BETA-CAROTENE PRODUCING MUTANTS OF PHAFFIA-RHODOZYMA

Like other carotenoid-producing organisms, Phaffia rhodozyma, a red as taxanthin-producing yeast, is supposed to synthesize carotenoids by th e following steps: formation of phytoene from geranylgeranyl pyrophosp hate, dehydrogenation of phytoene to lycopene, cyclization of lycopene to beta-carotene and oxidation of the latter to astaxanthin. Mutageni c treatments generated in P. rhodozyma a wide diversity of colour vari ants ranging from white to dark red. The identification of the corresp onding carotenoid compounds revealed the occurrence of beta-carotene-a ccumulating strains, phytoene-accumulating strains, and strains lackin g any carotenoid compound. These classes of strains are likely to resu lt from alterations in, respectively, the oxidation of beta-carotene, phytoene dehydrogenation and the phytoene synthetase step. Except for the cyclization of lycopene to beta-carotene, all the steps of caroten ogenesis in P. rhodozyma are represented by the above mutants. Further more, astaxanthin-overproducing mutants were also selected; they are l ikely to be affected in some upstream step, and certainly before beta- carotene, as after an additional mutagenesis they generated oxidaseles s strains that, in this case, overproduce beta-carotene. The latter st rains appear very promising for biotechnological production of natural beta-carotene.