Riboflavin Biosynthesis and Overproduction by a Derivative of the Human Gut Commensal Bifidobacterium longum subsp. infantis ATCC 15697

Ana Solopova,Alberto Amaretti,Douwe Van Sinderen,Elena Venturi Degli Esposti,Maddalena Rossi,Stefano Raimondi,Francesca Bottacini

doi:10.3389/fmicb.2020.573335

Abstract

Riboflavin or vitamin B2 is the precursor of the essential coenzymes flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD). Despite increased interest in microbial synthesis of this water-soluble vitamin, the metabolic pathway for riboflavin biosynthesis has been characterized in just a handful of bacteria. Here, comparative genome analysis identified the genes involved in the de novo biosynthetic pathway of riboflavin in certain bifidobacterial species, including the human gut commensal Bifidobacterium longum subsp. infantis (B. infantis) ATCC 15697. Using comparative genomics and phylogenomic analysis, we investigated the evolutionary acquisition route of the riboflavin biosynthesis or rib gene cluster in Bifidobacterium and the distribution of riboflavin biosynthesis-associated genes across the genus. Using B. infantis ATCC 15697 as model organism for this pathway, we isolated spontaneous riboflavin overproducers, which had lost transcriptional regulation of the genes required for riboflavin biosynthesis. Among them, one mutant was shown to allow riboflavin release into the medium to a concentration of 60.8 ng mL–1. This mutant increased vitamin B2 concentration in a fecal fermentation system, thus providing promising data for application of this isolate as a functional food ingredient.

Highlights

Riboflavin is a precursor of flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), cofactors acting as essential electron carriers in redox reactions of cell metabolism (LeBlanc et al, 2011)
The protein sequences deduced from the rib genes of B. infantis ATCC 15697 were utilized as query in a search aimed at identifying homologues in an open reading frames (ORFs) dataset that was extracted from 662 genomes, being representative of 83 bifidobacterialspecies
Our combined BLASTP and MCL clustering analysis revealed that de novo riboflavin biosynthesis appears to be a rather uncommon feature among members of the genus Bifidobacterium, since homologues of the complete rib operon were identified in just 16 out of 83 bifidobacterial species, most of which (14 out of 16) had been isolated from primates (Figure 2A)

Summary

Introduction

Riboflavin (i.e., vitamin B2) is a precursor of flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), cofactors acting as essential electron carriers in redox reactions of cell metabolism (LeBlanc et al, 2011). Riboflavin Biosynthesis in B. infantis biosynthesis (Bacher et al, 2000; Fischer et al, 2004). Humans need to regularly obtain this vitamin through their diet as they are unable to synthesize or store it. For this reason, riboflavin is an ingredient in various fortified foods and multivitamin supplements. Absorption of riboflavin occurs in the small and large intestine through specific carriers (Thakur et al, 2017)

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Conclusion