Vitamin B12 Uptake by the Gut Commensal Bacteria Bacteroides thetaiotaomicron Limits the Production of Shiga Toxin by Enterohemorrhagic Escherichia coli.

Charlotte Cordonnier,Jean-Guillaume Emond-Rheault,Josée Harel,Grégory Jubelin,Annie Garrivier,Guillaume Le Bihan

doi:10.3390/toxins8010014

Abstract

Enterohemorrhagic Escherichia coli (EHEC) are foodborne pathogens responsible for the development of bloody diarrhea and renal failure in humans. Many environmental factors have been shown to regulate the production of Shiga toxin 2 (Stx2), the main virulence factor of EHEC. Among them, soluble factors produced by human gut microbiota and in particular, by the predominant species Bacteroides thetaiotaomicron (B. thetaiotaomicron), inhibit Stx2 gene expression. In this study, we investigated the molecular mechanisms underlying the B. thetaiotaomicron-dependent inhibition of Stx2 production by EHEC. We determined that Stx2-regulating molecules are resistant to heat treatment but do not correspond to propionate and acetate, two short-chain fatty acids produced by B. thetaiotaomicron. Moreover, screening of a B. thetaiotaomicron mutant library identified seven mutants that do not inhibit Stx2 synthesis by EHEC. One mutant has impaired production of BtuB, an outer membrane receptor for vitamin B12. Together with restoration of Stx2 level after vitamin B12 supplementation, these data highlight vitamin B12 as a molecule produced by gut microbiota that modulates production of a key virulence factor of EHEC and consequently may affect the outcome of an infection.

Highlights

The human gut is colonized by microbiota that is a dense population of microorganisms, primarily bacteria belonging to two major phyla: Bacteroidetes and Firmicutes
Production of Shiga toxin 2 (Stx2) remained inhibited after growth of Escherichia coli (EHEC) in all B. thetaiotaomicron-conditioned media (Figure 1), indicating that the inhibitory compounds are unaltered in these conditions
We investigated the repressive effect of B. thetaiotaomicron on the ability of EHEC

Summary

Introduction

The human gut is colonized by microbiota that is a dense population of microorganisms, primarily bacteria belonging to two major phyla: Bacteroidetes and Firmicutes. Gut microbiota provides many benefits for humans, including the digestion of food and production of end-products available for the host; production of key vitamins and hormones; and development of the immune system [1]. Gut microbiota efficiently limits infection by intestinal pathogenic bacteria, a phenomenon termed colonization resistance [2]. This concept is supported by numerous studies showing disruption of the normal microbiota. The molecular basis for colonization resistance remains elusive and relies on four possible mechanisms [6].

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