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Applied and Environmental Microbiology, July 2008, p. 3996-4004, Vol. 74, No. 13
0099-2240/08/$08.00+0 doi:10.1128/AEM.00149-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Graduate School of Biostudies, Kyoto University, Kitashirakawa, Sakyo-ku, Kyoto 606-8502, Japan,1 National Food Research Institute, 2-1-12 Kannondai, Tsukuba, Ibaraki 305-8642, Japan,2 Research Institute for Bioresources and Biotechnology, Ishikawa Prefectural University, Nonoichi, Ishikawa 921-8836, Japan3
Received 16 January 2008/ Accepted 28 April 2008
Breast-fed infants often have intestinal microbiota dominated by bifidobacteria in contrast to formula-fed infants. We found that several bifidobacterial strains produce a lacto-N-biosidase that liberates lacto-N-biose I (Galβ1,3GlcNAc; type 1 chain) from lacto-N-tetraose (Galβ1,3GlcNAcβ1,3Galβ1,4Glc), which is a major component of human milk oligosaccharides, and subsequently isolated the gene from Bifidobacterium bifidum JCM1254. The gene, designated lnbB, was predicted to encode a protein of 1,112 amino acid residues containing a signal peptide and a membrane anchor at the N and C termini, respectively, and to possess the domain of glycoside hydrolase family 20, carbohydrate binding module 32, and bacterial immunoglobulin-like domain 2, in that order, from the N terminus. The recombinant enzyme showed substrate preference for the unmodified β-linked lacto-N-biose I structure. Lacto-N-biosidase activity was found in several bifidobacterial strains, but not in the other enteric bacteria, such as clostridia, bacteroides, and lactobacilli, under the tested conditions. These results, together with our recent finding of a novel metabolic pathway specific for lacto-N-biose I in bifidobacterial cells, suggest that some of the bifidobacterial strains are highly adapted for utilizing human milk oligosaccharides with a type 1 chain.
Published ahead of print on 9 May 2008.
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