Effects of various metabolites (sugars, carboxylic acids and alcohols) on riboflavin formation in non-growing cells of Ashbya gossypii.

Abstract

The effects of various sugars and sugar derivatives on flavinogenesis were examined using non-growing cells of a high flavinogenic mold, Ashbya gossypii. Glucose, fructose and galactose were found to be the most stimulative. Glycerol and glucono-delta-lactone were less stimulative; next in order were n-propanol, n-butanol, glycols and butanediols, which were likewise effective; acetate, lactate and pyruvate were slightly stimulative. In contrast, ribose, xylose, arabinose, ribitol, citrate, succinate, oxaloacetate, glyoxylate and malate were rather inhibitory, in additions at 1.0%. Among these compounds, ethanol (1%) greatly stimulated riboflavin formation. Maximum flavinogenesis with the above stimulants was attained by the additions of 1% ethanol, 1.25--3.0% glucose, 1.25% glycerol, 4.0--6.0% propane and butanediols, 1.0% pyruvate and 0.9% acetate after 37 hr incubation, respectively. These compounds inhibited flavinogenesis with increasing concentrations above their optimum concentrations. The stimulation effect of ethanol far exceeded those of other stimulants but ethanol had almost no effect on growth and pH values during incubation. With the addition of ethanol (1%) during incubation, maximum formation (1,776 microgram/g wet mycelia) of riboflavin was achieved when added at the start of incubation and the most effective utilization was observed when added at the logarithmic phase of flavinogenesis, although the maximum formation of riboflavin in the latter case was much lower than in the former case. The relation of sugar metabolism, especially ethanol metabolism, to flavinogenesis was discussed with the flavinogenic activities of these additives.