Induction of α-l-arabinofuranosidase activity by monomeric carbohydrates in Bifidobacterium longum and ubiquity of encoding genes

摘要

Bifidobacterium longum can be isolated from human faeces, some strains being considered probiotics. B. longum NIZO B667 produces an exo-acting α-l-arabinofuranosidase, AbfB, previously purified by us, that releases l-arabinose from arabinan and arabinoxylan. This activity was subjected to two–seven-fold induction by l-arabinose, d-xylose, l-arabitol and xylitol and to repression by glucose. Maximum activity was obtained at 48 h incubation except for d-xylose that was at 24 h. High concentrations (200 mM) of l-arabitol also caused repression of the arabinofuranosidase. A unique band of activity showing the same migration pattern as the purified AbfB was found in zymograms of cell free extracts, indicating that the activity was likely due to this sole enzyme. The assessment of the influence of inducers and repressors on the activity of AbfB and on the expression of the abfB gene by real time PCR indicated that regulation was transcriptional. DNA amplifications using a pair of degenerated primers flanking an internal fragment within α-l-arabinofuranosidase genes of the family 51 of glycoside hydrolases evidenced that these enzymes are widespread in Bifidobacterium. The aminoacidic sequences of bifidobacteria included a fragment of four to six residues in the position 136–141 that was absent in other microorganisms