Optimization of astaxanthin production by Rhodotorula toruloides CB6-10/1 using response surface methodology and its genome analysis.

Astaxanthin is a valuable carotenoid with potent antioxidant properties and has broad applications in the pharmaceutical, nutraceutical, and cosmetic industries. In this study, Rhodotorula toruloides CB6-10/1, isolated from Canna indica L. flowers, was evaluated for astaxanthin production. The orange-red pigment was confirmed as astaxanthin via thin-layer chromatography and high-performance liquid chromatography, with quantification performed by spectrophotometry. Comprehensive genome analysis and production optimization of R. toruloides CB6-10/1 confirmed the presence of key astaxanthin biosynthesis genes, such as CrtYB, CrtI, CrtW, CrtZ, and CrtR, which facilitate the conversion of β-carotene to astaxanthin through hydroxylation and ketolation. The key parameters, including carbon and nitrogen sources, their concentrations, trace elements, agitation speed, and pH, were systematically evaluated to optimize production. Although copper appeared beneficial in the Plackett-Burman screening, its effect and those of other metals were not significant. Optimization using Response Surface Methodology for cost-effective nitrogen sources determined that a combination of 1.10 g/L yeast extract, 10.0 g/L peptone, and 0.50 g/L ammonium sulfate yielded the maximum astaxanthin production of 4.728 mg/L, under cultivation conditions of pH 4.5, 200 rpm, and 30 g/L glucose, representing a fourfold increase compared with the basal medium. This optimization not only enhances pigment production efficiency but also reduces dependency on costly trace elements, improving process scalability and economic feasibility. Overall, these results demonstrate R. toruloides CB6-10/1 as a promising microbial source for sustainable astaxanthin production with potential further applications.