Abstract
Yellow mutants of the astaxanthin producing red yeast Phaffia rhodozyma were obtained by nitrosoguanidine mutagenesis. The carotenoid composition of the yelow mutants, Yan-1 and Ny-1, was mainly $\beta$ -carotene (> 95$%$) and torulene (< 5$$). Therefore, the yellow mutants are carotene oxygenation deficient mutants (CODMs). CODMs produced decreased quantities of carotenoids compared to their red parents and this indicated that carotene may regulate its synthesis. CODMs, Yan-1 and Ny-4, on plates containing 50 $\mu$ M antimycin, showed highly pigmented vertical papillae. Antimycin-induced mutants purified from the papillae showed increases in carotenoid content (up to 1 mg $\beta$-carotene/g yeast). CODMs, Yan-1 and Ay-1, were more sensitive to antimycin than red strains, Ant-1 and 67-385. This was probably due to lower antioxidant activity of $\beta$-carotene than that of astaxanthin. Light increased torulene and light+antimycin further increased the torulene. Yan-1 and Ny-4 could grow with succinate, though their red parents, Ant-1 and Anf-1p, could not. However, antimycin induced mutation of Yan-1 or Ny-4 destroyed the ability to grow with succinate.