Enrichment of Long-Chain Polyunsaturated Fatty Acids by Coordinated Expression of Multiple Metabolic Nodes in the Oleaginous Microalga Phaeodactylum tricornutum.

Microalgal long-chain polyunsaturated fatty acids (LC-PUFAs) have emerged as promising alternatives to depleting fish oils. However, the overproduction of LC-PUFAs in microalgae has remained challenging. Here, we report a sequential metabolic engineering strategy that systematically overcomes the metabolic bottlenecks and overproduces LC-PUFAs. Malonyl CoA-acyl carrier protein transacylase, catalyzing the first committed step in type II fatty acid synthesis, and desaturase 5b, involved in fatty acid desaturation, were coordinately expressed in Phaeodactylum tricornutum. Engineered microalgae hyper-accumulated LC-PUFAs, with arachidonic acid (ARA) and docosahexaenoic acid (DHA) contents of up to 18.98 μg/mg and 9.15 μg/mg (dry weight), respectively. Importantly, eicosapentaenoic acid (EPA) was accumulated up to a highest record of 85.35 μg/mg by metabolic engineering. ARA and EPA were accumulated mainly in triacylglycerides, whereas DHA was found exclusively in phospholipids. Combinatorial expression of these critical enzymes led to the optimal increment of LC-PUFAs without unbalanced metabolic flux and demonstrated the practical feasibility of generating sustainable LC-PUFA production.