microbial community and possess unique nutrient uptake systems that are centered around TonB‐dependent transporters (TBDTs), many of which work with nutrient‐binding lipoproteins. Here we provide a comprehensive look at the repertoire of TBDTs found in the Bacteroides thetaiotaomicron VPI‐5482 genome, revealing at least three distinct subtypes of these transporters that are presumably regulated in different ways to tune nutrient uptake.