Multiple transporters and glycoside hydrolases are involved in arabinoxylan-derived oligosaccharide utilization in Bifidobacterium pseudocatenulatum

Arabinoxylan hydrolysates (AXH) are the hydrolyzed products of the major components of dietary fiber arabinoxylan. AXH include diverse oligosaccharides varying in xylose polymerization and side residue modifications with arabinose at the O-2 and/or O-3 positions of xylose unit. Previous studies have reported that AXH exhibit prebiotic properties on gut bifidobacteria; moreover, several adult-associated bifidobacterial species (e.g., Bifidobacterium adolescentis and Bifidobacterium longum ssp. longum) are known to utilize AXH. Bifidobacterium pseudocatenulatum is a common bifidobacterial species found in adult feces; however, the underlying molecular mechanism by which the species utilizes AXH remains poorly investigated. In this study, we tried to elucidate the molecular mechanisms of AXH utilization by B. pseudocatenulatum YIT 4072T. We performed RNA-seq transcriptomic analysis, which identified three up-regulated gene clusters during AXH utilization. The gene clusters encoded three sets of ATP-binding cassette (ABC) transporters and five enzymes belonging to the glycoside hydrolase family 43 (GH43). By characterizing these recombinant proteins, we found that three solute-binding proteins of ABC transporters had different but overlapping substrate specificities: two arabinofuranosidases exhibited distinct specificity: and three xylosidases exhibited functionally identical activity. These data collectively suggest that the transporters and glycoside hydrolases encoded in the three gene clusters work together to utilize AXH with different sizes and side residue modifications. Thus, our study sheds light on the overall picture of how these proteins collaborate for utilization of dietary fiber-derived oligosaccharides AXH in B. pseudocatenulatum, and may explain the predominance of this human gut symbiont species in the adult gut.