Strain improvement of Phaffia rhodozyma for astaxanthin production

Abstract

Objective: The aim of the present study is to evaluate and optimize different carbon sources at different temperatures in shake flask for cell growth and astaxanthin accumulation in ultraviolet (UV) mutant Phaffia rhodozyma. The focus is to make the process cost-effective and fruitful with higher productivity. Materials and Methods: Adaptive strain development was carried out so that the P. rhodozyma can give the best astaxanthin at a higher temperature (35°C), increasing the process economy. P. rhodozyma was cultivated with three broad spectrum antibacterial drugs - streptomycin, gentamycin, and ampicillin (200 μL) and with antifungal drug - fluconazole (200 μL) to determine the effect on yeast growth and astaxanthin production. Rice, cane juice, and sucrose were selected as carbon source and compared with dextrose at different fermentation temperatures - 22°C, 30°C, 33°C, and 35°C for astaxanthin production. Results: P. rhodozyma was resistant to antibiotic drugs inhibiting bacterial and fungal contaminants. Rice being more economical was selected as carbon source, but the strain was not able to utilize starch-rich substrate leading to its rejection. When P. rhodozyma was grown in cane juice, biomass is highest (OD 2.77) at 30°C and 610 nm wavelength, whereas astaxanthin productivity is highest (OD 2.64) in dextrose media at 30°C and 450 nm. Comparative metabolic and growth results for UV mutants showed significantly higher biomass and astaxanthin productivity in comparison to wild strain. Conclusion: The most efficient carbon source in terms of penny-pinching and astaxanthin productivity was found to be dextrose containing media at 30°C.