Abstract
BackgroundThe synchronous triacylglycerol (TAG) production with the growth is a key step to lower the cost of the microalgae-based biofuel production. Phospholipid: diacylglycerol acyltransferase (PDAT) has been identified recently and catalyzes the phospholipid contributing acyl group to diacylglycerol to synthesize TAG, and is considered as the important source of TAG in Chlamydomonas reinhardtii.ResultsUsing a chimeric Hsp70A–RbcS2 promoter, exogenous PDAT form Saccharomyces cerevisiae fused with a chloroplast transit peptide was expressed in C. reinhardtii CC-137. Proved by western blot, the expression of ScPDAT showed a synchronous trend to the growth in the exponential phase. Compared to the wild type, the strain of Scpdat achieved 22% increase in the content of total fatty acids and 32% increase in TAG content. In addition, the fluctuation of C16 series fatty acid in monogalactosyldiacylglycerol, diacylglyceryltrimethylhomoserine and TAG indicated an enhancement in the TAG accumulation pathway.ConclusionThe TAG production was enhanced in the regular cultivation without the nutrient stress by strengthening the conversion of polar lipid to TAG in C. reinhardtii and the findings provide a candidate strategy for rational engineered strain to overcome the decline in the growth during the TAG accumulation triggered by nitrogen starvation.
Highlights
The synchronous triacylglycerol (TAG) production with the growth is a key step to lower the cost of the microalgae-based biofuel production
There were few successes in the establishment of engineered microalgae strains by way of enhancing the expression of enzymes involving in biosynthesis of fatty acid (FA) or lipids, e.g., acetyl-CoA carboxylases (ACCases), whose over-expression did not promote the simultaneous improvement of TAG with the growth [17, 18], or by modification of expression regulation, e.g., by transcription factors or promoters [19]
A CrPDAT chloroplast transit peptide (cTP)-fused ScPDAT in the upstream was constructed in the pChlamy vector and the transformants of C. reinhardtii CC-137 were screened by hygromycin B and PCR verification
Summary
The synchronous triacylglycerol (TAG) production with the growth is a key step to lower the cost of the microalgae-based biofuel production. As a promising source of biodiesel, microalgae have been a good model to investigate the biological process of triacylglycerol (TAG) production [1]. Even numerous trials have been carried out; it is still far from success to achieve the synchronized TAG production with cell growth, which is generally considered as an essential feature of the ideal strategy for economical TAG production. To improve the TAG production, besides the engineering approach, another way is to modify fatty acids and lipids’ metabolism flux relating to TAG synthesis by molecular biological methods, e.g., mutating key enzymes, reducing or increasing the expression and introducing exogenous genes. Widely concerned targets include the genes of acyltransferases such as glycerol-3-phosphate
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