Improvement Of γ-linoleic Acid Yield From Cunninghamella Echinulata By Pulsed High Magnetic Field Mutation

Polyunsaturated fatty acids (PUFAs) are of big importance for dietary system. Also theyare highly significant in both of the cosmetic and pharmaceutical field. γ-Linolenic acid(GLA) is a significant conditionally essential fatty acid (EFA). GLA is an omega-6PUFA,the fatty acid molecule consists of18carbon atoms with three double bonds. It is alsoknown18:3n-6;6,9,12-octadecatrienoic acid; cis-6, cis-9, cis-12-octadecatrienoic acid;and gamolenic acid. GLA was naturally found in the fatty acid fractions of a little plantseed oils. The most famous sources of GLA are evening primrose oil. Since these sourcescannot meet the growing market, fungal GLA are promising alternatives for agriculturalgoods, thus researchers have focused many studies on this area. In fact there is an urgentneed to development new sources of PUFAs production. An oleaginous fungus is regardedas a successful and attractive vehicle for PUFAs production, such as Cunninghamellaechinulata used in this area, has high potential of lipid production and GLA content. Ourstudy was focused on finding new way to improve lipid and GLA production. We haveused magnetic field mutation which is considered a new way to improve the production oflipid and GLA yield. Spore suspension of C. echinulata was exposed to differentintensities of pulsed high magnetic field for various time intervals. After mutation sporesuspension was spread on potato plate. Sixty four mutants were isolated and screened byNile red staining and fluorescence microscopic examination. Three mutants Mut-29, Mut-15and Mut-64were achieved exposed to further fermentation screening in PDB medium.The biomass, lipid and GLA content were higher than that of the parent strain (CK). GLAyield in Mut-29, Mut-15and Mut-64were increased by45.68%,21.97%and20.94%respectively compared to that of CK. In the best mutant Mut-29, the biomass, lipidcontent, lipid yield, GLA content and GLA yield were improved by4.55%,21.96%,26.21%,15.38and45.68%respectively. In order to improve lipid and GLA yield,influences of different factors on biomass, lipid and GLA yield were studied. Resultssuggested that the best carbon source in this study was8%glucose, the optimum nitrogensources were1%soybean powder and0.5%potassium nitrate. Under the conditions of8%glucose,1%soybean powder, at28°C and150rpm for7days fermentation, the biomass, lipid content, lipid yield, GLA content and GLA yield in Mut-29increased by7.88%,18.07%,27.385,1.285and27.93%, respectively, compared to that of CK. The GLA yieldwas achieved a highest level at1313mg/L. Replaced1%soybean powder with0.5%potassium nitrate as nitrogen source, GLA yield of Mut-29was1282mg/L, whichincreased by29.04%than that of CK. Using8%glucose as carbon source, and potassiumnitrate as nitrogen source, with a C/N ratio of50, GLA yield of Mut-29was1214mg/L,which increased by29.70%compared with that of CK.0.5%mixture of organic andinorganic nitrogen showed good level in GLA production with a yield of1225mg/L.There was no significant pH effect on the GLA yield of Mut-29, the GLA yield of Mut-29increased by14.70%-41.94%compared to that of CK from pH5.0-6.5. Although the GLAcontent was highest, lower fermentation temperature went against fungal growth but notsuitable for GLA production. Three metal ions (Mg2+, Zn2+and Fe2+) could slightlypromote GLA production, while Zn2+could inhibit lipid accumulation and fungal growth.If adding ethanol and methanol into the media as inducer before inoculation, they inhibitedfungal growth and lipid accumulation resulting in lower GLA yield, although GLAcontent was higher. In conclusion, pulsed high magnetic field mutation was an effectivemethod for oleaginous fungi breeding to improve lipid and GLA yield. Mut-29was stablefor GLA production.