Comparative proteome analysis of Bifidobacterium longum subsp. infantis grown on β-glucans from different sources and a model for their utilization.

Recent studies have demonstrated that β-glucans from different sources, which are considered as potential prebiotics, could enhance growth of bifidobacteria. To elucidate the metabolic pathway of β-glucans in the widely used probiotic B. longum subsp. infantis, a comparative proteomic analysis was carried out along with two-dimensional difference gel electrophoresis (2D-DIGE), real-time RT-PCR, and enzyme activity assay on samples obtained from cultures grown on β-glucans derived from barley, seaweed, and mushroom. Results showed that 77 spots were found to be differentially expressed among different cultures, and 17 of them were predicted to play a role in β-glucan catabolism, including ABC transporter for sugars, enolase, and phosphotransferase system protein. Among them, 6 genes encoding for 6 proteins were shown to be induced by β-glucans at the transcriptional level and had higher abundance. The enzyme activity assay detected intracellular glucanase activity present in the cultures grown on the β-glucans from seaweed and mushroom. On the basis of the above results, a model for catabolism of β-glucans in B. infantis is proposed as follows: β-glucan molecules in the medium are transported into the cell through the ABC (ATP-binding cassette) transport system and PTS (phosphotransferase system) proteins followed by hydrolysis through action of intracellular glucanase to glucose, which is subsequently incorporated into the central fermentative pathway 'bifid shunt'. This study for the first time reveals the possible degradation pathway of β-glucans by B. infantis, which has implications for potential use of these β-glucans as novel prebiotics in development of synbiotic application.