Bifidobacterium bifidum Extracellular Sialidase Enhances Adhesion to the Mucosal Surface and Supports Carbohydrate Assimilation.

Keita Nishiyama,Nobuhiko Okada,Makoto Sugiyama,Tadasu Urashima,Yuji Yamamoto,Satoru Fukiya,Takao Mukai,Atsushi Yokota,Takashi Takaki,Mark S Turner

doi:10.1128/mbio.00928-17

Abstract

ABSTRACTBifidobacterium is a natural inhabitant of the human gastrointestinal (GI) tract. We studied the role of the extracellular sialidase (SiaBb2, 835 amino acids [aa]) from Bifidobacterium bifidum ATCC 15696 in mucosal surface adhesion and carbohydrate catabolism. Human milk oligosaccharides (HMOs) or porcine mucin oligosaccharides as the sole carbon source enhanced B. bifidum growth. This was impaired in a B. bifidum ATCC 15696 strain harboring a mutation in the siabb2 gene. Mutant cells in early to late exponential growth phase also showed decreased adhesion to human epithelial cells and porcine mucin relative to the wild-type strain. These results indicate that SiaBb2 removes sialic acid from HMOs and mucin for metabolic purposes and may promote bifidobacterial adhesion to the mucosal surface. To further characterize SiaBb2-mediated bacterial adhesion, we examined the binding of His-tagged recombinant SiaBb2 peptide to colonic mucins and found that His-SiaBb2 as well as a conserved sialidase domain peptide (aa 187 to 553, His-Sia) bound to porcine mucin and murine colonic sections. A glycoarray assay revealed that His-Sia bound to the α2,6-linked but not to the α2,3-linked sialic acid on sialyloligosaccharide and blood type A antigen [GalNAcα1-3(Fucα1-2)Galβ] at the nonreducing termini of sugar chains. These results suggest that the sialidase domain of SiaBb2 is responsible for this interaction and that the protein recognizes two distinct carbohydrate structures. Thus, SiaBb2 may be involved in Bifidobacterium-mucosal surface interactions as well as in the assimilation of a variety of sialylated carbohydrates.

Highlights

Bifidobacterium is a natural inhabitant of the human gastrointestinal (GI) tract
We demonstrate that B. bifidum extracellular sialidase may modulate the assimilation of sialylated carbohydrates and B. bifidum-mucosal surface interactions based on the following observations. (i) SiaBb2 cleaved sialyl-Human milk oligosaccharides (HMOs) and -porcine mucin oligosaccharide (PMO) to produce utilizable oligosaccharides, which supported the growth of B. bifidum. (ii) SiaBb2 promoted B. bifidum adhesion to the mucosa via specific binding to sialyl(␣2,6)Gal residue and BgA antigen on mucin
These findings indicate that extracellular sialidase acts as a bifunctional enzyme that is potentially important for B. bifidum colonization (Fig. 5)

Summary

Introduction

Bifidobacterium is a natural inhabitant of the human gastrointestinal (GI) tract. We studied the role of the extracellular sialidase (SiaBb2, 835 amino acids [aa]) from Bifidobacterium bifidum ATCC 15696 in mucosal surface adhesion and carbohydrate catabolism. Mutant cells in early to late exponential growth phase showed decreased adhesion to human epithelial cells and porcine mucin relative to the wild-type strain These results indicate that SiaBb2 removes sialic acid from HMOs and mucin for metabolic purposes and may promote bifidobacterial adhesion to the mucosal surface. SiaBb2 enhanced B. bifidum adhesion to mucosal surfaces via specific interactions with the ␣2,6 linkage of sialyloligosaccharide and blood type A antigen on mucin carbohydrates. Bifidobacterial colonization of the human gastrointestinal (GI) tract occurs shortly after delivery; abundance declines with age such that this genus represents Ͻ10% of the human adult microbiota [2,3,4] Some species, such as Bifidobacterium bifidum, Bifidobacterium breve, Bifidobacterium longum subsp. The fimbria-associated BL0675 subunit found in several B. longum subsp. longum strains [16] promotes adhesion to mucin [17]

Methods

Results

Conclusion