Study On The Cultivation Strategy To Improve The Lipid Production Capacity Of Microalgae

As biofuel production species,microalgae have the advantages of rich species,rapid growth and reproduction,strong carbon fixation capacity and strong stress resistance ability.The lipids produced can replace traditional fossil fuels after simple processing.To improve the ability of microalgae to convert light energy into biofuel is actually to increase its lipid production capacity,which is determined by both biomass and lipid content.By exploring suitable microalgae culture methods,this paper tries to practically and effectively improve lipid production capacity from two aspects of both biomass and lipid content,and pay attention to the changes of the by-products,such as protein,total sugar,pigment and so on.The main results of this paper are as follows:1.Based on the compositon of culture medium,the effects of supply levels of nitrogen and phosphorus and salinity on the biocomponent production capacity of Dunaliella Salina were studied by orthogonal experiment.It was found that the concentration of phosphorus source had no significant effect on the production capacity of all substances.The salinity and nitrogen concentration of the culture medium had significant effects on the production capacity of some substances.Changing these three conditions did not significantly increase the production capacity of lipids,but promoted the synthesis of the by-products to a certain extent.Sufficient nitrogen source is beneficial to protein production,low salinity(20 ‰)is beneficial to protein and sugar production,medium concentration of nitrogen source(NaNO318.75 mg·L-1)and high salt(60 ‰)are beneficial to algal dry weight production.As a feed additive,Dunaliella Salina with high-protein content can be cultured with high salt and high nitrogen supply.If the comprehensive utilization is considered,the reasonable combination of various conditions can also improve the cultivation benefit.2.In order to quickly detect whether the lipid production capacity of the treated microalgae has been effectively improved,the relationship between the fluorescence intensity of algae solution stained with Nile red and the lipid content in algae cells was studied,and a suitable relation equation was tried to find out.Thus,the lipid content of algae culture was quantitatively detected by determination of its fluorescence intensity.The results showed that the relation equations of different microalgae were various.The relationship equations of Chlorella vulgaris and Nannochloris oculata were y=69.206x+1624.2 and y=209.76x+1396.5,respectively.The small algal cells,such as Nannochloris oculata,led to the more fully stained,the weaker the shielding effect on fluorescence detection.As the results,the relation equation obtained would be more close to the relation equation of y=224.05x-531.75 obtained from standard triglyceride.Therefore,it is suggested that the relation equations for different microalgae should be obtained through experiments,and the cell density of algal culture should be controlled in a lower level,which can effectively improve the accuracy in the calculation for lipid content using Nile red fluorescence intensity3.Illumination condition is an important factor affecting the growth and biosynthesis of microalgae.In this study,monochromatic red light(peak wavelength is 660nm)and blue light(peak wavelength is 455nm)were combined and used for the algal culture.In the experiment cultivating six kinds of microalgae(Chaetoceros gracilis,Phaeodactylum tricornutum,Nitzschia closterium,Chlorella sp.(Marine),Chlorella vulgaris,Chlorella pyrenoidosa)by 24-well plate,monochromatic blue light was found beneficial to the lipid accumulation of Chaetoceros gracilis and Phaeodactylum tricornutum,which was 75%and 55%higher than that of control white light,respectively.But combinded monochromatic light was not conducive to the growth of P.tricornutum,except for the growth of 6R1B being similar to that of control white light.The combinded red-blue light had no significant effect on the growth of Nitzschia closterium,Chlorella sp.(Marine),C.vulgaris and C.pyrenoidosa,and the high ratio of red/blue was beneficial to the lipid accumulation of these four kinds of algae.The fluorescence intensity of the algae culture under the combinded monochromatic light of 6R1B was 39%,35%,74%and 25%higher than that of the control white light,respectively.4.The effects of combinded monochromatic light on the growth and biocomponent production of Dunaliella Salina were examined.Monochromatic blue light did not significantly promote the growth of D.Salina,but did increase the celluar contents of lipid and protein,which was 35%and 17%higher than that of control white light,respectively.Compared with other monochromatic treatments,the content and yield of carotenoid in D.Salina cultured under control white light were the highest.Interestingly,the use of different proportions of monochromatic red and blue light significantly promoted not only the growth but also the lipid content of D.Salina cells,and led to higher lipid production.This result is different from the research reports on the single increase of biomass or cellular lipid content.The best ratio of red/blue in combinded monochromatic light is 4:3.Compared with the control white light,the lipid production capacity is increased by 35.33%.The results show that the combinded monochromatic light can increase the biomass and cellular lipid content of D Salina at the same time,which is of great significance for the production of biofuel.5.The effects of combinded monochromatic light on the growth and biocomponent production of Nannochloris ocuate were also examined.The results showed that a higher proportion of red light promoted the production of pigments and carbohydrates,but decreased the yield of biomass and lipid.Monochromatic blue light is more beneficial to the production of lipid than red and white light,and the lipid production capacity under monochromatic blue light is 17%higher than that of control white light.The protein production capacity of N.oculata under combinded monochromatic light with red/blue ratio of 4:3 or 5:2 is the highest.In the lipid produced by N.oculata,seven fatty acids were identified,among which the contents of C16:0,C18:0 and C18:3(n-3)were decreased with the increase of red/blue ratio,while the contents of C18:2(n-9),C16:2(n-6)and C20:0 decreased with the decrease of red/blue ratio.Therefore,the combinded monochromatic light is a promising illumination strategy for large-scale cultivation aiming for different biological components.