Modulation of riboflavin biosynthesis and utilization in mycobacteria.

The pathway for biosynthesis and utilization of riboflavin, the precursor of the essential coenzymes, FMN and FAD, is of particular interest in the flavin-rich pathogen, (Mtb), for two important reasons: (i) the pathway includes potential TB drug targets; and (ii) metabolites derived from the riboflavin biosynthesis pathway provide ligands for mucosal associated invariant T (MAIT) cells, which have been implicated in TB pathogenesis. However, the riboflavin pathway is poorly understood in mycobacteria, which lack canonical mechanisms to transport this vitamin and to regulate flavin coenzyme homeostasis. By assessing the impact of conditionally disrupting each step of the pathway on mycobacterial viability and on the levels of the pathway proteins as well as riboflavin, we genetically validate the riboflavin pathway as a target for TB drug discovery and provide a resource for further exploring the association between riboflavin biosynthesis, MAIT cell activation and TB infection and disease.