CAROTENOID BIOSYNTHESIS IN WILD-TYPE AND MUTANT STRAINS OF MUCOR-CIRCINELLOIDES

Carotenoid biosynthesis in wild type Mucor circinelloides has been inv estigated and the biochemical characterisation of the MS1 and MS9 muta nt strains, impaired in carotenoid formation, carried out. In liquid c ultures, all strains produced carotenoids (mainly beta-carotene, but a lso zeta-carotene, lycopene and gamma-carotene) at the onset of statio nary phase of growth. Carotenogenesis was light dependent. In liquid c ultures carotenoid formation in wild type was affected by diphenylamin e, which prevented desaturation, nicotine, resulting in reduced carote noid levels, but CPTA caused an increase in the total carotenoid conte nt but a reduced beta-carotene level, with the accumulation of lycopen e and gamma-carotene. The mutant strains MS1 and MS9 contained only 5. 0 and 11.5% of wild type carotenoid levels, respectively. Cell extract s of light-grown mycelia, incubated with 3(R)-[2-C-14] mevalonic acid, produced beta-carotene, but incorporations into carotenoids were subs tantially reduced in the cell extracts of MS1 and MS9. Analysis of pre nyl diphosphate intermediates indicated that, compared to wild type, g eranylgeranyl diphosphate accumulated in MS1. MS9 extracts produced a larger amount of prenyl phosphates and a more even distribution of rad ioactivity from mevalonic acid into farnesyl and geranylgeranyl diphos phates. Squalene and long chain prenyl phosphates were formed by the c ell extracts of all strains. It is proposed that the MS1 strain posses ses a mutation in a gene responsible for phytoene formation, whilst a regulatory mutation, affecting prenyl transferase activities, has occu rred in MS9.