The coenzyme B12 precursor 5,6-dimethylbenzimidazole is a flavin antagonist in Salmonella

Salmonella enterica subsp. sv. Typhimurium str. LT2 (hereafter S. Typhimurium) synthesizes adenosylcobalamin (AdoCbl, CoB12) de novo only under anoxic conditions, but it can assemble the lower ligand loop (a.k.a. nucleotide loop) and form unique C-Co bond present in CoB12 presence or absence of molecular oxygen. During studies assembly Typhimurium, we noticed that growth this bacterium could be ar-rested by nucleobase, namely 5,6-dimethylbenzimidazole (DMB). Here report vitro vivo evidence shows structural similarity DMB to isoalloxazine moiety flavin cofactors causes its deleterious effect on cell growth. We studied inhibition housekeeping dehydrogenase (Fre) three flavoenzymes initiate catabolism tricarballylate, succinate D-alanine Typhimurium. Notably, while with tricarballylate was inhibited 5-methyl-benzimidazole (5-Me-Bza) DMB, glycerol arrested not 5-Me-Bza. Neither unsubstituted benzimidazole nor adenine at inhibitory concentrations. Whole genome sequencing analysis spontaneous mutant strains grew concentrations identified mutations effecting cycA (encodes D-Ala/D-Ser transporter) dctA dicarboxylate genes coding sequence transporter (TcuC), suggesting increased uptake substrates relieved inhibition. discuss two possible mechanisms DMB.