Characterization of a novel β-galactosidase from Bifidobacterium adolescentis DSM 20083 active towards transgalactooligosaccharides

This paper reports on the effects of both reducing and nonreducing transgalactooligosaccharides (TOS) comprising 2 to 8 residues on the growth of Bifidobacterium adolescentis DSM 20083 and on the production of a novel beta-galactosidase (beta-Gal II). In cells grown on TOS, in addition to the lactose degrading beta-Gal (beta-Gal I), another beta-Gal (beta-Gal II) was detected and it showed activity towards TOS but not towards lactose, beta-Gal II activity,vas at least 20-fold higher when cells were grown on TOS than when cells were grown on galactose, glucose, and lactose. Subsequently, the enzyme was purified from the cell extract of TOS-grown B. adolescentis by anion-exchange chromatography, adsorption chromatography, and size-exclusion chromatography. beta-Gal II has apparent molecular masses of 350 and 89 kDa as judged by size-exclusion; chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis, respectively, indicating that the enzyme is active in vivo as a tetramer, beta-Gal II had an optimal activity at pH 6 and was not active below pH 5. Its optimum temperature was 35 degrees C. The enzyme show ed highest V-max values towards galactooligosaccharides with a low degree of polymerization. This result is in agreement with the observation that during fermentation of TOS, the di- and trisaccharides were fermented first. beta-Gal II was active towards beta-galactosyl residues that were 1-->4, 1-->6, 1-->3, and 1<->1 linked, signifying its role in the metabolism of galactooligosaccharides by B, adolescentis.