Overexpression of an endogenous type 2 diacylglycerol acyltransferase in the marine diatom Phaeodactylum tricornutum enhances lipid production and omega-3 long-chain polyunsaturated fatty acid content

Richard P Haslam; Mary L Hamilton; Chloe K Economou; Richard Smith; Kirsty L Hassall; Johnathan A Napier; Olga Sayanova

doi:10.1186/s13068-020-01726-8

Overexpression of an endogenous type 2 diacylglycerol acyltransferase in the marine diatom Phaeodactylum tricornutum enhances lipid production and omega-3 long-chain polyunsaturated fatty acid content

Biotechnol Biofuels. 2020 May 14:13:87. doi: 10.1186/s13068-020-01726-8. eCollection 2020.

Authors

Richard P Haslam^#¹, Mary L Hamilton^#^{1

2}, Chloe K Economou^{1

3}, Richard Smith^{1

4}, Kirsty L Hassall⁵, Johnathan A Napier¹, Olga Sayanova¹

Affiliations

¹ 1Department of Plant Sciences, Rothamsted Research, Harpenden, Herts AL5 2JQ UK.
² St Albans Girls School, St Albans, Hertfordshire, AL3 6DB UK.
³ 3School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London, E1 4NS UK.
⁴ Algenuity, Eden Laboratory, Broadmead Road, Stewartby, BEDS, Bedford, MK43 9ND UK.
⁵ 5Department of Computational and Analytical Sciences, Rothamsted Research, Harpenden, Herts AL5 2JQ UK.

^# Contributed equally.

Abstract

Background: Oleaginous microalgae represent a valuable resource for the production of high-value molecules. Considering the importance of omega-3 long-chain polyunsaturated fatty acids (LC-PUFAs) for human health and nutrition the yields of high-value eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) require significant improvement to meet demand; however, the current cost of production remains high. A promising approach is to metabolically engineer strains with enhanced levels of triacylglycerols (TAGs) enriched in EPA and DHA.

Results: Recently, we have engineered the marine diatom Phaeodactylum tricornutum to accumulate enhanced levels of DHA in TAG. To further improve the incorporation of omega-3 LC-PUFAs in TAG, we focused our effort on the identification of a type 2 acyl-CoA:diacylglycerol acyltransferase (DGAT) capable of improving lipid production and the incorporation of DHA in TAG. DGAT is a key enzyme in lipid synthesis. Following a diatom based in vivo screen of candidate DGATs, a native P. tricornutum DGAT2B was taken forward for detailed characterisation. Overexpression of the endogenous P. tricornutum DGAT2B was confirmed by qRT-PCR and the transgenic strain grew successfully in comparison to wildtype. PtDGAT2B has broad substrate specificity with preferences for C16 and LC-PUFAs acyl groups. Moreover, the overexpression of an endogenous DGAT2B resulted in higher lipid yields and enhanced levels of DHA in TAG. Furthermore, a combined overexpression of the endogenous DGAT2B and ectopic expression of a Δ5-elongase showed how iterative metabolic engineering can be used to increase DHA and TAG content, irrespective of nitrogen treatment.

Conclusion: This study provides further insight into lipid metabolism in P. tricornutum and suggests a metabolic engineering approach for the efficient production of EPA and DHA in microalgae.

Keywords: Acyl-CoA:diacylglycerol acyltransferase (DGAT); Docosahexaenoic acid; Eicosapentaenoic acid; Omega-3 fatty acids; Phaeodactylum tricornutum; Triacylgycerol.