SUMMARY: An orange mutant (M 5) obtained from a wild-type isolate of by u.v. irradiation was found to contain phytoene, β-carotene, γ-carotene, neo-lycopene A, lycopene, neurosporaxanthin and four unidentified pigments. It is suggested that this simultaneous production of several carotenoid pigments by a hitherto colourless fungus may be regarded as a de-repression leading to the synthesis of a specific precursor in the pathway of carotenoid synthesis. Ultraviolet irradiation of M 5 gave a number of secondary colour mutants that were again analysed: M 5.1, M 5.3 and M 5.4 contained the same pigments as the original M 5 but in widely differing amounts. M 5.2 was colourless like wild type and contained only phytoene. M 5.5 formed a hitherto undetected pigment, torulene, lacked neo-lycopene A and lycopene and produced very little neurosporaxanthin. M 5 and M 5.5 were further investigated over an extended growth period in order to elucidate the sequence of carotenoid formation. The results are discussed in relation to possible hypotheses of carotenoid biosynthesis.


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