INCREASED ASTAXANTHIN PRODUCTION BY PHAFFIA-RHODOZYMA MUTANTS ISOLATED AS RESISTANT TO DIPHENYLAMINE

To improve astaxanthin production by Phaffia rhodozyma, resistance to a carotenoid biosynthesis inhibitor was employed to screen higher asta xanthin producers. The wild type strain generated pinkish salmon-color ed colonies due to the intracellular astaxanthin accumulation, but the colonies have fumed white when grown in the presence of some of carot enoid biosynthesis inhibitors. Among the compounds tested, diphenylami ne (DPA) was selected as the most effective inhibitor that did not sig nificantly affect colony numbers and sizes, Upon mutagenesis and scree ning, DPA-resistant mutants were isolated as salmon-colored colonies o n plates containing DPA, and two of the DPA-resistant mutants exhibite d a two-fold increase in astaxanthin production over that of the wild type. In the DPA-treated wild type, 15-cis phytoene was identified as the major carotenoid, indicating that the target enzyme of DPA was lik ely to be phytoene desaturase (PDS). When treated with DPA and/or nico tine, an inhibitor of a lycopene cyclase, lycopene accumulation was si milarly enhanced in the resistant mutant, and the degrees of inhibitio n by DPA were also found analogous to astaxanthin formation in the wil d type and in the DPA-resistant mutant. These results indicated that t he enhanced carotenogenesis most probably occured at the PDS stage.