Lacticaseibacillus paracasei completely utilizes fructooligosacchrides in the human gut through β-fructosidase (FosE).

The fecal microbiota of two healthy adults was cultivated in a medium containing commercial fructooligosaccharides [FOS; 1-kestose (GF), nystose (GF), and 1-fructofuranosylnystose (GF)]. Initially, the proportions of lactobacilli in the two feces samples were only 0.42% and 0.17%; however, they significantly increased to 7.2% and 4.8%, respectively, after cultivation on FOS. Most FOS-utilizing isolates could utilize only GF; however, Lacticaseibacillus paracasei strain Lp02 could fully consume GF and GF too. The FOS operon (fosRABCDXE) was present in Lc. paracasei Lp02 and another Lc. paracasei strain, KCTC 3510, but fosE was only partially present in the non-FOS-degrading strain KCTC 3510. In addition, the top six upregulated genes in the presence of FOS were fosABCDXE, particularly fosE. FosE is a β-fructosidase that hydrolyzes both sucrose and all three FOS. Finally, a genome-based analysis suggested that fosE is mainly observed in Lc. paracasei, and only 13.5% (61/452) of their reported genomes were confirmed to include it. In conclusion, FosE allows the utilization of FOS, including GF and GF as well as GF, by some Lc. paracasei strains, suggesting that this species plays a pivotal role in FOS utilization in the human gut.