Abstract: The parent riboflavin-producing strain Bacillus subtilis C0 was treated with heavy-ion beam irradiation, then it was screened the mutagenic strains with 8-azaguanine. In further study, 4 high-yield strains were initially obtained from 60 mutant strains. After shake flask fermentation, the highest yield of mutant strain B13 reached( 401.8 ± 9.2) mg/L, which was 18.5% higher than that of the original strain. The new mutant strain BII7 was screened after second time of heavy-ion beam irradiation, and the riboflavin yield achieved (818.8±17.3) mg/L which was 77.7% higher than that of the mutation strain B13.The heavy-ion beam irradiation had good mutagenic effect. The optimal cultivation conditions of strain BII7 were: initial pH 7.7, culture temperature 37 ℃, and rotation speed 220 r/min. The riboflavin yield of mutant strain BII7 was 1 385.3 mg/L in 5 L fermenter (37 ℃, pH 7.7 and dissolved oxygen concentration 40%), which was 69.2% higher than that in shake flask. The fermentation time was shortened by 12 h. The results showed that the strain BII7 had good fermentation ability and stable genetic characteristics.

Key words: heavy-ion beam irradiation； mutation breeding, riboflavin, Bacillus subtilis