Characterization of GH2 and GH42 \u03b2-galactosidases derived from bifidobacterial infant isolates

Valentina Ambrogi,Francesca Bottacini,Cao Linqiu,Mary O’Connell Motherway,Margriet Schoterman,Barry Schoemaker,Douwe Van Sinderen,Joyce O’Sullivan

doi:10.1186/s13568-019-0735-3

Abstract

Bifidobacteria are among the first and most abundant bacterial colonizers of the gastrointestinal tract of (breast-fed) healthy infants. Their success of colonising the infant gut is believed to be, at least partly, due to their ability to metabolize available carbon sources by means of secreted or intracellular glycosyl hydrolases (GHs). Among these, β-galactosidases are particularly relevant as they allow bifidobacteria to grow on β-galactosyl-linked saccharidic substrates, which are present in copious amounts in the milk-based diet of their infant host (e.g. lactose and human milk oligosaccharides). In the present study we employed an in silico analysis to identify GH family 2 and 42 β-galactosidases encoded by typical infant-associated bifidobacteria. Comparative genome analysis followed by characterisation of selected β-galactosidases revealed how these GH2 and GH42 members are distributed among these infant-associated bifidobacteria, while their hydrolytic activity towards growth substrates commonly available in the infant gut were also assessed.

Highlights

Bifidobacteria are common members of the human gut microbiota, and are especially abundant in the gastrointestinal tract (GIT) of healthy, breast-fed infants (Milani et al 2017)
The current study focused on a survey and subsequent hydrolytic characterization of β-galactosidases identified from sequenced strains of bifidobacterial species which have been previously shown to be members of the infant gut microbiota (i.e. B. breve, B. bifidum, B. longum subsp. longum and B. longum subsp. infantis) (Lewis and Mills 2017; Milani et al 2017; Turroni et al 2012)
Employing this comparative search approach we established that the total number of predicted GH2 and GH42 β-galactosidase-encoding genes encoded by (34 representatives of ) these four bifidobacterial species is 137, of which 44, 45 and 48 were assigned to B. breve, B. bifidum and B. longum subsp. longum spp., respectively (Additional file 1: Table S1)

Summary

Introduction

Bifidobacteria are common members of the human gut microbiota, and are especially abundant in the gastrointestinal tract (GIT) of healthy, breast-fed infants (Milani et al 2017). Human milk glycans can be quite diverse and they are composed of 13 core structures generated through the elongation of lactose at the reducing end with one or more β1,3-linked lacto-N-biose (type-I chain) and/or β1,3/6-linked N-acetyllactosamine units (type-II chain) (Urashima et al 2012). These core structures (including lactose itself ) can in turn be substituted at terminal positions by fucose connected via α1,2/3/4 links, and/or sialic acid residues attached by α2,3/6 links (Smilowitz et al 2014). HMOs are especially rich in type-I chains and constitute a characteristic feature of human milk (Urashima et al 2012)

Methods

Results

Conclusion