Effects of oxidative stress on the production of carotenoid pigments byPhaffia rhodozyma (Xanthophyllomyces dendrorhous)

The resistance to killing by free radicals of two mutants ofPhaffia rhodozyma was determined. Mutant 5–7 did not produce astaxanthin but produced β-carotene, while mutant 3–4 did not produce any carotenoid pigments. The resistance of mutant 5–7 was the same as that of the wild type but mutant 3–4 was rapidly killed. Carotenoid pigments increased the resistance to killing by free radicals. We investigated the effects of free radicals, generated by H₂O₂ and Fe²⁺ added to the medium, on wild-type cells and mutants ofP. rhodozyma. Unpigmented mutants of basidiomycetous yeasts (Rhodotorula spp. and others) are more susceptible to killing by UV-irradiation than the pigmented, wild-type strains. Therefore, we investigated the effect of free radicals on a similar basidiomycetous yeast,P. rhodozyma, a species of economic importance, in the biological production of astaxanthin.