Aims:  To isolate a strain overproducing riboflavin and to improve riboflavin production for practical use in a biorefinery technology. Methods and Results:  Ashbya gossypii spores were mutagenized by exposure to UV light and mutant ZP4 strain, producing riboflavin threefold the riboflavin that of the wild‐type strain, was isolated by the first and second screenings. Proteomic analysis of ZP4 strain showed the expression patterns of eight types of genes related to riboflavin biosynthesis different from those of the wild‐type strain and those enzyme activities were investigated. When activated bleaching earth (ABE) containing 75 g l−1 rapeseed oil was added in the culture of the ZP4 strain with oxygen‐enriched air supplied, riboflavin concentration increased to 8·7 g l−1 at 5 days of culture. Riboflavin production yield was 0·17 g g−1 of consumed oil, which was eightfold higher than that of the wild‐type strain. Conclusions:  The results show that the mutant ZP4 strain shows potential for improving riboflavin production for practical utilization using vegetable oil as the sole carbon source. Significance and Impact of Study:  Our results indicate that the mutant ZP4 strain shows potential for producing riboflavin from vegetable oil, and therefore will be contributed to biorefinery technology.

The production of riboflavin from vegetable oil was increased using a mutant strain of Ashbya gossypii. This mutant was generated by treating the wild-type strain with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). Riboflavin production was 10-fold higher in the mutant compared to the wild-type strain. The specific intracellular catalase activity after 3 d of culture was 6-fold higher in the mutant than in the wild-type strain. For the mutant, riboflavin production in the presence of 40 mM hydrogen peroxide was 16% less than that in the absence of hydrogen peroxide, whereas it was 56% less for the wild-type strain. The isocitrate lyase (ICL) activity of the mutant was 0.26 mU/mg of protein during the active riboflavin production phase, which was 2.6-fold higher than the wild-type strain. These data indicate that the mutant utilizes the carbon flux from the TCA cycle to the glyoxylate cycle more efficiently than the wild-type strain, resulting in enhanced riboflavin production. This novel mutant has the potential to be of use for industrial-scale riboflavin production from waste-activated bleaching earth (ABE), thereby transforming a useless material into a valuable bioproduct.

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