USE OF A SERIES OF CHEMOSTAT CULTURES TO ISOLATE IMPROVED VARIANTS OFTHE QUORN(R) MYCOPROTEIN FUNGUS, FUSARIUM-GRAMINEARUM A3 5/

Variants (designated A23-S and A24-S) of the Quorn(R) myco-protein fun gus, Fusarium graminearum A3/5 were isolated from a series of glucose- limited cultures grown at a dilution rate of 0.18 h(-1) for a combined total of 109 d. These variants had unchanged mycelial morphologies bu t, when grown in mixed culture with the parental strain (A3/5) in gluc ose-limited chemostat culture at 0.18 h(-1), A23-S and A24-S had selec tion coefficients of 0.013 and 0.017 h(-1), respectively, and supplant ed A3/5. When a monoculture of A23-S was grown in a glucose-limited cu lture at a dilution rate of 0.18 h(-1), the appearance of highly branc hed (so-called colonial) mutants was delayed compared with their appea rance in chemostat cultures of the parental strain. Furthermore, when a monoculture of A24-S was grown in glucose-limited culture at 0.18 h( -1), the appearance of colonial mutants was delayed even further. Thus , it is possible to isolate advantageous (relative to A3/5) variants o f F. graminearum A3/5 which have unchanged mycelial morphologies, but in which the appearance of colonial mutants is delayed.