Research Of Astaxanthin-overproducing Strain Of Phaffia Rhodozyma By Evolutionary Engineering

Astaxanthin is a kind of carotenoid, which can high-efficiently quenching active oxygen, thus avoiding the destruction of organisms by active oxygen. It is a strong antioxidant, broad used in food, pharmaceutical, aquaculture and so on. Phaffia rhodozyma is a yeast that can produce astaxanthin highly. It has some advantages such as shorter period of fermentation, easy to culture in a high density, and so on. In this paper, an evolutionary engineering method was used for breeding Phaffia rhodozyma high-yield strains.The wild strain Phaffia rhodozyma As 2.1557, as the starting strain, was treated with UV and NTG, and Genetic diversity of strains library was got. In the shake flask,β- ionone, DPA, NaCl, TiO₂, H₂O₂, and NaClO was used as evolutionary pressures for evolutionary engineering. The transit time was 48h. The evolutionary engineering studies have found that these substances could inhibit the growth of Phaffia rhodozyma, thus high biomass strains was obtained when the pressure was disinherited. The impact of carotenoids synthetic inhibitors such asβ-ionone and DPA on the accumulation of astaxanthin is not obvious. But NaCl, TiO₂, H₂O₂, and NaClO which can produce active oxygen, are able to stimulate the accumulation of astaxanthin.We screened on the evolutionary yeasts, and got six astaxanthin-overproducing strains. Their physiological characteristics were studied. The results showed that evolution greatly changes the Biological traits. The yeast color of liquid culture changes from orange to pink, and the biomass increased more than twice. Compared with the wild type, the colony of plate culture has changed greatly. Its diameter became larger, and its color changes from orange to pink. different from the wild-type's flat, rough and dry colony, the colony evolved into convex, wet, suggesting that strains produced capsules. Microscopic observations on the evolutionary strains shows that, the evolutionary cells became smaller and tend to gather together, even form a false hyphae. The concentration of astaxanthin has also been improved. The highest astaxanthin yield is up to 1.223mg / L, compared to 0.825mg / L of the original strain yield, was about 48.2% higher.