Transcriptomics Of Thraustochytriidae At Different Growth Stages And Nitrogen Stress

DHA,also known as "brain gold",with the full name as docosahexenoic acid,is a kind of polyunsaturated fatty acid,which is difficult for human body to synthesize.Recently,the main source of DHA is marine fish with high fat content.However,due to the disadvantages of high cost,easily being oxidized and polluted,it is necessary to explore an alternative resource instead of fish oil.Therefore,microalgae has shown as a promising source for DHA production.In this study,we clarify the relationship between cell growth and oil content as well as components of four Thraustochytriidaes(Aurantiochytrium sp.PKU#Sw7,Aurantiochytrium sp.PKU#SW2,Thraustochytriidae sp.PKU#Mn4 and Thraustochytriidae sp.PKU#Mn16).The results showed that the content of DHA in four Thraustochytriidaes was about 32.56%?43.90%of total fatty acid.Cultivation time of 8h,20h,32h and 40h represented the slow growth stage,fast growth stage,plateau growth stage and slow senescence stage respectively.The main fatty acid compositions of Aurantiochytrium sp.PKU#Sw7 and Thraustochytriidae sp.PKU#Mnl6 were divided into DPA,DHA,EPA,HD A,PDA,as well as the total fatty acid was up to 71.74%and 69.81%of the cell dry weight,respectively.In this study,transcripts of Aurantiochytrium,sp.PKU#Sw7 and Thraustochytriidae sp.PKU#Mn16 were sequenced at different cultivation time(8h,20h,32h,40h).The differences in the related enzyme gene expression of fatty acid synthesis at different growth stages were clearly identified.The results showed that the high quality clean reads with an average ratio of 96.58%to the reference gene were obtained by second-generation sequencing.Based on the analysis of correlation coefficient of the gene expression level,the difference of gene expression decreased with the extension of growth time.For different microalgae,the gene expression pattern was similar in the same cultivation time.Through KEGG Pathway annotation,we identified the information for genes of the key enzyme(includes FAS,ACAA,CYP86 and fabG)related with the main pathway of fatty acid bio-synthesis,as well as constructed the synthetic pathway of fatty acid biosynthesis,including fatty acid biosynthesis,fatty acid extension,fatty acid desaturation,TAG synthesis and TAG metabolism.In this study,we compared the growth and oil composition of Thraustochytriidae sp.PKU#Mn16 nd Aurantiochytrium sp.PKU#Sw7 under different nitrogen sources,as well as clarified the effect of nitrogen regulation on the key enzymes of DHA synthesis.The research showed that the total bacterial lipid composition consistent with different nitrogen source culture,mainly are the fatty acid of C14:0,C16:0,C18:0,C18:3,C20:5,C22:5,C22:6.The two predominant compositions were C16:0 and C22:6(DHA),which is the same trend for the four growth stages.The maximum biomass and fatty acid production for Thraustochytriidae sp.PKU#Mn16 cultivated at:monosodium glutamate 5 mM,urea 50 mM,5 mM sodium nitrate,a mMonium sulfate,1 mM.The maximum biomass and fatty acid production for Thraustochytriidae sp.PKU#Sw7 cultivated at:monosodium glutamate 15 mM,urea30 mM,a mMonium sulfate 1 mM,sodium nitrate 50 mM.This study clarified the relationship of algal growth and DHA synthesis as well as lipid composition for different Thraustochytriidae.We also obtained DHA synthesis related enzyme gene of different cultivation time.By regulating with different nitrogen conditions,we explored the effect of difference nitrogen sources on the fatty acid synthesis in Thraustochytriidae.This research will lead a theoretical foundation for the study on the mechanism of DHA synthesis pathway.