Importance of cell mass and total pigment level-dependant changes in the relative β-carotene proportion for carotenoid production by the yeast variants of the Sporidiobolales

The extent of variation in the composition and amount of carotenoids among a large number of phenotypic variants, induced from a single wild type parent by N-methyl-N'-nitrosoguanidin treatment, has been compared between two strains of the carotenoid-rich, pink yeasts belonging to the order Sporidiobolales (Rhodotorula dairenensis Sag 17 and Rhodosporidium diobovatum Sea 2-11). We report, for the first time, the weight ratios of monocyclic to dicyclic carotenes in the variants changed differently between those originated from Sag 17 and Sea 2-11, with the decrease of total pigment levels compared to their wild type parents. In contrast, a lack of changes in the relative proportion of β-carotene was apparent for the variants whose total pigment levels are higher than the wild types. Our data clearly showed that the choice of the parent with low level of relative β-carotene content is critical to improve these carotenogenic yeasts by mutagenesis treatment with a view to preferential synthesis of monocyclic pigments having potent antioxidant activities. We further examined the effect of substrate concentration on pigment production by the Sag 17 variants. Use of the variants exhibiting high level of cell mass in the stationary phase was found to be essential for carotenoid production under high substrate concentrations, although they need to be selected based primarily on the pigment contents.