Breeding of high-temperature resistant Phaffia rhodozyma by compound mutation and fermentation condition optimization

To obtain a high-temperature-resistant astaxanthin-producing strain, using Phaffia rhodozyma AS2.1557 as the starting strain, the mutant strain was screened by multiple rounds of composite mutagenesis with ultraviolet (UV) light and ethyl methylsulfonate (EMS) in combination with high-temperature stress. The genetic stability of the mutant strain was verified through continuous transfer fermentation tests, and the fermentation conditions of the mutant strain were optimized by single factor tests and response surface tests. The results showed that a mutant strain UE-09 was obtained, which could grow normally and produce astaxanthin at 35 ℃. The mutant strain still had good genetic stability after eight subcultures. The optimal fermentation conditions for astaxanthin production were as follows: fermentation temperature 32 ℃, initial pH 5.5, inoculum 7.0%, and rotation speed 220 r/min. Under this optimal condition, the astaxanthin yield of this mutant strain reached up to 2.74 mg/L, which was 66.06% higher than that before optimization. This research would provide strain resources and theoretical guidance for the production of astaxanthin under high-temperature conditions.