| The accumulation of microalgal lipid is usually achieved under stress,so the screening of anti-stress algal strain from extreme environment has been paid more and more attention by researchers.As the desert saline-alkali water area possesses harsh environmental conditions,the microalgae growing in such environment are more resistant to stress,therefore,the collection and screening of lipid-producing desert microalgae resources will play an important role in exploitation and application of microalgal biodiesel.In this study,the screening and molecular identification of desert microalgae were carried out,and the growth and lipid accumulation of microalgae cells under salt stress were analyzed,meanwhile,the regulation mechanism for the cellular lipid synthesis was further interpreted,in order to improve the lipid production of microalgae.Firstly,18 microalgal strains were screened and isolated from the desert saline-alkali water area of the Tarim Basin in Xinjiang.After observation through a fluorescence microscope,it was found that a new microalgal strain numbered DT025 had the highest fluorescence intensity.After molecular identification,it was classified to be Chlorella sp.,and its pH tolerance was explored.It was found that pH tolerance range of the microalgal cell was wide,as the pH values ranged from 6 to 9,the cells showed better Growth.When the pH values were in the range of 7-8,the optimum oil production was obtained.And When the pH was 7.5,the cell's maximum oil yield and productivity can reach 1.58 g/L and 0.198 g/(L·d)respectively.Secondly,four salt concentrations of 0,15,30 and 40 g/L were designed in this study for cultivating the Chlorella sp.DT025,and the effects of salt stress on the growth and microalgal oil accumulation were investigated.The results showed that the inhibition on cell growth increased with the rising of salt concentration.In a salt concentration of 0 g/L,the cell concentration could reach 4.39×108 CFU/mL.At the salt concentration of 40 g/L as comparing to the initially inoculating concentration 3.97×107 CFU/mL,the cell concentration was only 9.1×107 CFU/mL,there's almost no increase in numbers.But the cellular lipid content increased with salt concentration in a certain range of salt concentrationIn a salt concentration of 30 g/L,the lipid content reached the maximum of 64.89%.In addition,the analysis of intracellular fatty acids with different treatments was used by GC-MS to find that salt stress also affects fatty acid components.Due to the increase in salt concentration,the percentage of saturated fatty acids C16:0 in the cells increases.But the percentage of unsaturated fatty acids C18:1 and C18:3 in the cells decreases.Finally,the transcriptional regulation mechanism of microalgae in different salt concentrations was interpreted.Through analysis of the RNA transcripts,it was found that the amount of gene expression involved in the synthesis and transport of cellular oils enhanced.The anabolic direction of glycerin is mainly directed to the synthesis of fatty acids,which are glucose-6-phosphate1-epimera,fructose-1,6-bisphosphatase I and lysophosphatidate acyltransferase.In addition,in a salt-stressed environment,the gene expression of pyruvate dehydrogenase E2 component was downregulated.It is beneficial to the accumulation of Acetyl-CoA and further promotion on the fatty acids synthesis.In summary,the oil content of microalgal cells can be improved with the salt stress.At the same time,the application of transcriptomic analysis favors the effectively mining of the metabolic pathways and the key genes for microalgal lipid synthesis.The theoretic basis and technical reference can be provided for further improving.the lipid production of Chlorella in the future. |
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