FIG 1 .

Schematic of the regulation of arabinan and arabinose utilization genes in B. thetaiotaomicron. Arabinan is extracellularly bound by two SusD-like proteins and imported into the periplasm by two SusC-like transporters. Large arabinan polymers are broken down into polymers of six to eight subunits in chain length (oligoarabinose) and eventually smaller arabino-oligosaccharides, such as arabinobiose, which are transported into the cytoplasm by AraP. These oligosaccharides are broken down to arabinose in the cytoplasm by an unknown glycoside hydrolase. Oligoarabinose binds to and activates the transcriptional regulator BT0366, which, in turn, promotes transcription of the arabinan utilization genes BT0365 to -60, BT0366, and BT0367 to -69. l-Arabinose is transported into the cell by an unknown mechanism. Cytoplasmic arabinose prevents binding of the transcriptional repressor AraR to the promoters of the arabinan utilization gene BT0365 and the arabinose utilization gene BT0356 (araM). The transcriptional regulator BT4338 is necessary for full activation of arabinan and arabinose utilization genes. The signal controlling the activity of BT4338 is at present unknown. OM, outer membrane; IM, inner membrane.