Catabolism Mechanism and Growth-Promoting Effect of Xylooligosaccharides in <i>Lactiplantibacillus plantarum</i> Strain B20

Prebiotics are food ingredients that result in specific changes in the composition and/or activity of the gastrointestinal microbiota, thus conferring benefits upon host health. Xylooligosaccharides (XOS) are prebiotic fibers made from xylan. Commercial XOS are mixtures of oligosaccharides containing β-1,4–linked xylose residues. Though they are widely added to foods at different doses, the molecular mechanisms of the catabolism and growth promotion of XOS in the innate gut microbes <i>Lactobacillus</i> spp. remain unknown. In this study, we evaluated the growth-promoting effect using a human fecal isolate, <i>Lactiplantibacillus plantarum</i> strain B20 (<i>Lb. plantarum</i> B20). Assays of bacterial growth and lactic acid production showed stronger growth promotion of XOS than other oligosaccharides did, in a dose- and fraction-dependent pattern. Using the <i>Lb. plantarum</i> strain SK151 genome as a reference, bioinformatic analysis failed to identify any previously characterized genes responsible for the uptake and catabolism of XOS. However, transcriptomic analysis of <i>Lb. plantarum</i> B20 yielded numerous differentially expressed genes (DEGs) during fermentation of XOS. Among these, an oligopeptide ABC transporter (RS03575-03595, composed of five proteins) and a hydrolase (RS06170) were significantly upregulated. Molecular docking analysis indicated that the substrate-binding protein RS03575 may mediate the import of XOS into the cell. Enzymatic assays further demonstrated that RS06170 possesses β-xylosidase activity and can effectively degrade XOS. In addition, functional enrichment analysis suggested that the growth-promoting effect of XOS may be attributed to the upregulation of genes involved in cellular component biogenesis and cell division, potentially through modulation of ribosome function and carbohydrate metabolism in <i>Lb. plantarum</i> B20. These results provide valuable insights into the mechanisms by which XOS promote growth and highlight potential targets for enhancing prebiotic–probiotic interactions.