Abstract: A method of systematically generating and isolating highly flavinogenic strains of Candida famata. The strains Candida famata GA18Y8-6#2 dgr and Candida famata GA18Y8-6#2#11 have been developed and produce yields of ca. 7.0 to 7.5 grams per liter per 6 days. The method includes a combination of iterative mutagenizing steps and protoplast fusion steps performed on the parent strain and the descendant strains which are selected following each step according to a screening protocol.

Abstract: Strains of yeast of the species Candida famata are disclosed which can produce 10 grams of riboflavin per liter in 6 days, and in particular, strains identified by ATCC Accession Nos. 20849 and 20850. Riboflavin yields of more than 20 grams per liter in 200 hours have been achieved. Strains of the present invention have increased sensitivity to iron inhibition of flavinogenesis and have enhanced riboflavin production per cell at increased iron concentrations in the fermentation medium. The invention also is directed toward a process for selecting improved microorganisms which are resistant to inhibition of growth by depleted medium. Such selected mircoorganisms are then tested for riboflavin overproduction. The present invention is also directed toward a selection process in which mutated microorganisms are cultured in the presence of tubercidin, a purine analog. Mutant strains resistant to tubercidin are then tested for riboflavin over-production.

Abstract: Strains of yeast of the species Candida famata are disclosed which can produce 10 grams of riboflavin per liter in 6 days, and in particular, strains identified by ATCC Accession Nos. 20849 and 20850. Riboflavin yields of more than 20 grams per liter in 200 hours have been achieved. Strains of the present invention have increased sensitivity to iron inhibition of flavinogenesis and have enhanced riboflavin production per cell at increased iron concentrations in the fermentation medium.