Effects of riboflavin on 6,7-dimethyl-8-ribityllumazine formation in growing cells of a riboflavin-adenine-deficient mutant, Bacillus subtilis.

The effects of riboflavin on the formation of 6,7-dimethyl-8-ribityllumazine (DMRL) were examined using the growing cells of a riboflavin, adenine deficient-mutant, Bacillus subtilis. The administration of low concentrations (50-500 ng/mL) of riboflavin to the basal medium significantly inhibited the formation of DMRL without any change in growth. Especially, the supplementation of more than 250 ng/mL riboflavin completely restricted the formation of DMRL under the experimental conditions. The results clearly indicate that a rigid negative feedback inhibition is operative for the biosynthetic pathway of riboflavin in B. subtilis.