Abstract: Eighteen Rhodotorula strains (SCAU 1 through 18) that can produce carotenoids were isolated from natural environment and subjected to preliminary screening with Sudan Black dye and further screening by shake-flask culture. As a result, strain SCAU-13 was found to have the highest lipid content of 14.63% and identified as Rhodotorula graminis. The strain was mutagenized respectively with UV light, diethyl sulfate (DES) and their combination, resulting in 13 mutants, and strain M124 containing the largest amount of lipids among the 13 mutants was screened out, which was 42.42% and 2.90 times as high as that of the original strain SCAU-13. Orthogonal array optimization showed that the optimal fermentation conditions for lipid production by strain M124 were glucose as carbon source, (NH4)2SO4 as nitrogen source, carbon-to-nitrogen ratio of 60:1, initial pH 6.0, peptone concentration of 1.8 g/L, yeast extract concentration of 4 g/L and MgSO4 ·7H2O concentration of 0.5 g/L. Under the optimal culture conditions, the cellular biomass and the lipid content of dry bacterial cells were (53.67 ± 0.17) % and (13.55 ± 0.10) g/L, respectively, and the yield of lipid (7.27 ± 0.03) g/L fermentation broth.

Key words: Rhodotorula, microbial oil, identification, mutation, culture optimization