Infant-Associated Bifidobacterial β-Galactosidases and Their Ability to Synthesize Galacto-Oligosaccharides.

Valentina Ambrogi,Eoghan Casey,Douwe Van Sinderen,Margriet Schoterman,Mary O’Connell Motherway,John O’Callaghan,Barry Schoemaker,Justin Van Breen,Linqiu Cao,Bas Kuipers,Francesca Bottacini

doi:10.3389/fmicb.2021.662959

Abstract

Galacto-oligosaccharides (GOS) represent non-digestible glycans that are commercially produced by transgalactosylation of lactose, and that are widely used as functional food ingredients in prebiotic formulations, in particular in infant nutrition. GOS consumption has been reported to enhance growth of specific bacteria in the gut, in particular bifidobacteria, thereby supporting a balanced gut microbiota. In a previous study, we assessed the hydrolytic activity and substrate specificity of seventeen predicted β-galactosidases encoded by various species and strains of infant-associated bifidobacteria. In the current study, we further characterized seven out of these seventeen bifidobacterial β-galactosidases in terms of their kinetics, enzyme stability and oligomeric state. Accordingly, we established whether these β-galactosidases are capable of synthesizing GOS via enzymatic transgalactosylation employing lactose as the feed substrate. Our findings show that the seven selected enzymes all possess such transgalactosylation activity, though they appear to differ in their efficiency by which they perform this reaction. From chromatography analysis, it seems that these enzymes generate two distinct GOS mixtures: GOS with a relatively short or long degree of polymerization profile. These findings may be the stepping stone for further studies aimed at synthesizing new GOS variants with novel and/or enhanced prebiotic activities and potential for industrial applications.

Highlights

The human gut microbiota consists of a large number of microorganisms, some of which have shown to be positively associated with human host health and well-being (Edgar et al, 2011; Valdes et al, 2018)
The seven enzymes of interest were selected from a set of seventeen previously assessed GH2 and GH42 β-galactosidases encoded by various infant-derived bifidobacteria (Ambrogi et al, 2019)
Seven β-galactosidases originating from infant-derived bifidobacteria were heterologously expressed and characterized in terms of their kinetics, storage stability, oligomeric state and suitability for GOS synthesis

Summary

Introduction

The human gut microbiota consists of a large number of microorganisms, some of which have shown to be positively associated with human host health and well-being (Edgar et al, 2011; Valdes et al, 2018). A considerable amount of scientific effort has been dedicated to the development of novel strategies aimed at maintaining a balanced microbiota. Among these are the supplementation of beneficial bacteria (probiotics), and/or the administration of mostly indigestible (i.e., by the host) dietary substances (referred to as prebiotics) to stimulate the proliferation and/or metabolic activity of desired bacteria in the gut (Lozupone et al, 2012; Cheng et al, 2017). Galacto-oligosaccharides (GOS), together with inulin and fructo-oligosaccharides (FOS), were among the first recognized prebiotics, as they have been shown to promote growth of beneficial bacteria, in particular bifidobacteria and lactobacilli, in the human gut (Gibson and Roberfroid, 1995). A mixture of 90% short chain GOS (scGOS) and 10% long chain FOS (lcFOS) have shown to elicit similar effects on intestinal microbiota composition and associated metabolic profile (Boehm et al, 2002; Knol et al, 2005; Moro et al, 2005)

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Results

Conclusion