Carbohydrate-controlled serine protease inhibitor (serpin) production in Bifidobacterium longum subsp. longum

S Duboux,M Kleerebezem,C J Bolten,J A Muller,A Mercenier,M Golliard,G Bergonzelli

doi:10.1038/s41598-021-86740-y

S Duboux, M Kleerebezem + Show 5 more

Open Access

https://doi.org/10.1038/s41598-021-86740-y

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Abstract

The Serine Protease Inhibitor (serpin) protein has been suggested to play a key role in the interaction of bifidobacteria with the host. By inhibiting intestinal serine proteases, it might allow bifidobacteria to reside in specific gut niches. In inflammatory diseases where serine proteases contribute to the innate defense mechanism of the host, serpin may dampen the damaging effects of inflammation. In view of the beneficial roles of this protein, it is important to understand how its production is regulated. Here we demonstrate that Bifidobacterium longum NCC 2705 serpin production is tightly regulated by carbohydrates. Galactose and fructose increase the production of this protein while glucose prevents it, suggesting the involvement of catabolite repression. We identified that di- and oligosaccharides containing galactose (GOS) and fructose (FOS) moieties, including the human milk oligosaccharide Lacto-N-tetraose (LNT), are able to activate serpin production. Moreover, we show that the carbohydrate mediated regulation is conserved within B. longum subsp. longum strains but not in other bifidobacterial taxons harboring the serpin coding gene, highlighting that the serpin regulation circuits are not only species- but also subspecies- specific. Our work demonstrates that environmental conditions can modulate expression of an important effector molecule of B. longum, having potential important implications for probiotic manufacturing and supporting the postulated role of serpin in the ability of bifidobacteria to colonize the intestinal tract.

Highlights

Bifidobacterium longum subsp. longum is a Gram-positive, high G+C content, anaerobic bacterium that is a member of the phylum Actinobacteria
We have here revealed that different carbohydrates control production of serpin, a protein playing a key role in the bioactivity of B. longum subsp. longum
Polyclonal antibodies obtained by immunizing rabbits with the previously purified B. longum NCC 2705 serpin recombinant p rotein[12] were used to develop a sandwich ELISA (Figure S1)

Summary

Introduction

Bifidobacterium longum subsp. longum is a Gram-positive, high G+C content, anaerobic bacterium that is a member of the phylum Actinobacteria. B. longum NCC 2705 produces a serine protease inhibitor (serpin) encoded by the BL0108 gene, which forms covalent products with pancreatic and neutrophil elastases thereby inhibiting their function[12] This serpin is proposed to play an important role in the colonization of bifidobacteria by protecting them against hostderived proteases and providing them with a survival advantage in the competitive intestinal e nvironment[12,13]. The serpin’s capacity to inhibit the Human Neutrophil E lastase[12] may be involved in the immunomodulatory capacities of the s train[14] as elastase is released by activated neutrophils at the sites of intestinal inflammation[15] In line with this role in dampening innate immunity, serpin was demonstrated to play a key role in the antiinflammatory effect of B. longum NCC 2705 in a mouse model of gluten sensitivity[16]. We have here revealed that different carbohydrates control production of serpin, a protein playing a key role in the bioactivity of B. longum subsp. longum

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