Carotenoid Mutants of Mucor circinelloides

The wild-type of the filamentous fungus Mucor circinelloides accumulates the yellow pigment β-carotene. At a continuous blue-light fluence rate of 0.1 W/m² the β-carotene content increases about eight fold over the dark controls. Among the mutants isolated after exposure of spores to either N-methyl-N'-nitro-N-nitrosoguanidine or ICR-170, a red mutant accumulating lycopene, white mutants accumulating phytoene and white mutants without carotenoids were found. The biosynthesis of carotenoids in M. circinelloides shows similarities with that of the fungus Phycomyces blakesleeanus such as the presence of mutants in the same structural genes and the induction by light of the pathway. However, negative end-product regulation by β-carotene on the biosynthetic pathway, as in Phycomyces, is absent in M. circinelloides. In contrast to Phycomyces carB and carR mutants, carotenoids in corresponding mutants of M. circinelloides are photoinduced.