Overproduction of riboflavin by an Arthrobacter sp. mutant resistant to 5-fluorouracil

Antagonistic action between 5-fluorouracil (5-FU) and riboflavin (RF) was investigated. The growth of Arthrobacter sp. was inhibited by 5-FU at 5 x 10(-5) M, and the inhibition was reversed by RF at 5 x 10(-5) M. 5-FU-resistant mutants of Arthrobacter sp. were isolated and excreted RF in relatively high yields, but the wild-type strain excreted no RF. One of the mutants, strain No. 28-35, produced 223.2 micrograms ml-1 of RF in culture medium at 4 days.