A mutant Rhodotorula rubra with enhanced carotenoid-synthesizing activity for synthesizing total carotenoids and β-carotene was obtained by N-methyl-N′-nitro-N-nitrosoguanidine mutagenesis. When co-cultivated with yogurt starter bacteria (Lactobacillus bulgaricus + Streptococcus thermophilus) in whey ultrafiltrate it produced 15.7 mg total carotenoids l-1 culture fluid or 946 μg total carotenoids g-1 dry cells of which 71% was β-carotene. Grown as a monoculture in glucose substrate, the mutant shown 1.4 times lower carotenoid-synthesizing activity, and the relative share of β-carotene in the total carotenoids was lower (63%). The individual pigments torulene and torularhodin were identified, whose mass fractions were (29% and 7%) and (24% and 4%), respectively, for the mutant grown as a monoculture and as a mixed culture with the yogurt bacteria.
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