Regulation of malate-pyruvate pathway unifies the adequate provision of metabolic carbon precursors and NADPH in Tetradesmus obliquus

Metabolic engineering has been hailed as a promising tool to impart oil productivity in fast-growing microalgae, thereby generating industry-suitable strains. However, complex regulatory networks in lipogenesis hampered the success to unify the abundance of metabolic carbon precursors and reducing equivalents towards lipogenesis. To obviate the biological bottlenecks, we attempted to rewire the pyruvate pathway, which could enhance the supply of NADPH by heterologously overexpressing a malic enzyme from the oleaginous diatom Phaeodactylum tricornutum (PtME) in fast-growing microalga Tetradesmus obliquus (previously known as Scenedesmus obliquus). PtME overexpression did not impair physiological properties and upheld lipogenesis by facilitating the adequate provision of CO2 and NADPH, respectively, through malate decarboxylation. The malate-pyruvate pathway played a role in elevating lipid content by 2.4-fold via coupling the carbon precursors and reducing equivalents. The malic enzyme activity increased by 9.9-fold, thereby elevated lipogenic NADPH. Together, these data exemplify the crucial role of PtME in pyruvate cycle for amalgamating the provision of metabolic carbon precursors and NADPH towards lipid accumulation and lay a strong foundation for metabolic engineering in algal industrialization.

Automated summary

Metabolic engineering in microalgae holds promise for increasing oil productivity, but complex regulatory networks have been a challenge. This study successfully rewired the pyruvate pathway in fast-growing microalgae to enhance NADPH supply for lipogenesis, resulting in a 2.4-fold increase in lipid content.