Screening Of Schizochytrium SL1101and Studies On Its Identification, Mutation Breeding And Fermentation Optimization

Docosahexaenoic acid (DHA) is one kind of the high polyunsaturate fatty acids in the ω-3family, which is essential to human and has important physiological functions, such as promoting the development of brain and eyes of infants, protecting eyesight and enhancing immunity ability and so on. Convention fish oils may not be suitable to meet the increasing demand for DHA owing to their limited supply, lower content of DHA and peculiar taste and odor. finite sources and strong fishy, thus the search for a new, safe and reliable source of DHA is very urgent. As a marine fungus, Schizochytrium is a promising route for commercial production of DHA that can take advantages of the fast-growing, easy to cultivate and high content of DHA.In this test,40strains were isolated from rotten leaves samples of different plants collected from Dongzhaigang Mangrove Nature Reserve of Hainan. Through a total cellular lipid content detection,20strains of them contents30%or more DHA. Especially strains SL1101has the highest DHA content. Strains SL1101was identified as Schizochytrium according to morphology and18S rRNA gene sequence analysis.In order to screen a DHA high-yield strain, the mutation breeding of strain SL1101was carried out by ultraviolet mutagenesis, and mutant strain NL025with the highest yield was screened based on bacteria concentration and DHA yield. The DHA product reached up to1.62g/L, increased by20.0%compared with the original strain. And the mutant strain maintains good genetic stability.The best optimal liquid fermentation conditions and medium components were searched. The effects of carbon source, nitrogen source, potassium ion and incubation volume on the production of DHA compounds were studied and the ratio of nutrition component was optimized by orthogonal experiment. The optimum culture media included:glucose9%, glycerol9%, corn meal1.5%,1%yeast extract, KCl5mmol/L,old sea water50%. The optimum culture conditions were found by single factor experiment and it includes:48h of seed age;8%of bacterialload;80ml/500ml of liquid level,6.0of initial pH value;25℃and4days for fermentation. Under this condition, the dry weight was up to20.6g/L and DHA yield of4.53g/L,2.79times than the parent.