Variation Of Fatty Acid Desaturation In Response To Nitrogen Deficiency In Auxenochlorella Pyrenoidosa And Analysis Of Fatty Acid Desaturase Function

Nitrogen starvation has dramatically affected the fatty acid desaturation of microalgae,which is closely related to the quality of biodiesel.Limited understanding of the molecular mechanisms underlying fatty acid desaturation seriously hinders the commercialization of microalgae biodiesel.This study focused on the influence of nitrogen concentration on the saturation of microalgae fatty acids and molecular mechanism.Fatty acid desaturation and expressions of relative delta-9,12 and 15 fatty acid desaturase genes（Δ9,Δ12 andΔ15FADs）in Auxenochlorella pyrenoidosa under different nitrate concentrations were investigated.Dynamic variations of fatty acid profiles suggested nitrate could induce desaturation of C18 fatty acids.The content of C18:3 in Auxenochlorella pyrenoidosa reached as high as 30.60%under 1.5 g L^-1 nitrate concentration.C18:1 was increased to34.40%at the expense of C18:3 at 0 g L^-1.The 330%upregulated expression ofΔ9FAD and 14%downregulated expression ofΔ15FAD in logarithmic phase at 0 g L^-1 resulted in C18:1 accumulation and C18:3 decrease.Moreover,nitrate replenishment caused a sharp reduction of C18:1 from34.79%to 0.22%and downregulation ofΔ9FAD expression to 1%of the nitrate absence level,indicating the pivotal role ofΔ9FAD in C18:1accumulation.Finally,overexpression ofΔ9FAD in Escherichia coli and Saccharomyces cerevisiae resulted in an increase of C18:1,confirming its ability of desaturating C18:0.The present study can provide a new approach and scientific guidance for improving the performance of biofuel production by means of integration of nitrogen absence and genetic engineering.