Regulating vitamin B12 biosynthesis via the <i>cbiM</i>Cbl riboswitch in <i>Propionibacterium</i> strain UF1.

Abstract

Vitamin B12 (VB12) is a critical micronutrient that controls DNA metabolic pathways to maintain the host genomic stability and tissue homeostasis. We recently reported that the newly discovered commensal <i>Propionibacterium</i>, P. UF1, regulates the intestinal immunity to resist pathogen infection, which may be attributed in part to VB12 produced by this bacterium. Here we demonstrate that VB12 synthesized by P. UF1 is highly dependent on <i>cobA</i> gene-encoding uroporphyrinogen III methyltransferase, and that this vitamin distinctively regulates the <i>cobA</i> operon through its 5' untranslated region (5' UTR). Furthermore, conserved secondary structure and mutagenesis analyses revealed a VB12-riboswitch, <i>cbiM</i>Cbl (140 bp), within the 5' UTR that controls the expression of downstream genes. Intriguingly, ablation of the <i>cbiM</i>Cbl significantly dysregulates the biosynthesis of VB12, illuminating the significance of this riboswitch for bacterial VB12 biosynthesis. Collectively, our finding is an in-depth report underscoring the regulation of VB12 within the beneficial P. UF1 bacterium, through which the commensal metabolic network may improve gut bacterial cross-feeding and human health.