Optimization Of Fermentation Conditions For Biodiesel Production With Thraustochytrids

Biodiesel,a clean renewable energy source,can alleviate the deteriorated environmental issues and energy crisis.And microbial oil became a promising biodiesel feedstock,due to its distinctive features,such as extensively accessible raw materials and short production cycle.Among oleaginous microbes,thraustochytrids have attracted wide attention because of their ability to accumulate high levels of fatty acids.Using their oil as biodiesel production raw materials can provide a theoretical basis for the large-scale production of biodiesel.At present,the researches of thraustochytrids mainly focused on the polyunsaturated fatty acids and terpenoids production,such as DHA,EPA and squalene.However,the influence of cultivation condition for saturated fatty acid(SFA)production with thraustochytrids are poorly described.In this study,we firstly screened thraustochytrid strains which are isolated from different ocean areas for SFA production.And two strains,Aurantiochytrium ZJWZ-7 and Aurantiochytrium PKU# SW7)were selected for further investigation.Their SFA yields were 1.5 g/L and 1.4 g/L,respectively,and their biomass were 7.8 g/L and 6.8 g/L,respectively.Then nutrient conditions(carbon source concentration,nitrogen source concentration,carbon source ratio)were optimized,and the optimum conditions for producing SFAs in flask were obtained.And 60 g/L glucose-ethanol(9:1)as carbon source and 2.5 g/L yeast extract as nitrogen source was favored for SFAs production.Under the optimal conditions,the saturated fatty acid yields of strains ZJWZ-7 and PKU# SW7 reached to 5.0 g/L and 5.3 g/L,respectively,with the biomass of 14.32 g/ L and 15.32 g/L respectively.The SFA yield increased by 22 % when compared with glucose as a single carbon source.Moreover,yeast extract as the single nitrogen source was more benefit for SFA accumulation when compared with the multiple nitrogen source.Subsequently,fed-batch fermentation was carried out in 5 L fermenter.The dissolved oxygen(DO)was maintained at 50 % saturation during 0~2 d,and then switched to 10 % during 3~10 d.And 100 mL of the carbon and nitrogen sources at one third of the optimal concentration were supplemented after fermented for 2 days and 3 day.The results showed that the biomass of ZJWZ-7 and PKU# SW7 reached to 11.0 g/L and 12.4 g/L,the SFA yields reached to 7.0 g/L and 8.5 g/L respectively,which were 4.6,6.1 times higher than those of the original strains.In addition,the fatty acid composition of the two strains before wintering conformed to the American standard of biodiesel(ASTM D6751),indicating that they were excellent strains for biodiesel production.In this study,SFA yields of the two thraustochytrid strains were greatly increased by optimizing the culture conditions,indicating that both strains have the potential of large-scale biodiesel fermentation,which provides a theoretical basis for large-scale biodiesel production with thraustochytrids.