Riboflavin Salvage Supports Glycolysis in Borrelia burgdorferi Through Flavin-Dependent NAD+ Regeneration.

Borrelia burgdorferi (Bb), the etiological agent of Lyme disease, lacks the genes for de novo riboflavin biosynthesis and depends on host-derived riboflavin to generate flavin cofactors FMN and FAD. Riboflavin salvage by Bb has demonstrated importance to infection and metabolic homeostasis, though the critical roles of flavin cofactors to central metabolism are not well defined. Here, we demonstrate that riboflavin availability directly controls glycolytic flux through regulation of intracellular redox balance. Disruption of riboflavin uptake by deletion of gene bb0318 encoding the putative ATPase component of the riboflavin transporter resulted in impaired glycolysis as indicated by reduced intracellular pyruvate and a perturbed NADH/NAD+ ratio driven by faulty NAD+ regeneration. We identified coenzyme A disulfide reductase (CoADR) as a key flavin-dependent mediator of glycolytic flux. A Δcdr mutant mimicked the glycolytic dysregulation of the Δbb0318 mutant, but was not rescued by exogenous riboflavin, placing BbCoADR downstream of riboflavin salvage. Biochemical analyses of recombinant BbCoADR demonstrated FAD-dependent NADH oxidase activity. Targeted mutagenesis of predicted FAD-binding residues impaired cofactor binding and NADH oxidase activity, further confirming the dependence of BbCoADR on FAD. Together, this work reveals a direct link between riboflavin acquisition and core metabolic processes driven by BbCoADR-mediated flavin-dependent redox metabolism.