Studies on Variation and Mutation in Ashbya Gossypii

SUMMARY

The spores of Ashbya gossypii, NRRL Y-1056, have been treated with ultraviolet radiation, X-radiation, and CH₃-bis-β-chloroethylmethylamine hydrochloride. The general tendency was for these mutagenic agents to induce the formation of degenerate types with greatly retarded flavinogenic abilities. Limited evidence of natural variation was obtained in the study. Some treated substrains were characterized by an unsustained ability to produce greater amounts of riboflavin than the parent. The desirability of adequate maintenance of stock cultures was demonstrated. The addition of sodium dithionate to stock culture media in 0.1% concentration enhanced pigment formation and tended to maintain the organism in its highly flavinogenic state.

A practical procedure for the evaluation of riboflavin production by substrains of A. gossypii was developed. By employing peptone and increased concentrations of selected corn steep liquor in fermentation media, by careful attention to stock cultures, and by critical control of inoculum preparation and use, yields of the order of 1000 μg. of riboflavin per ml. of fermentation medium were regularly obtained with the parent strain.

The results of this study have given a somewhat clearer picture of the actual potentialities of A. gossypii as a source of riboflavin and further indicate its excellence as a microbial producer of this vitamin. Variations still encountered in replicate fermentations, and the occurrence of both abnormal and normal fermentations in replicate flasks, indicate a possibility for added improvement in procedures.