Screening And Regulated Culture Of Several Oleaginous Microalgae

With the rapid development of the global economy,worldwide environmental pollution has becoming increasingly serious.Non-renewable resources were exhausted,and there was an urgent need to find an alternative clean energy.Biomass energy was considered to be an important part of the sustainable development of the future society because of its environmental protection and renewable characteristics.The types of bioenergy produced by microalgae were biofuels such as bioethanol,biogas,biodiesel,solid fuels and bioelectricity.In order to explore the effects of different environmental factors on the growth and oil production of microalgae and the effect of nitrogen sources on key enzymes in the metabolism of Tribonema sp.In this study,62 oleaginous algal strains have been selected for screening,and 5 algal strains with high oil content have been screened as the research objects.They were subjected to growth experiments under different environmental factors,lipid determination and lipid metabolism-related enzyme determination experiments.Five strains of oleaginous microalgae have been explored for optimal growth and oleaginous culture conditions,comparing Navicula amphiceropsis,Nitzschia amphibia,Melosira varians.Scenedesmus bijuga and Tribonema sp.biomass and oil content,and the key gene enzymes of Tribonema sp.in the process of lipid metabolism at different nitrogen concentrations were determined.The results were as following:62 strains of microalgae were evaluated(44 strains of Diatoms,17 strains of Chlorophyta,and 1 strain of Xanthophyta),and were determined by the method methanol-chloroform.According to the level of oil content,5 strains were screened out with oil content over 27.5%.They were Navicula amphiceropsis,Nitzschia amphibia,Tribonema sp.,Scenedesmus bijuga and Melosira varians.Comparing the biomass under the optimal growth conditions of the three diatoms,the study found that the biomass of Nitzschia amphibia was higher than that of Navicula amphiceropsis when the light intensity was 4000 Lx,20 mg·L^-1K₂HPO₄,6 g·L^-1Na Cl,and there was a significant increase in the biomass.When the ventilation rate was 1 V·V^-1·min^-1,the biomass of Nitzschia amphibia was significantly higher than that of Melosira varians(P<0.05).Among three strains of diatoms,Nitzschia amphibia has the largest biomass and the fastest growth.Comparing the three diatoms under the optimal conditions for oil accumulation,it found that the oil content and oil yield of Nitzschia amphibia both reached their maximum values of 33.89%and 2.82 mg·L^-1·d^-1when the initial density was 40 ml·L^-1,significantly higher than Navicula amphiceropsis and Melosira varians(P<0.05).The effects of different environmental factors on the growth and oil production of the Scenedesmus bijuga:the temperature was 20?,p H=7.0,the ventilation volume was1 V·V^-1·min^-1,the light intensity was 4000 Lx,and the light-dark cycle was 12 h:12 h was the most suitable for the growth of Scenedesmus bijuga.At 0.1 g·L^-1KNO₃,the biomass of Scenedesmus bijuga reached a maximum of 0.779 g·L^-1,and at 20 mg·L^-1K₂HPO₄,its oil content and oil yield reached a maximum of 38.07%and 3.17 mg·L^-1·d^-1.The biomass of Scenedesmus bijuga was between the three diatoms and the Tribonema sp.,but the oil content was lower than that of the Tribonema sp.and the three diatoms.Effects of different environmental factors on the growth and oil production of Tribonema sp.:in aeration to culture,when the temperature was up to 20?,the light intensity was 4000 Lx,p H=7.0,the growth of Tribonema sp.was significantly increased under the culture conditions where N and P were added to the medium,and at 20 mg·L^-1K₂HPO₄,the biomass of Tribonema sp.reached a maximum of 7.37 g·L^-1,and the oil content and oil yield reached a maximum of 51.93%and 14.83 mg·L^-1·d^-1.The biomass and oil content of Tribonema sp.were higher than those of the three diatoms and Scenedesmus bijuga.Influence on the key genes and enzymes in the process of lipid metabolism in Tribonema sp.under different nitrogen concentrations:The activity of uridine diphosphate glucose pyrophosphorylase(UGPase)was positively correlated with the initial nitrogen concentration,whose enzyme activity gradually increased with the increase of culture time decreased,while diacylglycerol acyltransferase(DGAT),?-1,3-glucanase(?-1,3-Glu)and acyl-Co A carboxylase(ACCase)activities increased with the growth of culture time heightening first and then lowering.This study by the environmental regulation of five oleaginous algal strains,Navicula amphiceropsis,Nitzschia amphibia,Tribonema sp.,Scenedesmus bijuga and Melosira varians,found that their optimal culture environments were almost the same.The biomass,oil content,oil yield and oil distribution of the five strains of microalgae will change specifically under different environmental factors.The results of this study increase the number of known oleaginous microalgae,and provide basic data for reference which supports for large-scale cultivation of microalgae.The effects of different nitrogen concentrations on the key enzymes in the oil metabolwism of Tribonema sp.algae were studied,which provided a basis for rationally controlling the nitrogen source concentration in the production of microalgae oil.