Optimizing Cultivation And Mechanism Of Lipid Accumulation Research In Chlorococcum Sphacosum GD

Nowadays,lots of works have focused on the biodiesel production using microalgae,a promising green energy production area.However,comparing to fossil fuel,high cost and complex processes of biodiesel production has impeded its development and industrialization.To overcome the bottleneck,several steps need to be optimized.Such as,selection of the proper algae with high oil composition,easier and lower cost culture method,highly efficient and lower energy cost harvest and dehydration process,as well as environment-friendly biofuel extraction protocol.In this study,Chlorococcum sphacosum GD,a microalga strain with high lipid composition,which was the collected from Guandi Mountain,Shanxi Province,were selected as an possible biodiesel production strain.The basic characters,including growth rate,biomass and oil accumulation as well as its physiological changes,which are important for biofuel,has been delicately examined under different culture conditions.First,the illumination effect on both biomass and oil accumulation has been examined.After cultured on BG-11 medium at 25?,the dry weight reached to 0.38 g/L,0.34 g/L,and 0.32 g/L under illumination of 3000 lx,7000 lx,and 11000 lx,respectively,indicating that strong illumination inhibits the growth of C.sphacosum GD.However,in contrast,the neural lipid composition as well as the total oil increased at strong illumination,with 24.01%?32.23%?35.55%,respectively,suggesting that high illumination promotes oil accumulation.Second,the C.sphacosum GD growth under different carbon supplements has been analyzed.After nine days culture with 0.02 g/L NaCO3? 10.00 g/L glucose,the total dry weight reached to 0.36 g/L and 3.75 g/L,respectively.In medium with glucose,the biomass dramatically increased in the first three days,the growth rate reached the peak at day 3,and then reduced,which means highly efficient usage of organic carbons.However,the neutral lipid increased at a relatively slow rate.On the other hand,in medium with NaCO3,either the biomass or neutral lipid accumulation were much fewer compared with those in medium with glucose.Third,we have also tested the different nitrogen supplement effects on the growth rate of both biomass and neutral lipid.Our results showed that there is no obvious effect on neutral lipid accumulation with all three nitrogen supplements tested,NaNO3,NH4 Cl and CO(NH2)2.Nevertheless,the biomass growth rate was highest in medium with NaNO3,then following with CO(NH2)2 and NH4 Cl,suggesting that NaNO3 is much more fit for C.sphacosum GD growth.Fourth,the effect of sodium concentration on biomass and neutral lipid was evaluated as well.Although the higher concentration of NaCl inhibited the growth rate of biomass,it efficiently promoted the accumulation of neural lipid in cells.The optimal NaCl concentration for neutral lipid production was 8.00g/L.In addition,the high concentration of NaCl increased the C18:3 and C22:1 in C.sphacosum GD.Taken together,it can be concluded that in order to increase the growth of biomass and accumulation of the neutral lipid,the optimal conditions are: increasing illumination,using glucose as carbon supplements,using NaNO3 as nitrogen supplements and high NaCl concentration(8.00g/L).Our results have provided important experimental data and theoretical information for further biofuel application of lipid rich algae.