Genetic and enzymatic basis of xylooligosaccharide metabolism by Bifidobacterium longum

Bifidobacteria are common members of the human gut microbiota and are associated with host health. Bifidobacterium longum subsp. longum (B. longum) is prevalent across host ages and can utilise diverse plant-derived glycans, including xylooligosaccharides (XOS), that are indigestible by humans. Here, we show that XOS utilisation is strain specific among members of B. longum. In B. longum NCIMB 8809, growth on XOS induced transcription of genes encoding three glycoside hydrolases (XouA, XouB, and XouC), together with adjacent genes (xouDEF) predicted to encode an ABC-type carbohydrate uptake system. Biochemical analyses demonstrated that XouA and XouC are β-xylosidases, whereas XouB is an α-arabinofuranosidase. Genetic disruption and complementation experiments showed that XouA and the XouDEF uptake system are required for growth on XOS. Together, these findings identify the genetic and enzymatic basis of XOS utilisation in B. longum and highlight how strain-level variation in carbohydrate metabolism may inform the design of targeted prebiotic and synbiotic strategies to promote gut health.