Characterization of peptides available to different bifidobacteria

Nitrogen source is a limiting factor for bifidobacterial growth. It is generally believed that the nitrogen metabolism system varies a lot in bifidobacteria, which has a low utilization efficiency of nitrogen sources in the medium. This study aimed to analyze the rules of peptide utilization and to improve the utilization efficiency of nitrogen sources in bifidobacteria. Casein hydrolysates were prepared to assess their growth-promoting effects on different Bifidobacterium. The quantity, molecular weight, and amino acid composition of transportable peptides in each strain were analyzed by ultrafiltration, gel chromatography, and nano-LC-MS/MS. The results revealed that bifidobacteria had a high affinity for hydrophilic peptides containing growth-promoting amino acids and the transportable peptides varied among the strains. B. bifidum could transport peptides containing up to 14 residues and had a high preference for peptides containing 2, 3, or 9 residues. While B. longum could transport peptides containing up to 20 residues and B. brevis mainly transported peptides with 2–4 and 8–20 residues. Significant differences in the amino acid and peptide transport systems were revealed by the genome sequence analysis. This study highlighted the importance of specific peptides as nitrogen sources rather than macromolecules, which can significantly promote the growth of different bifidobacteria.