Breeding Of Crypthecodinium Cohnii And Fermentation Optimization

Docosahexaenoic acid (DHA) is an essential polyunsaturated fatty acid (PUFA) to the human body. There is a high content of DHA in the brain and retina. DHA plays an important role in the development of brain and eyes for infants, and it is beneficial for cardiovascular disease and body immunity. DHA has attracted great interest and got extensive application due to its distinctive physiological function. Owing to its noticeable advantage, DHA production by microorganism has become one of hotspots in the research field around the world. Microalgae is the more potential source of DHA production. After screening out the best mutant of Crypthecodinium cohnii , effects of medium components and culture conditions on the growth, lipid and DHA accumulation in this mutant was mainly studied using flask in this dissertation.The original strain was exposed under ultraviolet radiation for 180 seconds, after screened randomly, the DHA yield and lipid content of mutation strain are increased by 34.7% and 6.1% respectively.Effects of medium components on the growth and DHA accumulation in Crypthecodinium cohnii are very important. After compared the effects of several different carbon and nitrogen sources on the biomass,lipid content and DHA yield in mutation strain, it could be concluded that glucose (20g/L) was optimal carbon source, and yeast extract (2g/L) was optimal nitrogen source, and the DHA yield was highest respectively with this condition. When sea salt concentration was 25g/L, it was beneficial to growth and DHA accumulation of the mutation strain.Effects of culture conditions on the growth and DHA accumulation in Crypthecodinium cohnii are also very important, especially temperature and initial pH. In this research, it was concluded that the DHA content was highest with 25℃and initial pH6.5 respectively.After studied the effects of several different inoculums and culture types on the biomass,lipid content and DHA yield in the mutant, it showed that the optimal fermentation condition was : 20g/L glucose, 2g/L yeast extract, 25g/L sea salt, initial pH 6.5, 25℃,5% inoculum, flask culture 3d. The biomass,lipid content and DHA yield in the mutant was 6.95 g/L,31.2%,1263mg/L respectively with this optimal condition. The biomass,lipid content and DHA yield in Crypthecodinium cohnii was increased obviously by ultraviolet induced mutation and fermentation optimization. This study also provides foundation for the industrial production of DHA .