NEW MUTANTS OF PHYCOMYCES-BLAKESLEEANUS FOR BETA-CAROTENE PRODUCTION

The accumulation of beta-carotene by the zygomycete Phycomyces blakesl eeanus is increased by mutations in the carS gene. The treatment of sp ores of carS mutants with N-methyl-N'-nitro-N-nitrosoguanidine led to the isolation, at very low frequencies, of mutants that produced highe r levels of beta-carotene. Strain S556 produced about 9 mg of beta-car otene per g of dry mass when it was grown on minimal agar. Crosses inv olving strain S556 separated the original carS mutation from a new, un linked mutation, carF. The carF segregants produced approximately as m uch carotene as did carS mutants, but they were unique in their abilit y to produce zygospores on mating and in their response to agents that increase carotenogenesis in the wild type. The carotene contents of c arF segregants and carF carS double mutants were increased by sexual i nteraction and by dimethyl phthalate but were not increased by light o r retinol. Mixed opposite-sex cultures of carF carS mutants contained up to 33 mg of beta-carotene per g of dry mass. Another strain, S444, produced more beta-carotene than did S556 but was marred by slow growt h, defective morphology, and bizarre genetic behavior. In all the stra ins tested, the carotene concentration was minimal during the early gr owth phase and became higher and constant for several days in older my celia.