Possibility of diacetyl and related compounds as the 4-carbon compound necessary for the formation of riboflavin in Ashbya gossypii.

The effects of various compounds (0.5%) involved in the butanediol and the glycolytic pathways on riboflavin formation in whole cells of Ashbya gossypii at rest were examined. The addition of acetate, glycerol and diacetyl inhibited riboflavin formation, while the addition of acetoin had no effect on it, and the addition of ethanol, 2,3-butanediol, pyruvic acid and glucose accelerated it. The relation of diacetyl and acetoin to riboflavin formation during resting cell incubation in the presence of 0.5% ethanol and various concentrations of 2,3-butanediol was examined. The results quantitatively revealed a precursor-product relation between riboflavin formation and the formation of diacetyl and acetoin. The results obtained provide evidence that a high flavinogenic agent, ethanol, was converted to acetaldehyde, pyruvic acid, acetoin and diacetyl in this order, that a week flavinogenic agent, 2,3-butanediol, was transferred to diacetyl through acetoin, and that the diacetyl produced can be utilized as the 4-carbon compound for riboflavin formation in the flavinogenic mold, Ashbya gossypii. It remains obscure whether diacetyl is enzymatically involved in riboflavin formation.