Fig. 1.

Overview of the starch utilization system (Sus) in B. thetaiotaomicron. The sus locus is transcribed from two divergent promoters. Transcription of susR occurs independently from the rest of the locus, which allows the inner membrane-spanning protein SusR to sense the disaccharide inducer, maltose, in the periplasm and subsequently drive the transcription of susABCDEFG. Starch is bound to the surface of the cell by the starch-binding outer membrane lipoproteins SusDEF. Subsequent hydrolysis by a similarly membrane- tethered α-amylase, SusG, generates oligosaccharides small enough to transit through the TonB-dependent transporter. Once in the periplasm, SusA and SusB, a neopullulanase and α-glucosidase, respectively, process oligosaccharides into glucose. The monosaccharide is then shuttled into the cytoplasm by an unknown transporter. The stoichiometry and assembly of the Sus is unknown